Cセミナー 2024

English発表者

渡慶次孝気 (ICRR)

日程/場所

6月12日(水)10:30-@ES606

題名

Stochastic methods in inflationary cosmology

概要

Nonperturbative behaviours of quantum fluctuations generated
during inflation can be captured by the so-called stochastic formalism
of inflation in a classical but stochastic way. Though the formalism has
extensively been used in the context of primordial black holes in recent
years, other applications where nonperturbative fluctuations give
interesting outcomes will be presented, based on our works using the
stochastic formalism, 2310.16649 and 2304.02592.

発表者

川口遼大 (早稲田大)

日程/場所

6月10日(月)15:00-@ES606

題名

Higher-order correlation functions in cosmology using path integral formalism

概要

In this talk, I will introduce how the correlation function of the cosmological perturbative quantity is evaluated in the path integral formalism and compare it with other formalisms, i.e. field redefinition and direct operator formalisms. The role of the boundary and EOM terms in the Lagrangian, which are negligible in the field redefinition approach, will be clarified and mainly the calculation of the three-point correlation function will be presented. I will also discuss the one-loop correction of the power spectrum.

発表者

Maxime Paillassa (Nagoya-U.)

日程/場所

6月5日(水)13:30-@ES606

題名

Source detection in wide-field surveys and convolutional neural networks.

概要

In the scope of wide-field survey cosmology, millions of galaxies need to be detected and measured. Hence, source detection techniques can present serious limitations in terms of completeness and reliability for further analysis. After briefly reviewing current source detection methods, we will see how neural networks, in particular convolutional neural networks (CNNs), can provide new solutions for source detection. As an application, I will present a project leveraging CNNs to tackle the more specific problem of blending detection in Hyper-Suprime-Cam (HSC) images.

発表者

新居舜 (Kobayashi-Maskawa Institute)

日程/場所

5月29日(水)13:30-@ES606

題名

A tale of gravity by a young cosmologist: story never-ending but being better converged

概要

Gravity is the fundamental force to form the Universe in its whole lifetime. However, it is complex to capture its essence among from theory, observation, or even from the literature of science, making it challenging to understand how the Universe genuinely looks like. In this seminar, I’d provide a way to involve in exploring gravity by following a bit unconventional path.
In the first part, for a pedagogical purpose, I’d shortly introduce how to derive Einstein’s general relativity in two ways: the conventional derivation invented by A.Einstein and a particle theory approach in R.Feynman’s lecture note. Then we argue possible departure from the general relativity.
In the second part, we face on the problems of cosmic acceleration and quantum gravity in terms of gravitational physics, as long as supporting the general relativity.
In the final part, we describe how the up-to-date cosmology with handful of observables in high precision serve to pin down the true theory of gravity for the first time in the history. Particularly within my scope of research, I’d introduce a state-of-the art model of gravity based on Horndeski’s theory of scalar-tensor system, with remarks of recently-unveiled knowledge and on-going research works. I’d rather go into running projects, if someone may get interested in.

発表者

市來淨與

日程/場所

5月22日(水)13:30-@ES606

概要

The optical depth of cosmic reionization, as estimated from the CMB polarization by the WMAP satellite, was initially found to be larger than expected. However, detailed observations by the Planck satellite later revealed that the value was smaller than anticipated. This smaller value is mainly determined by Planck's large-angle E-mode power spectrum. According to a recent paper by William Giarè, Eleonora Di Valentino, and Alessandro Melchiorri (PRD, 2024), we discuss that the optical depth measurement independently of the E-mode can be done, resulting in slightly larger values of tau=0.07. We also discuss that this optical depth is useful in resolving the lensing and curvature anomalies in the CMB that were discussed a few years ago. On the other hand, these anomalies seem to be relaxed in likelihoods published after the Planck2018 results.

発表者

松本寿弥・石田幸子先生

日程/場所

5月15日(水)13:30-@ES606

概要

This ‘Wellness Program’ is one of the tutorial courses to support your university life through think over your research environment (in terms of psychoeducation and organizational development).
In this time, we mainly focus on ‘communication’ and ‘awareness’. Through this course, we aim to improve these abilities.
Good relationships and communications are based on trust and empathy between you and others.
Firstly, we do group work and discussion about the experiences related to these topics and then think again about your research environment and daily life.
Finally, we discuss and consider how you can spend more fulfilling research life.

発表者

横山修一郎

日程/場所

5月8日(水)13:30-@ES606

題名

Primordial non-Gaussianity in Large-Scale Structure

概要

Primordial non-Gaussianity has been extensively discussed as a probe of the physics of the early Universe. Planck CMB observations gave a tight constraint on such a primordial non-Gaussianity, but still we have a chance to test it by making use of ongoing/upcoming large-volume and precise measurements of the large-scale structure.
In this seminar, I'd like to give a brief review of the characteristic impacts of primordial non-Gaussianity in large-scale structure, in particular,enhancement/reduction of halo mass function, scale-dependent bias, ...
To evaluate these effects quantitatively to some extent, I would like to employ the so-called peak formalism and explain it by using the blackboard in the seminar. Through this seminar, I hope we can start new collaborations across the subgroups.

発表者

嵯峨承平

日程/場所

5月1日(水)13:30-@ES606

題名

Dynamics of cold dark matters around collapse

概要

Cold dark matter (CDM) is microscopically modelled as a self-gravitating collisionless fluid obeying the Vlasov-Poisson equations. The cold nature suggests that the CDM phase-space structure is described as a three-dimensional sheet evolving in six-dimensional phase space. At the initial stage, the phase-space sheet represents a single-stream flow, but as a consequence of the non-linear evolution under self-gravity, the phase-space sheet self-interacts, and subsequently the phase-space sheet becomes a multi-stream flow. I will present how the multi-stream appears, and will discuss the importance of considering the effects of multi-stream regions in analysing the dynamics of CDM.

発表者

Suchetha Cooray

日程/場所

4月10日(水)13:30-@ES606

題名

Empirical Galaxy Formation Modeling

概要

I will introduce a class of models used for modeling the galaxy-halo connection. The motivation is that we need flexible models that can match all the observations self-consistently, which state-of-the-art cosmological hydrodynamical simulations have been unable to achieve. By extending this framework, we can try to extract the maximal information about galaxy formation and cosmology from observed images of telescopes (field-level inference). I will give an overview of the direction the field is heading towards as well as show some of my progress in the modeling side.

発表者

市來淨與

日程/場所

4月10日(水)13:30-@ES606

題名

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概要

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