DMWG Seminar

Seminar

DMWG Seminar

Precise WIMP Dark Matter Abundance and Standard Model Thermodynamics

June 24 at 16:30 - 17:30, 2021

Dr. Satoshi Shirai (Project Assistant Professor, 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

Seminar

DMWG Seminar

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

May 12 at 10:00 - 11:00, 2021

Dr. 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

Seminar

DMWG Seminar

Mapping the Milky Way by VLBI Astrometry

February 16 at 13:30 - 15:00, 2021

Dr. 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

Seminar

DMWG Seminar

Directional dark matter search and the technologies

December 3 at 10:00 - 11:00, 2020

Dr. 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

Seminar

DMWG Seminar

Composite Dark matter and gravitational waves

October 20 at 10:00 - 11:00, 2020

Dr. Enrico Rinaldi (Visiting Scientist (Industry), 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

Seminar

DMWG Seminar

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

October 1 at 14:00 - 15:00, 2020

Dr. 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<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.

Venue: via Zoom

Event Official Language: English

Seminar

DMWG Seminar

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

July 22 at 15:30 - 17:00, 2020

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

Venue: via Zoom

Event Official Language: Japanese

Seminar

DMWG Seminar

Search for ultralight dark matter with laser interferometric gravitational wave detectors

July 13 at 10:00 - 11:00, 2020

Dr. Yuta Michimura (assistant professor, Department of Physics, The University of Tokyo)

Venue: via Zoom

Event Official Language: English

Seminar

DMWG Seminar

Dark Matter Heating vs. Rotochemical Heating in Old Neutron Stars

June 22 at 16:00 - 17:00, 2020

Prof. Koichi Hamaguchi (Associate professor, School of Science, The University of Tokyo)

*Detailed information about the seminar refer to the email

Venue: via Zoom

Event Official Language: English

Seminar

DMWG Seminar

The effect of the early kinetic decoupling in a fermionic dark matter model

June 12 at 10:00 - 11:00, 2020

Dr. Tomohiro Abe (Assistant Professor, Division of Theoretical Studies, Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University)

*Detailed information about the seminar refer to the email

Venue: via Zoom

Event Official Language: English

Seminar

DMWG Seminar

Characterizing the continuous gravitational-wave signal from boson clouds around Galactic isolated black holes

April 27 at 16:00 - 17:00, 2020

Dr. Sylvia Zhu (Postdoctoral Researcher, Deutsches Elektronen-Synchrotron DESY, Germany)

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.

Venue: via Zoom

Event Official Language: English

Seminar

DMWG Seminar

Mining for Dark Matter substructure: Learning from lenses without a likelihood

February 17 at 14:00 - 15:30, 2020

Dr. Johann Brehmer (Postdoctoral Researcher, New York University)

Dr. Brehmer gives us a talk about a method to deduce DM small structures. Please join us!

Venue: #424-426, Main Research Building

Event Official Language: English

Seminar

DMWG Seminar

Weak lensing cosmology by Subaru HSC survey

December 12 at 10:30 - 12:00, 2019

Dr. Chiaki Hikage (Project Associate Professor, Kavli IPMU, The University of Tokyo)

Place: IPMU seminar room C

Venue: Kavli IPMU Building

Event Official Language: English

Seminar

DMWG Seminar

Haloes at the low-mass end in wino dark matter

October 21 at 13:00 - 15:00, 2019

Dr. Toyokazu Sekiguchi (RESCEU, The University of Tokyo)

Venue: Seminar Room #160

Event Official Language: English

Seminar

DMWG Seminar

A new lamppost in dark matter searches: Composite Dark Matter

October 1 at 10:00 - 18:00, 2019

Dr. Enrico Rinaldi (Research Part-time Worker, iTHEMS)

Venue: #424-426, Main Research Building

Event Official Language: English