Coming Seminars
Seminars in July
Speaker
Shun Arai
Date/Place
13:30-, 19th(Wed.), July. @ES635
Title
An elaborate time lapse of CMB lensing
Abstract
A measured CMB lensing signal is able to be decomposed into the minuter redshift shells, provided that the angular cross power between a lensing mass and
a CMB lensing map is better localised in redshifts at higher SNR. We aim to create a time lapse of CMB lensing meeting such requirements. Collectively utilising
cross-correlation statistics between a given lensing mass and reference spectroscopic samples i.e. SDSS, the lensing mass distribution is quantitatively reconstructed
in multiple redshift bins with its wide sky coverage. We find that the combination of 3GHz radio map (composed of reconstructed submaps) and Planck PR4 \kappa map (MV)
provides a time lapse of the CMB lensing with deserved quality.
Speaker
Koichiro Nakashima
Date/Place
13:30-, 12th(Wed.), July. @ES035
Title
RSD analysis with Lyman alpha forest
Abstract
The Lyman alpha forest (LAF), a series of HI absorption lines in the quasar spectra, can be a strong tool for cosmology at redshifts (z>2)
that are generally hard to access with other probes. We present a measurement of the LAF anisotropic power spectrum from the hydrodynamic
simulations with the GADGET3-OSAKA code and analyze the full shape to measure the growth rate of the structure through redshift space distortions.
Understanding the power spectrum on small scales is essential to further improve the accuracy of cosmological analysis. We measured the 3D power
spectrum for 5 simulation models which include different astrophysical feedback. We tested the joint analysis of the 2 × 2 correlation with different
simulation models and gained more stringent constraints on $f\sigma_8$ for $k_\mathrm{max} = 3.0 h/\mathrm{Mpc}$ than that of $k_\mathrm{max} = 1.0 h/\mathrm{Mpc}$,
but it’s biased. In this talk, I will discuss the analysis method to constrain $f\sigma_8$ correctly.
Speaker
Ryoto Inui
Date/Place
13:30-, 5th(Wed.), July. @ES635
Abstract
The cosmological stochastic gravitational waves background (SGWB) has attracted much attention as a method to explore the
universe before the Cosmic Microwave Background (CMB), and mechanisms of generating such SGWB in the early universe before
the CMB have been actively investigated. One of them is the second-order induced gravitational waves which are induced by
large amplitude primordial density fluctuations. The amplitude of the primordial density fluctuation can be constrained by
observing the SGWB. Recent work has evaluated the amplitude of the primordial density fluctuation from the latest data obtained
by the LIGO-VIRGO-KAGRA collaboration. However, this analysis was based on the assumption that the primordial density fluctuations
follow a Gaussian distribution. On the other hand, recent theoretical studies have shown that inflationary models that generate
large amplitude primordial density fluctuations tend to have statistical properties that deviate from a Gaussian distribution
(non-Gaussianity). The presence or absence of non-Gaussianity affects the amplitude and shape of the second-order induced gravitational
waves spectrum. Therefore, the constraint would be changed if one takes the non-Gaussianity into account in the analysis. In this work,
we consider the non-Gaussianity of the primordial density fluctuation and constraint the amplitude and non-Gaussianity of the primordial
density fluctuation from the third observing run data of the LIGO-VIRGO-KAGRA collaboration.
Seminars in June
Speaker
PENG Qi
Date/Place
13:30-, 28th(Wed.), June. @ES635
Title
From Precessions to Gravitational Waves
Abstract
This paper presents a simple exploration of celestial mechanics, specifically focusing on Mercury’s orbit and its
implications in the context of general relativity.
Speaker
Takuma Miwa
Date/Place
13:30-, 10th(Wed.), June. @ES635
Title
Possibility of parameter restrictions from observations by LiteBIRD and CMB-S4
Abstract
This presentation is a review of [1].
Inflation theory can solve the initial condition problems of the standard Big Bang theory.
The existence of inflation is supported by CMB observations. After inflation, the universe undergoes a
reheating epoch. The reheating epoch is the process of producing Standard Model particles from the energy
of the scalar field that causes inflation. However, the mechanism of reheating is not well known, such as
the temperature at the end of the reheating epoch.
The purpose of this work is to consider the possibility of restrictions the temperature at the end of r
eheating in the model of interest based on the next generation CMB observations such as Lite BIRD and CMB-S4.
In this study, we focus on a model called mutated hilltop inflation, which is one of the slow-roll inflation models
in which inflation is drawn by a single scalar field. First, the relationship between model parameters and CMB
observables is investigated. Then, we created pseudo data assuming the previously mentioned next-generation
observations and estimated the model parameters using a Markov chain Monte Carlo method. We found that Lite BIRD and
CMB-S4 can restrict the reheating temperature and so on. This is expected to provide new insights into the Standard Model.
[1]M.Drewes, L.Ming, I.Oldengott, LiteBIRD and CMB-S4 Sensitivities to Reheating in Plateau Models of Inflation, 2303.13503v1,79,2023
Speaker
Mitsuyasu Yoshizaki
Date/Place
13:30-, 28th(Wed.), June. @ES635
Abstract
In general relativity, gravity is interpreted as the curvature of spacetime. Within this curved spacetime, there may exist
singularities. To avoid these singularities and smoothly connect spacetime, two candidates are considered: wormholes and
negative mass. Wormholes are hypothetical structures that appear as spherically symmetric solutions in Einstein's equations
and can be thought of as tunnels connecting distant points in spacetime. The wormhole we will consider in this study is the
Ellis wormhole (EWH), which is a wormhole with zero mass. On the other hand, negative mass is a hypothetical concept of matter
with mass of the opposite sign to normal matter, producing repulsive gravity. Negative mass has been discussed since the 19th century,
but there is no evidence supporting its existence.
In this study, we assume the existence of EWHs and compact objects with negative mass and estimate their abundance through gravitational
lensing observations in the Sloan Digital Sky Survey Quasar Lens Search (SQLS). The lensing effect of EWHs and negative mass compact
objects creates multiple images of quasars. By estimating the upper limits of their abundance based on the size of EWHs, the mass
of negative mass compact objects, and the probability of experiencing lensing effects, we found that the upper limit on the abundance
of negative mass compact objects is smaller than that of galaxies and galaxy clusters. Additionally, the upper limit on the abundance
of EWHs is found to be smaller than that of stars. By improving the precision of observations and discovering more quasars affected
by lensing effects, we can expect stronger constraints on EWHs and negative mass compact objects. This presentation is a review
based on reference [2].
References:
[1]H.G. Ellis, J. Math. Phys. 14 (1973) 104
[2]R. Takahashi, H. Asada, Astrophys.J.Lett. 768 (2013) L16
Speaker
Yuri Yamashita
Date/Place
13:30-, 21th(Wed.), June. @ES635
Title
Damping of primordial magnetic fields on the early universe
Abstract
Magnetic fields exist everywhere in the universe. For example, it is known that magnetic fields of about 10^-6 G
exist in galaxies and galaxy clusters, and magnetic fields of about 10^-15-10^-20 G exist in low-density intergalactic regions called voids.
Several theories have been proposed to explain the origin of the magnetic fields that exist widely in the universe, and one of them is to find
the origin in the magnetic fields generated in the early universe before the clear up of the Universe(hereinafter referred to as "primordial magnetic field").
The generation of the primordial magnetic field may be due to inflation or density fluctuations, but after its generation, the magnetic field lines move with
the cosmic plasma fluid and decay with B∝a^(-2). However, scenarios explaining this damping have conventionally neglected the damping effects of various waves
generated by the plasma fluid in a magnetic field. In a plasma fluid in a magnetic field, various longitudinal and transverse waves called
magneto-hydro-dynamics modes (MHD modes) are generated. Therefore, the damping of the primordial magnetic field can be explained with higher accuracy by considering the damping of these waves.
In this presentation, we discuss the mechanism of the decay of MHD modes with wavelengths below the mean free path of both particles during
the decoupling of neutrinos and photons from the cosmic plasma fluid in the early universe (before redshift z~1100). As a means of analysis,
the dispersion relation was derived by Fourier transforming the linearized relativistic MHD equation, and the propagation velocity and decay
rate of MHD modes were calculated. The results suggest that the damping may be very large compared to the previously predicted B∝a^(-2).
In this presentation, we will discuss the calculation results of the propagation velocity and damping rate of MHD modes.
Speaker
Kazuya Furusawa
Date/Place
13:30-, 21th(Wed.), June. @ES635
Abstract
To reveal the mystery of the formation and evolution of a supermassive black hole (SMBH),
the estimate of SMBH at high redshift from observational results is meaningful. And gravitational wave (GW)
observations are expected to estimate the SMBH growth and formation at high redshift in the most populated
region that we cannot approach using the Quasi-Stellar Object (QSO) datasets. To discuss the possibility, in
this study, we construct a dark matter halo-SMBH coevolution model and calculate the mass evolution of SMBH only
via merger at $0\leq z \leq6$. Then we calculate the GW radiations generated from the coalescence of SMBH binaries
and consider their detectability by pulsar timing arrays (PTAs) and Laser Interferometer Space Antenna (LISA).
In this C-seminar, I will explain how we describe DM halo-SMBH coevolution and calculate GWs from SMBH binaries.
Also, I'll discuss in detail how the detectability of GWs constrains the formation and evolution of SMBH in this model.
Speaker
Takahiro Yamamoto
Date/Place
13:30-, 14th(Wed.), June. @ES635
Title
CWs from boson clouds around nearest BHs
Abstract
I will talk about my recent thought on CWs from boson clouds around the nearest BHs. After talking
about the motivation, I will give
a brief review of the data analysis method for CWs from binary systems.
If possible, I want to discuss the possibility of the detection.
Seminars in May
Speaker
Maxime Paillassa
Date/Place
13:30-, 24th(Wed.), May. @ES635
Title
Source detection and deblending: from classical algorithms to machine learning.
Abstract
In this C-seminar, I will present source detection techniques for wide-field imaging surveys.
I will first review how astronomical images form and the classical approaches for source detection.
Then, we will see how those methods can be naturally extended with machine learning techniques.
Finally, after reviewing some applications of machine learning for source detection and deblending,
I will present our work about blend identification for HSC images.
Speaker
Santiago Jaraba (IFT UAM-CSIC)
Date/Place
13:30-, 17th(Wed.), May. @ES635
Title
Stochastic gravitational wave background constraints from Gaia DR3 astrometry
Abstract
astrometric surveys can be used to constrain the stochastic gravitational wave background (SGWB) at
very low frequencies. The European Space Agency’s (ESA) Gaia mission, launched in 2013 and with a recent
data release (DR3) in 2022, shows great potential for this purpose. In this talk, I will review the formalism
that relates astrometry to gravitational waves and talk about a recent work in which we used Gaia DR3 to set
constraints on the SGWB amplitude. I will also comment on previous works which computed similar constraints and
discuss the potential of future Gaia data releases to impose tighter bounds.
Speaker
Takuma Miwa
Date/Place
13:30-, 10th(Wed.), May. @ES635
Title
Self introduction
Abstract
Self introduction
Speaker
Mitsuyasu Yoshizaki
Date/Place
13:30-, 10th(Wed.), May. @ES635
Title
Self introduction
Abstract
Self introduction
Seminars in April
Speaker
Xiaolin LIU
Date/Place
13:30-, 26th(Wed.), Apr. @ES635
Title
Study on the gravitational waves from elliptical two-body system with spin-precessing effects based on effective-one-body formalism
Abstract
Binary systems are the most common sources of gravitational waves in the universe. In the detection and data processing of gravitational waves, modeling of gravitational wave sources is crucial. Binary black hole systems have very complex dynamical properties. For a long time, mainstream gravitational wave models only supported the computation of non-memory effect gravitational waves from circular orbit binary black hole systems. With the improvement in sensitivity of future gravitational wave detectors and the launch of space detector projects, there will be an increasing demand for gravitational wave templates with a larger parameter range and higher accuracy. In this work, we computed the orbital dynamics and decomposed waveform that simultaneously support eccentricity and spin precession in the effective-one-body formalism with second-order post-Newtonian accuracy. We then tested this new model and compared its performance in circular orbit situations, and discussed the parameter estimation bias that would result from ignoring this effect in future O4 observations through simulated parameter estimation.
Speaker
Kazuya Furusawa
Date/Place
13:30-, 19(Wed), Apr. @ES635
Title
Self Introduction
Abstract
Self Introduction
Speaker
Yuri Yamashita
Date/Place
13:30-, 19(Wed), Apr. @ES635
Title
Self Introduction
Abstract
Self Introduction
Speaker
Kiyotomo Ichiki
Date/Place
13:30-, 19(Wed), Apr. @ES635
Title
Policy speech
Abstract
Policy speech