C-lab Seminar 2022 | Seminar | Nagoya University Cosmology Group (C-lab)

C-lab Seminar 2023

日本語

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

Title
Constraints on Non-Gaussian primordial density perturbation from the LIGO-Virgo-KAGRA third observing run

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

Title
Observational upper bound on the abundance of negative-mass compact objects and Ellis wormholes from SQLS

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

Title
Constraint on $M_{\mathrm{BH}}$-$M_{\mathrm{halo}}$ Relation at $z=6$ from Detectability of Gravitational Waves in DM Halo-SMBH Coevolution Model

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

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