Cセミナー 2024

English発表者

Zhenjie Liu (Shanghai Jiao Tong University/上海交通大学)

日程/場所

10月30日(水)13:30-@ES606

題名

Fourier_Quad Shear Measurement and Its Applications in Cosmology

概要

Accurately measuring cosmic shear presents significant challenges, as shear signals are typically at the one-percent level and are impacted by various systematics. To enhance the reliability of weak lensing results, it is beneficial to cross-validate findings with multiple shear catalogs or diverse statistical approaches. The Fourier_Quad (FQ) method provides shear estimators based on the quadrupole moments of galaxy power spectra, which has developed into a full-fledged shear measurement pipeline. In this presentation, I will briefly introduce the FQ method and show its application in two cosmological investigations using PDF-symmetrization statistical techniques. First, we utilize a quasi-2D shear two-point correlation functions to constrain cosmological parameters, yielding robust results. Additionally, we apply the FQ catalog to detect dark matter halo shapes using halo-shear-shear three-point correlation functions.

発表者

Matteo Cataneo (Ruhr University Bochum and University of Bonn)

日程/場所

10月18日(金)14:00-@ES606

題名

mochi_class: Bridging and bolting Horndeski’s landscape

概要

I will introduce mochi_class, an extension of the popular Einstein-Boltzmann solver hi_class optimised for calculations within the Horndeski gravity framework. Thanks to (i) a re-parametrisation of Horndeski functions, (ii) a more accurate quasi-static approximation, and (iii) support for external time-dependent inputs, mochi_class enhances hi_class capabilities and nicely complements other public Einstein-Boltzmann solvers. Additionally, I will present a non-parametric approach that, when integrated with Principal Component Analysis, can effectively reconstruct Horndeski functions from well-studied modified gravity models, extending the exploration of scalar-tensor theories beyond conventional parametrisations. I will conclude by briefly highlighting practical applications where mochi_class can prove instrumental in analysing current and forthcoming large-scale structure data.

発表者

Baptiste Blachier (LPENS)

日程/場所

10月18日(金)10:00-@ES606

題名

Small-scale clustering of primordial black holes: Cloud-in-cloud and exclusion effects

概要

Using an excursion-set approach, I will revisit the initial spatial clustering of Primordial Black Holes (PBHs) originating from the Hubble reentry of large Gaussian density fluctuations in the early Universe. The two-point correlation functions of PBHs, properly accounting for the “cloud-in-cloud” mechanism is derived and I will show that this novel expression naturally and intrinsically correlate the formation of pairs of PBHs, which is a key difference with the Poisson model of clustering. The approach also effectively includes short-range exclusion effects and clarifies the clustering behaviors at small scale: PBHs are anticorrelated at short distances. Using a scale-independent collapse threshold, we derive explicit expressions for the excess probability to find pairs of PBHs separated by a distance r, as well as the excess probability to find pairs with asymmetric mass ratio. The framework is model independent by construction, and I discuss possible other applications.

発表者

宮武広直

日程/場所

10月16日(水)13:30-@ES606

題名

Cosmology with gravitational lensing

概要

Large scale structure of the Universe is one of the powerful probes of cosmology. The fact that about 80% of matter in the Universe is dark matter makes it difficult to measure large scale structure in an unbiased way. Gravitational lensing offers a unique way to measure large scale structure because of the sensitivity to gravitational potential created by both ordinary and dark matter. In this talk, I will review results from the large scale structure measurements by galaxy surveys which used the phenomena called weak gravitational lensing, including the Subaru Hyper Suprime-Cam Survey led by Japan, and future prospects with upcoming galaxy surveys. I will also discuss large scale structure measurements at high redshifts with a distant galaxy sample and gravitational lensing of cosmic microwave background.

発表者

中島光一朗

日程/場所

10月9日(水)13:30-@ES606

概要

The universe we live in is like an ocean of vast data. The structure of galaxies, the distribution of dark matter, and faint traces from the early universe—these are like pages in a giant book written by the cosmos itself. But reading this book is no easy task. This is where modern machine learning comes into play. It’s becoming a powerful tool for deciphering the mysteries of the universe. So, how exactly is AI being used to uncover the secrets of the cosmos? Let’s dive into that today.

発表者

三倉祐輔

日程/場所

10月2日(水)13:00-@ES606

題名

Small deformation of Palatini-Higgs inflation and the particle spectrum

概要

Palatini-Higgs inflation would be a representative example of Higgs inflation in the realm of metric-affine gravity. Its inflationary predictions are known to be in perfect agreement with CMB if the Higgs couples to gravity very strongly. However, this strong coupling is notorious as the EFT scale decreases significantly. While it calls out for UV completion, nobody has succeeded in constructing its UV theory or providing a no-go. In this talk, I search for a different theory which is connected to a well-behaved UV theory. To this end, I will deform the Palatini-Higgs inflation, include quantum corrections in the large-N limit, and study in what parameter region the theory is free of pathological propagation.

発表者

乾玲冬

日程/場所

7月17日(水)13:00-@ES606

題名

Gravitational lensing of gravitational waves

概要

The first detection of gravitational waves (GWs) from the black hole mergers opened a new era to investigate our Universe. The GWs have been utilized in various contexts, for example, the test of gravity theory, the study of the early Universe, the dark matter survey, and measuring the Hubble parameter … etc. Recently, the gravitational lensing of GWs has been attracting some attention as a new method to explore our Universe. In this seminar, I will give the basics of the gravitational lensing of GWs with some comparisons with the gravitational lensing of light.

発表者

多田祐一郎

日程/場所

7月10日(水)13:00-@ES606

題名

Scalar-induced gravitational wave and cosmological crossover

概要

Our universe has experienced phase transitions/crossovers several times throughout its thermal history. Gravitational waves (GWs) as a state-of-the-art probe can survey such a history thanks to their high penetration ability. In particular, GWs sourced by oscillations of density contrasts, called scalar-induced GWs (SIGWs), have sensitivity not only to the background expansion rate but also to the plasma sound speed and hence could serve more information of crossovers. Furthermore, they are closely related to the exotic astrophysical object: primordial black holes. In this talk, I’ll review the researches in this context by several authors including Ryoto and Albert, and introduce my ongoing project.

発表者

小野田康平

日程/場所

6月26日(水)13:00-@ES606

題名

Progress report for summer school

概要

The Lyman-alpha (Lyα) forest is a powerful tool for probing the structure formation of the intergalactic medium (IGM) at high redshifts (z > 2). Studying this formation history can help address the S8 tension and explore beyond ΛCDM models. To interpret observations accurately, it is crucial to use hydrodynamical simulations to examine the impact of astrophysical feedback from processes like supernovae and active galactic nuclei (AGN) on the IGM. However, such simulations are computationally expensive, and few examples are conducted at box sizes that can account for cosmological impacts. For instance, the CAMELS project has only performed simulations in volumes of (25 cMpc/h)^3.
At the summer school, I plan to use the CROCODILE simulation, which includes the latest feedback models, to study their impact on the Lyα forest power spectrum with a box size of (100 cMpc/h)^3. As I do not yet have the simulation results, I will introduce the foundational paper for this project, “Probing Feedback via IGM Tomography and the Lyα Forest with Subaru PFS, TMT/ELT, and JWST” (Nagamine et al. 2020), and the CAMELS project. I will also outline the research I intend to undertake in the summer school.

発表者

伊藤勘太

日程/場所

6月26日(水)13:00-@ES606

題名

Progress report for summer school

概要

This presentation is a review of [1]. About one fourth of energy budget in the current universe is occupied with the dark matter (DM). Its existence is confirmed in many observations and theories but it is not sure what composes it. One of the most promissing candidates is Axion. Here the word "Axion" means the QCD Axion, which solves strong CP problem in particle physics and the Axion Like Particles, which has a wide range of mass (ALPS). In this paper, Axion graviton coupling, which is less constrained than axion photon coupling, is considered. By such coupling, parity violated gravitational waves(GWs) are produced and GWs produced in the inflation are amplified through the parametric resonance. When considering this model, in high-k region negative energy modes (ghost mode) appears. By introducing appropriate cutoff in k space, authors succeeded to avoid ghost mode and separate the parameter space into ghost regions and parametric resonance regions. After this regularization, parametric resonance affects a particular mode meets $k/a = m_a/2$ and amplifies such GWs at most 10^6 times in terms of energy density. By such amplification, energy density of GWs by the inflation reaches from 10^-14 to 10^-10 at the specific peak frequency and they find to be detectable by future detectors i.e. Taiji, LISA, IPTA, and SKA. Future GWs detections can lead to constraints to the Axion mass as a DM and specify what the DM is.

発表者

𠮷岡隼

日程/場所

6月26日(水)13:00-@ES606

題名

Progress report for summer school(Redshift evolution of cosmic birefringence)

概要

In summer school, I will review the paper “Redshift evolution of cosmic birefringence in CMB anisotropies” by Galaverni et al., 2023. This paper mainly discuss about cosmic birefringence. Cosmic birefringence is rotation of linear polarization plane of CMB and is considered to be caused by pseudoscalar field. To solve equation of pseudoscalar field, they derive CMB anisotropies C_l. Finally, I will show some numerical calculations using CAMB.

発表者

由良海翔

日程/場所

6月19日(水)13:00-@ES606

題名

Progress report for summer school

概要

My theme of summer school is to review the paper “Constraint on the primordial vector mode and its magnetic field generation from seven-year Wilkinson Microwave Anisotropy Probe observations” written by Ichiki et al.. In this paper, they discuss the generation of primordial magnetic fields and give constraints on it by primordial vector mode which has a growing mode in the existence of anisotropic stress by free-streaming particles such as neutrinos. I will mainly explain the contents of this paper in this seminar. Also, I have been studying and performing the analyses in the paper using Planck data, so I will present my current progress.

発表者

鵜飼祥

日程/場所

6月19日(水)13:00-@ES606

題名

Progress report for summer school

概要

Galaxies and active galactic nuclei(AGN) are thought to be sources of ionizing photons, which trigger cosmic reionization, but the extent of their contributions is still under discussion. For summer school, I will review “Constraining the contribution of galaxies and active galactic nuclei to cosmic reionization” by Yoshiura et al. (2017). In this paper, they calculate the reionization history considering galaxies and AGN as ionizing photon sources, and constrain their contributions using observational data. In addition, I will present the latest observations of galaxies and AGNs by James Webb Space Telescope and update the constraints accordingly.

発表者

寺田隆広

日程/場所

6月12日(水)13:00-@ES606

概要

Gravitational waves (GWs) emitted in the early Universe can reach us because of their feeble interactions, so they may give us some information about the early Universe. In this talk, we discuss the secondary GWs induced by primordial curvature perturbations, which can have information on inflation as well as post-inflationary cosmic history. Specifically, we focus on effects of an (early) matter-dominated era on the induced GWs. We find that the intensity of the induced GWs sensitively depend on the quickness of the transition from the matter-dominated era to the subsequent cosmic era. In particular, the induced GWs can be significantly enhanced when the transition is rapid (the poltergeist mechanism), examples of which include a primordial-black-hole-dominated scenario and an axion-rotation scenario. If time remains, we also discuss the recent nanohertz GWs found by the worldwide pulsar timing array observations focusing on their spectral index. We introduce three possibilities in which the induced GWs can explain the spectral index.

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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