発表者
古澤和也

日程/場所
7月23日(水)13:30-@ES606

題名
Searching parity violation via gravitational waves by the LISA-Taiji network

概要
Since the first direct detection of gravitational waves (GWs) in 2015, GW observations are expected to be a powerful tool for probing new physics in the early universe. Like electromagnetic waves, GWs can be decomposed into left-handed and right-handed polarization modes. If parity violation exists in gravity and affects the generation and propagation of GWs, it can induce an asymmetry between the two modes, namely circular polarization. Therefore, the circular polarization of GWs is regarded as a promising observable for testing parity-violating physics in the early Universe. One possible source of GWs in the early Universe is primordial magnetic fields (PMFs), which can generate a stochastic GW background (SGWB) through their anisotropic stress. In particular, if parity violation is present in the production of primordial magnetic fields (PMFs), it generates the helical component of PMFs, leading to the circular polarization in the SGWB. In this study, we assume the existence of helical PMFs at the end of inflation phenomenologically, and compute the spectrum of SGWB. By comparing the sensitivity of the LISA-Taiji network, we discuss the future constraints on the helical PMFs for various assumed power spectra.

発表者
成瀬元希

日程/場所
7月16日(水)13:30-@ES606

題名
Making a more scrutinized 21cm forest spectrum for future observation

概要
One of the current themes in cosmology is to verify the validity of the DM model. To do this, we have to investigate the structure formation on as small a scale as O(100kpc) or less. To get physical information on such a small scale, minihalos, which are thought to exist at the epoch of reionization and before, are very promising targets, and it is the 21 cm absorption lines in the spectrum of background sources (so-called 21 cm forest) that enable us to observe them. Previous studies so far have expected the value of parameters about the DM and X-ray abundance by using some simulations to get the 21 cm forest. However, these studies don’t have enough halo mass resolution and don’t take the effect of the background radiation on the halo profile, either. In our work, we use the 2 types of simulation, one is MERAXES, which can resolve the higher halo mass resolution to see 10^5 solar mass order, and the other is START, which focuses on one minihalo and simulates the radiation effect on a minihalo. Combining these two datasets, we aim to get a more physically scrutinized 21 cm forest spectrum. In this seminar, we will mention up to the current result.

発表者
水口由莉乃

日程/場所
7月9日(水)13:30-@ES606

題名
Shapes and orientations of massive halos in the statistically anisotropic universe

概要
Statistical isotropy is one of the fundamental assumptions in cosmology. Recent observations of the cosmic microwave background (CMB) and the large-scale structure of galaxies generally support this assumption. However, inflationary models such as anisotropic inflation, which include vector fields, suggest the possibility of statistical anisotropy in the primordial density fluctuations. Therefore, testing the validity of statistical isotropy is essential for understanding the early universe.In this study, we focused on quadrupolar statistical anisotropy in the matter distribution and investigated its effects on the shapes and orientations of massive halos. To this end, we performed N-body simulations incorporating statistical anisotropy. We found no significant impact on the 3D shape parameters of halos, but we observed that the principal axes of halo shapes tend to align either parallel or perpendicular to the anisotropic direction. Notably, this alignment becomes stronger for more massive halos. These results suggest a new potential observational test for statistical anisotropy, for example, through measurements of projected halo shapes using galaxy cluster–galaxy lensing.In this talk, I will introduce the background of my research and present these results in detail.

発表者
刘珍洁

日程/場所
7月2日(水)13:30-@ES606

題名
Lyman-α Emitters for HSC-Medium Bands and Cosmological Forecast

概要
LAEs are promising tracers of large-scale structure at z > 2.5. Upcoming wide-field imaging surveys using medium-band (MB) filters on the Subaru Telescope (HSC) and Blanco Telescope (DECam) aim to detect LAEs, with DESI-2 providing spectroscopic follow-up. To support the target selection and scientific planning of the HSC-MB survey, we construct realistic mock LAE catalogs and forecast the resulting cosmological constraints.

発表者
小林信房

日程/場所
6月25日(水)11:00-@ES606

題名
Domain-wall quintessence (Progress report)

概要
Understanding the origin of dark energy, which drives the accelerated expansion of the universe, remains one of the central challenges in modern cosmology. In recent years, extensive efforts have been devoted to addressing this problem. Among the proposed candidates, quintessence models have received considerable attention. Moreover, observational evidence suggesting the presence of statistical anisotropy on cosmological scales has been gradually accumulating[1]. Given this context, there is a need for a theoretical framework that can simultaneously account for both quintessence and large-scale anisotropy. A previous study [2] introduced phase defects a Hubble scale monopole into a quintessence model to reproduce an anisotropic universe. In the present work, we extend this approach by considering a domain wall as the phase defects. Specifically, we construct a novel theoretical model in which a flat domain wall with a thickness on the order of the Hubble scale generates a potential responsible for the currently observed accelerated expansion of the universe. In this model, it is analytically shown that the spacetime near the domain wall acquires an approximately homogeneous but anisotropic structure, which in turn induces global anisotropy in the universe. Furthermore, we demonstrate that the time evolution of this system depends solely on the vacuum expectation value of the scalar field, denoted by \eta, and through numerical analysis, we confirm that local accelerated expansion occurs under the condition \eta>>0.25 m_p. We also analyze the behavior of light along null geodesics in the constructed background spacetime, and by comparing the resulting distance moduli of Type Ia supernovae with observational data, we derive constraints on the spatial position of the domain wall in our universe. [1] PERIVOLAROPOULOS, Leandros. arXiv:1401.5044v1 [2] SANCHEZ, Juan C. Bueno; PERIVOLAROPOULOS, Leandros. arXiv:1110.2587v3

発表者
石川陽

日程/場所
6月25日(水)13:30-@ES606

題名
A Unified Analysis of Interacting Dark Energy Models Using IDECAMB

概要
I will give an interim report in preparation for my presentation at the summer school. In this talk, I will summarize my current understanding of the paper I am reviewing and outline my plans going forward.In the current standard cosmological model, dark energy is considered to be the cosmological constant Λ. However, the results from the latest large-scale galaxy survey, DESI DR2, suggest deviations fromthe standard model [1].One proposed model that could potentially explain such deviations is the Interacting Dark Energy (IDE) model, which assumes an interaction between dark energy and dark matter—two components believed to play different roles in the evolution of the universe. The IDE framework is expected to address several unresolved issues in cosmology. Indeed, attempts to explain the DESI observations using IDE models have been reported in [2] and [3].While numerous IDE models have been proposed, comparing them with observational data has required individually modifying the CAMB package (a code used to compute CMB anisotropies) for each model. To address this issue, a modified version of CAMB, known as IDECAMB, has recently been developed and released [4]. IDECAMB allows systematic parameterization of models, enabling efficient analysis across a wide range of IDE models—including coupled quintessence models and coupled fluid models, which previously faced challenges such as large-scale instabilities. This advancement is expected to further accelerate progress in IDE research.In this talk, we will present a comprehensive discussion on the current status and future prospects of IDE model studies, incorporating the latest observational results, through a review of reference [4] [1] DESI Collaboration(2025), arXiv:2503.14738 [2] A. Chakraborty et al., arXiv:2503.10806 [3] W. Giarè et al., Phys. Rev. Lett, 133, 251003, 2024 [4] Yun-He Li and Xin Zhang, JCAP09(2023)046

発表者
姫野諒汰

日程/場所
6月25日(水)13:30-@ES606

題名
Reconstructing the Matter Density Field at Recombination Using Machine Learning

概要
The current structure of galaxies (on scales of approximately 0.01 Mpc) has evolved through nonlinear growth influenced by gravity and other forces. As a result, the matter distribution observed in the present universe partially obscures the imprints of physical phenomena from the early universe. Due to this, it is currently difficult to discuss early-universe physics based solely on the observed present-day matter distribution. To address this issue, research has been conducted on reconstructing the matter distribution of the early universe from current matter distribution maps. Previous studies have developed algorithms to reconstruct baryon acoustic oscillations (BAO)—traces of sound waves generated in the early universe—based on linear perturbation theory [2]. However, it is known that reconstructionsbased on linear perturbation theory are less accurate on small scales, such as collapsed galaxies, where nonlinear gravitational evolution is significant.In response, Shallue & Eisenstein (2023) introduced a machine learning-based approach in addition to traditional methods rooted in linear perturbation theory. Their method enables more accurate reconstruction of the early-universe matter distribution at small scales, such as halos and galaxies. Specifically, instead of explicitly modeling gravitational dynamics, their approach learns a direct mapping between the initial and final states in simulations, thereby achieving a more precise reconstruction of the initial density field. As a result, the scale at which the correlation between the initial and reconstructed power spectra exceeds 95% was improved bya factor of two.This presentation reviews the study by Shallue & Eisenstein (2023) and discusses how their findings can be applied to the analysis of the current galaxy distribution. [1] Shallue, Christopher J. & Eisenstein, Daniel J. (2023). Reconstructing cosmological initial conditions from late-time structure with convolutional neural networks, MNRAS. [2] Eisenstein et al. (2007). Improving cosmological distance measurements by reconstruction of the baryon acoustic peak, The American Astronomical Society.

発表者
牧野泰紀

日程/場所
6月18日(水)13:30-@ES606

題名
A theoretical analysis of the spectrum of primordial gravitational waves based on the Standard Model

概要
TBA

発表者
田中芙由子

日程/場所
6月18日(水)13:30-@ES606

題名
Mass estimation of nearby galaxy clusters using gravitational lensing effects

概要
The density fluctuations in the early universe grew amid the interplay between gravitational interactions caused by dark matter and accelerated expansion caused by dark energy, leading to the formation of celestial bodies such as galaxies and galaxy clusters. Galaxy clusters, in particular, are the most massive objects in the universe, composed mainly of hot gas and dark matter. Their total mass can be measured using the “weak gravitational lensing effect,” in which the gravity of the foreground galaxy cluster bends light from background galaxies. The mass function, which represents the number density of galaxy clusters as a function of mass, is sensitive to cosmological parameters such as the energy density of matter Ωm and the amplitude of matter density fluctuations σ8. Generally, galaxy clusters are detected using X-ray luminosity, Sunyaev-Zel'dovich signals, and the spatial concentration of galaxies. Establishing a mass-observational quantity relationship is essential to link the mass function with these observational quantities. In this study, we focus on X-ray-detected X-ray-luminous nearby galaxy clusters and aim to establish a precise mass-X-ray luminosity relationship. As a first step, we performed mass estimation using weak gravitational lensing effects for 9 galaxy clusters with high X-ray luminosities (0.1–2.4 keV) observed by the Subaru Telescope Hyper Suprime-Cam (HSC) at redshifts 0.03 < z < 0.12. We report the results of this study.

発表者
谷田幸貴

日程/場所
6月11日(水)13:30-@ES606

題名
Toward a phenomenological test of gravity using the COCOA pipeline

概要
The current standard cosmological model, the ΛCDM model, describes the geometric and structural evolution of the universe and has been supported by various cosmological observations, including large-scale structures. However, the ΛCDM model requires the assumption of the existence of unknown matter (dark matter) that serves as a gravitational source for galaxy formation, and unknown energy (cosmological constant or dark energy) that drives accelerated expansion. In the ΛCDM model, gravitational interactions are described by general relativity (GR), but attempts have also been made to explain accelerated expansion without introducing dark energy by modifying the theory of gravity at cosmological scales from GR. This is known as “modified gravity theory.” In recent years, improvements in observational accuracy have yielded results from large-scale structure measurements that suggest a breakdown of the ΛCDM model. It is expected that future surveys, such as the Nancy Grace Roman Space Telescope (hereinafter Roman), will further advance the verification of modified gravity theory on a cosmological scale.We have implemented the Boltzmann code MGCAMB, which enables power spectrum calculations compatible with modified gravity theory, into the cosmological analysis pipeline COCOA currently under development for Roman. Furthermore, we aim to analyze the final data from the Subaru Telescope HSC in advance and verify gravity theory. MGCAMB is independent of specific theories and can handle modifications to gravity felt by non-relativistic/relativistic components as phenomenological parameters (μ-Σ parameters).In this presentation, we will discuss the predicted results of cosmological parameter constraints using COCOA with MGCAMB and the prospects for constraints on modified gravity theories.

発表者
石川慶太朗

日程/場所
6月4日(水)13:30-@ES606

題名
Differentiable Cosmological Emulators for Halo Assembly Bias Studies

概要
Galaxies form in dark matter haloes. The spatial distribution of dark matter haloes, and the distribution and the number of galaxies within a dark matter halo, depend primarily on the halo mass. However, they are also known to depend on halo properties other than mass, such as halo formation history (Wechsler et al. 2006). This secondary dependence is called assembly bias. In this work, to construct a halo statistics emulator that also predicts the assembly bias, we focused on the concentration of haloes as a representative secondary parameter, and measured the cross-correlation function of various halo samples selected according to the mass and concentration using Dark Quest II simulation data. We then constructed an accurate power spectrum emulator for these statistics as inputs of halo mass and concentration using a feed-forward neural network. By taking partial derivatives of the emulator output with respect to halo mass, we demonstrate that the network successfully captures how variations in concentration modulate the power amplitude. In this talk, we will discuss the implementation of automatic differentiation (AD) for both emulator-based gradient evaluations and point‐estimation workflows, highlighting the accuracy advantages of AD based on JAX or PyTorch over simple finite‐difference approximations when compared to simulated galaxy power spectra. Finally, we will outline prospects for integrating automatic‐differentiation‐compatible Hamiltonian Monte Carlo (HMC) methods into cosmological inference pipelines, exploiting the synergistic strengths of AD and HMC for efficient, high‐dimensional parameter exploration.

発表者
嵯峨承平

日程/場所
5月28日(水)13:30-@ES606

題名
Relativistic effects on redshift-space distortions: towards detection with Euclid

概要
The observed galaxy distribution via galaxy redshift surveys appears distorted due to redshift-space distortions (RSD). One dominant contribution to RSD comes from the Doppler effect induced by the peculiar velocity of galaxies. The other relativistic effects induce the asymmetric distortions, which contains qualitatively different cosmological information from the standard RSD analysis. I will present my recent contributions to Euclid on the asymmetric galaxy clustering.

発表者
宮武広直

日程/場所
5月21日(水)13:30-@ES606

題名
TBA

概要
TBA

発表者
市來淨與

日程/場所
5月14日(水)13:30-@ES606

題名
What does Planck tell us about inflation? - and beyond -

概要
The scattering of cosmic microwave background radiation (CMB) in galaxy clusters induces a polarization signal according to the quadrupole anisotropy of the photon distribution at the location of the cluster. This "remote quadrupole" derived from measurements of the induced polarization provides an opportunity to reconstruct primordial fluctuations on large scales. By comparing the local quadrupole of the CMB predicted by the primordial fluctuations reconstructed in this way with direct observations by CMB satellites, we discuss how the dark energy can be tested by CMB observations beyond the indefinite nature of the cosmic variance.

発表者
横山修一郎

日程/場所
5月7日(水)13:30-@ES606

題名
What does Planck tell us about inflation? - and beyond -

概要
Recent precise CMB measurements, such as Planck and BICEP/Keck, have given us a deeper understanding of cosmic inflation. In fact, conventional simple models (e.g., proposed in the early '80s) are in tension. In this talk, I would like to give a brief review of inflation, in particular, introduce how to classify the slow-roll inflationary models on the ns-r plane. I would also like to talk with you about what to expect in the future.

発表者
新居舜

日程/場所
4月30日(水)13:30-@ES606

題名
Dreaming for making an elaborate time lapse of LSS formation: CMB-lensing tomography to the beginning of the Universe

概要
Gravitational lensing has been a remarkable observational tool for over the past century, providing insights into gravitational physics through its relativistic and geometric signatures. Meanwhile, the large-scale structure (LSS) of the Universe encapsulates the dynamic interplay between gravitational infall and cosmic expansion. Recent literature of cosmology has drawn the attention to utilise gravitational lensing of the cosmic microwave background (CMB lensing), sourced by LSS, to reveal the detailed evolutionary history of cosmic structures, especially during their early formation stages at high redshifts (z > 1).In this seminar, we will introduce the concept of "CMB-lensing tomography," a method that employs angular two-point correlation statistics measured across distinct redshift slices. We will outline a strategic programme aimed at achieving precise CMB-lensing tomography at high redshifts. To the last minutes, we will illustrate this methodology using recent observations of Lyman-break galaxies obtained with the Subaru Telescope.

発表者
石川陽

日程/場所
4月23日(水)13:30-@ES606

題名
Self introduction

概要
Self introduction

発表者
田中芙由子

日程/場所
4月23日(水)13:30-@ES606

題名
Self introduction

概要
Self introduction

発表者
姫野諒汰

日程/場所
4月23日(水)13:30-@ES606

題名
Self introduction

概要
Self introduction

発表者
牧野泰紀

日程/場所
4月16日(水)13:30-@ES606

題名
Self introduction

概要
Self introduction

発表者
小林信房

日程/場所
4月16日(水)13:30-@ES606

題名
Self introduction

概要
Self introduction

発表者
市來淨與

日程/場所
4月16日(水)13:30-@ES606

題名
所信表明

概要
所信表明