2024.03.26
Speaker: Dr. Saikat Das
Title:
Multimessenger probes of superheavy dark matter decay and annihilation
Abstract:
We revisit constraints on decaying very heavy dark matter (VHDM) using the latest ultrahigh-energy cosmic-ray (UHECR; E >1e18 eV) data and ultrahigh-energy (UHE) gamma-ray flux upper limits, measured by the Pierre Auger Observatory. We present updated limits on the VHDM lifetime for masses up to ∼ 1e15 GeV, considering decay into quarks, leptons, and massive bosons. In particular, we consider not only the UHECR spectrum but their composition data that favors heavier nuclei. Such a combined analysis improves the limits at <1e12 GeV because VHDM decay does not produce UHECR nuclei. We also show that the constraints from the UHE gamma-ray upper limits are ∼ 10 times more stringent than that obtained from cosmic rays, for all of the Standard Model final states we consider. The latter improves our limits to VHDM lifetime by a factor of two for dark matter mass >1e12 GeV. We also provide constraints using neutrino flux from dark matter decay, including the neutrino-induced cascades. We consider the interaction of UHE neutrinos with the cosmic neutrino background, leading to the attenuation of the extragalactic flux reaching Earth, which improves our analysis to obtain tighter constraints.
2024.01.22
Speaker: Mr.Thanaporn Sichanugrist and Dr. Shion Chen
Title:
Wave-like Dark Matter Search Using Qubits
Abstract:
The rapid controllability required for quantum computers makes the currently proposed quantum bit modalities also attractive as electromagnetic field sensors. One of the promising applications is wave-like dark matter searches, where the electric field converted from the coherent dark matter excites the qubits, leading to detectable signals [Phys. Rev. Lett. 131, 211001]. The quantum coherence between the qubits can be utilized to enhance the signal rate in a multi-qubit system. By designing an appropriate quantum circuit to entangle the qubits, it was found that the signal rate can scale proportionally to $n_q^2$, with $n_q$ being the number of sensor qubits, rather than linearly with $n_q$ [arXiv: 2311.10413]. In the seminar, we overview the theoretical framework of the search, elaborate on the signal-enhancing mechanism driven by quantum entanglement with specific examples of the quantum circuits, and discuss how the scheme can be implemented in the platform of future fault-tolerant quantum computers. We also provide the introduction of the experimental realization, and report the status of the experimental works carried out in UTokyo/ICEPP.
2023.11.24
Speaker: Dr. Derek Inman
Title:
Early Formation of Dark Matter Halos
Abstract:
Cosmological observations have led to an extremely precise understanding of the large-scale structure of the Universe. A common assumption is to extrapolate large-scale properties to smaller scales; however, whether this is correct or not is unknown and many well-motivated early Universe scenarios predict substantially different structure formation histories. In this seminar I will discuss two scenarios where nonlinear structures form much earlier than is typically assumed. In the first case, the initial fluctuations are enhanced on small scales leading to either primordial black holes clusters or WIMP minihalos right after matter-radiation equality. In the second, I will show that an additional attractive dark force leads to structure formation even in the radiation dominated Universe. I will furthermore discuss possible observations of such early structure formation including changes to the cosmic microwave background, dark matter annihilation, and when the first galaxies form.
2023.10.24
Speaker: Mr. Simon Thor
Title:
Searching for dark neutrinos through exotic Higgs decays at the ILC
Abstract:
In this study we investigate the feasibility of detecting heavy dark neutrinos (N_d) through exotic Higgs decays at the proposed International Linear Collider (ILC), specifically in the channel of e^+ e^- to qq~ H with H to nu N_d to nu~lW to nu l~qq. Analyses based on full detector simulations of the ILD are performed at the center-of-mass energy of 250 GeV for two different beam polarization schemes with a total integrated luminosity of 2 {ab}^{-1}. A range of dark neutrino masses between the Z boson and Higgs boson masses are studied. The 2\sigma significance reach for the joint branching ratio of BR(H to nu N_d)\cdot BR(N_d to lW) is about 0.1%, nearly independent of the dark neutrino masses, while the 5sigma discovery is possible at a branching ratio of 0.3%. Interpreting these results in terms of constraints on the mixing parameters |epsilon_{id}|^2 between SM neutrinos and the dark neutrino, it is expected to have a factor of 10 improvement from current constraints.
2023.09.25
Speaker: Dr. Wen Yin
Title:
Thermal production eV dark matter with bose-enhancement
Abstract:
A very simple production mechanism of feebly interacting dark matter (DM) that rarely annihilates is thermal production, which predicts the DM mass around eV. This has been widely known as the hot DM scenario. Despite there are several observational hints from background lights suggesting a DM in this mass range, the hot DM scenario has been considered strongly in tension with the structure formation of our Universe. In this talk, I show that the previous conclusions are not always true depending on the reaction for bosonic DM because of the Bose-enhanced reaction at very low momentum. By utilizing a simple $1 \leftrightarrow 2$ decay/inverse decay process to produce DM, I demonstrate that eV range bosonic DM can be thermally produced in a cold manner from a hot plasma. I also discuss some caveats arising from this phenomenon in the freeze-in production of DM, and present a related system that can suppress the hot plasma with thermal reaction.
2023.07.10
Speaker: Dr. Silvia Manconi
Title:
Searching for dark matter subhalos among Fermi-LAT sources with Bayesian neural networks
Abstract:
Machine learning techniques are powerful tools to tackle diverse tasks in current astroparticle physics research. For example, Bayesian neural networks provide robust classifiers with reliable uncertainty estimates, and are particularly well suited for classification problems that are based on comparatively small and imbalanced data sets, such as the gamma-ray sources detected by Fermi-Large Area Telescope (LAT).
About one third of the gamma-ray sources collected in the most recent catalogs remain currently unidentified. Intriguingly, some of these could be exotic objects such as dark subhalos, which are overdensities in dark matter halos predicted to form by cosmological N-body simulations. If they exist in the Milky Way, they could be detected as gamma-ray point sources due to the annihilation or decay of dark matter particles into Standard Model final states.
In this talk I will discuss our recent work* in which, after training on realistic simulations, we use Bayesian neural networks to identify candidate dark matter subhalos among unidentified gamma-ray sources in Fermi-LAT catalogs. Our novel framework allows us to derive conservative bounds on the dark matter annihilation cross section, by excluding unidentified sources classified as astrophysical-like.
2023.04.25
Speaker: Dr. Tomohiro Inada
Title:
Search for TeV-scale WIMP Dark Matter by observing Gamma rays around the Galactic Centre with the MAGIC telescopes and future prospects
Abstract:
Line-like features in TeV γ rays constitute a "smoking gun" for TeV-scale particle dark matter and new physics. Probing the Galactic Centre region with ground-based Cherenkov telescopes enables the search for TeV spectral features in immediate association with a dense dark matter reservoir at a sensitivity out of reach for satellite γ-ray detectors, and direct detection and collider experiments. I will report on about seven years of observations of the Galactic Centre region with the MAGIC stereoscopic telescope system reaching γ-ray energies up to 100 TeV. We constrain the cross-section for dark matter annihilation into two photons, achieving the best limits to date for a dark matter mass above 20 TeV and a cuspy dark matter profile at the Galactic Centre. I would like to discuss how to constrain supersymmetric wino models, which are one of the most popular dark matter candidates in the context of the Lightest Supersymmetric Particles (LSPs).
2023.02.09
Speaker: Dr. Jowett Chan
Title:
The Present and Future of Fuzzy Dark Matter Simulation
Abstract:
The Fuzzy dark matter (FDM) model was suggested to be a promising dark matter candidate , for which its equation of motion is governed by the coupled Schroedinger-Poisson equations. Although the non-linear structure can be different, it is argued to be as equally competitive as the traditional cold dark matter (CDM) model. We will recap some of the recent observational constraints, and adopted numerical schemes by different groups, such as the spectral method and those applied to non-uniform mesh simulations. Among all of the simulated wave phenomenology, we will focus on our recent finding, the diversity of the core-halo structure of the FDM model, which is closely related to the observed inner structure of faint dwarf galaxies within the Milky Way. I will conclude with a prospect on the future direction for FDM simulations.
2022.12.19
Speaker: Dr. Maria Manuela Saez
Title:
The ANDES Deep Underground Laboratory in South America: status and prospects
Abstract:
The construction of the Agua Negra tunnels that will link Argentina and Chile under the Andes mountains opens the possibility of building a deep underground laboratory in the Southern Hemisphere.
Dark Matter particles can be detected directly via their elastic scattering with nuclei, and next-generation experiments can eventually find physical evidence about dark matter candidates. I will show you our predictions for the expected direct dark matter signal and the ANDES site laboratory, whose location in the Southern Hemisphere should play a significant role in understanding dark matter modulation signals. Additionally, since planned next-generation large-scale direct detection experiments will measure the coherent elastic scattering of neutrinos on protons and nuclei, we have calculated the SN neutrino signal expected for the location. Finally, to study the background, we have calculated the contributions to the neutrino floor by considering the reactor’s neutrinos and geoneutrinos at the laboratory site. We hope these studies might contribute to dark matter detection strategies that maximize the future ANDES laboratory detection capabilities.
2022.10.28
Speaker: Dr. Oscar Macias
Title:
Gamma-ray emission from the Sagittarius Dwarf Spheroidal galaxy due to millisecond pulsars
Abstract:
The Fermi Bubbles are giant, gamma-ray emitting lobes emanating from the nucleus of the Milky Way discovered in ~1-100 GeV data collected by the Fermi Gamma-Ray Space Telescope. Previous work has revealed substructure within the Fermi Bubbles that has been interpreted as a signature of collimated outflows from the Galaxy's super-massive black hole. In this talk, I will show that much of the gamma-ray emission associated to the brightest region of substructure -- the so-called cocoon -- is likely due to the Sagittarius dwarf spheroidal (Sgr dSph) galaxy. This large Milky Way satellite is viewed through the Fermi Bubbles from the position of the Solar System. As a tidally and ram-pressure stripped remnant, the Sgr dSph has no on-going star formation, but I will demonstrate that the dwarf's millisecond pulsar (MSP) population can plausibly supply the observed gamma-ray signal. This finding plausibly suggests that MSPs produce significant gamma-ray emission amongst old stellar populations, potentially confounding indirect dark matter searches in regions such as the Galactic Centre, the Andromeda galaxy, and other massive Milky Way dwarf spheroidals.
2022.06.06
Speaker: Dr. Eijima
Title:
Axion electrodynamics in neutron stars
Abstract:
Axions are pseudo-Goldstone bosons that provide a solution to the strong CP problem, and are prominent candidates for dark matter. In neutron stars, it has been shown recently that the potential of the QCD axion acquires finite density corrections that shift the axion field expectation value, which can be large compared to the vanishing expectation value in vacuo. Such a shift leaves an imprint on typical neutron star observables such as the redshifted thermal luminosity, which can be used to constrain the axion parameter space. In this talk we focus on the coupling of axions with photons, which modifies Maxwell’s equations and alters the neutron star magnetic field. By performing state-of-the-art magneto-thermal simulations, we calculate the axion-induced perturbations to the neutron star’ magnetic field, and show that they grow on relatively short time-scales. At the same time, intense electric currents form, leading to enhanced ohmic dissipation, which increases the stars’ observable thermal luminosity. The activation of such mechanisms depends on the axion decay constant and the axion mass, two long-sought parameters at the center of several experimental and theoretical investigations. Both parameters can be constrained by comparing our simulations to observations of thermally-emitting neutron stars. The latter do not exhibit uncontrolled growth of the magnetic field that causes enhanced ohmic dissipation, allowing us to place bounds on axion parameters. Our results open a new astrophysical avenue to constrain axions, extending significantly the parameter range that can be probed with direct axion searches.
2022.06.06
Speaker: Dr. Eijima
Title:
Sterile neutrino dark matter and Lepton asymmetry generation
Abstract:
Introducing right-handed neutrinos to the Standard Model can potentially explain dark matter (DM), the baryon asymmetry of the Universe, and non-vanishing neutrino masses at the same time. The lightest of introduced particles is a testable DM candidate known as sterile neutrino DM, and heavier species (Heavy Neutral Leptons, HNLs in short) are responsible for other issues through the seesaw mechanism and leptogenesis. The DM is produced by scattering with SM particles through mixing with ordinary neutrinos. This production scenario, however, conflicts with cosmological observations. This situation is improved by the enhancement of the mixing with large lepton asymmetry at the DM production.
In this seminar, I will briefly introduce the sterile neutrino DM and discuss lepton asymmetry generation for the resonant production of the DM with GeV-scale HNLs.
2022.01.31
Speaker: Dr. Kadota
Title:
Mixed dark matter scenarios consisting of primordial black hole dark matter and WIMPs
Abstract:
While the possibility for the primordial black holes (PBHs) to constitute all of the dark matter (DM) is being narrowed by the astrophysical observations such as the gravitational microlensing, the PBH as a partial DM component is still an intriguing possibility. I will discuss the scenarios where the rest of the dark matter consists of the widely discussed weakly interacting massive particles (WIMPs) and show that PBH and WIMP cannot co-exist with an emphasis on the astrophysical probes including the gamma ray, 21cm and CMB observations.
2022.01.17
Speaker: Dr. Mori
Title:
Axion-like particles from core-collapse supernovae
Abstract:
Axion-like particles (ALPs) are a class of hypothetical pseudoscalar particles which feebly interact with ordinary matter. The hot plasma of stars and core-collapse supernovae is a possible laboratory to explore physics beyond the standard model including ALPs. Once produced in a supernova, some of the ALPs can be absorbed by the supernova matter and affect energy transfer. We recently calculated the ALP emission in core-collapse supernovae and the backreaction on supernova dynamics consistently. It is found that the stalled bounce shock can be revived if the coupling between ALPs and photons is as high as $g_{a\gamma}\sim 10^{-9}$ GeV$^{-1}$ and the ALP mass is 40-400 MeV. In this talk, I will briefly review stellar and supernova constraints on ALPs and then discuss our recent results.
2021.12.15
Speaker: Dr. Otono
Title:
The FASER experiment
Abstract:
FASER, the ForwArd Search ExpeRiment, is an experiment dedicated to searching for light, extremely weakly-interacting particles at the LHC. Such particles may be produced in the LHC’s high-energy collisions and then decay to visible particles in FASER, which is placed 480 m downstream of the ATLAS interaction point. FASER, also includes a sub-detector, FASER$\nu$, designed to detect neutrino’s produced in the LHC collisions and to study their properties. This seminar will describe the physics motivations, detector design, expected performance of FASER, and current status, as well as the physics prospects.
2021.10.20
Speaker: Dr. Toma
Title:
Distinctive signals of boosted dark matter from semi-annihilations
Abstract:
The recent dark matter direct detection experiments impose the stringent upper bound on the elastic scattering cross section with nucleons. This implies that the cross section is suppressed by small dark matter velocity. However such dark matter can be probed if it is boosted by some mechanism. In this talk, we show that the specific semi-annihilation channel where two dark matter particles annihilate into a pair of anti-dark matter and neutrino indicates signals distinctive from the other semi-annihilation and standard dark matter annihilation processes. Since the boosted dark matter produced by this semi-annihilation is regarded as a high energy neutrino, the total flux of the dark matter and the accompanying neutrino yields double peaks at the energy close to the dark matter mass. Both of the particles can be detectable at large volume neutrino detectors.
2021.09.14
Speaker: Dr. Tulin
Title:
Strongly self-interacting dark matter: from galaxies to the lattice
Abstract:
Are dark matter particles effectively collisionless on galactic scales, or do they have a sizable cross section for scattering with one another? The latter, known as self-interacting dark matter, can explain longstanding astrophysical anomalies and arises for a strongly-coupled non-abelian dark sector. I describe how astrophysics can dramatically narrow the landscape of strongly-coupled dark matter theories. I discuss some recent progress toward calculating the properties of strongly self-interacting dark matter on the lattice in minimal models based on SU(2) gauge theory.
2021.06.24
Speaker: Dr. Shirai
Title:
Precise WIMP Dark Matter Abundance and Standard Model Thermodynamics
Abstract:
A weakly interacting massive particle (WIMP) is a leading candidate of the dark matter. The WIMP dark matter abundance is determined by the freeze-out mechanism. Once we know the property of the WIMP particle such as the mass and interaction, we can predict the dark matter abundance. There are, however, several uncertainties in the estimation of the WIMP dark matter abundance. In this talk, we focus on the effect from Standard Model thermodynamics. We revisit the estimation of the WIMP dark matter abundance and its uncertainty due to the equation of state (EOS) in the Standard Model. We adopt the up-to-date estimate of the EOS of the Standard Model in the early Universe and find nearly 10% difference in the 1–1000 GeV dark matter abundance, compared to the conventional estimate of the EOS.
2021.05.12
Speaker: Dr. Nishimichi
Title:
Emulation for lensing and clustering observables of the cosmological large-scale structure
Abstract:
Recent developments in observational technologies open exciting opportunities to map out the detailed structure of the universe.
Remarkably, the unique combination of imaging and spectroscopic galaxy surveys is now becoming well established as a standard
analysis methodology for precision cosmology. While the former can access directly the underlying clustering of mass dominated
by dark matter projected on the sky through the weak gravitational lensing effect, the latter provides us with the three dimensional
map of the structure traced by galaxies. One can mitigate the galaxy-bias uncertainty, which has been the major obstacle for cosmology
based on galaxy surveys, by jointly analyzing these effects. We still need, however, a robust and versatile theoretical and statistical
framework to interpret these datasets. The Dark Quest project, launched in 2015, is a structure formation simulation campaign precisely
for this purpose. We have developed an emulation tool, dubbed as Dark Emulator, based on a large database of simulated dark matter
halos in virtual universes with different cosmologies efficiently sampled in six-dimensional parameter space. Dark Emulator employs
a simple machine-learning architecture with Gaussian process at its core. It makes predictions of various statistical measures of dark
matter halos, both lensing and clustering observables, for a given cosmological parameters in a few seconds on laptop computers
without running a new simulation. This AI-aided tool, once supplemented with recipes for the halo-galaxy connection, is therefore
applicable to real-data analyses as the theoretical template, which typically requires hundreds of thousands of function calls in the
course of parameter inference. I will introduce this project and report the status of its application to Subaru HSC data.
2021.02.16
Speaker: Dr. Sakai
Title:
Mapping the Milky Way by VLBI Astrometry
Abstract:
Astrometry is the only way to obtain 6D (position-velocity) phase space information for astronomical objects.
The unique capability allows us to examine the past, present, and future of the Milky Way.
Firstly, I will introduce history and basics of astrometry. Secondly, I will overview astrometric projects in the world. Thirdly,
I will highlight recent astrometric results about the Galactic structure.
Lastly, I will introduce astrometric research in Korea as well as future astrometric projects and sciences in 2020s and 30s.
2020.12.03
Speaker: Dr. Naka
Title:
Directional dark matter search and the technologies
Abstract:
For identification of the dark matter, various methodologies are required. Especially, the direct detection is one of the most important goals to directly understand itself. Now, there are various technologies for direct detection, but almost all detectors have no direction sensitivity. We can obtain essential information such as dependence of motion between the earth and the dark matter, velocity distribution and background from direction information, therefore that becomes a very important methodology to identify the dark matter for future as long as we consider “particle dark matter”. In this seminar, I report about the potential of direction sensitive dark matter search and current experimental effort.
2020.10.20
Speaker: Dr. Rinaldi
Title:
Composite Dark matter and gravitational waves
Abstract:
With non-perturbative lattice calculations we investigate the finite-temperature confinement transition of a composite dark matter model. We focus on the regime in which this early-universe transition is first order and would generate a stochastic background of gravitational waves. Future searches for stochastic gravitational waves will provide a new way to discover or constrain composite dark matter, in addition to direct-detection and collider experiments. As a first step to enabling this phenomenology, we determine how heavy the dark fermions need to be in order to produce a first-order stealth dark matter confinement transition.
2020.10.1
Speaker: Dr. Ishiyama
Title:
The Uchuu Simulations: Data Release 1 and Dark Matter Halo Concentrations
Abstract:
We introduce the Uchuu suite of large high-resolution cosmological N-body simulations. The largest simulation, named Uchuu, consists of 2.1 trillion dark matter particles in a box of 2.0 Gpc/h. The highest resolution simulation, called Shin-Uchuu, consists of 262 billion particles in a box of 140 Mpc/h. Combining these simulations we can follow the evolution of dark matter haloes (and subhaloes) spanning from dwarf galaxies to massive galaxy cluster hosts. We present basic statistics, dark matter power spectra and halo (subhalo) mass function, to demonstrate the huge dynamic range and superb statistics of the Uchuu simulations. From the analysis of the evolution of the power spectra we conclude that our simulations are accurate enough from the Baryon Acoustic Oscillations up to very small scales. We also provide parameters of a mass-concentration model, which describes the evolution of halo concentrations, that reproduces our simulation data within 5% error for haloes with masses spanning nearly eight orders of magnitude at redshift 0<z<14. We make publicly available various N -body products, as part of Uchuu Data Release 1, on the Skies & Universes site. We also plan to release gravitational lensing maps, mock galaxy, X-ray cluster and active galactic nuclei catalogues in the near future.
2020.7.22
Speaker: Dr. Yamashita
Title: The result of the XENON1T experiment and its implications
The seminar slide available here!
2020.7.13
Speaker: Dr. Michimura
Title:
Search for ultralight dark matter with laser interferometric gravitational wave detectors
Abstract:
Ultralight dark matter has masses ranging from 10^{-22} eV to 1 eV. Because of its oscillatory feature, it is a class of dark matter models well motivated from cosmology. Recently, search for various kinds of ultralight dark matter using laser interferometers of gravitational wave detectors has been drawing a lot of attention, and many novel methods are being proposed. In this talk, I will first review the basic ideas of laser interferometry, and present our proposal to detect axion-like particles with masses below ~10^{-10} eV [1,2]. I will present the prospected sensitivity of Advanced LIGO, KAGRA and future gravitational wave detectors, and show the current status of table-top experiment in Tokyo. Also, the possibility of detecting vector bosons that couple to B-L charge [3] and scalar bosons that give variations in the fine-structure constant [4] with laser interferometers will be discussed. I will then present our new ideas to use auxiliary length signals from gravitational wave detectors to improve the sensitivity, and show the estimated sensitivity of KAGRA during its first observing run in April 2020.
2020.6.22
Speaker: Dr. Hamaguchi
Title: Dark Matter Heating vs. Rotochemical Heating in Old Neutron Stars
Abstract:
Dark matter (DM) particles in the Universe accumulate in neutron stars (NSs) through their interactions with ordinary matter. It has been known that their annihilation inside the NS core causes late-time heating, with which the surface temperature becomes a constant value of Ts ~ (2-3) × 10^3 K for the NS age t > 10^6-10^7 years. This conclusion is, however, drawn based on the assumption that the beta equilibrium is maintained in NSs throughout their life, which turns out to be invalid for rotating pulsars. The slowdown in the pulsar rotation drives the NS matter out of beta equilibrium, and the resultant imbalance in chemical potentials induces late-time heating, dubbed as rotochemical heating. This effect can heat a NS up to Ts ~ 10^6 for t ~ 10^6-10^7 years. In fact, recent observations found several old NSs whose surface temperature is much higher than the prediction of the standard cooling scenario and is consistent with the rotochemical heating. Motivated by these observations, in this work, we reevaluate the significance of the DM heating in NSs, including the effect of the rotochemical heating. We then show that the signature of DM heating can still be detected in old ordinary pulsars, while it is concealed by the rotochemical heating for old millisecond pulsars. In any cases, a discovery of a very cold NS can give a robust constraint on the DM heating, and thus on DM models.
2020.6.12
Speaker: Dr. Abe
Title: The effect of the early kinetic decoupling in a fermionic dark matter model
Abstract:
We study the effect of the early kinetic decoupling in a model of fermionic dark matter (DM) that interacts with the standard model particles only by exchanging the Higgs boson. There are two DM-Higgs couplings, namely CP-conserving and CP-violating couplings. If the mass of the DM is slightly below half of the Higgs boson mass, then the couplings are suppressed to obtain the measured value of the DM energy density by the freeze-out mechanism. In addition, the scattering processes of DM off particles in the thermal bath are suppressed by the small momentum transfer if the CP-violating DM-Higgs coupling is larger than the CP-conserving one. Due to the suppression, the temperature of the DM can differ from the temperature of the thermal bath. By solving coupled equations for the number density and temperature of the DM, we calculate the DM-Higgs couplings that reproduce the right amount of the DM relic abundance. We find that the couplings have to be larger than the one obtained without taking into account the difference in the temperatures. A consequence of the enhancement of the DM-Higgs couplings is the enhancement of the Higgs invisible decay branching ratio. The enhancement is testable at current and future collider experiments.
2020.4.27
Speaker: Dr. Zhu
Title: Prospects on detecting the axion annihilation signal using continuous gravitational-wave searches
Abstract: Bosons such as axions or axion-like particles can form enormous clouds around black holes via the superradiance instability. As the bosons annihilate in the presence of the black hole, they produce a long-lived, slowly-evolving continuous gravitational-wave signal that is potentially detectable using the current generation of gravitational-wave interferometers.A non-detection can disfavor the existence of axions in certain mass ranges, although this is highly dependent on the Galactic black hole population. In this talk, I will discuss the expected annihilation signal from the population of isolated stellar-mass black holes in the Galaxy, and the prospects for detecting the signal using standard searches for continuous gravitational waves.
2020.2.17
Speaker: Dr. Brehmer
Title: Mining for Dark Matter substructure: Learning from lenses without a likelihood
Abstract: The subtle imprint of dark matter substructure on extended arcs in strong lensing systems contains a wealth of information about the small-scale distribution of dark matter and, consequently, about the underlying particle physics. However, teasing out this effect is challenging since the likelihood function for realistic simulations of population-level parameters is intractable. Structurally similar problems appear in many other scientific fields ranging from particle physics to neuroscience to epidemiology, which has prompted the development of powerful simulation-based inference techniques based on machine learning. We give a broad overview over these methods, and then apply them to the problem of substructure inference in galaxy-galaxy strong lenses. In this proof-of-principle application to simulated data, we show that these methods can provide an efficient and principled way to simultaneously analyze an ensemble of strong lenses, and can be used to mine the large sample of lensing images deliverable by near-future surveys for signatures of dark matter substructure.
2019.10.21
Speaker: Dr. Sekiguchi
Title: Haloes at the low-mass end in wino dark matter
Abstract: Neutral wino is a natural candidate of dark matter in split-supersymmetry. Indirect detection is a promising probe of wino dark matter, with its annihilation enhanced non-perturvatively (i.e. Sommerfeld enhancement). In theoretical prediction, halo formation at the low-mass end is a key ingredient. For this purpose, we investigate kinetic decoupling of wino dark matter and consequent dark matter density perturbations. We show that inelastic processes involving charged wino, which are relevant for kinetic equilibrium at late times, shuts off abruptly. This results in boosted acoustic peaks in density power spectrum at horizon scales around the kinetic decoupling. Based on an analytic modeling of subhalo evolution, we estimate the subhalo mass function of (dwarf) galaxy-sized haloes and effects on the annihilation boost factor. We also discuss application of our analysis to SU(2)_L multiplet minimal dark matter.
2019.10.1
Speaker: Dr. Rinaldi
Title: A new lamppost in dark matter searches: Composite Dark Matter
Abstract: In the search for the nature of dark matter many particle physics models are proposed.
Models originating from a new strongly coupled dark sector, similar to QCD and Nuclear Physics, give rise to Composite Dark Matter particles.
These models are hard to study, but they have a very interesting phenomenology with clear signals that are distinct from the usual
WIMP candidates.
To make robust predictions in Composite Dark Matter models one often needs to investigate non-perturbative effects due to the
strong dynamics.
In my talk I will explain how Lattice Field Theory methods and numerical simulations are well suited for this task and contribute to a solid uncertainty quantification.
A variety of detection signals can be studied with lattice simulations, from dark matter self interactions to interactions with regular matter and even signals of dark phase transitions generating primordial gravitational waves.
2019.12.12
Speaker: Dr. Chiaki Hikage
Title: weak lensing cosmology by Subaru HSC survey
2019.9.24
Speaker: Dr. Tom Melia
Title: What's going on at an MeV?