Schedule

December 23, 2021, 11:30am (KST)

• Speaker: Prof. Seongchan Park (Yonsei U. & KIAS)

• 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.

December 21, 2021, 3:30pm (KST)

• Speaker: Dr. Tarak Nath Maity (Indian Institute of Science)

• Title: Indirect searches for dark matter: gamma rays and neutrinos

• Abstract: Gamma rays and neutrinos being charge-neutral are useful messengers in search for dark matter. In this talk, we will explore the prospect of recently discovered sub-PeV diffuse gamma rays by Tibet AS gamma in search of decaying dark matter. While for indirect search through neutrinos we focus on neutrinos produced from captured dark matter annihilation in a galactic distribution of neutron stars. We will see that both of these scenarios may probe unexplored regions of the parameter space for heavy dark matter.

December 17, 2021, 11:30am (KST)

• Speaker: Sung Mook Lee (Yonsei U.)

• Title: Reheating Predictions and Phenomenology from Inflation with Non-minimal Coupling

• Abstract: In the inflationary paradigm, reheating processes have potentially rich phenomenology. First, for the observational side, this affects predictions on cosmological observables. We study the effects of reheating on inflationary predictions of models with general non-minimal coupling possessing asymptotically flat potential, including Higgs inflation. We consider a wide range of non-minimal coupling in both metric and Palatini formalisms. Second, for the connection of BSM physics, we propose a scenario of spontaneous leptogenesis during the reheating in Higgs inflation, considering two higher order non-renormalizable terms responsible for lepton number violation and spontaneous CPT violation, respectively.

December 14, 2021, 4pm (KST)

• Speaker: Natsumi Nagata (U Tokyo)

• Title: Axion Quality Problem Alleviated by Non-Minimal Coupling to Gravity

December 9, 2021, 10am (KST)

• Speaker: Hiroshi Okada (APCTP)

• Title: Dark Matter Stability at fixed points of a modular A(4) symmetry

December 7, 2021, 5pm (KST)

• Speaker: Peter Millington (University of Nottingham)

• Title: Non-Hermiticity: a new paradigm for model building in particle physics

• Abstract: Non-Hermitian quantum theories have been applied in many other areas of physics. In this talk, I will review recent developments in the formulation of non-Hermitian quantum field theories, highlighting features that are unique compared to Hermitian theories [1]. I will describe their crucial discrete symmetries and how continuous symmetry properties are borne out, including Noether's theorem [2], the Goldstone theorem [3] and the Englert-Brout-Higgs mechanism [4,5]. As examples, I will describe non-Hermitian deformations of (scalar) QED [4], the Higgs-Yukawa theory [6] and flavour oscillations [7], illustrating the potential implications of non-Hermitian model building for the neutrino sector [6]. I will also discuss a supersymmetric non-Hermitian model [8]. Together, these results pave the way for a systematic programme for building non-Hermitian extensions of the Standard Model of particle physics.

December 2, 2021, 5pm (KST)

• Speaker: Yining You (University of Florida)

• Title: sub-GeV Dark Matter Direct Detection using superfluid Helium-4

November 30th ,2021, 5pm (KST)

• Speaker: Jinno Ryuske (DESY)

• Title: Dark matter from dark photons: a taxonomy of dark matter production

November 16, 2021, 10am (KST)

• Speaker: Manuel A. Buen-Abad (Maryland U.)

• Title: Cosmological Constraints on Dark Matter Interactions with Ordinary Matter

• Abstract: Dark matter interactions with electrons or protons during the early Universe leave imprints on the cosmic microwave background and the matter power spectrum, and can be probed through cosmological and astrophysical observations. We explore these interactions using a diverse suite of data: cosmic microwave background anisotropies, baryon acoustic oscillations, the Lyman- α forest, and the abundance of Milky-Way subhalos. We derive constraints using model-independent parameterizations of the dark matter--electron and dark matter--proton interaction cross sections and map these constraints onto concrete dark matter models. Our constraints are complementary to other probes of dark matter interactions with ordinary matter, such as direct detection, big bang nucleosynthesis, various astrophysical systems, and accelerator-based experiments.

November 11, 2021, 5pm (KST)

• Speaker: Kai Schmitz (CERN)

• Title: Pulsar hints for gravitational waves from cosmic strings?

• Abstract: All major pulsar timing array (PTA) collaborations—NANOGrav, Parkes PTA, and EPTA—are now seeing indications of a new stochastic process in their latest data sets. If confirmed in the future, this new signal may turn out to be the first glimpse of a stochastic gravitational-wave background at nanohertz frequencies. In this talk, I will review the properties of the new signal and discuss its interpretation in terms of gravitational waves emitted by a network of cosmic strings in the early Universe. I will especially distinguish between stable and metastable cosmic strings, both of which represent realistic and intriguing possibilities in the context of grand unified theories (GUTs). As for metastable cosmic strings, I will present some theoretical advancements in the description of gravitational-wave emission by a decaying cosmic-string network based on recent work in collaboration with Wilfried Buchmüller and Valerie Domcke [2107.04578]. This will lead to the conclusion that metastable cosmic strings are not only capable of explaining the new PTA signal in the nanohertz band; unlike stable cosmic strings, they also predict a signal within the reach of current-generation ground-based interferometers in the audio band. On their way to design sensitivity, existing gravitational-wave experiments will thus have a realistic chance to probe particle physics processes close to the GUT scale via the observation of gravitational waves from metastable cosmic strings.

November 4, 2021, 10am (KST)

• Speaker: Sunghoon Jung (Seoul National University)

• Title: Hubble selection of the weak scale from QCD quantum phase transition

• Abstract: If the strange quark were lighter, QCD phase transition could have been first order. This implies that QCD may have quantum critical points as the Higgs vev vh is varied from its Standard Model value. We show that inflationary quantum evolution of vh with the relaxion can drive our universe toward those critical points, realizing the weak scale close to the observed value while explaining its closeness to ΛQCD. We first explore quantum critical points of Nf=3 QCD, parameterized by vh at T=0, and present a basic model for the weak scale. It results in a sharply localized probability distribution of the weak scale, which is critical not to the crossover at zero but to the quantum transition at ∼ΛQCD.

October 28, 2021, 2pm (KST)

• Speaker: Disha Bhatia(IMSc)

• Title: Frugal $U(1)_X$ models with non-minimal flavor violation for $b

• Abstract: We present a class of $U(1)_X$ models which are can simultaneously explain the neutrino mixings and flavor anomalies in neutral B decays. The frugal set up apart from additional $Z^\prime$, requires additional singlet scalar for neutrino mixings and an additional scalar doublet for quark mixings. Our set up identifies a class of symmetries wherein all generations of quarks are necessarily charged, rendering collider constraints to be stringent. We show all our models with the assumption of CKM-like mixings are ruled out from the current data. Introduction of a single source parameter for non-minimal mixings allows for a wider class of models consistent with the data. We show the viable symmetry patterns are of the form $L_e - 3 L_\mu - L_\tau$, $L_e - 3 L_\mu + L_\tau$, and $L_e + 3 L_\mu - L_\tau$.

October 19, 2021, 6pm (KST)

• Speaker: Yu Hamada (KEK)

• Title: Electroweak-Skyrmion as Asymmetric Dark Matter

• Abstract: We propose a scenario that the Electroweak-Skyrmion, a solitonic object made of the Higgs field and the electroweak gauge fields, is identified as an asymmetric dark matter. In this scenario, the relic abundance of the dark matter is related to the baryon asymmetry of the Universe through a sphaleron-like process. We show that the observed ratio of dark matter abundance to the baryon asymmetry can be explained by this scenario with an appropriate choice of model parameters that is allowed by currently available experimental constraints.

October 14, 2021, 2pm (KST)

• Speaker: Seong-Sik Kim (Chung-Ang University)

• Title: Self-resonant Dark Matter

• Abstract: We present a novel mechanism for Sommerfeld enhancement for dark matter interactions without the need for light mediators. Considering a model for two-component scalar dark matter with a triple coupling, we find that there appears an u-channel resonance in dark matter elastic scattering. From the sum of the corresponding ladder diagrams, we obtain a Bethe-Salpeter equation with a delay term and identify the Sommerfeld factor for two-component dark matter from the effective Yukawa potential for the first time. We discuss the implications of our results for enhancing dark matter self-scattering and annihilation.

October 12, 2021, 12pm (KST)

• Speaker: Nicolas Bernal (Antonio Narino University)

• Title: UV FIMP Dark Matter

• Abstract: If the interaction rates between the visible and the dark sectors were never strong enough, the observed dark matter relic abundance could have been produced in the early Universe by non-thermal processes. This is what occurs in the so-called freeze-in mechanism. In the simplest version of the freeze-in paradigm, after dark matter is produced from the standard model thermal bath, its abundance is frozen and remains constant. However, the dark matter dynamics could be not so simple. Here we will study a couple of scenarios, one where the dark matter possess sizable self-interactions (https://arxiv.org/abs/2104.10699), and the other where the dark matter genesis is deeply related inflation (https://arxiv.org/abs/2106.03950).

October 7, 2021, 4pm (KST)

• Speaker: Manuel Drees (Universität Bonn)

• Title: A light Lμ–Lτ gauge boson for gμ–2, dark matter and a few other things

• Abstract: The difference of lepton numbers, Lμ–Lτ, can be gauged in the SM without introducing anomalies. This new gauge boson can explain the measurement of the anomalous magnetic moment of the muon, if its mass is sufficiently small. Adding a dark matter candidate to the model leads to a very constrained region of parameter space with the correct thermal relic density, improved description of cosmological data ("Hubble tension"), and a partial explanation of the excess of 511 keV photons from the galactic center; all in agreement with various astrophysical and accelerator constraints.

September 30, 2021, 4 - 6 pm

• Speaker: Tevong You (University of Cambridge & CERN)

• Title: New Positivity Bounds on Effective Field Theories

• Abstract: Effective field theory (EFT) is a powerful framework and organising principle for characterising phenomena at different energy scales. The effects of heavier ultra-violet (UV) degrees of freedom become encapsulated in the Wilson coefficients of higher-dimensional operators at low energies in the infra-red (IR). Positivity bounds place general constraints on these coefficients using only fundamental properties of the UV theory such as locality, unitarity, and causality. I will review the derivation of these positivity bounds before presenting recent work extending their applicability to the case of EFTs involving massive spinning particles.

June 24, 2021, 4pm - 5:30pm

• Speaker: Prof. Fuminobu Takahashi (Tohoku U.)

• Title: Cosmic Birefringence and Axion

• Abstract: Recently, it was reported that the Planck 2018 polarization data of cosmic microwave background (CMB) favors a nonzero value of isotropic cosmic birefringence (CB) with statistical significance of 2.4 sigma. The observed rotation angle of the CMB polarization can be explained by an axion-like particle that has changed by about the decay constant from the time of recombination to the present. I will introduce two scenarios which naturally explain the hinted isotropic CB. One is the axion domain wall, and the other is an axion coupled to dark matter density. The former also predicts a peculiar anisotropic CB, which can be searched for with future CMB observations.

June 22, 2021, 10am

• Speaker: Prof. Kaladi Sankaran Babu (Oklahoma State University)

• Title: Unified Framework for Flavor Anomalies, Muon g-2 and Neutrino masses

• Abstract: In this talk I shall explore a unified description of flavor anomalies reported in the decays of B mesons, the discrepancy between theory and experiment in muon g-2, and the generation of small neutrino masses via radiative corrections. An explicit model based on R2 and S3 leptoquarks will be discussed and its experimental tests will be outlined. Limits on the leptoquark Yukawa couplings to the first two family quarks will be derived from non-resonant dilepton production searches at the LHC. In addition, it will be shown that sizable muon g-2 can arise in a context that explains naturally a large neutrino magnetic moment which may be relevant for the XENON1T excess.

May 20, 2021, 4pm

• Speaker: Dr. Junichiro Kawamura (IBS CTPU)

• Title: TeV-scale vector leptoquark from Pati-Salam unification with vectorlike families

• Abstract:

May 18, 2021, 10am

• Speaker: Prof. Lam Hui (Columbia U.)

• Title: Wave Dark Matter

• Abstract: We review the physics and phenomenology of wave dark matter: a bosonic dark matter candidate lighter than about 30 eV. Such particles have a de Broglie wavelength exceeding the average inter-particle separation in a galaxy like the Milky Way, and are well described as classical waves. We outline the particle physics motivations for them, including the QCD axion and ultra-light axion-like-particles such as fuzzy dark matter. The wave nature of the dark matter implies a rich phenomenology: (1) Wave interference leads to order unity density fluctuations on de Broglie scale. A manifestation is vortices where the density vanishes and around which the velocity circulates. There is one vortex ring per de Broglie volume on average. (2) For sufficiently low masses, soliton condensation occurs at centers of halos. The soliton oscillates and random walks, another manifestation of wave interference. The halo/subhalo abundance is suppressed at small masses, but the precise prediction from numerical wave simulations remains to be determined. (3) For ultra-light ~10^{-22} eV dark matter, the wave interference substructures can be probed by tidal streams/gravitational lensing. The signal can be distinguished from that due to subhalos by the dependence on stream orbital radius/image separation. (4) Axion detection experiments are sensitive to interference substructures for moderately light masses. The stochastic nature of the waves affects the interpretation of experiments and motivates the measurement of correlation functions. Current constraints and open questions, covering detection experiments and cosmological/galactic/black-hole observations, are discussed.

May 13, 2021, 4pm

• Speaker: Dr Philipp Schicho (University of Helsinki)

• Title: Cosmological phase transition: Robust thermal resummation

• Abstract: Thermal field theories exhibit a rigorous scale hierarchy and their bosonic sector is rendered non-perturbative in the infrared. Hence, to reliably describe the thermodynamics of the electroweak phase transition both perturbative and non-perturbative methods are needed. At the intersection between these methods, one can construct a 3-dimensional effective theory that has thermal resummations systematically built in to all orders.

I apply computer algebraic multi-loop tools of perturbation theory for finite-temperature theories to determine this dimensionally reduced theory. Therefore, I demonstrate how to calculate the effective potential to describe cosmological first-order phase transitions in Beyond the Standard Model theories with extended Higgs sectors. The theoretical uncertainties for such transitions are contrasted with other approaches to resummation.

May 11, 2021, 10am - 11:30am

• Speaker: Prof. Keith Olive (Minnesota U.)

• Title: Recent updates to Big Bang Nucleosynthesis

• Abstract: TBA

May 6, 2021, 10am - 11:30am

• Speaker: Prof. Jessie Shelton (UIUC)

• Title: Perturbative benchmark models for a dark shower search program

• Abstract: We provide five benchmark hidden valley models with perturbative parton showers, which span a wide range of dark shower phenomenology. We consider production through an s-channel, heavy mediator, which can be identified with the SM Higgs. By assuming a set of well-motivated decay portals, one can moreover fix both the branching ratios of the dark mesons and set a lower bound on their lifetime. We provide a public python tool which can be used to generate self-consistent PYTHIA 8 cards for our benchmark models.

April 29, 2021, 4pm - 5pm

• Speaker: Prof. Fancesco D'Eramo (U. Padua and INFN)

• Title: Hunting for FIMPs at particle colliders and in the sky

• Abstract: Feebly Interacting Massive Particles (FIMPs) are dark matter candidates that are produced in the early universe via a mechanism known as freeze-in. Their couplings to visible particles are very tiny and therefore searching for FIMPs is extremely challenging. In this talk, I will discuss two strategies to unveil the properties of these elusive particles. Displaced events at colliders are a promising way, even though typical decay lengths as obtained from relic density calculations are way too large to observe anything in our detectors. I will show how motivated modifications of the cosmological history naturally lead to displaced events; intriguingly, the observation of a displaced event could reveal something about the thermal history of our universe. Furthermore, if the FIMP particle is light enough then it can suppress cosmological structures at small scales. Working in a model-independent fashion, I will present lower bounds on the FIMP mass for different production mechanisms.

April 27, 2021, 5pm

• Speaker: Prof. Dominik Stöckinger (TU Dresden)

• Title: The new muon g-2 result and potential implications for new physics

• Abstract: The new Fermilab g-2 result has confirmed the previous measurement. The deviation to the SM prediction has now a significance of 4.2 sigma and the indications for physics beyond the SM (BSM) are strengthened. In the talk we discuss which BSM scenarios would be able to explain this deviation how such scenarios are constrained. A basic point to notice is that the deviation is larger than the contributions from the SM weak interactions. For this reason only BSM scenarios with specific enhancement mechanisms are able to accommodate the deviation, and such scenarios typically involve intriguing connections to the muon mass generation mechanism and/or to dark matter and are often strongly constrained by other experiments.

March 2, 2021, 10am - 11am

• Speaker: Prof. Pavel Fileviez Perez (Case Western Reserve University)

• Title: New Forces, Dark Matter and the LHC

• Abstract: New theories for physics beyond the Standard Model are discussed. In these gauge theories the existence of dark matter is predicted from anomaly cancellation and one finds that the new physics scale must be below the multi-TeV scale. I discuss in detail the phenomenological and cosmological aspects of these theories. In this context the new Higgs responsible for the breaking of the gauge symmetry also generates mass for the dark matter candidate. We discuss the correlation between the Higgs decays and dark matter phenomenology. The testability of these theories and the unique signatures at the Large Hadron Collider are discussed in detail.

March 4, 2021, 5pm - 6:30pm

• Speaker: Andreas Ringwald (Deutsches Elektronen-Synchrotron DESY)

• Title: Hunting the axion

• Abstract: We review the physics case for the axion and discuss different methods to hunt for it in current and future experiments.

• Note: This talk is going to be accessible to non-experts (including PhD students) as well as experts on physics of axions, therefore enjoyable to a broader class of physicists.)

March 9, 2021, 5pm - 6pm

• Speaker: Prof. Silvia Pascoli (Durham U., IPPP)

• Title: A Dark Seesaw Solution to Low Energy Anomalies: MiniBooNE, the muon (g−2), and BaBar

• Abstract: A recent update from MiniBooNE has strengthened the observed 4.8σ excess of e-like events. Motivated by this and other notable deviations from standard model predictions, such as the muon (g−2), we propose a solution to low energy anomalies through a dark neutrino sector. The model is renormalizable and can also explain light neutrino masses with an anomaly-free and dark U(1)′ gauge symmetry broken at the GeV scale. Large kinetic mixing leads to s-channel production of heavy neutral leptons at e+e− colliders, where we point out and explain a ≳2σ excess observed in the BaBar monophoton data. Our model is also compatible with anomalous e-like events seen at old accelerator experiments, as well as with an excess of double vertex signatures observed at CCFR.

March 11, 2021, 5pm - 6pm

• Speaker: Prof. Maurizio Piai (Swansea University)

• Title: A Near-Conformal Composite Higgs Model

• Abstract: We analyze a composite Higgs model based on the confining SU(3)SU(3) gauge theory with N_f = 8N Dirac fermions in the fundamental representation. This gauge theory has been studied on the lattice and shown to be well described by a dilaton effective field theory (EFT). Here we modify the EFT by assigning standard-model quantum numbers such that four of the composite pseudo-Nambu-Goldstone boson (pNGB) fields form the standard-model Higgs doublet, by coupling it to the top quark, and by adding to the potential a term that triggers electroweak symmetry breaking. The model contains a pNGB Higgs boson, a set of heavier pNGBs, and an approximate dilaton in the same mass range. We study the phenomenology of the model, and discuss the amount of tuning required to insure consistency with current direct and indirect bounds on new physics, highlighting the role of the dilaton field.

March 16, 2021, 5pm - 6pm

• Speaker: Prof. Thomas Hambye (Brussels U.)

• Title: Dark matter from dark photons: a taxonomy of dark matter production

• Abstract: We analyse how dark matter (DM) can be produced in the early universe, working in the framework of a hidden sector charged under a U(1)' gauge symmetry and interacting with the Standard Model through kinetic mixing. Depending on the masses of the dark matter particle and of the dark photon, as well as on the hidden U(1)' gauge coupling and the kinetic mixing parameter, we classify all the distinct regimes along which the observed dark matter relic density can be accounted for. We find that 9 regimes are potentially operative to produce the DM particles and this along 5 distinct dynamical mechanisms. Among these, 4 regimes are new and correspond to regimes in which the DM particles are produced by on-shell dark photons. One of them proceeds along a new dynamical mechanism, which we dub sequential freeze-in. We argue that such regimes and the associated dynamical mechanisms are characteristic of DM models for which, on top of the Standard Model and the dark sector, there are other massive, but relatively light particles -- akin to the dark photon -- that interact both with the SM and the DM sectors.

March 18, 2021, 2pm - 3pm

• Speaker: Dr. Rupert Coy (Brussels U.)

• Title: Neutrino lines from DM decay induced by high-scale seesaw interactions

• Abstract: If the stability of the dark matter (DM) particle is due to an accidental symmetry, nothing prevents UV physics from destabilising it by inducing DM decays suppressed by powers of the UV scale. The seesaw physics, presumably at the origin of neutrino mass, could induce such a decay. We show that if the seesaw scale lies around the usual Weinberg operator scale, the induced DM decay could generically lead to neutrino lines whose intensity is of the order of the present sensitivity of neutrino telescopes. We illustrate this possibility with models in which the DM is made of the gauge boson(s) of an abelian or non-abelian gauge symmetry.

March 23, 2021, 10am - 11am

• Speaker: Dr. Isabel Garcia Garcia (Santa Barbara, KITP)

• Title: P not PQ

• Abstract: Parity solutions to the strong CP problem are a compelling alternative to approaches based on Peccei-Quinn symmetry, particularly given the expected violation of global symmetries in a theory of quantum gravity. The most natural of these solutions break parity at a low scale, giving rise to a host of experimentally accessible signals. We assess the status of the simplest parity based solution in light of LHC data and flavor constraints, highlighting the prospects for near future tests at colliders, tabletop experiments, and gravitational wave observatories. The origin of parity breaking and associated gravitational effects play crucial roles, providing new avenues for discovery through EDMs and gravity waves. These experimental opportunities underline the promise of generalized parity, rather than Peccei-Quinn symmetry, as a robust and testable solution to the strong CP problem.

March 25, 2021

• Speaker: Prof. Viatcheslav Mukhanov (Ludwig Maxmillian University & KIAS)

• Title: Quantum fluctuations and new instantons

April 20, 2021, 5pm - 6pm

• Speaker: Prof. Enrico Nardi (INFN Frascati)

• Title: Axion quality from gague flavour symmetries

• Abstract: The strong CP problem is elegantly solved by the Peccei-Quinn (PQ) mechanism, that postulates the existence of a global Abelian symmetry endowed with a mixed $U(1)_{PQ}$-$SU(3)_C$ anomaly, and broken spontaneously. Implementing the PQ mechanism in UV complete models poses some challenges: (i) being anomalous, the PQ symmetry cannot be fundamental, so which is its origin? (ii) being global, it is not respected by quantum gravity corrections, so how can it remain protected? I will argue that a class of local gauge groups can automatically produce PQ symmetries with the required level of protection. Within the standard model, these symmetries would play the role of flavour symmetries, providing interesting connections between the axion quality problem and the flavour puzzle.

April 15, 2021, 5pm

• Speaker: Dr. Carlo Giunti (INFN Torino & U Torino)

• Title: Status of the reactor antineutrino anomalies and implications for active-sterile neutrino mixing

• Abstract: In this talk I discuss the current status of the reactor antineutrino anomaly, that is a deficit of electron antineutrino events observed in many short-baseline neutrino oscillation experiments with respect to the Huber-Muller theoretical prediction. I discuss the global analysis of the data of reactor short-baseline neutrino oscillation experiments in the framework of active-sterile neutrino mixing. I also discuss the statistical significance of the Neutrino-4 signal.

April 13, 2021, 10am - 11am

• Speaker: Dr. Manibrata Sen (UC Berkeley and Northwestern U.)

• Title: Dodelson-Widrow Mechanism In the Presence of Self-Interacting Neutrinos

• Abstract: keV-scale gauge-singlet fermions, allowed to mix with the active neutrinos, are elegant dark matter (DM) candidates. They are produced in the early universe via the Dodelson-Widrow mechanism and can be detected as they decay very slowly, emitting X-rays. In the absence of new physics, this hypothesis is virtually ruled out by astrophysical observations. Here, we show that new interactions among the active neutrinos allow these sterile neutrinos to make up all the DM while safely evading all current experimental bounds. The existence of these new neutrino interactions may manifest itself in next-generation experiments, including DUNE.

April 8, 2021, 4pm - 5pm

• Speaker: Yuto Minami (Osaka University)

• Title: Search for parity-violating physics in the polarisation of the cosmic microwave background, so called “Cosmic Birefringence”

• Abstract: Polarised light of the cosmic microwave background, the remnant light of the Big Bang, is sensitive to parity-violating physics, cosmic birefringence. In this presentation we report on a new measurement of cosmic birefringence from polarisation data of the European Space Agency (ESA)’s Planck satellite. The statistical significance of the measured signal is 2.4 sigma. If confirmed with higher statistical significance in future, it would have important implications for the elusive nature of dark matter and dark energy.

April 6, 2021

• Speaker: Prof. Andreas Weiler (Technical University of Munich)

• Title: The Present and Future of Four Top Operators

• Abstract: We study the phenomenology of a strongly-interacting top quark at future hadron and lepton colliders, showing that the characteristic four-top contact operators give rise to the most significant effects. We demonstrate the extraordinary potential of a 100 TeV proton-proton collider to directly test such non-standard interactions in four-top production, a process that we thoroughly analyze in the same-sign dilepton and trilepton channels, and explore in the fully hadronic channel. Furthermore, high-energy electron-positron colliders, such as CLIC or the ILC, are shown to exhibit an indirect yet remarkable sensitivity to four-top operators, since these constitute, via renormalization group evolution, the leading new-physics deformations in top-quark pair production. We investigate the impact of our results on the parameter space of composite Higgs models with a strongly-coupled (right-handed) top quark, finding that four-top probes provide the best sensitivity on the compositeness scale at the future energy frontier. In addition, we investigate mild yet persisting LHC excesses in multilepton plus jets final states, showing that they can be consistently described in the effective field theory of such a new-physics scenario.

April 2, 2021, 3pm - 4pm

• Speaker: Prof. Kaoru Hagiwara (KEK) and Prof. Benjamin Fuks (LPTHE and Inst. U. de France)

• Title: Signatures of toponium formation in LHC run 2 data

• Abstract: We study reported deviations between observations and theoretical predictions associated with the production of a pair of di-leptonically decaying top quarks at the LHC, and we examine the possibility that they reflect a signal of toponium formation. We investigate the production by gluon fusion of a color-singlet spin-0 toponium bound state of a top and anti-top quark, that then decays di-leptonically. We find strong correlations favoring the production of di-lepton systems featuring a small angular separation in azimuth and a small invariant mass. Although toponium production only contributes to 0.8% of the total top-quark pair-production cross section at the 13 TeV LHC, there is a possibility that it can account for observed excesses in the narrow edges of phase space. We propose a method to discover toponium formation by `reconstructing' both its top and anti-top quark constituents in the di-lepton channel.

April 2, 2021, 4pm - 5pm

• Speaker: Prof. Bruce Mellado (University of the Witwatersrand & iThemba LABS)

• Title: The anatomy of the multi-lepton anomalies at the LHC

• Abstract: In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC will be given. These include the excess production of opposite sign leptons with and without b-quarks, including a corner of the phase-space with a full hadronic jet veto; same sign leptons with and without b-quarks; three leptons with and without b-quarks, including also the presence of a Z. Excesses emerge in corners of the phase space where a range of SM processes dominate, indicating that the potential mismodeling of a particular SM process is unlikely to explain them. A procedure is implemented that avoids parameter tuning or scanning the phase-space in order to nullify potential look-else-where effects or selection biases. The internal consistency of these anomalies and their interpretation in the framework of a simplified model will be presented. Implications on the SM Higgs boson measurements, the muon g-2 and astrophysics will also be briefly discussed.

Inquiry

JeongEun Yoon / avecyoon@kias.re.kr