THEP Group Meeting

Journal club is to have an informal discussion on recent papers and subjects of the seminar speakers.

It takes place on Thursdays at 4pm in 104-212 or 310-B113-1.

The titles are subject to changes at a short notice.

Fall 2025

Sept 4 (4pm, 103-104), Show and tell.

Sept 11 (310-B113-1), Group meeting: Journal club - Hyun Min Lee

Sept 18, no meeting

Sept 25, no meeting

Oct 2, Group meeting: Seminar

Oct 9, Group meeting: Journal club - Jeonghak Han, Rojalin Padhan

Oct 16, Group meeting: Journal club - Lucca Justino, Sarif Khan

Oct 23, midterm break

Oct 30, no meeting

Nov 6, Group meeting: Journal club - Jungho Song, Arghyajit Datta

Nov 13, no meeting

Nov 20, no meeting

Nov 27, Group meeting: Journal club - Junho Kang, Sanghun Lee

Dec 4, Group meeting: Seminar

Dec 11, Group meeting: Seminar or Journal club

Summer 2025

Aug 13 (2pm, 102-110), Group meeting: Seminar - Hiroki Takahashi (Tokyo Univ).

Aug 7 (2pm, 104-212), Group meeting: Journal club - Hyun Min Lee, Sarif Khan, Arghyajit Datta, Rojalin Padhan

Discussed papers:

https://arxiv.org/abs/2503.18120 (DESI and Axion DE)

https://arxiv.org/abs/2508.04314v1 ; https://arxiv.org/abs/2508.02794v1 (Phase transition & GW from heavy particles)

https://arxiv.org/abs/2504.03837 (First-order phase transition and low-scale leptogenesis)

https://arxiv.org/abs/2508.00761v1 (Muon collider and neutrino NSI)

https://arxiv.org/abs/2508.03819v1 (Indirect detection for sub-GeV DM)

July 31 (2pm, 104-212), Group meeting: Journal club - Hyung Jun Park, Songmin Lee

Speaker: Hyung Jun Park

Title: Higgs modular inflation

Ref: https://arxiv.org/abs/2504.01622

Speaker: Songmin Lee

Title: Higgs-like inflation with radiative corrections

Ref: https://arxiv.org/abs/2504.06002

Speaker: Hyun Min Lee

Title: Goofy symmetry for hierarchy problem

Ref: https://arxiv.org/abs/2507.22111

July 15 (2pm, 310-B113-1), Group meeting: open discussion (Lucca Justino: news from ICTP summer school ; Sarif Khan: interesting talks from Cospa 2025)

Spring 2025

June 12 (310-B113-1), Group meeting: Journal club (Note. June 11, HEP center seminar)

June 5 (310-B113-1), Group meeting: Seminar - Prof. Jeong Han Kim (Chungbuk National Univ). (Note. June 4, HEP center journal club - Seongsik Kim's PhD defense talk)

May 29 (310-B113-1), Group meeting: Seminar - Dr. Minxi He (IBS CTPU-PTC)

May 22 (310-B113-1), Group meeting: Journal club - Myeongjung Seong, Sanghun Lee

Speaker: Myeongjung Seong

Title: Black Hole Metamorphosis and Stabilization by Memory Burden

Ref: https://arxiv.org/abs/2006.00011

Speaker: Sanghun Lee

Title: ν limits from Super-Kamiokande on dark matter-electron scattering in the Sun

Ref: https://arxiv.org/abs/2503.07713

May 15 (310-B113-1), Group meeting: Journal club - Open discussion

Discussed papers.

https://arxiv.org/abs/2505.04812

https://arxiv.org/abs/2505.07946

https://arxiv.org/abs/2505.06001

https://arxiv.org/pdf/2505.05405

May 8 (310-B113-1), Group meeting: Journal club - Sungbo Sim, Junho Kang (Note. May 7, HEP center seminar - Prof. Seung J. Lee (KIAS))

Speaker: Sungbo Sim

Title: Inverse bubbles from broken supersymmetry

Ref: https://www.arxiv.org/abs/2503.01951

Speaker: Junho Kang

Title: Search for Dark Matter in 2HDMS at LHC and future Lepton Colliders

Ref: https://arxiv.org/abs/2504.14529

May 1 (310-B113-1), No group meeting.

April 17 (310-B113-1), Group meeting: Journal club - Arghyajit Datta, Jeonghak Han

Speaker: Arghyajit Datta

Title: "Supercooled Audible Axions"

Ref:

https://arxiv.org/pdf/2504.05386

https://arxiv.org/abs/1811.01950

Speaker: Jeonghak Han

Title: Affleck-Dine Leptogenesis from higgs inflation and Affleck-Dine inflation

Ref:

https://arxiv.org/abs/2106.03381

https://arxiv.org/abs/1909.12300

April 10 (310-B113-1), Group meeting: Journal club - Sarif Khan, Jucca Justino (Note. April 9, HEP center seminar)

Speaker: Sarif Khan

Title: Gravitational waves from cosmic strings

Abstract: In this talk, I summarise a few earlier works on cosmic strings and gravitational wave production. I will talk about cosmic string formation in the early Universe and how it can explain the GW and its potential to be able to explain the NanoGrav signal as a Stochastic Gravitational Wave Background.

List of references in this direction:

https://arxiv.org/pdf/2009.06555

https://arxiv.org/pdf/1711.03104

https://arxiv.org/pdf/1808.08968

https://arxiv.org/pdf/2405.03740

https://arxiv.org/pdf/1304.2445

https://arxiv.org/pdf/2002.01079

Speaker: Lucca Radicce Justino

Title: Dark Matter and Neutrino Physics

Ref:

https://inspirehep.net/literature/2871523

https://inspirehep.net/literature/2899823

https://inspirehep.net/literature/2899847

https://inspirehep.net/literature/2904416

April 3 (310-B113-1), Group meeting: Seminar - Prof. Valerie Domcke (CERN).

March 27 (310-B113-1), Group meeting: Journal club - Rojalin Padhan, Junho Song. Discussion with Prof. Myeonghun Park (Seoultech).

Speaker: Rojalin Padhan

Title: Quantum observables at Collider

References: https://arxiv.org/abs/2003.02280

https://arxiv.org/abs/2401.08751

https://arxiv.org/abs/2310.17696

Speaker: Junho Song

Title: Spontaneous baryogenesis

References: https://arxiv.org/abs/2311.09005

https://arxiv.org/abs/1712.03312

March 20 (310-B113-1), Group meeting: Journal club - Jongkuk Kim, Seongsik Kim (Note. March 19, HEP center seminar)

Discussion on the recent results on Atacama Cosmology Telescope (ACT).

https://inspirehep.net/literature?sort=mostrecent&size=25&page=1&q=t%20Atacama%20Cosmology%20Telescope&ui-citation-summary=true

Speaker: Dr. Jongkuk Kim

Title: A 220 PeV neutrino event: KM3-230213A

References:

https://inspirehep.net/literature/2895769

https://inspirehep.net/literature/2896204

https://inspirehep.net/literature/2897394

Title: DM phenomenology with ALPs

References:

https://inspirehep.net/literature/2870996

https://inspirehep.net/literature/2877700

Speaker: Seong Sik Kim

Title: Prospects of future MeV telescopes in probing weak-scale Dark Matter

https://arxiv.org/abs/2503.04907

March 13 (310-B113-1), Group meeting: Journal club - Hyun Min Lee

Title: On axion production from curvature perturbations.

https://arxiv.org/abs/2503.04880

https://arxiv.org/abs/2503.04888

Winter 2024

Feb 27, Group meeting: journal club.

Feb 13, Group meeting: Special seminar - Prof. Kang Sin Choi (Ewha Womans University).

Jan 20, Group meeting: Special seminar - Dr. Reginald Christian Bernado (APCTP).

Fall 2024

Dec 12, Group meeting: seminar - Prof. Joern Kersten (Bergen/Yonsei).

Dec 5, Group meeting: seminar - Prof. Eung Jin Chun (KIAS).

Nov 21, Group meeting: Journal club - Lucca Justino.

Speaker: Lucca Justino

Title: Exploring the inert doublet model of dark matter with very high-energy gamma-rays observatories

Reference: https://www.teses.usp.br/teses/disponiveis/76/76134/tde-12062024-114530/pt-br.php

Nov 14, Group meeting: (zoom) seminar - Dr. Yohei Ema (Minnesota/CERN).

Nov 7, Group meeting: Journal club - Sarif Khan (self-introduction), Sungbo Sim.

Speaker: Sarif Khan

Topic: Self-introduction and presentation of work.

Speaker: Sungbo Sim

Title: Gravitational waves from cosmological first-order phase transitions with precise hydrodynamics

Reference: https://inspirehep.net/literature/2831924

Oct 31, Group meeting: seminar - Dr. Jong-Hyun Yoon (Chungnam National Univ).

Oct 17, Group meeting: Journal club - Myeongjung Seong, Junho Song.

Speaker: Jun-Ho Song

Title: Big Bang Nucleosynthesis constraints on resonant DM annihilation

Reference: https://inspirehep.net/literature/2831966

Speaker: Myeong-Jung Seong

Title: Plausible constraints and inflationary production for dark photons

Reference: https://inspirehep.net/literature/2831898

Oct 10, Group meeting: Journal club - Rojalin Padhan.

Speaker: Rojalin Padhan

Title: The cosmology of ultralight scalar dark matter coupled to right-handed neutrinos

Reference: https://inspirehep.net/literature/2833953

Sept 26, Group meeting: Journal club.

Speaker: Jongkuk Kim

Title: Neutrino and Gamma-Ray Signatures of Inelastic Dark Matter Annihilating outside Neutron Stars

Reference: https://inspirehep.net/literature/2777866

Title: Z' mediated dark matter freeze-in at stronger coupling

Reference: https://inspirehep.net/literature/2824792

Sept 19, Group meeting: seminar - Dr. Shuntaro Aoki (IBS).

Sept 12, Group meeting: Journal club.

Speaker: Hyun Min Lee

Title: Supergroup symmetries and the hierarchy problem

Abstract:

We show that the mass of a scalar field transforming in the fundamental of an SU(N|N+1) supergroup internal symmetry is protected against one-loop corrections from quartic, gauge, and yukawa interactions. Although the negative-norm states responsible for this protection are likely fatal to a unitary interpretation of the theory, such ultraviolet insensitivity may open a new avenue to understanding the lightness of the Higgs.

Reference: https://arxiv.org/abs/2409.03824 & https://arxiv.org/abs/2409.08325

Summer 2024

August 22 (4pm, 104-212), Group meeting: Journal club.

August 14 (Wed, 2pm, 310-B113-1), Group meeting: Journal club.

August 8 (4pm, 104-212), Group meeting: Journal club.

July 25 (2pm, 310-B113-1), Group meeting: Journal club.

July 18 (4pm, 310-B113-1), Group meeting: random journal clubs. 2407.02462 & 2406.18641 (Jongkuk, refractive neutrino mass, milicharged DM and neutrino mass), 2407.12738 (Rojalin, meson decays with neutrinophilic mediators), 2407.02555 (Adriana, ULDM of galaxy scale), 2407.07529 (Seongsik, freeze-in production for KK graviton).

Spring 2024

June 20, Endterm: no meeting.

June 13, Group meeting: Journal club - Jongkuk Kim, Rojalin Padhan

June 6, National Holiday: no meeting.

May 30, THEP seminar: Prof. Wan-Il Park (Jeonbuk National Univ).

May 23, THEP seminar (on zoom): Prof. Francesco Riva (Univ Geneva) & Journal club (by Jongkuk Kim) in 310-B113-1.

May 16, THEP seminar: Dr. Suruj Jyoti Das (IBS CTPU).

May 9, Group meeting: Journal club - Myeongjung Seong, Sungbo Sim.

Title: Axion dark matter from inflation-driven quantum phase transition. (Myeongjung Seong)

Abstract: We propose a new mechanism to produce axion dark matter from inflationary fluctuations. Quantum fluctuations during inflation are strengthened by a coupling of the axion kinetic term to the inflaton, which we parametrize as an effective curvature κ in the axion equation of motion. A nonvanishing curvature breaks the scale invariance of the axion power spectrum, driving a quantum phase transition with κ as the order parameter. The axion power spectrum is proportional to the inverse comoving horizon to the power of κ. For positive κ the spectrum gets a red tilt, leading to an exponential enhancement of the axion abundance as the comoving horizon shrinks during inflation. This enhancement allows sufficient axion production to comprise the entire dark matter relic abundance despite the ultralight mass. Our mechanism predicts a significantly different parameter space from the usual misalignment mechanism. It allows for axion-like particle dark matter with a much lower decay constant and thus a larger coupling to Standard Model particles. Much of the parameter space can be probed by future experiments including haloscopes, nuclear clocks, CASPEr, and CMB-S4. We can also generate heavier QCD axion dark matter than the misalignment mechanism.

Ref. https://arxiv.org/abs/2402.08716

Title: False Vacuum Decay Rate From Thin To Thick Walls. (Sungbo Sim)

Abstract: We consider a single real scalar field in flat spacetime with a polynomial potential up to ϕ^4, that has a local minimum, the false vacuum, and a deeper global minimum, the true vacuum. When the vacua are almost degenerate we are in the thin wall regime, while as their difference in potential energy increases, we approach the thick wall regime. We give explicit simple formulae for the decay rate of the false vacuum in 3 and 4 spacetime dimensions. Our results include a careful treatment both of the bounce action, which enters at the exponent of the decay rate, and of the functional determinant at one loop, which determines the prefactor. The bounce action is computed analytically as an expansion in the thin wall parameter in generic D dimensions. We find that truncating such an expansion at second order we obtain a remarkably accurate bounce action also deep into thick wall regimes. We calculate the functional determinant numerically in 3 and 4 dimensions and fit the results with simple polynomials of the same thin wall parameter. This allows us to write the complete one-loop decay rate as a compact expression, which works accurately from thin to thick wall regimes.

Ref. https://arxiv.org/abs/2404.17632

May 2, Group meeting: seminar - Junho Song

Title: Axiogenesis

Abstract: We propose a mechanism called axiogenesis where the cosmological excess of baryons over antibaryons is generated from the rotation of the QCD axion. The Peccei-Quinn (PQ) symmetry may be explicitly broken in the early universe, inducing the rotation of a PQ charged scalar field. The rotation corresponds to the asymmetry of the PQ charge, which is converted into the baryon asymmetry via QCD and electroweak sphaleron transitions. In the concrete model we explore, interesting phenomenology arises due to the prediction of a small decay constant and the connections with new physics at the LHC and future colliders and with axion dark matter.

Ref. https://arxiv.org/abs/1910.02080

April 25, midterm, KPS: no meeting.

April 18, Group meeting: Journal club - Adriana Menkara.

Title: Axi-majoron for almost everything

Abstract: The details of the minimal cosmological standard model (MCSM) proposed in Ref. [1] are discussed. The model is based on the scale-symmetry and the global Peccei-Quinn(PQ) symmetry with a key assumption that the latter is broken only in the gravity sector in a scale-invariant manner. We show that the model provides a quite simple unified framework for the unknown history of the universe from inflation to the epoch of big-bang nucleosynthesis, simultaneously addressing key puzzles of high energy theory and cosmology: (i) the origin of scales, (ii) primordial inflation, (iii) matter-antimatter asymmetry, (iv) tiny neutrino masses, (v) dark matter, and (vi) the strong CP-problem. Scale symmetry can be exact, and the Planck scale is dynamically generated. The presence of Gauss-Bonnet term may safely retain dangerous non-perturbative symmetry-breaking effects negligible, allowing large-field trans-Planckian inflation along the PQ-field. Iso-curvature perturbations of axi-majorons are suppressed. A sizable amount of PQ-number asymmetry is generated at the end of inflation, and conserved afterwards. Domain wall problem is absent due to the PQ-number asymmetry. Baryogenesis can be realized by either inflationary Affleck-Dine mechanism or spontaneous leptogenesis thanks to the PQ-number asymmetry, or by resonant leptogenesis. Dark matter can be purely cold axi-majorons from the mis-alignment contribution only with the symmetry-breaking scale of (1012)GeV. Hot axi-majorons from the decay of the inflaton become a natural source for a sizable amount of dark radiation. Inflationary gravitational waves are expected to have information about some masse parameters of the left-handed and the right-handed neutrinos, thanks to the presence of an early matter-domination era driven by at least a long-lived right-handed neutrino species.

Ref. https://arxiv.org/abs/2403.08675

April 11, Group meeting: Journal club - Seongsik Kim.

Title: Composite Dark Matter with Forbidden Annihilation

Abstract: A dark matter model based on QCD-like SU(Nc) gauge theory with electroweakly interacting dark quarks is discussed. Assuming the dark quark mass m is smaller than the dynamical scale Λd∼4πfd, the main component of the dark matter is the lightest G-parity odd dark pion associated with chiral symmetry breaking in the dark sector. We show that nonzero dark quark mass induces the universal mass contribution to both G-parity odd and even pions, and their masses tend to be degenerate. As a result, dark pion annihilation into heavier G-parity even dark pion also affects the dark matter relic abundance. Thus, our setup naturally accommodates forbidden dark matter scenario and realizes heavy dark matter whose mass is (1-100) TeV, which is different from conventional electroweakly interacting dark matter such as minimal dark matter. We also discuss CP-violation from θ-term in the dark gauge sector and find that the predicted size of electron electric dipole moment can be as large as ∼10−32 e cm.

Ref. https://arxiv.org/abs/2404.03963

April 4, No group meeting. (KIAS lectures on Higgs inflation)

March 28, Group meeting: journal clubs from all.

March 21 (310-B113-1), Group meeting: Journal club - Carlo Branchina.

Title : On the perturbative expansion at high temperature and implications for cosmological phase transitions

Abstract : We revisit the perturbative expansion at high temperature and investigate its convergence by inspecting the renormalisation scale dependence of the effective potential. Although at zero temperature the renormalisation group improved effective potential is scale independent at one-loop, we show how this breaks down at high temperature, due to the misalignment of loop and coupling expansions. Following this, we show how one can recover renormalisation scale independence at high temperature, and that it requires computations at two-loop order. We demonstrate how this resolves some of the huge theoretical uncertainties in the gravitational wave signal of first-order phase transitions, though uncertainties remain stemming from the computation of the bubble nucleation rate.

Ref. https://arxiv.org/abs/2104.04399

March 14 (310-B113-1), Group meeting: Journal club - Hyun Min Lee.

Title: Nonthermal Heavy Dark Matter from a First-Order Phase Transition

Abstract : We study nonthermal production of heavy dark matter from the dynamics of the background scalar field during a first-order phase transition, predominantly from bubble collisions. In scenarios where bubble walls achieve runaw

ay behavior and get boosted to very high energies, we find that it is possible to produce dark matter with mass several orders of magnitude above the symmetry breaking scale or the highest temperature ever reached by the thermal plasma. We also demonstrate that the existing formalism for calculating particle production from bubble dynamics in a first-order phase transition is not gauge invariant, and can lead to spurious results. While a rigorous and complete resolution of this problem is still lacking, we provide a practical prescription for the computation that avoids unphysical contributions and should provide reliable order-of-magnitude estimates of this effect. Furthermore, we point out the importance of three-body decays of the background field excitations into scalars and gauge bosons, which provide the dominant contributions at energy scales above the scale of symmetry breaking. Using our improved results, we find that scalar, fermion, and vector dark matter are all viable across a large range of mass scales, from O(10) TeV to a few orders of magnitude below the Planck scale, and the corresponding phase transitions can be probed with current and future gravitational wave experiments.

Ref. https://arxiv.org/abs/2403.03252

Winter 2023

Feb 28 (310-B113-1), Group meeting: QFT study (Myeongjung, Junho).

Feb 14 (310-B113-1), Group meeting: QFT study (Adriana, Jeonghak).

Feb 7 (310-B113-1), Group meeting: Special seminar (Rojalin Padhan), QFT study (Seongsik, Sungbo).

Speaker: Rojalin Padhan

Title: Phenomenology of neutrino mass model and Dark Matter model at present and future collider experiments

Abstract: Despite its tremendous success, the Standard Model (SM) of particle physics fails to explain a few major experimental observations, such as the tiny neutrino masses, their mixings, and the observed relic density of dark matter. This observation compels us to go beyond the Standard Model (BSM) physics. In this talk, I will discuss the collider phenomenology of a particular class of BSM models that can accommodate neutrino masses via the "Seesaw Mechanism" and a dark matter candidate.

Jan 31, Group meeting: introduction of a new member (Rojalin Padhan), QFT study (Jeonghak, Myeongjung, Junho, Junsik).

Jan 24, No group meeting (High1 workshop).

Jan 17, No group meeting (BRL workshop in Yeoju).

Jan 3, THEP seminar: Dr. Jae Hyuk Chang (Univ Chicago Illinois)

Fall 2023

Dec 14, Group meeting: discussion (Journal club by Carlo Branchina)

Dec 7, No group meeting (PNU-IBS workshop)

Nov 30, THEP seminar: Prof. Kwang Sik Jeong (Pusan National Univ)

Nov 23, Group meeting: Journal club - Sungbo Sim + undergraduate students

Title: Explaining The Muon g−2 Anomaly and New CDF II W-Boson Mass in the Framework of (Extra)Ordinary Gauge Mediation (Sungbo Sim)

Abstract: The SUSY contributions Δaμ to muon g−2 anomaly can not even reach 3σ in ordinary gauge mediated SUSY breaking (GMSB) scenarios because of the strong correlations between the colored sparticle masses and the uncolored EW sparticle masses. An interesting extension to GMSB is the (Extra)Ordinary Gauge Mediation (EOGM), which can relax the correlations between squarks and sleptons with non-universal choices for Neff,3 and Neff,2. We find that EOGM scenarios with Neff,3≪Neff,2 can explain the muon g−2 anomaly within 3σ range, however can not explain the new W-boson mass by CDF II. We also propose to extend EOGM with additional adjoint Σ8 and Σ3 messengers at a high scale of order 1.0×10^14 GeV, which can shift the gauge coupling unification scale to the string scale. Such EOGM extension scenarios with adjoint messengers could spoil the unwanted gaugino mass ratios and give large SUSY contributions to Δaμ for Neff,3≪Neff,2, which can explain the muon g−2 anomaly up to 1σ. Besides, because of the large messenger scale of order 1.0×1014 GeV, such scenarios will in general lead to large |At| at the EW scale, which can accommodate the 125 GeV Higgs easily and possibly lead to smaller EWFT as well as BGFT. We discuss the possibility to explain the new CDF II W-boson mass in the GMSB-type framework. We find that SUSY contributions can marginally account for the new W-boson mass in the region with sleptons and wino both being light.

https://arxiv.org/abs/2204.04286

Nov 17, THEP special seminar: Prof. Deog Ki Hong (Pusan National Univ)

Nov 16, THEP seminar: Prof. Jinn-Ouk Gong (Ewha Womans Univ)

Nov 9, Group meeting: Journal club - Junho Song, Myeongjung Seong

Title: Gravitational waves from axion wave production (Myeongjung Seong)

Abstract: We consider a scenario with axions/axion-like particles Chern-Simons gravity coupling, such that gravitational waves can be produced directly from axion wave tachyonic instability in the early universe after inflation. This axion gravity term is less constrained compared to the well-searched axion photon coupling and can provide a direct and efficient production channel for gravitational waves. Such stochastic gravitational waves can be detected by either space/ground-based gravitational wave detectors or pulsar timing arrays for a broad range of axion masses and decay constants.

https://arxiv.org/abs/2309.08407

Title: Axiogenesis (Junho Song)

https://arxiv.org/abs/1910.02080

Nov 2, THEP seminar: Prof. Sungwoo Hong (KAIST)

Oct 26, No group meeting (KPS)

Oct 19, Group meeting: discussion for KPS

Oct 12, Group meeting: discussion on the projects of students

Oct 11, CAU HEP center: seminar - Prof. Tae Jeong Kim (Hanyang University)

Sept 21, Group meeting: Journal club - Seongsik Kim

Title : Primordial Black Hole versus Inflaton: Two Chief Systems of the World

Abstract : We compare the dark matter(DM) production processes and its parameters space in the background of reheating obtained from two chief systems in the early Universe: the inflaton ϕ and the primordial black holes (PBHs). We concentrated on the mechanism where DMs are universally produced only from the PBH decay and the generation of the standard model plasma from both inflton and PBHs. Whereas the distribution of Primordial Black Holes behaves like dust, the inflaton phenomenology depends strongly on its equation of state after the inflationary phase, which in turn is conditioned by the nature of the potential V(ϕ). Depending upon the initial mass and population of PBHs, a large range of DM mass is shown to be viable if reheating is controlled by PBHs itself. Inflaton-dominated reheating is observed to further widen such possibilities depending on the initial population of black holes and its mass as well as the coupling of the inflaton to the standard model sector.

https://arxiv.org/abs/2309.06505

Sept 20, CAU HEP center: journal club - Carlo Branchina

Title: On Thermodynamic Stability of Black Holes. Part I: Classical Stability

Abstract:

We revisit the classical thermodynamic stability of the standard black hole solutions by implementing the intrinsic necessary and sufficient conditions for stable global and local thermodynamic equilibrium. The criteria for such equilibria are quite generic and well- established in classical thermodynamics, but they have not been fully utilized in black hole physics. We show how weaker or incomplete conditions could lead to misleading or incorrect results for the thermodynamic stability of the system. We also stress the importance of finding all possible local heat capacities in order to fully describe the classical equilibrium picture of black holes. Finally, we thoroughly investigate the critical and phase transition curves and the limits of the classical analysis. This paper is the first in the line of intended works on thermodynamic stability of black holes in modified theories of gravity and holography.

https://arxiv.org/pdf/2302.11998v2.pdf

Sept 18 (Mon at 4:30pm, 102-106), department colloquium - Prof. Sang Min Lee (SNU)

Sept 14, Group meeting: Journal club - Hyun Min Lee

Title : Axion-Gauge Coupling Quantization with a Twist

Abstract : The possible couplings of an axion to gauge fields depend on the global structure of the gauge group. If the Standard Model gauge group is minimal, or equivalently if fractionally charged color-singlet particles are forbidden, then the QCD axion's Chern-Simons couplings to photons and gluons obey correlated quantization conditions. Specifically, the photon coupling can have a fractional part which is a multiple of 1/3, but which is determined by the gluon coupling. A consequence of this result is that, among all theories with a minimal gauge group and minimal axion coupling to gluons, the smallest possible axion-photon amplitude |gaγγ| arises for E/N=8/3. This provides a new motivation for experiments targeting this axion-photon coupling.

https://arxiv.org/abs/2309.03939

cf. htps://arxiv.org/abs/2309.03937 https://arxiv.org/abs/2309.03934

Sept 7, Show and tell.

Summer 2023

August 17 (Thu at 4pm, 104-212), discussion on the new results on muon g-2 (Fermilab) and SGWB from NanoGrav.

Spring 2023

June 26 (Tue at 2pm, 310-B113-1), Study of Thermal Field Theory (Laine, Chap 9).

June 23 (Tue at 2pm, 310-B113-1), Study of Thermal Field Theory (Laine, Chap 9).

June 1, Group meeting: Journal club - undergraduate students (Junsik Yu, Jeonghak Han)

May 30 (Tue at 4pm, 310-B113-1), Study of Thermal Field Theory (Laine, Chap 6).

May 18, Group meeting: Journal club - graduate students (Myeongjung Seong, Junho Song, Sungbo Sim)

May 9 (Tue at 4pm, 310-B113-1), Study of Thermal Field Theory (Laine, Chap 5).

April 26, CAU HEP center: journal club - Seongsik Kim

Title: Early Dark Energy for Hubble tension

Refs: F. Niedermann & M.S. Sloth; “New Early Dark Energy,” arXiv:1910.10739, and “Resolving the Hubble Tension with New Early Dark Energy,” arXiv:2006.06686

April 25 (Tue at 4pm, 310-B113-1), Study of Thermal Field Theory (Laine, Chap 4).

April 13, Group meeting: Journal club - Carlo Branchina

Title : Quantum Fluctuations and New Instantons I: Linear Unbounded Potential

Abstract : We consider the decay of a false vacuum in circumstances where the methods suggested by Coleman run into difficulties. We find that in these cases quantum fluctuations play a crucial role. Namely, they naturally induce both an ultraviolet and infrared cutoff scales, determined by the parameters of the classical solution, beyond which this solution cannot be trusted anymore. This leads to the appearance of a broad class of new O(4) invariant instantons, which would have been singular in the absence of an ultraviolet cutoff. We apply our results to a case where the potential is unbounded from below in a linear way and in particular show how the problem of small instantons is resolved by taking into account the inevitable quantum fluctuations.

Ref. https://arxiv.org/abs/2009.12445

April 5, CAU HEP center: journal club - Shuntaro Aoki

Title: Review of Hubble tension and solution by neutrino self-interaction

Ref: [1902.00534] The Neutrino Puzzle: Anomalies, Interactions, and Cosmological Tensions (arxiv.org)

March 30, Group meeting: Journal club - Adriana Menkara

Title : Decay of ALP Condensates via Gravitation-Induced Resonance

Abstract : Oscillating scalar field condensates induce small amplitude oscillations of the Hubble parameter which can induce a decay of the condensate due to a parametric resonance instability [1]. We show that this instability can lead to the decay of the coherence of the condensate of axion-like particle (ALP) fields during the radiation phase of standard cosmology for rather generic ALP parameter values, with possible implications for certain experiments aiming to search for ALP candidates. As an example, we study the application of this instability to the QCD axion. We also study the magnitude of the induced entropy fluctuations.

Ref. https://arxiv.org/abs/2303.14800

March 23, Group meeting, discussed papers: 2303.09866 (EFT for Higgs-Starobinsky inflation), 2303.11344 (absorption of vector dark matter), 2303.01747 (Wilson line scalar mass, cf. 1703.10418).

March 16, Group meeting: Journal club - Shuntaro Aoki

Title : Detectable Gravitational Wave from Graviton Bremsstrahlung during Reheating

Abstract : We revisit graviton production via Bremsstrahlung from the decay of the inflaton during inflationary reheating. Using two complementary computational techniques, we first show that such 3-body differential decay rates differ from previously reported results in the literature. We then compute the stochastic gravitational wave (GW) background that forms during the period of reheating, when the inflaton perturbatively decays with the radiative emission of gravitons. By computing the number of relativistic degrees of freedom in terms of ΔNeff, we constrain the resulting GW energy density from BBN and CMB. Finally, we project current and future GW detector sensitivities in probing such a stochastic GW background, which typically peaks in the GHz to THz ballpark, opening up the opportunity to be detected with microwave cavities and space-based GW detectors.

Ref. https://arxiv.org/abs/2301.11345

March 9, Group meeting: Journal club - Hyun Min Lee

Title : Dark Radiation from Neutrino Mixing after Big Bang Nucleosynthesis

Abstract : A light (mνd≲ MeV) dark fermion mixing with the Standard Model neutrinos can naturally equilibrate with the neutrinos via oscillations and scattering. In the presence of dark sector interactions, production of dark fermions is generically suppressed above BBN, but then enhanced at later times. Over much of the parameter space, we find that the dark sector equilibrates, even for mixing angles θ_0 as small as 10^{−13}, and equilibration occurs at Tequil≃mνd(θ20MPl/mνd)1/5 which is naturally at most a few orders of magnitude above the dark fermion mass. The implications of this are twofold: one, that light states are often only constrained by the CMB and LSS without leaving an imprint on BBN, and two, that sectors which equilibrate before recombination will typically have a mass threshold before recombination, as well. This can result in dark radiation abruptly transitioning from non-interacting to interacting, or vice-versa, a ``step'' in the amount of dark radiation, and dark matter with similar transitions in its interactions, all of which can leave important signals in the CMB and LSS, and may be relevant for cosmological tensions in observables such as H0 or S8. Minimal models leave an unambiguous imprint on the CMB above the sensitivity of upcoming experiments.

Ref. https://arxiv.org/abs/2301.10792

Title : Sterile neutrino dark matter: relativistic freeze-out

Abstract : Long-lived sterile neutrinos can play the role of dark matter. We consider the possibility that such neutrinos form a thermal bath with a singlet scalar, while not being in thermal equilibrium with the Standard Model fields. Eventually, the neutrino dark matter undergoes freeze-out in the dark sector, which can occur in both non-relativistic and relativistic regimes. To account for the latter possibility, we use the full Fermi-Dirac and Bose-Einstein distribution functions with effective chemical potential in the reaction rate computation. This allows us to study the freeze-out process in detail and also obtain the necessary thermalization conditions. We find that relativistic freeze-out occurs in a relatively small part of the parameter space. In contrast to the standard weakly-interacting-massive-particle (WIMP) scenario, the allowed dark matter masses extend to 10^4 TeV without conflicting perturbativity.

Ref: https://arxiv.org/abs/2302.09515

March 2, Show and tell. (Hyun Min Lee: short summary of CAU BSM workshop)

Winter 2023

Feb 20-24, CAU BSM Workshop.

Feb 16 (Thu at 2pm, 305-310), Study of Thermal Field Theory (Laine, Chap 3).

Jan 26 (Thu at 2pm, 104-212), Study of Thermal Field Theory (Laine, Chap 2).

Jan 17 (Tue at 2pm, 305-310), Study of Thermal Field Theory (Laine, Chap 1).

Fall 2022

Dec 22 (Thu at 6pm), Prof. Seong Chan Park (Yonsei Univ), Axion quality problem, Proca seminars, zoom.

Dec 8, No group meeting.

Dec 7 (Wed at 2pm, 104-217), Special group meeting: Welcome seminar by Dr. Carlo Branchina.

Dec 1 (Thu at 1pm), THEP seminar: Prof. Jisuke Kubo (Toyama Univ), Spontaneous Generation of Masses and Hierarchy Problem, zoom.

Nov 24 (Thu at 6pm), THEP seminar: Prof. Admir Greljo (Bern Univ), Model building and phenomenology with leptoquarks, zoom.

Nov 24 (Thu at 1pm), Group meeting: Special tutorial on collider tools Part II - Kimiko Yamashita.

Nov 23 (102-106 at 3:00pm), HEP Center journal club: poster presentations from undergraduates.

Myeong-Jung Seong, Strong CP problem and axion.

Jun Ho Song, Searching for right-handed Majorana neutrino mass in thermal leptogenesis.

Sung-Bo Sim, Gauge coupling unification and proton decay.

Nov 17, No group meeting.

Nov 10, Group meeting: Journal club - Seongsik Kim.

Title : The Continuum Dark Matter Zoo

Abstract : We generalize the recently proposed continuum dark matter model to the case where the dark matter consists of a spin-1/2 or spin-1 gapped continuum. We construct simple continuum analogs of weakly interacting massive particles annihilating through the Z portal. We discuss all existing experimental constraints, with the strongest bounds arising from indirect detection and limits on continuum decays from the cosmic microwave background. Our models are phenomenologically viable for gap scales of 60-200 GeV (spin-1/2) and 35-90 GeV (spin-1), owing to the strong kinematic suppression of direct detection bounds which is unique to continuum states. We comment on future prospects for detection and suggest directions for further continuum model building.

Ref. https://arxiv.org/abs/2210.16326

Oct 27 (Thu at 6pm), Prof. Kiwoon Choi (IBS, CTPU), Distinguishing different axion models with precision low energy axion couplings, Proca seminars, zoom.

Oct 27, Group meeting: Special lecture on cosmological collider - Shuntaro Aoki.

Abstract : I will give an introductory review on cosmological collider physics based on the original paper

[0911.3380] Quasi-Single Field Inflation and Non-Gaussianities (arxiv.org)

After briefly reviewing the bispectrum of primordial curvature perturbation in the standard inflation scenario, I will discuss the effects of massive particles on the bispectrum, which can be sizable and leave a unique imprint.

Oct 26 (Wed at 4pm), THEP seminar: Dr. Jongkuk Kim (KIAS), Dark matter physics with dark Higgs.

Oct 13 (Thu at 6pm), Prof. Chang Sub Shin (Chungnam National Univ), Dark Light Boson Emission from Supernovae, Proca seminars, zoom.

Oct 13, Group meeting: Special tutorial on collider tools - Kimiko Yamashita. talk video.

Abstract:

We introduce collider tools for estimating cross section, kinematical distributions, and amplitude squared with your interesting process from the Beyond the Standard Model interaction terms, i.e., FeynRules, MadGraph, CalcHEP, and MadAnalysis5. As an illustration of using "FeynRules," we implement the Lagrangian for a spin-1 mediated model for Dirac dark matter in the computer code. In this model, Dirac dark matter indirectly interacts with the Standard Model quarks via the spin-1 mediator. Then, we compute the production cross section at LHC by using "MadGraph," for example, for dark matter production processes with a monojet. Using "CalcHEP," we also derive the analytic formulas for dark matter annihilation, which are used to compute the relic density. Finally, we see some kinematical distributions of that monojet process by using "MadAnalysis5" with MadGraph output.

References:

https://arxiv.org/abs/1908.06357

https://feynrules.irmp.ucl.ac.be/wiki/DMsimp

GitHub webpage for program installation.

Oct 6 (Thu at 1pm), THEP seminar: Dr. Yusuke Yamada (Waseda Univ), QFT description of particle scattering during preheating, zoom.

Sept 29, THEP seminar: Dr. Neil Barrie (IBS, CTPU), Type II Seesaw leptogenesis.

Sept 28 (102-106 at 3:30pm), HEP Center journal club: Shuntaro Aoki.

Title: The Ostrogradsky instability can be overcome by quantum physics.

Refs:

[2105.00898] The Ostrogradsky instability can be overcome by quantum physics (arxiv.org)

[1908.02416] Unitarity, stability and loops of unstable ghosts (arxiv.org)

Sept 22 (102-105 at 1pm), Dr. Adil Jueid (KIAS), Leptoquark solutions to the dark matter problem and the R_D anomalies.

Sept 15, Group meeting: Journal club - Adriana Menkara.

Title : Axion Dark Matter from Lepton flavor-violating Decays

Abstract : We propose simple scenarios where lepton flavor-violating couplings generate the observed dark matter abundance through freeze-in of an axion-like particle with mass in the few keV range. Com- pared to flavor-diagonal freeze-in, this mechanism enhances dark matter stability, softens stellar cooling constraints and improves the experimental sensitivity of accelerator-based searches. These scenarios can be tested by future X-ray telescopes, and in some cases will be almost entirely probed by new searches for lepton flavor violation at high-intensity experiments such as Mu3e and MEG II.

https://arxiv.org/abs/2209.03371

Sept 8, Group meeting: Journal club - Hyun Min Lee.

https://arxiv.org/abs/2106.10576

Title : A Causal Framework for Non-Linear Quantum Mechanics

Abstract : We add non-linear and state-dependent terms to quantum field theory. We show that the resulting low-energy theory, non-linear quantum mechanics, is causal, preserves probability and permits a consistent description of the process of measurement. We explore the consequences of such terms and show that non-linear quantum effects can be observed in macroscopic systems even in the presence of de-coherence. We find that current experimental bounds on these non-linearities are weak and propose several experimental methods to significantly probe these effects. The locally exploitable effects of these non-linearities have enormous technological implications. For example, they would allow large scale parallelization of computing (in fact, any other effort) and enable quantum sensing beyond the standard quantum limit. We also expose a fundamental vulnerability of any non-linear modification of quantum mechanics - these modifications are highly sensitive to cosmic history and their locally exploitable effects can dynamically disappear if the observed universe has a tiny overlap with the overall quantum state of the universe, as is predicted in conventional inflationary cosmology. We identify observables that persist in this case and discuss opportunities to detect them in cosmic ray experiments, tests of strong field general relativity and current probes of the equation of state of the universe. Non-linear quantum mechanics also enables novel gravitational phenomena and may open new directions to solve the black hole information problem and uncover the theory underlying quantum field theory and gravitation.

https://arxiv.org/abs/2208.10567

Title : Out of this world neutrino oscillations (application of the above paper)

https://arxiv.org/abs/2208.08453

Title : Bouncing Dark Matter (mentioned)

https://arxiv.org/abs/2209.03305

Title : UV/IR Mixing, Causal Diamonds and the Electroweak Hierarchy Problem (mentioned)

Sept 1, Show and tell.

Spring 2022

June 23, Group meeting - journal club: Shuntaro Aoki, Myeongjung Seong, Junho Song

Speaker: Shuntaro Aoki

Title: [2204.11869] Large-Field Inflation and the Cosmological Collider (arxiv.org)

Speaker: Myeong-Joong Seong

Title: https://arxiv.org/abs/2108.11295 Cosmological Relaxation through the Dark Axion Portal

Speaker: Joon-Ho Song

Title: https://arxiv.org/abs/1501.05310 Naturalness in the Dark at the LHC

https://arxiv.org/abs/2203.05531 Review of Neutral Naturalness

June 2, THEP seminar: Prof. Myeonghun Park (Seoultech)

May 26, THEP seminar: Prof. Ki-Young Choi (Sungkyunkwan Univ)

May 19, No group meeting. CDF W-boson workshop in Univ of Seoul.

May 12, Group meeting - journal club: Hyun Min Lee (journal club), Kimiko Yamashita (more models on W mass anomaly).

Title: Revealing the Cosmic History with Gravitational Waves

Abstract:

The characteristics of the cosmic microwave background provide circumstantial evidence that the hot radiation-dominated epoch in the early universe was preceded by a period of inflationary expansion. Here, we show how a measurement of the stochastic gravitational wave background can reveal the cosmic history and the physical conditions during inflation, subsequent pre- and reheating, and the beginning of the hot big bang era. This is exemplified with a particularly well-motivated and predictive minimal extension of the Standard Model which is known to provide a complete model for particle physics -- up to the Planck scale, and for cosmology -- back to inflation.

Paper: https://arxiv.org/abs/2203.00621

May 4, HEP Center journal club: Hyun Min Lee and Kimiko Yamashita (Review on W-boson mass calculations and models).

April 28, THEP seminar: Dr. Sebastian Zell (EPFL Laussanne)

April 14, THEP seminar: Prof. Ranjan Laha (Indian Institute of Science)

April 7, THEP seminar: Dr. Wenyuan Ai (Kings College London)

March 31, Group meeting - journal club: Adriana Menkara

Title: Dilaton-Axion Inflation with PBHs and GWs

Abstract: We discuss two-stage dilaton-axion inflation models [1] and describe α-attractor models with either exponential or polynomial approach to the plateau. We implement one of the models of primordial black hole production proposed in [2] in the α-attractor context, and develop its supergravity version. The predictions of this model following from its polynomial attractor properties are: ns and r are α-independent, r depends on the mass parameter μ defining the approach to the plateau. The tachyonic instability at the transition point between the two stages of inflation is proportional to the negative curvature of the hyperbolic space K=−2/3α. Therefore the masses of primordial black holes (PBHs) and the frequencies of small-scale gravitational waves (GWs) in this model show significant dependence on α.

Paper: https://arxiv.org/pdf/2203.10437

March 24, THEP seminar: Prof. Matthew Mccullough (CERN)

March 17, Group meeting - journal club: Seongsik Kim

Title: A fermionic portal to a non-abelian dark sector

Abstract:

We introduce a new class of renormalisable models, consisting of a dark

SU(2)D gauge sector connected to the Standard Model (SM) through a Vector-Like (VL) fermion mediator, not requiring a Higgs portal, in which a massive vector boson is the Dark Matter (DM) candidate. These models are labelled Fermion Portal Vector Dark Matter (FPVDM). Multiple realisations are possible, depending on the properties of the VL partner and of the scalar potential. One example is discussed in detail. FPVDM models have a large number of applications in collider and non-collider experiments, depending on the mediator sector.

Paper: https://arxiv.org/abs/2203.04681

March 10, Group meeting - journal club: Kimiko Yamashita

Title: Origin of Neutrino Masses on the Convex Cone of Positivity Bounds

Abstract:

We exhibit the geometric structure of the convex cone in the linear space of the Wilson coefficients for the dimension-8 operators involving the left-handed lepton doublet L and the Higgs doublet H in the Standard Model effective field theory (SMEFT). The boundary of the convex cone gives rise to the positivity bounds on the Wilson coefficients, while the extremal ray corresponds to the unique particle state in the theory of ultra-violet completion. Among three types of canonical seesaw models for neutrino masses, we discover that only right-handed neutrinos in the type-I seesaw model show up as one of extremal rays, whereas the heavy particles in the type-II and type-III seesaw models live inside the cone. The experimental determination of the relevant Wilson coefficients close to the extremal ray of type-I seesaw model will unambiguously pin down or rule out the latter as the origin of neutrino masses. This discovery offers a novel way to distinguish the most popular seesaw model from others, and also strengthens the SMEFT as an especially powerful tool to probe new physics beyond the Standard Model.

Paper: https://arxiv.org/abs/2202.12907

March 3, Show and tell.

Fall 2021

Dec 10, HEP Center Journal club - hybrid

Speaker: Kimiko Yamashita

Title: Festina-Lente Bound on Higgs Vacuum Structure and Inflation

Abstract:

The recently suggested Festina-Lente (FL) bound provides a lower bound on the masses of U(1) charged particles in terms of the positive vacuum energy. Since the charged particle masses in the Standard Model (SM) are generated by the Higgs mechanism, the FL bound provides a testbed of consistent Higgs potentials in the current dark energy-dominated universe as well as during inflation. We study the implications of the FL bound on the UV behavior of the Higgs potential for a miniscule vacuum energy, as in the current universe. We also present values of the Hubble parameter and the Higgs vacuum expectation value allowed by the FL bound during inflation, which implies that the Higgs cannot stay at the electroweak scale during this epoch.

Paper: https://arxiv.org/abs/2111.04010

Dec 9, Group meeting - offline Journal club

Speaker: Hyun Min Lee

Title: Thermal Dark Matter from Freezeout of Inverse Decays

Abstract: We propose a new thermal dark matter candidate whose abundance is determined by the freezeout of inverse decays. The relic abundance depends parametrically only on a decay width, while matching the observed value requires that the coupling determining the width-and the width itself-should be exponentially small. The dark matter is therefore very weakly coupled to the Standard Model, evading conventional searches. This INverse DecaY ('INDY') dark matter can be discovered by searching for the long-lived particle that decays into the dark matter at future planned experiments.

Paper: https://arxiv.org/abs/2111.14857

Dec 2, Group meeting - offline Journal club

Speaker: Jiseon Song

Title: How warm are non-thermal relics? Lyman-α bounds on out-of-equilibrium dark matter

Abstract: We investigate the power spectrum of Non-Cold Dark Matter (NCDM) produced in a state out of thermal equilibrium. We consider dark matter production from the decay of scalar condensates (inflaton, moduli), the decay of thermalized and non-thermalized particles, and from thermal and non-thermal freeze-in. For each case, we compute the NCDM phase space distribution and the linear matter power spectrum, which features a cutoff analogous to that for Warm Dark Matter (WDM). This scale is solely determined by the equation of state of NCDM. We propose a mapping procedure that translates the WDM Lyman-α mass bound to NCDM scenarios. This procedure does not require expensive ad hoc numerical computations of the non-linear matter power spectrum. By applying it, we obtain bounds on several NCDM possibilities, ranging from mDM≳EeV for DM production from inflaton decay with a low reheating temperature, to sub-keV values for non-thermal freeze-in. We discuss the phenomenological implications of these results for specific examples which include strongly-stabilized and non-stabilized supersymmetric moduli, gravitino production from inflaton decay, Z′ and spin-2 mediated freeze-in, and non-supersymmetric spin-3/2 DM.

Paper: https://arxiv.org/abs/2011.13458

Nov 25, Group meeting - offline Journal club

Speaker: Seongsik Kim

Title: Hadrophilic Dark Sectors at the Forward Physics Facility

Abstract:

Models with light dark sector and dark matter particles motivate qualitatively new collider searches. Here we carry out a comprehensive study of hadrophilic models with U(1)B and U(1)B−3Lτ gauge bosons coupled to light dark matter. The new mediator particles in these models couple to quarks, but have suppressed couplings to leptons, providing a useful foil to the well-studied dark photon models. We consider current bounds from accelerator and collider searches, rare anomaly-induced decays, neutrino non-standard interactions, and dark matter direct detection. Despite the many existing constraints, these models predict a range of new signatures that can be seen in current and near future experiments, including dark gauge boson decays to the hadronic final states π+π−π0, π0γ, K+K−, and KSKL in FASER at LHC Run 3, enhancements of ντ scattering rates in far-forward neutrino detectors, and thermal dark matter scattering in FLArE in the HL-LHC era. These models therefore motivate an array of different experiments in the far-forward region at the LHC, as could be accommodated in the proposed Forward Physics Facility.

Paper: https://arxiv.org/abs/2111.10343

Nov 18, Group meeting - offline Journal club

Speaker: Adriana Menkara

Title: Reheating in Models with Non-minimal Coupling in metric and Palatini formalisms

Abstract:

We study reheating of inflationary models with general non-minimal coupling K(ϕ)R with K(ϕ)∼V(ϕ)‾‾‾‾‾√ where R is the Ricci scalar and V is the inflaton potential. In particular, when we take the monomial potential K(ϕ)∝ϕm with m∈ℤ+, we provide general analytic expressions for cosmological observables. We consider a wide range of non-minimal coupling ξ∈[0,∞) in metric and Palatini formalisms and derive the predictions for cosmological observables and the reheating temperature taking a general equation of state parameter wreh.

Paper: https://arxiv.org/abs/2111.00825

Oct 29, HEP Center Journal club - hybrid

Speaker: Shuntaro Aoki

Title: Gravitational Wave and CMB Probes of Axion Kination

Abstract:

Rotations of an axion field in field space provide a natural origin for an era of kination domination, where the energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. Remarkably, no entropy is produced at the end of matter domination and hence these eras of matter and kination domination may occur even after Big Bang Nucleosynthesis. We derive constraints on these eras from both the cosmic microwave background and Big Bang Nucleosynthesis. We investigate how this cosmological scenario affects the spectrum of possible primordial gravitational waves and find that the spectrum features a triangular peak. We discuss how future observations of gravitational waves can probe the viable parameter space, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis. For QCD axion dark matter produced by the kinetic misalignment mechanism, a modification to the inflationary gravitational wave spectrum occurs above 0.01 Hz and, for high values of the energy scale of inflation, the prospects for discovery are good. We briefly comment on implications for structure formation of the universe.

Paper: https://arxiv.org/abs/2108.09299

Oct 28, Group meeting - hybrid Journal club

Speaker: Kimiko Yamashita

Title: Elastic positivity vs extremal positivity bounds in SMEFT: a case study in transversal electroweak gauge-boson scatterings

Abstract:

The positivity bounds, derived from the axiomatic principles of quantum field theory (QFT), constrain the signs of Wilson coefficients and their linear combinations in the Standard Model Effective Field Theory (SMEFT). The precise determination of these bounds, however, can become increasingly difficult as more and more SM modes and operators are taken into account.

We study two approaches that aim at obtaining the full set of bounds for a given set of SM fields:

1) the traditional elastic positivity approach, which exploits the elastic scattering amplitudes of states with arbitrarily superposed helicities as well as other quantum numbers,

and

2) the newly proposed extremal positivity approach, which constructs the allowed coefficient space directly by using the extremal representation of convex cones.

Considering the electroweak gauge-bosons as an example, we demonstrate how the best analytical and numerical positivity bounds can be obtained in several ways.

We further compare the constraining power and the efficiency of various approaches, as well as their applicability to more complex problems. While the new extremal approach is more constraining by construction, we also find that it is analytically easier to use, numerically much faster than the elastic approach, and much more applicable when more SM particle states and operators are taken into account. As a byproduct, we provide the best positivity bounds on the transversal quartic-gauge-boson couplings, required by the axiomatic principles of QFT, and show that they exclude ≈99.3% of the parameter space currently being searched at the LHC.

Paper: https://arxiv.org/abs/2009.04490

Sep 30, Group meeting - online Journal club

Speaker: Shuntaro Aoki

Title: Thermal Misalignment of Scalar Dark Matter

Abstract:

The conventional misalignment mechanism for scalar dark matter depends on the initial field value, which governs the oscillation amplitude and present-day abundance. We present a mechanism by which a feeble (Planck-suppressed) coupling of dark matter to a fermion in thermal equilibrium drives the scalar towards its high-temperature potential minimum at large field values, dynamically generating misalignment before oscillations begin. Unlike conventional misalignment production, the dark matter abundance is dictated by microphysics and not by initial conditions. As an application of the generic mechanism, we discuss a realistic scenario in which dark matter couples to the muon.

Paper: https://arxiv.org/abs/2109.04476

Sep 23, Group meeting - online Journal club, Discussed papers: 2109.10811 (Endo et al, B->D+M decays at 4.4sigma); 2109.10367 (Strumia et al, Pole inflation and non-minimal coupling); 2108.06095 (G. Ross et al, Higgs/R^2 inflation and hierarchy problem).

Speaker: Bin Zhu

Title: Directional Detection of Light Dark Matter in Superconductors

Abstract:

Superconducting detectors have been proposed as outstanding targets for the direct detection of light dark matter scattering at masses as low as a keV. We study the prospects for directional detection of dark matter in isotropic superconducting targets from the angular distribution of excitations produced in the material. We find that dark matter scattering produces initial excitations with an anisotropic distribution, and further show that this directional information can be preserved as the initial excitations relax. Our results demonstrate that directional detection is possible for a wide range of dark matter masses, and pave the way for light dark matter discovery with bulk superconducting targets.

Paper: https://arxiv.org/abs/2109.04473

Sep 16, Discussed papers: 2109.07423 (E. J. Chun) & 2109.04476 (B. Batell et al), thermal displacement for scalar dark matter; 2109.07176 (G. Giudice, review on hierarchy problem); 2109.06201 (G. Hiller et al, new Z' model for B-anomalies); 2109.04473 (Y. Hochberg et al, directional detection of light dark matter).

Sep 15, THEP seminar, Dr. Liliana Velasco (Bergen Univ and KIAS), Swampland de Sitter Conjectures in No-Scale Supergravity Models, online.

Sep 9, Discussed papers (2109.02650 and 2109.03800, multileptons, 151GeV diphoton resonance + MET at LHC).

Sep 2, Show and tell. Discussed papers: 2108.13245 (Hamaguchi et al, Axion quality problem); 2108.13422 (Toro et al, exothermic dark matter).

Summer 2021

August 11, Ch. 8 - Junho & Ch.9 - Shuntaro

July 21, Ch.6 - Jiseon & Ch.7 - Yoojin, (Mentioned papers: Hooper et al, 2107.09067 (muon g-2 and dark matter with Lmu-Ltau), J. Zupan et al, 2107.07518 (muon g-2, RK with extra U(1)), Y. Mambrini et al, 2107.07472, O. Lebedev et al, 2107.06292, dark matter production from reheating )

July 14, Ch.4 - Adriana & Ch.5 - Seongsik, (Mentioned papers: J. Cline et al, 2107.04045 (Twin inflatons and asymmetric reheating), P. Ko et al, 2107.04375 (SIMP portal), 2107.06237 (Light boson dark matter and boson stars). )

July 7, Group study based on Peskin's Concepts of Elementary Particle Physics, Ch.2 - Jiyoon & Ch.3 - Myeongjung

June 30 (2pm), CAU seminar, Dr. Takahiro Terada (IBS-CTPU), online, Minimal Supergravity Inflation and (Not) Slow Gravitino.

June 24, Myeongjung (Vacuum decay), Jiyoon (Klein's paradox).

Spring 2021

June 3, Group meeting - online journal club.

Speaker: Seongsik Kim

Title: On the single leptoquark solutions to the B-physics anomalies

Abtract:

We revisit the possibilities of accommodating the experimental indications of the lepton flavor universality violation in

b-hadron decays in the minimal scenarios in which the Standard Model is extended by the presence of a single (1TeV) leptoquark state. To do so we combine the most recent low energy flavor physics constraints, including R_K(∗) and R_D(∗), and combine them with the bounds on the leptoquark masses and their couplings to quarks and leptons as inferred from the direct searches at the LHC and the studies of the large pT tails of the pp→ℓℓ differential cross section. We find that none of the scalar leptoquarks of mLQ≃1÷2 TeV can accommodate the B-anomalies alone. Only the vector leptoquark, known as U1, can provide a viable solution which, in the minimal setup, provides an interesting prediction, i.e. a lower bound to the lepton flavor violating b→sμ^±τ^∓ decay modes, such as B(B→Kμτ)≳0.7×10−7.

Paper: https://arxiv.org/abs/2103.12504

May 27, Group meeting - online journal club.

Speaker: Ji-Seon Song

Title: Radiative Production of Non-thermal Dark Matter

Abstract:

We compare dark matter production from the thermal bath in the early universe with its direct production through the decay of the inflaton. We show that even if dark matter does not possess a direct coupling with the inflaton, Standard Model loop processes may be sufficient to generate the correct relic abundance.

Paper: https://arxiv.org/abs/1901.04449

May 20, Group meeting - online journal club.

Speaker: Adriana Menkara

Title: Explaining g_µ - 2 and R_{K(*)} using the light mediators of U(1)_{T3R}.

Abstract:

Scenarios in which right-handed light Standard Model fermions couple to a new gauge group, U(1)_{T3R} can naturally generate a sub-GeV dark matter candidate. But such models necessarily have large couplings to the Standard Model, generally yielding tight experimental constraints. We show that the contributions to g_µ − 2 from the dark photon and dark Higgs largely cancel out in the narrow window where all the experimental constraints are satisfied, leaving a net correction which is consistent with recent measurements from Fermilab. These models inherently violate lepton universality, and UV completions of these models can include quark flavor violation which can explain R_{K(∗)} anomalies as observed at the LHCb experiment after satisfying constraints on Br(Bs → µµ) and various other constraints in the allowed parameter space of the model. This scenario can be probed by FASER, SeaQuest, SHiP, LHCb, Belle, etc.

Paper: https://arxiv.org/pdf/2105.07655.pdf

May 13, Group meeting - online journal club.

Speaker: Shuntaro Aoki

Title: "Recent papers on gravitino production and swampland".

Papers:

https://arxiv.org/abs/2102.10113

https://arxiv.org/abs/2103.10437

https://arxiv.org/abs/2104.03749

https://arxiv.org/abs/2104.05731

https://arxiv.org/abs/2104.08288

https://arxiv.org/abs/2104.10181

https://arxiv.org/abs/2105.03784

April 29, Group meeting - online journal club.

Speaker: Hyun Min Lee

Paper: https://arxiv.org/abs/2104.10699

Title: Gravitational SIMPs

cf. https://arxiv.org/abs/2007.14688

April 15, Group meeting - online journal club.

Speaker: Bin Zhu

Title: "Very Incomplete summary of Muon g-2 Interpretations".

April 8, Group meeting - online journal club, New results on muon g-2 from Fermilab (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.141801). Group meeting - online journal club

Speaker: Yang-Hwan Ahn

Paper: https://arxiv.org/abs/2104.02574

Title: Photophilic hadronic axion from heavy magnetic monopoles

Authors: Anton V. Sokolov, Andreas Ringwald

Abstract: We propose a model for the QCD axion which is realized through a coupling of the Peccei-Quinn scalar field to magnetically charged fermions at high energies. We show that the axion of this model solves the strong CP problem and then integrate out heavy magnetic monopoles using the Schwinger proper time method. We find that the model discussed yields axion couplings to the Standard Model which are drastically different from the ones calculated within the KSVZ/DFSZ-type models, so that large part of the corresponding parameter space can be probed by various projected experiments. Moreover, the axion we introduce is consistent with the astrophysical hints suggested both by anomalous TeV-transparency of the Universe and by excessive cooling of horizontal branch stars in globular clusters. Assuming infrared Abelian dominance in QCD, we show that the leading term for the cosmic axion abundance is not changed compared to the conventional pre-inflationary QCD axion case for much of the allowed parameter space.

April 1, Some recent analysis with updated RK data (Isidori et al, 2103.16558, Altmannshofer, 2103.13370), April Fool's day papers (M. Reece et al, 2103.17198; J. Ruderman et al, 2103.16572), Models for muon g-2 on alert (e.g. H.M. Lee et al, hep-ph/0103054), Designated speakers in the group will give Journal clubs from April 8th.

March 25, THEP Seminar, Prof. Kwang Sik Jeong (PNU), Axion-driven hybrid inflation over a barrier.

March 18, Summary of the new paper from our group (Flux-mediated dark matter, 2103.07592) - Y. Kang & J. Song, EFT interpretation of lepton magnetic dipole moments (2102.08954) - H.M. Lee.

March 12, HEP Center Journal club

Speaker: Bin Zhu

Title: A Time-Varying Fine Structure Constant from Naturally Ultralight Dark Matter

Paper: https://arxiv.org/abs/2012.02787

March 11, Announcement for muon g-2 results from Fermilab on April 7, Angular distribution of B^+->K^{+*}mu mu (new measurement at LHCb, LHCb-PAPER-2020-041), ANAIS rules out DAMA-LIBRA more than 2 sigma (2103.01175) - H.M. Lee, 2013.05295 (LFV and leptogenesis in scotogenic model, Y. Ahn), 2103.05890 (Migdal effect for exothermic DM, B. Zhu), 2103.02615 (Metric couplings and FIMP dark matter, Y. Kang).

March 4, Show and tell.

Winter 2021

Feb 26 (Friday at 2pm), CAU seminar: Dr. Shuntaro Aoki (Waseda Univ), Disentangling mass spectra of multiple fields in cosmological collider. https://cau.zoom.us/j/4611373590

Feb 24 (at 1pm), Group meeting - online journal club.

Speaker: Seongsik Kim

Paper: https://arxiv.org/abs/1612.07295

Title: Dark Matter's secret liaisons: phenomenology of a dark U(1) sector with bound states

Authors: Marco Cirelli, Paolo Panci, Kalliopi Petraki, Filippo Sala, Marco Taoso

Abtract: Dark matter (DM) charged under a dark U(1) force appears in many extensions of the Standard Model, and has been invoked to explain anomalies in cosmic-ray data, as well as a self-interacting DM candidate. In this paper, we perform a comprehensive phenomenological analysis of such a model, assuming that the DM abundance arises from the thermal freeze-out of the dark interactions. We include, for the first time, bound-state effects both in the DM production and in the indirect detection signals, and quantify their importance for Fermi, AMS, and CMB experiments. We find that DM in the mass range 1 GeV to 100 TeV, annihilating into dark photons of MeV to GeV mass, is in conflict with observations. Instead, DM annihilation into heavier dark photons is viable. We point out that the late decays of multi-GeV dark photons can produce significant entropy and thus dilute the DM density. This can lower considerably the dark coupling needed to obtain the DM abundance, and in turn relax the existing constraints.

Speaker: Jiseon Song

Paper: https://arxiv.org/abs/1512.05701

Title: Post-Inflationary Gravitino Production Revisited

Authors: John Ellis, Marcos A. G. Garcia, Dimitri V. Nanopoulos, Keith A. Olive, Marco Peloso

Abstract: We revisit gravitino production following inflation. As a first step, we review the standard calculation of gravitino production in the thermal plasma formed at the end of post-inflationary reheating when the inflaton has completely decayed. Next we consider gravitino production prior to the completion of reheating, assuming that the inflaton decay products thermalize instantaneously while they are still dilute. We then argue that instantaneous thermalization is in general a good approximation, and also show that the contribution of non-thermal gravitino production via the collisions of inflaton decay products prior to thermalization is relatively small. Our final estimate of the gravitino-to-entropy ratio is approximated well by a standard calculation of gravitino production in the post-inflationary thermal plasma assuming total instantaneous decay and thermalization at a time t≃1.2/Γϕ. Finally, in light of our calculations, we consider potential implications of upper limits on the gravitino abundance for models of inflation, with particular attention to scenarios for inflaton decays in supersymmetric Starobinsky-like models.

Feb 17 (at 1pm), Group meeting - online journal club.

Speaker: Yang-Hwan Ahn

Talk title: Anomalies on orbifold (hep-th 0103135 Nima Arkani-Hamed, Andrew G. Cohen and Howard Georgi)

Abstract:

We discuss the form of the chiral anomaly on an S1/Z2 orbifold with chiral boundary conditions. We find that the 4-divergence of the higher-dimensional current evaluated at a given point in the extra dimension is proportional to the probability of finding the chiral zero mode there. Nevertheless the anomaly, appropriately defined as the five dimensional divergence of the current, lives entirely on the orbifold fixed planes and is independent of the shape of the zero mode. Therefore long distance four dimensional anomaly cancellation ensures the consistency of the higher dimensional orbifold theory.

Feb 9 (Tue at 1pm), Group meeting - online journal club.

Speaker: Hyun Min Lee

Paper: https://arxiv.org/abs/2101.06275

Title: TwInflation

Abstract:

The general structure of Hybrid Inflation remains a very well-motivated mechanism for lower-scale cosmic inflation in the face of improving constraints on the tensor-to-scalar ratio. However, as originally modeled, the "waterfall" field in this mechanism gives rise to a hierarchy problem (η−problem) for the inflaton after demanding standard effective field theory (EFT) control. We modify the hybrid mechanism and incorporate a discrete "twin" symmetry, thereby yielding a viable, natural and EFT-controlled model of non-supersymmetric low-scale inflation, "Twinflation". Analogously to Twin Higgs models, the discrete exchange-symmetry with a "twin" sector reduces quadratic sensitivity in the inflationary potential to ultra-violet physics, at the root of the hierarchy problem. The observed phase of inflation takes place on a hilltop-like potential but without fine-tuning of the initial inflaton position in field-space. We also show that all parameters of the model can take natural values, below any associated EFT-cutoff mass scales and field values, thus ensuring straightforward theoretical control. We discuss the basic phenomenological considerations and constraints, as well as possible future directions.

Feb 1-3, CAU BSM Workshop, online.

Jan 27 (at 1pm), Group meeting - online journal club.

Speaker: Bin Zhu

Paper: https://arxiv.org/abs/2009.03917

Title: The Axion Quality Problem: Global Symmetry Breaking and Wormholes

Abstract: Continuous global symmetries are expected to be broken by gravity, which can lead to important phenomenological consequences. A prime example is the threat that this poses to the viability of the Peccei-Quinn solution to the strong CP problem. In this paper, we explore the impact of wormholes as a source of global symmetry breaking by gravity. We review the current status of wormholes and global symmetries and note that, surprisingly, the axion has a quality problem within non-perturbative Einstein gravity. Although these wormholes lead to a large breaking of global symmetries, we show that their effect is nonetheless relevant for the model building of gauge protected axions. We also find wormhole solutions within two scenarios: (i) an extended global symmetry group within Einstein gravity, and (ii) U(1) wormholes within the low-energy limit of an open String Theory. The former allows us to show that the concept of a global symmetry in General Relativity is somewhat ill-defined. The latter illustrates that for motivated values of the string coupling constant, axions appear to have a quality problem within the open String Theory we consider.

Ref. Newton 1665 physics seminar by Miguel Escudero. video link.

Jan 20 (at 1pm), Group meeting - online journal club.

Speaker: Adriana Menkara

Paper: https://arxiv.org/abs/2006.02811

Title: Weyl Scaling Invariant R^2 Gravity for Inflation and Dark Matter

Abstract: Inflation in the early universe can generate the nearly conformal invariant fluctuation that leads to the structures we observe at the present. The simple viable Starobinsky R^2 inflation has an approximate global scale symmetry. We study the conformal symmetric Weyl Rˆ2 and general F(Rˆ) theories and demonstrate their equivalence to Einstein gravity coupled with a scalar and a Weyl gauge field. The scalar field in Weyl Rˆ2 gravity can be responsible for inflation with Starobinsky model as the attractor, potentially distinguishable from the latter by future experiments. The intrinsic Weyl gauge boson becomes massive once the Einstein frame is fixed, and constitutes as a dark matter candidate with mass up to ∼ 5 × 10^16 GeV.

Jan 14, 15, 21, 22, CAU Winter School on Particle Physics and Cosmology, online.

Jan 13 (at 1pm), Group meeting - online journal club.

Speaker: Yoo-Jin Kang

Paper: https://arxiv.org/abs/2012.15284

Title: Light Dark Matter through Resonance Scanning

Authors: Djuna Croon, Gilly Elor, Rachel Houtz, Hitoshi Murayama, and Graham White

Abstract: We propose a new out-of-equilibrium production mechanism of light dark matter: resonance scanning. If the dark matter mass evolved in the early Universe, resonant production may have occurred for a wide range of light dark matter masses today. We show that the dark matter relic abundance may be produced through the Higgs portal, in a manner consistent with current experimental constraints.

Jan 6 (at 1pm), Group meeting - plans for winter break. (Journal clubs, Workshops/schools in CAU, QFT study group (organizer: Adriana), New postdoc fellow: Shuntaro Aoki from Waseda Univ from April 2021.)

Fall 2020

Dec 17 (at 10am), Group meeting.

Dec 14 (at 2pm), CAU lectures: Prof. Joern Kersten (Bergen Univ, Norway), Neutrino Physics: Theory and Latest Experimental News.

Dec 10 (at 10am), CAU seminar: Dr. Yu-Dai Tsai (Fermilab), New Models, Experiments, and Neutrino Searches at the High-Energy Intensity Frontier – Resonant SIDM, FORMOSA, LongQuest, and Forward Neutrino Campus..

Dec 3 (at 5pm), CAU seminar: Dr. Chang Sub Shin (IBS CTPU), Exploring the Universe with Dark Light Scalars.

Dec 3 (at 11am), MS defense for Soobin Kim.

Nov 27 (at 10:30am), PhD defense for Yoo-Jin Kang.

Nov 26 (at 10am), Group meeting.

Nov 19 (at 10am), Group meeting. Poster on dark matter from phase transition (Jiyoon Sun), Recent papers (2011.02510, Dark matter from PBH (Yoojin), 2011.04679, Analytic self-scattering of dark matter in semi-classical region (Bin Zhu)).

Nov 12 (at 10am), CAU seminar: Dr. Kimiko Yamashita (IHEP), Higgs Inflation, Vacuum Stability, and Leptogenesis.

Oct 29 (at 5pm), CAU seminar: Dr. Javier Rubio (Instituto Superior Técnico, Lisbon), Higgs inflation and the nature of gravity.

Oct 15 (at 5pm), CAU seminar: Dr. Bibhushan Shakya (CERN), Light Extended Neutrino Sectors: Foundations and Phenomenology.

Oct 8 (at 5pm), CAU seminar: Dr. Yohei Ema (DESY), Higgs Inflation, Unitarity, and Emergence of Scalaron.

Sept 24, Online group meeting.

Sept 17, Soo-Min Choi, Review on light dark matter.

Sept 10, Online group meeting. Discussion on the tension on solar neutrino vs reactor neutrino (Dr. Ahn). Introduction on KPS and seminar schedules.

Sept 3, Online group meeting. Show and tell. Review on group members, activities and future plans

Summer 2020

August 19, Online meeting. Review on IBS school and CUBES workshop. Discussed papers: 2008.06618 (J. Maldacena et al, wormholes), 2008.06505 (Davoudiasl et al, ultra light fermion dark matter), 2008.05029 (Shakeri et al, NSI for sterile neutrinos and Xenon1t, cf. 2007.05513, I. Shoemaker, up-scattering), 2008.07555 (C. Vafa et al, bubbles and swampland).

July 29, Offline meeting. Mentioned papers: Axion quality (W. Yin), E8 unification (A. Aranda), CKM substructure (J. Ruderman), Vacuum decay (T. Moroi), Neutron lifetime anomaly (B. Grinstein), DM substructure and electron recoil (JiJi Fan), Diversity problem (K. Hayashi, M. Chiba, T. Ishiyama).

July 22, Offline meeting. Exothermic dark matter.

July 15, Offline meeting: discussion on XENON1T excess and dark matter interpretations.

Spring 2020

May 21, Online Journal club

Speaker : Yoo-Jin Kang

Title : Dark matter self-interactions from spin-2 mediator

Paper : https://arxiv.org/pdf/2002.12779.pdf

(supplement : https://arxiv.org/pdf/2003.09290.pdf)

Abstract :

We propose a new mechanism for making dark matter self-interacting in the presence of a massive spin-2 mediator. The derived Yukawa-type potential for dark matter is independent of the spins of dark matter, so are the resulting Sommerfeld effects for the dark matter self-scattering. We find that both the Born cross section and relatively mild Sommerfeld effects assist to make the self-scattering cross section velocity-dependent. We discuss how to evade the current indirect bounds on dark matter annihilations and show that the model is marginally compatible with perturbative unitarity in the ghost-free realization of the massive spin-2 particle.

May 14, Online Journal club

Title : Basic idea of relaxing the Higgs mass with four-form flux and cosmological constant problem and reheating.

https://arxiv.org/abs/1910.09171, https://arxiv.org/abs/1907.05370

Speaker : Jiseon Song

Abstract :

We consider the cosmological relaxation of the Higgs mass and the cosmological constant due to the four-form fluxes in four dimensions. We present a general class of models with a singlet scalar field containing four-form couplings where the Higgs mass is relaxed to a right value and the Universe reheats to a sufficiently high reheating temperature after the last membrane nucleation. We also discuss some of interesting features in the cases of singlet scalar fields with non-minimal or minimal couplings to gravity and show how the new scalar fields can play a role for dark matter production.

April 30, Online Journal club

Title : Exponential Hierarchies from Anderson Localization in Theory Space

(https://arxiv.org/abs/1710.01354)

Speaker: Soonbin Kim

Abstract :

We present a new mechanism for generating exponential hierarchies in four-dimensional field theories inspired by Anderson localization in one dimension, exploiting an analogy between the localization of electron energy eigenstates along a one-dimensional disordered wire and the localization of mass eigenstates along a local "theory space" with random mass parameters. Mass eigenstates are localized even at arbitrarily weak disorder, with exponentially suppressed couplings to sites in the theory space. The mechanism is quite general and may be used to exponentially localize fields of any spin. We apply the localization mechanism to two hierarchies in Standard Model parameters --- the smallness of neutrino masses and the ordering of quark masses --- and comment on possible relevance to the electroweak hierarchy problem. This raises the compelling possibility that some of the large hierarchies observed in and beyond the Standard Model may result from disorder, rather than order.

April 23, Online Journal club

Title: Dark Matter Freeze Out during an Early Cosmological Period of QCD Confinement

Speaker: Prof. Hyun Min Lee

Abstract:

Standard lore states that there is tension between the need to accommodate the relic density of a weakly interacting massive particle and direct searches for dark matter. However, the estimation of the relic density rests on an extrapolation of the cosmology of the early Universe to the time of freeze out, untethered by observations. We explore a nonstandard cosmology in which the strong coupling constant evolves in the early Universe, triggering an early period of QCD confinement at the time of freeze out. We find that depending on the nature of the interactions between the dark matter and the Standard Model, freeze out during an early period of confinement can lead to drastically different expectations for the relic density, allowing for regions of parameter space which realize the correct abundance but would otherwise be excluded by direct searches.

Ref: https://arxiv.org/abs/2004.06727

April 16, Online Journal club

Title: Superradiance in rotating stars and pulsar-timing constraints on dark photons

Speaker: Dr. Bin Zhu

Abstract:

I will introduce the basic concept of superradiance and how it is related with ultra-light boson fields in BSM. As an application, superradiance in stars and pulsar-timing constraints on dark photons are given explicitly.

Ref. 1704.06151 and 1501.06570

April 9, Online journal club

Title: Heavy Thermal Relics from Zombie Collisions

Speaker: Soo-Min Choi

Abstract :

We propose a new thermal freezeout mechanism which results in dark matter masses exceeding the unitarity bound by many orders of magnitude, without violating perturbative unitarity or modifying the standard cosmology. The process determining the relic abundance is χζ† → ζζ, where χ is the dark matter candidate. For mζ < mχ < 3mζ , χ is cosmologically long-lived and scatters against the exponentially more abundant ζ. Therefore, such a process allows for exponentially heavier dark matter for the same interaction strength as a particle undergoing ordinary 2 → 2 freezeout; or equivalently, exponentially weaker interactions for the same mass. We demonstrate this mechanism in a leptophilic dark matter model, which allows for dark matter masses up to 10^9 GeV.

Ref. 2003.04900

April 2, Online Journal club

Title : Predictions for the neutrino parameters in the minimal gauged U(1)_{L_\mu-L_\tau} model

Speaker: Dr. Yanghwan Ahn

Abstract :

We study the structure of the neutrino mass matrix in the minimal gauged U(1)Lμ−Lτ model, where three right-handed neutrinos are added to the Standard Model in order to obtain non-zero masses for active neutrinos. Because of the U(1)Lμ−Lτ gauge symmetry, the structure of both Dirac and Majorana mass terms of neutrinos is tightly restricted. In particular, the inverse of the neutrino mass matrix has zeros in the (μ,μ) and (τ,τ) components, namely, this model offers a symmetric realization of the so-called two-zero-minor structure in the neutrino mass matrix. Due to these constraints, all the CP phases-the Dirac CP phase δ and the Majorana CP phases α2 and α3-as well as the mass eigenvalues of the light neutrinos mi are uniquely determined as functions of the neutrino mixing angles θ12, θ23, and θ13, and the squared mass differences Δm221 and Δm231. We find that this model predicts the Dirac CP phase δ to be δ≃1.59π-1.70π (1.54π-1.78π), the sum of the neutrino masses to be ∑imi≃0.14-0.22 eV (0.12-0.40 eV), and the effective mass for the neutrinoless double beta decay to be ⟨mββ⟩≃0.024-0.055 eV (0.017-0.12 eV) at 1σ

Ref: https://arxiv.org/abs/1705.00419

March 26, Online Journal club

Speaker : Yoojin Kang

Title : Systematizing the Effective Theory of Self-Interacting Dark Matter

Abstract :

If dark matter has strong self-interactions, future astrophysical and cosmological observations, together with a clearer understanding of baryonic feedback effects, might be used to extract the velocity dependence of the dark matter scattering rate. To interpret such data, we should understand what predictions for this quantity are made by various models of the underlying particle nature of dark matter. In this paper, we systematically compute this function for fermionic dark matter with light bosonic mediators of vector, scalar, axial vector, and pseudoscalar type. We do this by matching to the nonrelativistic effective theory of self-interacting dark matter and then computing the spin-averaged viscosity cross section nonperturbatively by solving the Schrodinger equation, thus accounting for any possible Sommerfeld enhancement of the low-velocity cross section. In the pseudoscalar case, this requires a coupled-channel analysis of different angular momentum modes. We find, contrary to some earlier analyses, that nonrelativistic effects only provide a significant enhancement for the cases of light scalar and vector mediators. Scattering from light pseudoscalar and axial vector mediators is well described by tree-level quantum field theory.

Ref: https://arxiv.org/abs/2003.00021

Fall 2019

December 12, Journal club

Speaker: Soo-Min Choi

Topic: Filtered Dark Matter at a First Order Phase Transition 1912.02830

Abstract: We describe a new mechanism of dark matter production in the early Universe, based on the dynamics of a first order phase transition. We assume that dark matter particles acquire mass during the phase transition, making it energetically unfavourable for them to enter the expanding bubbles of the massive phase. Instead, most of them are reflected off the advancing bubble walls and quickly annihilate away in the massless phase. The bubbles eventually merge as the phase transition is completed, and only the dark matter particles which have entered the bubbles survive to constitute the observed dark matter today. This mechanism can produce dark matter with masses from the GeV scale to above the PeV scale, including a large region of viable parameter space beyond the Griest–Kamionkowski bound. Current and future direct detection and collider experiments can probe much of the viable parameter space.

November 28, Journal club

Speaker: Dr. Yang Hwan Ahn.

Topic: Short baseline neutrino oscillations

Abstract: https://arxiv.org/pdf/1903.09008.pdf

November 14, Journal club

Speaker: Adriana Guerrero Menkara

Topic: Planck evidence for a closed Universe and a possible crisis for cosmology 1911.02087

Abstract: The recent Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in CMB power spectra compared to that predicted in the standard ΛCDM model. A closed universe can provide a physical explanation for this effect, with the Planck CMB spectra now preferring a positive curvature at more than 99% C.L. Here we further investigate the evidence for a closed universe from Planck, showing that positive curvature naturally explains the anomalous lensing amplitude and demonstrating that it also removes a well-known tension within the Planck data set concerning the values of cosmological parameters derived at different angular scales. We show that since the Planck power spectra prefer a closed universe, discordances higher than generally estimated arise for most of the local cosmological observables, including BAO. The assumption of a flat universe could therefore mask a cosmological crisis where disparate observed properties of the Universe appear to be mutually inconsistent. Future measurements are needed to clarify whether the observed discordances are due to undetected systematics, or to new physics, or simply are a statistical fluctuation.

November 7, Journal club

Speaker: Dr. Bin Zhu

Topic: Dark Kinetic Heating of Neutron Stars and An Infrared Window On WIMPs, SIMPs, and Pure Higgsinos 1704.01577 1707.09442 1906.10145

Abstract: We identify a largely model-independent signature of dark matter interactions with nucleons and electrons. Dark matter in the local galactic halo, gravitationally accelerated to over half the speed of light, scatters against and deposits kinetic energy into neutron stars, heating them to infrared blackbody temperatures. The resulting radiation could potentially be detected by the James Webb Space Telescope, the Thirty Meter Telescope, or the European Extremely Large Telescope. This mechanism also produces optical emission from neutron stars in the galactic bulge, and X-ray emission near the galactic center, because dark matter is denser in these regions. For GeV - PeV mass dark matter, dark kinetic heating would initially unmask any spin-independent or spin-dependent dark matter-nucleon cross-sections exceeding 2 × 10−45 cm2 , with improved sensitivity after more telescope exposure. For lighter-than-GeV dark matter, cross-section sensitivity scales inversely with dark matter mass because of Pauli blocking; for heavier-than-PeV dark matter, it scales linearly with mass as a result of needing multiple scatters for capture. Future observations of dark sectorwarmed neutron stars could determine whether dark matter annihilates in or only kinetically heats neutron stars. Because inelastic inter-state transitions of up to a few GeV would occur in relativistic scattering against nucleons, elusive inelastic dark matter like pure Higgsinos can also be discovered.

October 31, Journal club

Speaker: Yoo-Jin Kang

Topic: Minimal Warm Inflation 1910.07525

Abstract: Slow-roll inflation is a successful paradigm. However we find that even a small coupling of the inflaton to other light fields can dramatically alter the dynamics and predictions of inflation. As an example, the inflaton can generically have an axion-like coupling to gauge bosons. Even relatively small couplings will automatically induce a thermal bath during inflation. The thermal friction from this bath can easily be stronger than Hubble friction, significantly altering the usual predictions of any particular inflaton potential. Thermal effects suppress the tensor-to-scalar ratio r significantly, and predict unique non-gaussianities. This axion-like coupling provides a minimal model of warm inflation which avoids the usual problem of thermal backreaction on the inflaton potential. As a specific example, we find that hybrid inflation with this axion-like coupling can easily fit the current cosmological data.

October 17, Journal club

Speaker: Soo-Min Choi

Topic: A Practical and Consistent Parametrization of Dark Matter Self-Interactions, 1908.06067

Abstract: Self-interacting dark matter has been proposed to explain the apparent mass deficit in astrophys- ical small-scale halos, while observations from galaxy clusters suggest that the corresponding cross section depends on the velocity. Accounting for this is often believed to be highly model-dependent with studies mostly focusing on scenarios with light mediators. Based on the effective-range for- malism, in this work we point out a model-independent approach which accurately approximates the velocity dependence of the self-interaction cross section with only two parameters. We illustrate how this parameterization can be simultaneously interpreted in various well-motivated scenarios, including self-interactions induced by Yukawa forces, Breit-Wigner resonances and bound states. We investigate the astrophysical implications and discuss how the approximation can be improved in certain special regimes where it works poorly.

October 10, Journal club

Speaker: Soon-Bin Kim

Topic: Clockwork Inflation, 1611.03316

Abstract: We investigate the recently proposed clockwork mechanism delivering light degrees of freedom with suppressed interactions and show, with various examples, that it can be efficiently implemented in inflationary scenarios to generate flat inflaton potentials and small density perturbations without fine-tunings. We also study the clockwork graviton in de Sitter and, interestingly, we find that the corresponding clockwork charge is site- dependent. As a consequence, the amount of tensor modes is generically suppressed with respect to the standard cases where the clockwork set-up is not adopted. This point can be made a virtue in resurrecting models of inflation which were supposed to be ruled out because of the excessive amount of tensor modes from inflation.

September 19, Journal club

Speaker: Dr. Yang Hwan Ahn.

Topic: Short baseline neutrino oscillations, 1903.09008

Abstract: We interpret the neutrino anomalies in neutrino oscillation experiments and the high energy neutrino events at IceCube in terms of neutrino oscillation in a scenario where three light neutrinos become Pseudo-Dirac particles by introducing light sterile neutrinos on top of the standard model. Our model is different from the so-called 3+n model with n sterile neutrinos suggested to interpret short baseline anomalies in terms of neutrino oscillations. While the Pontecorvo-Maki-Nakagawa- Sakata (PMNS) matrix in 3 + n model is simply extended to n × n unitary matrix, the neutrino mixing matrix in our model is parameterized so as to keep the 3 × 3 PMNS mixing matrix for three active neutrinos unitary. There are also no flavor changing neutral current interactions leading to the conversion of active neutrinos to sterile ones or vice versa. We derive new forms of neutrino oscillation probabilities containing the new interference between the active and sterile neutrinos which are characterized by additional new parameters ∆m2 and θ, and show how the short baseline neutrino anomalies can be explained in terms of oscillations, and the results for the high energy events from IceCube can be accommodated. New phenomenological effects attributed to the existence of the sterile neutrinos are discussed.

Summer 2019

August 16 (Fri in 305-310), Four-form field and hierarchy problem/inflation (Hyunmin, 1908.04252, 1908.05475), electron and muon g-2 in SUSY (M. Motoi et al, 1906.08768 and Badziak et al, 1908.03607), Relativistic Freeze-in (O. Lebedev et al, 1908.05491).

August 1, Dr. Bin Zhu joined CAU. Show and Tell.

July 11, No meeting.

July 4, Dr. Y.-H Ahn (self-introduction on research topics - axion and flavor symmetry), Yoojin (Overview on ICTP summer school).

Spring 2019

June 20, End-semester meeting

June 13, No meeting

June 6, National holiday

May 30, CAU seminar

May 23, No meeting

May 16, CAU seminar

May 9, No meeting

May 2, Student presentation (Soonbin: clockwork & axion inflation, 1902.05559; Jiseon: ANITA, 1902.04584, 1803.05088; Seunghyun: HEFT, 1902.05556, 1902.05936). Lecture on QFT and SUSY VIII (Spontaneous SUSY breaking, MSSM, Higgs mass)

April 18, KPS presentations

April 11, Journal: Hyunmin (Supermassive black hole in M87 from Event Horizon Telescope on April 10, 2019 (news article) ; CR-DM scattering, M. Pospelov et al, 181010543 ; Weyl photon, Y. Tang et al, 1904.04493), Ligong (Electroweak phase transition with general potential), Lecture on QFT and SUSY VII (Soft SUSY breaking, SUSY non-abelian gauge theories)

April 4, CAU seminar

March 28, Journal: Yoojin (1903.07638, S. Profumo et al, positron flux from two-component decaying dark matter), Taegyu (1903.10632, J. Kumar et al, quark vector-current portal datk matter, diffuse emission + Draco), Lecture on QFT and SUSY VI (SQED)

March 21, Journal: Ligong (Unrestored EW symmetry, 1807.07578), Soomin (Decaying dark matter & H0, 1903.06220), Lecture on QFT and SUSY V (Vector superfields)

March 14, Discussed papers (Antiproton excess from AMS-02 (~5sigma), 1903.01472, 1903.02549; Ultralight DM, baryons and galaxy rotation curves, 1903.03402; Planck mass dark matter, 1903.00492; photo-production of ALP at PrimEx, 1903.03586; Axion dark matter and CMB polarization, 1903.02666)

March 7, Show and Tell. Discussed papers (naturalness without new particles, 1902.06758; relaxation C.C., 1902.06793; Higgs parity, 1902.07726; Freeze-in from plasmon decays, 1902.08623; ALP inflation, 1903.00462)

Winter 2019

Feb 19, Lecture on QFT and SUSY IV (Chiral superfields, Wess-Zumino model)

Feb 8, Lecture on QFT and SUSY III (SUSY transformations, Superspace)

Jan 17, Lecture on QFT and SUSY II (SUSY algebra, SUSY multiplets)

Jan 15, Lecture on QFT and SUSY I (Lorentz symmetry and spinors, Coleman-Mandula theorem, Haag-Sohnius-Lopuszanski theorem)

Fall 2018

Dec 12, Journal club: Taegyu (EDM and new physics: Pomarol et al, 1810.09413; Reece et al, 1810.07736)

Nov 21, Journal club: Yoojin (Phase transition in twin Higgs models: K. Fujikura et al, 1810.00574), Soomin (Swampland conjecture: Murayama et al, 1809.00478)

Nov 14, CAU seminar by Dr. Kimiko Yamashita

Oct 17, Journal club: Hyun Min (X. Chu et al, 1810.04709)

Sep 19, Journal club: Ligong

Title : When dark matter meets cosmological phase transition.

Main paper : 1809.01198 / Strong gravitational radiation from a simple dark matter model

1712.03962 / Dynamic Freeze-In: Impact of Thermal Masses and Cosmological Phase Transitions on Dark Matter Production

Sep 12, Journal club: Min-Seok

Main paper : 1607.06814 / Can Gravitational Instantons Really Constrain Axion Inflation?

Sep 6 (in 305-310), Show and tell, WGC for natural inflation and effects of gravitational instantons (Min-Seok), Discrete symmetries and Higgs mass/phase transition (Hyunmin, Ligong), Dates of journal clubs to be decided.

Summer 2018

August 22 (at 2pm), Discussion on neutral naturalness and cosmology.

August 13 (at 2pm), Recent status of neutral naturalness (from CERN TH workshop).

July 17 (at 2pm), Progress on leptoquark projects in KIAS.

Spring 2018

June 11 (at 2pm) in 104-212, Summer plans and discussion on ICHEP presentations.

June 4 (at 2:30pm) in 305-310, MiniBooNE results on neutrino oscillations (1805.12028 ).

May 18 (at 2pm) in KIAS, Supercool dark matter (1805.01473).

April 16 (at 2pm) in 305-310, Discussed papers:

Ligong (F. Kahlhoefer, On the LHC sensitivity for non-thermalized hidden sectors, 1801.07621),

Soomin (A. Kamada et al, Self-heating dark matter via semi-annihilation, 1707.09238),

Minseok (D. Baumann et al, Probing ultralight bosons with binary black holes, 1804.03208),

Yoojin (J. Kim and J. McDonald, Freeze-in dark matter from a sub-Higgs mass clockwork sector via the Higgs portal, 1804.02661).

April 2 (at 2pm) in 305-310, No meeting.

March 26 (at 2pm) in 305-310, No meeting.

March 19 (at 3pm) in 104-212, Seminar: Dr. Ligong Bian, Higgs inflation and cosmological electroweak phase transition with N scalar in the post-Higgs era.

Abstract:

We study the Higgs inflation and the cosmological electroweak phase transition with the N-scalar extended standard model of particle physics (SM). The number of N is strictly bounded by the unitarity, the current Higgs precisions and electroweak precision observables. When the scalars respects an extra O(N)symmetry, the masses of the N scalars are bounded to TeV scale in the inflation viable parameter regions, and therefore impossible to saturate the DM candidates. The electroweak precision observables(here, S and T parameters) bounds the N to be smaller than 4 and therefore make the cosmological electroweak phase transition never being strongly first order. The O(N) symmetry preserved by the N-scalar can be spontaneous broken to be O(N − 1) with remnant N − 1 Goldstones, which can fake the neutrinos or gain masses through non-perturbative gravity effects and therefore contribute to dark radiations. The cosmological phase transition has been investigated in the Higgs inflation fleasible parameter spaces, where the phase transition can be strongly first order through one- step or two-step types. The mixing of extra heavy Higgs with the SM Higgs confronts with severely constraints from LHC, especially CEPC, ILC, FCC-ee. The bounds of the mixing angle from CEPC, ILC, FCC-ee might easily test the possibility to obtain Higgs inflations and SFOEWPT.

March 12 (at 3pm) in 104-212, Seminar: Dr. Min-Seok Seo, Symmetry at large scale.

Abstract:

Recently, infrared behaviors of gauge boson and graviton have drawn many interests as soft theorem was claimed to be connected to asymptotic symmetry. In this talk, we investigate the algebraic structure of asymptotic symmetry, and also discuss its applicability to cosmology.

March 7 (at 5pm), The first group meeting in spring semester. Discussed papers (A. Hook, Solving the Hierarchy Problem Discretely(1802.10093), K. Hamaguchi et al, Supersymmetric Flaxion(1802.07739), K. -Y. Choi et al, Non-thermal WIMP baryogenesis(1803.00820). Mentioned: 1803.01038 (Primordial GW), 1803.00993 (SN1987A bounds), 1802.09554 (Quantum no-hair), 1710.02149 (off-shell H->ZZ)).

Winter 2018

Feb 14 (at 3pm), Weak gravity conjecture (Min-Seok, https://arxiv.org/abs/1801.08546), B-meson anomalies and leptoquarks (Soomin, Taegyu).

Feb 7 (at 3pm), Self-interacting spin-2 dark matter (Yoojin), No missing satellite problem (Soomin), Thermal effects for dark matter (Ligong), g-2 corrections due to gravity & neutron lifetime and light dark matter (Hyunmin).

Jan 3 (at 3pm), First meeting of the new year.

Fall 2017

December 20 (at 3pm), Papers mentioned in journal clubs: Heavy Higgs decay(https://arxiv.org/abs/1712.06593), Pseudo-scalar mediator(https://arxiv.org/abs/1712.06597), Detection of light dark matter(https://arxiv.org/abs/1712.06598), Flavor physics(https://arxiv.org/abs/1712.06862), GUT and SUSY(https://arxiv.org/abs/1712.06894), Neutron star merger and GW(https://arxiv.org/abs/1710.05893).

December 13, Brain-storming discussion on DAMPE and cosmics rays. (Fits to DAMPE: 1711.10989, 1712.00372, 1712.02744, Z' models: 1711.10995, 1711.11563, charged-portal dark matter: 1712.00037, 1712.02744, Decaying dark matter: 1712.00370).

October 11, Review on PBH and inflation (Ligong).

September 20, Discussion on projects. PBH & QCD-EW mixed EWPT will be discussed by Ligong in the next meeting.

September 13, Show and tell. Papers mentioned in journal clubs: Primordial Black Holes (https://arxiv.org/abs/1709.03500), QCD-EW mixed EWPT (https://arxiv.org/abs/1704.04955, dark QCD and GW: https://arxiv.org/abs/1504.07263), EWPT and high temperature approximation (https://arxiv.org/abs/1709.03232), Quantum scale invariance (https://arxiv.org/abs/1508.00595 ; https://arxiv.org/abs/1608.05336 ; https://arxiv.org/abs/1612.09120).

Summer 2017

August 29 (Tue at 2pm), Discussion on group meetings in new semester.

August 4 (Fri at 2pm in 102-805), Summary of PiTP 2017 (Soomin, Candidates for dark matter (N. Weiner) and Searches for dark sector (R. Essig); Yoojin, LHC physics (L-T. Wang)), Discussion on U(1)' & flavor structure and clockwork theory (Hyunmin).

July 6 (Thu at 2pm), Welcome meeting for Dr. Ligong Bian.

June 27 (Tue at 2pm), Details on Clockwork theory (Hyunmin).

Spring 2017

June 15, Discussion on group meetings in summer.

June 8, Sommerfeld effects from Feynman diagram approach (Taegyu, 0910.5713, 0902.0688); Retrospects on CERN-CKC Jeju workshop.

May 18 (at 11am), Discussion on B-meson anomalies and dark matter. (Soomin: Altmannshofer et al, Explaining dark matter and B decay anomalies with an Lμ−Lτ model, Yoojin: J. Cline et al, Hidden sector explanation of B-decay and cosmic ray anomalies, Taegyu: 1512.06828, G. Hiller et al, 1704.05444).

April 27 & May 11 (at 11am), Discussion on B-meson anomalies (Hyunmin, Exps: 1403.8044 (B->K^*), 1406.6482 (B->K), 1506.08614 (B->D*), CERN seminar/LHCP/CERN LHCC, BSM: 1408.1627, 1704.05340, 1704.05446, Reviews: hep-ph/9806471, 1501.05283, 1606.02756, 1705.02693, 1704.05438, etc.).

April 14 (at 11am), Practice talks for KPS (Soomin, On thermal averages for higher-order annihilation of dark matter; Yoojin, SIMP dark matter and forbidden mechanism).

March 28 (at 3pm), Enabling Forbidden Dark Matter (Yoojin, J. Cline et al, hep-ph/1702.07716); Discussion on Sommerfeld enhancement and dark matter annihilation (assigned to Taegyu for the detailed calculations).

March 9 (at 3pm), Show and tell, Review and prospective of group activities (Hyunmin).

Winter 2017

Feb 16 (at 3pm), 1.5 Higgs Production in Gluon Fusion (Skip 1.3, 1.4. )

Feb 2 (at 3am), 1.2 The Standard Model (~1.2.7 Coleman-Weinberg Potential)

Jan 17 (at 2pm), 1.2 The Standard Model (~1.2.5 Top-Higgs Renormalization Group: Taegyu, Yoojin, Soomin), Review on Sommerfeld enhancement (Taegyu).

Jan 5 (at 3pm), 1.1 Electroweak Symmetry Breaking (T. Plehn, Lectures on LHC Physics: Taegyu, Soomin, Yoojin)

Fall 2016

Dec 23 (at 5pm), Dark Matter's secret liaisons: phenomenology of a dark U(1) sector with bound state (Yoojin); Clockwork WIMP (Soomin); Higgs Boson Production and Decay at Hadron Colliders, Sommerfeld effect for Coulomb force (Taegyu).

Dec 9 (at 11am), Axial vector case for Beryllium anomalies (Yoojin); strong bounds on self-interacting dark matter (Soomin): CP violations in Higgs effective field theory (Taegyu).

Nov 11 (at 11am), Practice talk for CAU poster: New physics from Higgs searches (Taegyu).

Nov 3 (at 3pm), Berylium and dark matter/inflation (Yoojin, Soomin, Taegyu).

Oct 12 (at 11pm), Practice talks for KPS: Phases of light dark matter and self-interactions (Soomin), Collider and astrophysical probes of dark matter with mediators (Yoojin).

Oct 6 (at 3pm), A project on Berylium (Yoojin).

Sep 30 (at 11am), A project on Berylium (Yoojin, Soomin).

Sep 8 (at 3pm), Berylium anomalies (Taegyu).

Sep 1 (at 3pm), First meeting in new semester.

Summer 2016

July 19 (at 3pm), Presentation on SIMP dark matter for Summer Institute 2016 (Soomin), Review on Boltzmann equations (Yoojin).

June 30 (at 4pm), Presentation on diphoton resonance and dark matter (Yoojin).

June 23 (at 4pm), Group discussion on summer activities.

Spring 2016

May 25 (at 3pm), Relaxion mechanism (Soomin), Prospects from CTA (Yoojin).

May 24 (at 3pm), Searches for long-lived particles at the LHC (Taegyu).

May 21 (Sat at 2pm), Snail lecture on dark matter (Jong-Chul Park) in Chung-Ang University.

May 10, Light mediators at the LHC (Taegyu).

April 14, Practice talks for KPS (Soomin on inflection point inflation, Yoojin on diphoton and dark matter).

April 7, Practice talks for KPS (Soomin on inflection point inflation, Yoojin on diphoton and dark matter); Higgs-flavor mixing (Sangwon, 1603.06614 [hep-ph]); Diphoton excess through dark mediators (Taegyu, 1603.01256 [hep-ph]).

March 17, Introduction to SUSY (Hyunmin).

March 10, First meeting in new semester. LHC 750GeV diphoton and gravity waves from LIGO (Hyunmin); Sterile neutrinos and NEOS (Siyeon).

Winter 2016

February 12, Status report 1 for Flavor anomalies (Tae-Gyu); Summary of GGI winter school (Soo-Min).

January 19, Status report 1 for 2HDM (Sang-Won)

January 12, Status report 1 for dark matter calculation (You Jin), SUSY and 2HDM (Hyun Min).

January 5, First meeting in the new year (Papers distributed: 1512.06828 (Flavor anomalies & diphoton excess; Tae-Gyu), 1512.08963 & 1601.00006 (2HDM & diphoton resonance; Sang-Won). )

Fall 2015

November 26, Presentation based on CAU posters (research students).

November 17 at 4pm, Practice talks for CAU Poster (Kang Cheol, You Jin, Tae Gyu, Sang Won).

November 11 at 3pm, Preliminary results for CAU Poster (Kang Cheol, You Jin, Tae Gyu, Sang Won).

November 5, SU(2) gauge theories (led by Kang Cheol), Higgs mechanism (led by Sang Won).

October 13 at 4pm, U(1) gauge theories (led by You-Jin). It will take place in 107-602.

September 24, Scalar fields (led by Tae Gyu).

September 10, Dirac fermion and Maxwell equations (led by Sang Won).

Summer 2015

August 25

Soo Min Choi - Reconciling naturally keV line and self interacting dark matter, arxiv : 1506.02032v1

Kang Cheol Kim - Hilltop Inflation

You Jin Kang - Forbidden Dark Matter, arxiv : 1505.07107v2

Sang Won Ahn - On the Trail of the Higgs Boson, arxiv : 1506.08185v3

Tae Gyu Ro - Scalar Singlet Dark Matter and Gamma Lines, arxiv : 1508.04418v1

August 11, Srednicki Chap. 15, 16 (led by Kang Chul).

July 28, Srednicki Chap. 12, 13, 14 (led by Sang Won, Sumin).

July 14, Srednicki Chap. 10, 11 (led by Kang Chul).

Spring 2015

June 2, Srednicki Chap. 9 (led by Sumin Choi).

May 19, Srenicki Chap. 8 (led by Chang Hwan Jang).

May 12, Srednicki Chap. 7 (led by Kang Chul Kim).

April 30, Srednicki Chap. 6 (led by Jieun Lee).

April 7, Srednikci Chap. 5 (led by Sumin Choi).

March 31, Srednicki Chap. 4 (led by Chang Hwan Jang).

March 24, Srednicki Chap. 3 (led by Hyun Min Lee).

March 17, Srednicki Chap. 2 (led by Jieun Lee).

March 10, Reading club for Srednicki Chap. 1 (Quantum Field Theory). (led by Kang Chul Kim).

March 3, Kick-off meeting.

Winter 2015

Feb 3, SIMP Dark Matter (Sumin), Natural Inflation & WGC (Kang-Cheol).

Jan 13, Non-abelian gauge theories (Jieun).

Jan 6, Reheating and preheating in inflation models (Kang-Cheol, Sumin).

Jan 6 - Feb 3 on every Tuesday at 1pm, Group meeting during winter break.

Fall 2014

Dec 22, Number of efoldings and reheating temperature (Sumin, Kang-Cheol), A review on the SM (Ji Eun).

Dec 3, Student presentations (Sumin, Kang-Cheol, Ji Eun).

Nov 7, Introduction to Higgs signals.

Oct 29, Introduction to FRW universe and inflation.

Oct 14, Discussion on the projects for poster session on physics day at CAU.

Oct 7, Boltzmann equation for the relic density of dark matter. Ref: Kolb & Turner, The Early Universe; F. Gondolo & G. Gelmini, Nucl. Phys. B360 (1991) 145.

Sept 30, Dark matter models for keV lines. Ref: H. M. Lee, arXiv: 1404.5446.

Sept 24, Chi-square analysis for Higgs data; WIMP dark matter and cosmic rays. Ref: S.-J. Lin et al, 1409.6248 [astro-ph.HE], AMS-02, PRL113 (2014) 121101.

Sept 16, Displaced vertices from X-ray lines (Sumin). Ref: A. Falkowski et al, arXiv:1409.2872

Sept 3 - endterm, Reading club to be continued for Quantum Field Theory (Ref. Chap. III.4 - VII, Quantum field theory in a nutshell by A. Zee)

Summer 2014

July 1 - August 5 (on Tuesdays at 2pm), Reading club for Quantum Field Theory (Ref. Chap I - III.3, Quantum field theory in a nutshell by A. Zee)

Feynman brought quantum field theory to the masses. --- J. Schwinger

Spring 2014

June 25, A meeting for summer schedule.

June 11, End-term meeting.

June 3, After Planck 2014 (Hyunmin)

May 21, On dark matter signal from Fermi bubbles (Hyunmin)

May 14, Lecture by Myeonghun Park.

May 7, Magnetic dark matter (Youngmin Kim), on Vacuum instability.

April 30, Inflaton perturbations by Sumin Choi.

April 9, EDM (related to M. Seo)

April 2, Supersymmetry II (related to K. Lee, S. Jung and M. Seo)

March 26, Cosmic inflation (Sumin Choi), Supersymmetry I (related to K. Lee, S. Jung and M. Seo)

March 19, Lyth bound (Sumin Choi), Dark matter and CMB II (related to S. Lee and K. -Y Choi)

March 12, Dark matter and CMB I (related to S. Lee and K. -Y. Choi)

March 5, Composite Higgs (related to T. Flacke)

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