今後のセミナー
4月のセミナー
発表者
神田翔平
日程/場所
6月17日(水)10:30-@ES606
概要
The fine-structure constant α is a dimensionless constant that sets the strength of the electromagnetic
interaction, and within the Standard Model of particle physics its value is taken to be invariant in space and time.
To date, tests have been carried out using laboratory atomic-clock experiments as well as cosmological-scale probes
such as quasar absorption lines (e.g., the Many-Multiplet method) and the cosmic microwave background,
all of which have suggested its invariance to high precision.
Some theories, however, predict a cosmological temporal variation of α. Moreover, if such a temporal variation of α is allowed,
it could offer new insights into the nature of dark matter and the Hubble tension problem,
making such tests highly significant from the standpoints of both fundamental physics and cosmology.
In this study, we test the temporal variation of α on cosmological scales using emission-line galaxy spectra obtained with the Prime Focus
Spectrograph (PFS) on the Subaru Telescope. Exploiting the fact that the wavelength separation of the [OII] λλ3726,3729 doublet depends on α², we
place statistical constraints on the temporal variation across the broad redshift range 0.6 < z < 2.4. In our method, we use night-sky (airglow)
emission lines as the reference for wavelength calibration. These lines, which originate from emission in the Earth's atmosphere, have known
rest-frame wavelengths and are detected simultaneously with the observations, allowing us to correct for systematic errors. By combining this
approach with the large PFS sample, we aim to place stringent constraints on Δα/α over a wider redshift range and with greater statistical
precision than achieved in previous work.
発表者
渡邊大将
日程/場所
6月17日(水)10:30-@ES606
題名
Exploring the statistical anisotropy of primordial curvature perturbations
with pulsar timing arrays
概要
Recent pulsar timing array observations have provided evidence for a stochastic gravitational-wave background, but its origin remains unresolved.
Although supermassive black hole binaries are a leading astrophysical candidate, scalar-induced gravitational waves are also a promising
cosmological candidate, offering a way to probe small-scale primordial curvature perturbations.Anisotropy provides an additional way to test such
a cosmological origin. In PTAs, gravitational waves perturb pulse arrival times, and the resulting deviations from the timing model are called
timing residuals. Spatial correlations of these residuals between pulsar pairs are described by the overlap reduction function. If the background
is generated by statistically anisotropic primordial perturbations, this anisotropy can leave characteristic signatures in the PTA correlation
pattern.
Motivated by this, I review Ref. [1], which studies scalar-induced gravitational waves generated from dipole-type anisotropic primordial curvature
perturbations. This work shows that primordial anisotropy induces anisotropic scalar-induced gravitational waves and leads to frequency-dependent
overlap reduction functions. I summarize the motivation, theoretical framework, modification of the overlap reduction function, and constraints
obtained from current PTA data.
[1] F. Xie, Z.-C. Zhao, Q.-H. Zhu and X. Li, “Exploring the statistical anisotropy of primordial curvature perturbations with pulsar timing arrays,
”arXiv:2604.21642 (2026).
発表者
本家智也
日程/場所
6月17日(水)10:30-@ES606
題名
Investigating Systematic Effects of Fiber Assignment on Cosmological Analysis Using PFS HOD Mocks
概要
The spatial distribution of galaxies is an important observable for studying the large-scale structure of the Universe. By measuring statistics
such as the correlation function and the power spectrum, we can extract cosmological information from BAO and RSD. The Prime Focus Spectrograph
(PFS) on the Subaru Telescope is a next-generation multi-object spectroscopic survey. It aims to measure the three-dimensional distribution of
high-redshift galaxies over a wide redshift range.
However, in PFS, the target density is high, and not all target galaxies can be assigned to fibers at once. Each fiber has physical size and a
limited patrol region, so nearby targets cannot always be observed at the same time. For this reason, PFS uses robotic fiber positioners to change
the fiber configuration for each observation. However, this fiber assignment process can change the observed galaxy sample from the original
target sample.
The goal of this study is to evaluate the systematic effects of fiber assignment on galaxy clustering measurements and cosmological parameter
estimation in PFS. To do this, I construct mock galaxy catalogs for PFS using an HOD model, and compare the galaxy distribution and clustering
signals before and after fiber assignment. Through this comparison, I investigate how observational selection effects caused by fiber assignment
can affect cosmological analysis.
発表者
嵯峨承平
日程/場所
6月10日(水)10:30-@ES606
題名
Post-collapse Lagrangian perturbation theory
概要
The gravitational collapse of collisionless matter leads to shell-crossing
singularities that challenge the applicability of standard perturbation
theory. Here, we present the first fully perturbative approach in three
dimensions by using Lagrangian coordinates that asymptotically captures the
highly nonlinear nature of matter evolution after the first shell-crossing
(Post-collapse Lagrangian perturbation theory, PCPT). We validate the PCPT
predictions against high-resolution Vlasov-Poisson simulations and
demonstrate that PCPT provides a robust framework for describing the early
stages of post-collapse dynamics. Although I will introduce these our
recent results, most of the talk will be devoted to a broader review of the
dynamics of cold dark matter and recent theoretical developments in this
field.
発表者
Ziang Yan
日程/場所
6月3日(水)11:00-@ES606
題名
The star formation, dust, and abundance of galaxies with CIB cross-correlations
概要
The cosmic infrared background (CIB) is the accumulated infrared radiation
mainly generated from dust emissions in star-forming galaxies. It bears
rich information about star formation history, dust thermodynamics, and
galaxy abundance in the distant Universe. The CIB auto- and
cross-correlations with other large-scale structure (LSS) tracers have been
used to probe the star formation, dust, and abundance of galaxies. In this
talk, I will present our recent works (https://arxiv.org/abs/2204.01649,
https://arxiv.org/abs/2310.10848) on constraining cosmic star formation
history, dust spectral energy distribution (SED), and halo occupation (HOD)
model with CIB-galaxy cross-correlations. With the galaxy data from KiDS
and unWISE catalogs, we measured very significant (43\sigma with KiDS and
194\sigma with unWISE) cross-correlation signals and made informative
constraints on star formation, dust SED, and galaxy HOD. I will also
present a forecast on CIB cross-correlations with data from future galaxy
surveys. This study, together with related studies, has shown that 1) CIB
is a powerful tool to explore the aforementioned topics, and 2) CIB x LSS
are generally consistent with IR flux-based studies. We conclude that our
understanding of stars, dust, and galaxy abundance from different
observations is reaching a converged picture. Future datasets from CSST,
LSST, Euclid, etc will yield more precise CIB cross-correlations, thus we
will need to improve the CIB models to yield more accurate and
comprehensive constraints.
発表者
赤間進吾
日程/場所
5月27日(水)11:00-@ES606
題名
Observational Predictions of General Bounce Cosmology
概要
Inflation is widely regarded as the most successful paradigm for the early
universe. Nevertheless, alternative scenarios have also been studied,
motivated in particular by the conceptual problems of inflation, such as
the initial singularity problem and the trans-Planckian problem. In this
talk, I will first introduce various aspects of bouncing cosmology as an
alternative to inflation, including its successes and challenges. In the
latter half, I will present a general framework of bouncing cosmology that
admits a parameter space capable of explaining the observed CMB
fluctuations, as inflation does. Finally, among its observational
predictions, I will discuss the statistical properties of CMB B-mode
polarization.
発表者
Federica Tarsitano
日程/場所
5月20日(水)11:00-@ES606
題名
Optical-to-near-infrared studies of AGN and dual AGN systems with Euclid and the HSC-Niji survey
概要
Supermassive black holes (SMBHs), almost ubiquitous in galaxies, are
polyglot citizens of the Universe: we observe them igniting as Active
Galactic Nuclei (AGN) across the electromagnetic spectrum, and
potentially hear the ripples in spacetime, the gravitational waves (GW),
they create in collisions. The upcoming Laser Interferometer Space
Antenna (LISA) mission will be sensitive to the GW signals from SMBH
coalescence, complementing Pulsar Timing Array (PTA) observatories. The
ESA Euclid space mission, surveying billions of galaxies in the optical
to near-infrared (NIR) with unmatched high-resolution imaging and wide
field of view, will bring remarkable advances in the study of the
co-evolutionary path of SMBHs and their host galaxies. A fundamental yet
poorly explored stage of this evolution is represented by dual AGN
systems, which trace the pathway to SMBH coalescence, and can be used to
set empirical priors for LISA GW events. Despite their high scientific
value, instrumental challenges have limited the number of dual AGN
detections confirmed so far, as exquisite spatial and spectral
resolution is needed to characterise the galaxy nuclear light, and most
surveys lack the necessary statistical power. In this talk, I will
discuss recent efforts to build up the first systematic census of dual
AGN in Euclid, and to advance our understanding of AGN activity and
feedback by exploiting unprecedented synergies with HSC-Niji, a new
medium-band survey with the Subaru telescope. The latter will also
enable the study of AGN-linked populations, such as Little Red Dots, as
well as cosmology-focused analyses, including the multi-wavelength
characterisation of galaxy shapes and more accurate galaxy SED
reconstruction and photo-z estimates, all relevant for weak-lensing
analyses in current and future Stage IV surveys.
発表者
吉浦伸太郎
日程/場所
5月13日(水)11:00-@ES606
概要
After the birth of the Universe, the universe went through three important
epochs: the Dark Ages, when no astronomical objects had yet formed; the
Cosmic Dawn, when the first stars were born; and the Epoch of Reionization,
when ultraviolet radiation from young galaxies ionized hydrogen in
intergalactic medium. Although these epochs are crucial for understanding
the early history of galaxy formation and cosmology, many aspects remain
observationally unexplored.
One promising approach is to observe the 21-cm line, a radio signal emitted
by neutral hydrogen atoms at a rest frequency of approximately 1420 MHz. By
detecting the signal from hydrogen that filled the early Universe, we can
probe the cosmology of the Dark Ages and the formation of the first cosmic
structures. Due to the expansion of the Universe, this 21-cm signal is
redshifted to lower frequencies and is observed as low-frequency radio
signal below about 200 MHz. In particular, for the Dark Ages, the 21-cm
line is almost the only available observational probe.
To correctly extract physical information from 21-cm observations,
researchers are developing cosmological models as well as instruments and
analysis methods that can deal with foreground emission, such as radio
emission from our Galaxy. In this seminar, I will first give a brief
introduction to studies of the distant Universe using the 21-cm line. I
will then explain how the latest observational experiments are working
toward the detection of this signal.
発表者
市來淨與
日程/場所
4月15日(水)11:00-@ES606
題名
所信表明
概要
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