DMWG Seminar

Thermal production eV dark matter with bose-enhancement

September 25 (Mon) at 15:00 - 16:30, 2023

Wen Yin (Assistant Professor, Department of Physics, Graduate School of Science, Tohoku University)

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.

Venue: via Zoom

Event Official Language: English

Searching for dark matter subhalos in the Fermi-LAT catalog with Bayesian neural networks

July 10 (Mon) at 16:30 - 18:00, 2023

Slivia Manconi (Marie Skłodowska-Curie Fellow, Laboratoire d'Annecy-Le-Vieux de Physique Theorique (LAPTh), CNRS, France)

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.

Venue: via Zoom

Event Official Language: English

Search for TeV-scale WIMP Dark Matter by observing Gamma rays around the Galactic Centre with the MAGIC telescopes and future prospects.

April 25 (Tue) at 11:00 - 12:00, 2023

Tomohiro Inada (Shuimu Tsinghua Fellow, Department of Physics, National Tsinghua University, Beijin, China)

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).

Venue: via Zoom

Event Official Language: English

Fuzzy DM simulation (TBA)

February 9 (Thu) at 11:00 - 12:00, 2023

Jowett Chan (Postdoc, Physics Division, National Center for Theoretical Sciences, Taiwan)

Venue: via Zoom

Event Official Language: English

The ANDES Deep Underground Laboratory in South America: status and prospects

December 19 (Mon) at 12:30 - 13:30, 2022

Maria Manuela Saez (Postdoctoral Researcher, iTHEMS)

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.

Venue: via Zoom

Event Official Language: English

Gamma-ray emission from the Sagittarius Dwarf Spheroidal galaxy due to millisecond pulsars

October 28 (Fri) at 17:00 - 18:00, 2022

Oscar Macias (Faculty of Science, University of Amsterdam, Netherlands)

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.

Venue: via Zoom

Event Official Language: English

Cosmological phenomena with sterile neutrino

June 6 (Mon) at 16:30 - 18:00, 2022

Shintaro Eijima (Institute for Cosmic Ray Research (ICRR), The University of Tokyo)

Event Official Language: English

Mixed dark matter scenarios consisting of primordial black hole dark matter and WIMPs

January 31 (Mon) at 11:00 - 12:00, 2022

Kenji Kadota (Senior faculty scientist, Hangzhou Institute for Advanced Study at University of Chinese Academy of Sciences (HIAS-UCAS), International Center for Theoretical Physics-Asia Pacific (ICTP-AP) Hangzhou Branch, China)

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.

Venue: via Zoom

Event Official Language: English

Axion-like particles from core-collapse supernovae

January 17 (Mon) at 11:00 - 12:00, 2022

Kanji Mori (Research Institute of Stellar Explosive Phenomena (REISEP), Fukuoka University)

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} ~ 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.

Venue: via Zoom

Event Official Language: English

The FASER experiment

December 15 (Wed) at 17:00 - 18:00, 2021

Hidetoshi Otono (Assistant Professor, Research Center for Advanced Particle Physics, Kyushu University)

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.

Venue: via Zoom

Event Official Language: English

Distinctive signals of boosted dark matter from semi-annihilations

October 20 (Wed) at 10:00 - 11:30, 2021

Takashi Toma (Assistant Professor, Institute of Liberal Arts and Science, Kanazawa University)

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.

Venue: via Zoom

Event Official Language: English

Precise WIMP Dark Matter Abundance and Standard Model Thermodynamics

June 24 (Thu) at 16:30 - 17:30, 2021

Satoshi Shirai (Project Assistant Professor, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)

We are now living in the era of precision cosmology. The relic abundance of dark matter (DM) is now observationally well-determined, and its error is smaller than O(1)%. This means that the same or much higher precision is required when we make theoretical predictions. Weakly Interacting Massive Particle (WIMP) has long been the leading candidate for DM because of its beautiful mechanism to predict the observed relic abundance. WIMP is in the same thermal bath as the Standard Model particles in the beginning. At a certain point when the temperature of the Universe is smaller than the DM mass, it decouples to fix its number density. The yield of the DM is determined by its annihilation cross-section to the Standard Model sector. It seems that there is no ambiguity in the calculation of this process at first: the cross-section is purely theoretical and all the remainings are described in the Standard Model physics. However, the source of the uncertainty does remain in the Standard Model sector. The dilution of the number density of DM particle depends on the expansion rate of the Universe, which is determined by the Standard Model particles. The effective degree of freedom (d.o.f) of the relativistic species controls this factor. We have to deal with the non-equilibrium dynamics to precisely describe the time-evolution of the d.o.f, in which we need numerical approaches. In this talk, he introduced his work to update these calculations. By implementing the latest findings in the non-equilibrium dynamics in i) the neutrino decoupling, ii) the QCD phase transition, iii) the electroweak phase transition, and iv) the perturbative calculations, they found that the final d.o.f is smaller than the previous estimate in more than 1%. This is larger than the level of precision in observations. It is also important that the uncertainty is quantified by them. Another good news is that he makes the calculated d.o.f with its error publically available. With these updates, we now correctly know the points to probe DM!

Venue: via Zoom

Event Official Language: English

Emulation for lensing and clustering observables of the cosmological large-scale structure

May 12 (Wed) at 10:00 - 11:00, 2021

Takahiro Nishimichi (Yukawa Institute for Theoretical Physics, Kyoto University)

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. We are looking forward to seeing you online.

Venue: via Zoom

Event Official Language: English

Mapping the Milky Way by VLBI Astrometry

February 16 (Tue) at 13:30 - 15:00, 2021

Nobuyuki Sakai (Korea Astronomy and Space Science Institute (KASI), Republic of Korea)

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.

Venue: via Zoom

Event Official Language: English

Directional dark matter search and the technologies

December 3 (Thu) at 10:00 - 11:00, 2020

Tatsuhiro Naka (Lecturer, Department of Physics, Toho University / Specially Appointed Assistant Professor, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)

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.

Venue: via Zoom

Event Official Language: English

Composite Dark matter and gravitational waves

October 20 (Tue) at 10:00 - 11:00, 2020

Enrico Rinaldi (Visiting Scientist, iTHEMS / AI Researcher/Engineer, Arithmer Inc.)

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.

Venue: via Zoom

Event Official Language: English

The Uchuu Simulations: Data Release 1 and Dark Matter Halo Concentrations

October 1 (Thu) at 14:00 - 15:00, 2020

Tomoaki Ishiyama (Associate Professor, Institute of Management and Information Technologies)

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

Venue: via Zoom

Event Official Language: English

DMWG special seminar : “The result of the XENON1T experiment and its implications”

July 22 (Wed) at 15:30 - 17:00, 2020

Masaki Yamashita (Associate Professor, Cosmic-ray Research Division, Institute for Space–Earth Environmental Research, Nagoya University)

Venue: via Zoom

Event Official Language: Japanese

Search for ultralight dark matter with laser interferometric gravitational wave detectors

July 13 (Mon) at 10:00 - 11:00, 2020

Yuta Michimura (Assistant Professor, Department of Physics, Graduate School of Science, The University of Tokyo)

Venue: via Zoom

Event Official Language: English

Dark Matter Heating vs. Rotochemical Heating in Old Neutron Stars

June 22 (Mon) at 16:00 - 17:00, 2020

Koichi Hamaguchi (Associate Professor, Graduate School of Science, The University of Tokyo)

*Detailed information about the seminar refer to the email

Venue: via Zoom

Event Official Language: English