発表者
Maxime Paillassa

日程/場所
2月18日(木)13:00-

題名
Impact of the first star on ionization history proved by CMB polarization

概要
Extracting reliable source catalogs from images is crucial for a broad range of astronomical research topics. However, the efficiency of current source detection methods becomes severely limited in crowded fields, or when images are contaminated by optical, electronic and environmental defects. Here I propose new methods to produce more robust and reliable source catalogs using convolutional neural networks (CNNs). I first present MaxiMask, a CNN trained to automatically identify image defects in astronomical exposures. Then I introduce a prototype of multi-scale CNN-based source detector robust to image defects, which is shown to outperform current state-of-the-art algorithms.

発表者
角谷健斗

日程/場所
2月4日(木)13:00-

題名
Measuring cosmological density fields twice

概要
When we look at things, we can only see them at one time. Therefore, the growth rate cannot be measured directly. So we aim to establish a method for reconstructing the perturbation at the time of recombination from the information of CMB photon that is polarized by the galaxy cluster. I will show concrete theory and simulation results about this method, and discuss the scrutiny of the cosmological model using this method.

発表者
坂本陽菜

日程/場所
2月4日(木)13:00-

題名
Impact of the first star on ionization history proved by CMB polarization

概要
Intergalactic medium (IGM) is likely to have been ionized at z>6 by starlight escaped from early galaxies, and the process is called cosmic reionization. The Early and young galaxies were born in minihalos (MHs) and atomic cooling halos (ACHs), where the gas's main coolant is molecular hydrogen and atomic hydrogen, respectively. Although the gas in MHs was more difficult to form stars due to lower cooling efficiency than the gas in ACHs, it is not clear whether the contribution of MHs to the reionization history was so small that we could ignore it. In this study, we consider two models: models that consider only ACHs as the ionization photon source, and the others are models that consider both ACHs and MHs as the ionization photon source. We use the results of the ionization histories obtained by cosmological reionization simulations. By comparing the reionization histories using the PCA analysis of the CMB E-mode polarization power spectrum, we estimate the impact of MHs on cosmic reionization.

発表者
大河内雄志

日程/場所
1月28日(木)10:00-

題名
Phenomenological modified gravity constraints through weak lensing and galaxy clustering measurements

概要
The possibility of deviations from general relativity on cosmological scales has been motivated by the expectation that an alternative gravity theory could explain for the accelerated expansion of the Universe. So, I aim to constrain two phenomenological parameters express deviations from general relativity. These parameters modify the strength of gravity on non-relativistic and relativistic particles, respectively. To constrain these parameters, I use measurements of cosmic shear, galaxy-galaxy clustering, and galaxy-galaxy lensing.

発表者
三倉祐輔

日程/場所
1月24日(木)13:00-

題名
Conformal inflation in the metric-affine geometry

概要
Systematic understanding for classes of inflationary models is investigated from the viewpoint of the local conformal symmetry and the slightly broken global symmetry in the framework of the metric-affine geometry. In the metric-affine geometry, which is a generalization of the Riemannian one adopted in the ordinary General Relativity, the affine connection is also an independent variable rather than being given by the Levi-Civita connection. Thanks to this independency, the metric-affine geometry can preserve the local conformal symmetry in each term of the Lagrangian contrary to the Riemannian geometry, and then the local conformal symmetry can be compatible with much more kinds of global symmetries.

発表者
森下薫能

日程/場所
1月14日(木)13:00-

題名
Multi-field inflation with the Curvaton

概要
Inflation models are constrained by the observation of Planck, and V∝φ^n models are seemed to be disfavoured in the case of single field. So I try to rescue this models by using additional scalar fields.In my previous study, inflaton+inflaton model was not consistent with Planck ,and then I attempted using curvaton which is another scalar field uninvolved with inflation. I will introduce models consists with inflaton and curvaton, and compare my calculations with previous paper.

発表者
近藤寛人

日程/場所
1月7日(木)13:00-

題名
The high-z galaxy cluster cosmology with HSC and Spitzer data

概要
In this work, we are aiming to constrain the cosmological parameters using high-z galaxy clusters detected with HSC and Spitzer data. With combining infrared data with HSC data, we can improve galaxy redshift estimation at high redshift. This combining analysis enable to construct more precise galaxy cluster catalog and constrain cosmological parameters at high redshift. I will talk about cluster cosmology briefly and report recent progress.

発表者
阿部克哉

日程/場所
12月17日(木) 12:30-

題名
The constraint on the number density of Pop III pair-instability supernovae with Planck polarization measurement

概要
In this work, we investigate the effect of supernova explosion~(SN) of the Pop III stars on the global ionization fraction. Due to the explosion, the shock shell will be ionized and expand toward the outside about sub-kpc in physical scale. Depending on the SNe's number density, the global ionization fraction can be changed. Then, the CMB photons suffer more scattering, and the E-mode angular power spectrum of CMB traces it. Using Markov Chain Monte-Carlo(MCMC) method with the Planck 2018 polarization data, we constrain the amount of SNe events. After showing the result, I will discuss what we can obtain about Pop III stars through this result.

発表者
安藤梨花

日程/場所
12月10日(木)13:00-

題名
Reconstructing HI power spectrum with minimal parameters using the dark matter distribution beyond halos

概要
Intensity mapping of 21-cm line by several radio telescope experiments will probe the large-scale structure of the Universe in the post-reionization epoch. It requires a theoretical framework of neutral hydrogen (HI) clustering, such as modelling of HI power spectrum for Baryon Acoustic Oscillations (BAO) analysis. We propose a new method for reconstructing the HI map from dark matter distribution using N-body simulations. Several studies attempt to compute the HI power spectrum with N-body simulations by pasting HI gas at the dark matter halo centre, assuming the relation between the halo and HI masses. On the other hand, the method proposed in this paper reproduces the HI power spectrum from simulated dark matter distribution truncated at specific scales from the halo centre. With this method, the slope of HI power spectrum is reproduced well at large scales. We discuss how our method works by comparing the density profiles of HI and dark matter around the dark matter halo.

発表者
迫田康暉

日程/場所
11月26日(木)13:00-

題名
Measuring CMB lensing

概要
The effect of Cosmic Microwave Background (CMB) gravitational lensing is the phenomenon that primordial CMB is distorted by gravity between Last Scattering Surface and us. From the effect we can obtain information on matter distribution and primordial gravitational waves. The Quadratic Estimator method has been used to detect the lensing effect. Since the lensing effect produces the lensing B-mode from the primordial E-mode, planned B-mode experiments from space, such as and LiteBird, will significantly enhance the sensitivity of the lensing effect. I calculate CMB lensing from simulation data (LiteBIRD’s spec).

発表者
古郡国彦

日程/場所
11月19日(木)13:00-

題名
The 21-cm signals from ultracompact minihalos as a probe of primordial small-scale fluctuations

概要
Ultracompact minihaloes (UCMHs) can form after the epoch of matter–radiation equality, if the density fluctuations of dark matter have significantly large amplitude on small scales. The constraint on the UCMH abundance allows us to access such small-scale fluctuations. In this paper, we present that, through the measurement of 21-cm fluctuations before the epoch of reionization, we can obtain a constraint on the UCMH abundance. We calculate the 21-cm signal from UCMHs and show that UCMHs provide the enhancement of the 21-cm fluctuations. We also investigate the constraint on the UCMH abundance and small-scale curvature perturbations.

発表者
植田郁海

日程/場所
11月19日(木)13:00-

題名
Induced gravitational waves as a cosmological probe of the sound speed during the QCD phase transition

概要
We investigate the measurement of the equation of state parameter w and the sound speed cs of the phase transition plasma with use of the gravitational waves (GWs) of the universe. Though the propagation of GW is insensitive tocsin itself, the sound speed value affects the dynamics of primordial density (or scalar curvature) perturbations and the induced GW by their horizon reentry can thus be an indirect probe both of w and cs. We numerically reveal the concrete spectrum of the predicted induced GW with two simple examples of the scalar perturbation spectrum: the monochromatic and scale-invariant spectra. In the monochromatic case, we see that the resonant amplification and cancellation scales of the induced GW depend on the cs values at different time respectively. The scale-invariant case gives a more realistic spectrum and its specific shape will be compared with observations. In particular, the QCD phase transition corresponds with the frequency range of the pulsar timing array (PTA) observations. If the amplitude of primordial scalar power is in the range of 10−4.Aζ.10−2, the induced GW is consistent with current observational constraints and detectable in the future observation in Square Kilometer Array. Futhermore the recent possible detection of stochastic GWs by NANOGrav 12.5 yr analysis can be explained by the induced GW if Aζ∼√7×10−3.

発表者
山本菜々花

日程/場所
11月5日(木)13:00- @ES635 and with zoom

題名
Cluster mass calibration and galaxies number-mass relation with CMB gravitational lensing

概要
The number density of galaxy clusters as a function of the mass and redshift is sensitive to the structure growth since clusters are the most massive object. However, most of the mass in the Universe is thought to consist of dark matter, which cannot be detected directly. Gravitational lensing is a powerful way to estimate the halo mass including dark matter.In particular, CMB gravitational lensing that uses the cosmic microwave background as the light source makes it possible to estimate the mass of high-z (even z>1) clusters. And, the relation between the number of the galaxies contained in each cluster (richness) and the mass is important to constrain cosmology. I will talk about cluster mass calibrations and the constraint on the richness-cluster mass relation by using the CMB temperature data from Atacama Cosmology Telescope (ACT) and CAMIRA S19A cluster catalog from Subaru Hyper Suprime-Cam (HSC).

発表者
村上広椰

日程/場所
11月5日(木)13:00- @ES635 and with zoom

題名
Constraint on dark matter mass with deep learning

概要
The mass of dark matter prevent the cosmic large scale structure from glowing at the small scale, so the analysis of the large scale structure enable us to study the mass of dark matter. In general, the large scale structure is studied with the two-point correlation function of the matter density fluctuation. But at the small scale, the non-linear growth of the structure make the information of two-point correlation escape to the higher order statistics. Therefore, we need the method of analyzing this higher order statistics and focus on Convolutional Neural Network(CNN). CNN extract the complex information from images with the filters. In this work, we use the image of the dark matter distribution from the N-body simulation for training and testing CNN. And then, by CNN and two-point correlation, we discriminate the model of cold dark matter, which is too heavy to prevent the growth of the structure, and non-cold dark matter. We compare the results from two methods and show CNN can extract more complex information than two-point correlation. In addition, we perform the random Gauss simulation which have only the information of two-point correlation of our N-body simulation, and compare this results with the results from the other two methods.

発表者
簑口睦美

日程/場所
10月29日(木)13:00-

題名
Alcock-Paczynski Test with the voids in HI intensity mapping survey

概要
The recent observations with improving accuracy have revealed the issue called “Hubble tension”, which is the unsolved tension lies between the local measurements of the expansion rate of the universe and the expansion rate inferred from the cosmic microwave background observation assuming standard cosmology. Therefore, it is important to test standard cosmology independently from the various observables. Alcock-Paczynski test is one of the ways of estimating Hubble history, which uses the shape of the originally isotropic object distorted in redshift space according to universal expansion. We assume that the (stacked) void in the HI intensity map is the spherical object. In this talk, I will introduce the details of the methods I use and will present the results currently obtained.

発表者
小粥一寛

日程/場所
10月22日(木)13:00-

題名
QCD axion clump formation

概要
Axions are some of the hopeful scalar particles motivated beyond the Standard model. Although QCD axion was introduced to solve the strong-CP problem at first, it has a potential to explain a dark matter. When the initial field misalignment is large, which corresponds to the fine-tuned initial condition around the hilltop of the potential, the attractive self-interaction becomes effective. In this case, considering the adiabatic perturbation, Arvanitaki et al.(20) pointed out that the axion fluctuation enhanced. Since the effective potential for QCD axion depends on time, the axion perturbation also depends on the perturbation of the radiation density. However, because this point was not discussed in the previous work, we restudy the behavior perturbation including this. Here I will talk about some of the interesting behavior as possible.

発表者
橋本大輝

日程/場所
10月15日(木)13:00-

題名
Constraining the Nature of Annihilating Dark Matter with PDF of LSBG catalog

概要
Deriving a number of target regions such as the Galactic Center and Milky Way dwarf spheroidal galaxies (dSphs), indirect searches for dark matter (DM) annihilation signals have been proved. In our study, we use a low surface brightness galaxie (LSBGs) catalog as novel targets which contains about 800 objects discovered by the Hyper Suprime-Cam (HSC). LSBGs are known to have very large DM contents and be less contaminated by extragalactic gamma-ray sources (e.g., blazars) compared to star forming galaxies or ordinally galaxies. Unfortunately in the present, most of distances for HSC-LSBGs are not measured precisely, therefore they are not able to be derived in the analysis for the indirect research. In this time, we will introduce the method of the new approach using the probability distribution function of the LSBG catalog.

発表者
箕田　鉄兵

日程/場所
10月8日(木)13:00-

題名
Constraining the primordial power spectrum from 21-cm global signal with ultracompact minihalos

概要
The gravitational growth of small-scale primordial density fluctuations possibly leads to the formation of low-mass halos with dense centers at high redshifts (z>1000), which are called ultracompact minihalos (UCMHs). We calculate the heating rate for the baryon gas by the dark matter annihilation inside a UCMH and estimate the abundance of UCMHs from 21-cm line observations to give an upper limit on the amplitude of small-scale primordial density fluctuations below Mpc. This result is presented in this seminar.

発表者
田中 俊行

日程/場所
10月1日(木)13:00-

題名
Detailed modeling of mini-haloes in cosmological 21-cm simulation

概要
To extract fruitful information on the high-redshift Universe from the neutral hydrogen 21-cm line signal, theoretically modeling the statistics of the 21-cm signal accurately is the key. We have conducted the semi-numerical simulations which incorporate the time-evolving escape fraction of ionizing photons, which reflects increasing minimum halo mass for star formation due to the Lyman-Werner (LW) negative feedback. We also develop a new methodology to account for the UV photo-heating which has ever been neglected. We find that the escape fraction becomes nearly zero until redshift ~35 owing to the growth of LW intensity, so that the ionization fraction of the Universe remains small compared with the case with conventionally used constant escape fraction. Such high neutral fraction results in deep absorption in the 21-cm global signal and negligible impact of UV heating on 21-cm statistics. However, we also find that if the Universe is ionized more than only percentage level, the UV heating has non-negligible impact on the global signal to roughly the same extent as ionization on the global signal. Moreover, our results show that the UV heating steepens the slope of the 21-cm power spectrum by decreasing the power by nearly one order of magnitude at scale k~0.1 [/Mpc] which is the very target scale of current and future 21-cm observations. Thus, we suggest that both the time-evolving escape fraction and the UV heating can be essential to accurately simulate 21-cm signals at high redshift.

発表者
Aryan Bansal

日程/場所
7月27日(月)13:00-

題名
Evolution of Supermassive Black Holes inside Dark Matter Halos

概要
There is positive observational evidence that most of the galaxies have a central supermassive black hole (SMBH) with mass in range of 106 – 109.5 M☉, but no convincing or conclusive theory that proves the origin of these black holes. Furthermore, there is a clicking proportionality relation between the mass of central black hole and that of the bulge. This could indicate, although uncertain, the formation of galaxies from the black holes. Certain quasar observations also proffer the idea of SMBH existing at very high redshifts. Using merger phenomenon of Black holes and accretion history, we study the evolution of SMBH inside Dark Matter Halos. We start with the already known relation between masses of Dark Matter Halos and central Black Holes, which is valid only for z=0. Hence, we modify this known relation to work for different redshifts. For this purpose, we generate merger histories of 500 Dark Matter Halos- 100 each of mass 1010, 1011, 1012, 1013 and 1014 solar mass respectively. We find progenitors of these Halos at various redshifts (z=0.2, z=3, z=6) and assign a black hole to each of these halos. Then, by evolving these black holes (assuming negligible accretion) we compare our results with the observations and hence, study the deviation. Through this, we modify the relation to compensate for the deviation and finally validate the modified relation.

発表者
森下薫能

日程/場所
7月27日(月)13:00-

題名
複数場に拡張したインフレーションモデルの検証

概要
本研究ではPlanckの観測によるインフレーション理論への制限に着目する。 その観測結果から単一場のV=φ^nモデルは否定的なものと考えられているため、複数場のV = φ^n + σ^n モデルを考える。 φ, σ が共にインフラトンとして振る舞う場合は以前計算したが、パワースペクトルの傾きn_sを下げられる一方、 テンソル・スカラー比rは単一場モデルと同様であった。そのため、本発表では φ がインフラトン、σ がカーバトンとして振る舞うモデルを考え、rを下げる仕組みについて議論する。 また、カーバトンの特徴である曲率ゆらぎの非ガウス性についても紹介する。

発表者
小林洸

日程/場所
7月20日(月)13:00-

題名
アクシオン暗黒物質の宇宙論的帰結

概要
暗黒物質としてのアクシオンに対する宇宙論的制限をレビューします。基本的な計算を紹介する事に重点を置きます。時間が余れば、自分の最近の研究についても述べます。

発表者
三倉祐輔

日程/場所
7月13日(月)13:00-

題名
Non-minimal Inflation in the Palatini formalism

概要
Einstein Hilbert 作用において, 計量のみを変数として扱う metric formalismと計量と接続を変数として扱う Palatini formalism は完全に等価となる. しかし作用に非最小結合を持つようなモデルを考える場合, その２つの形式では異なる予言を与える. 重力とスカラー場が φ^2R の形で結合しポテンシャルが φ^n で書かれる時に, インフレーション理論でよく扱うスペクトル指数 n_s とテンソル・スカラー比 r が e-folds number を用いてどうなるのかを将来の観測も絡めて Palatini formalism を用いて議論する.

発表者
坂本陽菜

日程/場所
7月13日(月)13:00-

題名
初代星が再電離に与える影響と将来観測機器での観測可能性

概要
銀河間物質(IGM)は，宇宙の密度ゆらぎの成長の結果誕生した天体からの電離光子により，z~6より前までに電離が行われたことが観測的に示唆されている．このIGMが電離される過程を宇宙再電離という．IGMを電離する電離光子源の有力な候補は若い銀河で，星形成において水素分子が必要であるミニハロー(MH)と原子冷却ハロー(ACH)で形成される．ところが再電離の一般的なシミュレーションではMHからの寄与は無視されることが多いが，その寄与が無視できるほど小さいかは明らかではない． 本研究では，まず宇宙論的スケールでの輻射流体シミュレーションをMH有無の場合で行い，MHが再電離史に与える影響を見積もる．この電離史の違いがCMBのE-mode偏光のパワースペクトルの大角度スケールに現れると期待される．そのため，CMBを主成分分析(PCA)と呼ばれる統計手法を用い解析することで，MHの影響を調査する．

発表者
大河内雄志

日程/場所
7月06日(月)14:30-

題名
すばるHSCのデータを用いた銀河のクラスタリングと弱重力レンズ効果の二点相関による重力理論の検証法

概要
宇宙論的スケールでの重力理論を検証するために、暗黒物質分布を高赤方偏移まで高解像度で測定できるすばる望遠鏡Hyper Suprime-Cam(HSC)による撮像銀河サーベイのデータを用いる。本研究では非相対論的物質と相対論的物質が受ける重力の強さを修正する現象論的な二つのパラメータを導入して、重力の理論を一般相対論から修正する。galaxy clustering、galaxy-galaxy lensing、cosmic shearについて観測と理論の比較して、これらのパラメータに制限をつけることが本研究の目標である。

発表者
角谷健斗

日程/場所
7月06日(月)14:30-

題名
銀河団によるCMB偏光を用いたゆらぎの再構築法

概要
宇宙論を精査するために、宇宙の大規模構造の進化、ひいては密度ゆらぎの発展を知ることは非常に重要である。しかし、宇宙空間の構造を観測した場合、観測点が遠く離れるほど過去の姿を観測することになり、同じ地点の構造を異なる時刻で観測することができない。そのため異なる地点の構造から推定される物質ゆらぎの成長率は不定性を大きく含んでいる。この問題の解決策として、同じ地点の構造を異なる時刻で観測する新しい手法を確立しゆらぎの成長率を直接測ることが挙げられる。 今回は異なる時刻における構造を測定する方法として銀河団によって散乱されるCMBの偏光を観測し、最終散乱面から我々の間の領域の晴れ上がり時でのCMB温度ゆらぎを再現することを考えた。この手法はCMB光子が銀河団を通過する際に、銀河団内部の自由電子に散乱され、銀河団 まわりの最終散乱面上でのCMB温度ゆらぎの四重極成分に由来する偏光を生じることを用いる。多数の銀河団に対してこの偏光を観測することで、最終散乱面から我々の間の領域の晴れ上がり時でのCMB温度ゆらぎを再構築することが期待できる。 本発表では手法の説明と今後行うシミュレーションの内容についての議論を行う。

発表者
西澤淳

日程/場所
6月29日(月)13:00-

題名
21cm line cosmology

概要
Recent studies related to the 21 cm cosmology, mainly focused on the post reionization epoch will be introduced. Also we will present our new attempts to remove the foreground emission, such as synchrotron radiation from our Galaxy in the context of taking a cross-correlation between the CMB-lensing which might be the unique way to extract the cosmological 21 cm line signals.

発表者
多田祐一郎

日程/場所
6月15日(月)13:00-

題名
A manifestly covariant theory of stochastic inflation in phase space

概要
We formulate the stochastic approach to inflation in a covariant way with respect to the inflatons’ target space. The stochastic formalism is an effective theory for the superhorizon coarse-grained fields, where the dynamics is described as a diffusion system with stochastic noise sourced by the subhorizon modes continuously exiting the horizon. In a previous letter, we pointed out that the naive stochastic approach suffers from the “stochastic anomaly” due to the non-differentiability of noise. That is, the theory violates its covariance or exhibits a spurious dependence on the orthonormal decomposition of noise, or both. In this talk, we show that there is in fact a preferred noise frame corresponding with the basis of annihilation/creation operators, and then the theory's covariance can be saved if the differential equation is discretized in the midpoint prescription, i.e., Stratonovich. We also show the equivalent prepoint (Ito) discretisation for practical usefulness.

発表者
長谷川賢二

日程/場所
6月08日(月)13:00-

題名
Predicting 21cm-line map from Lyman α emitter distribution with Generative Adversarial Networks

概要
The radio observation of 21cm-line signal from the Epoch of Reionization (EoR) is useful to study the evolution of galaxies and intergalactic medium in the early universe. In our study, we attempt to generate 21cm-line images from the distribution of the Lyman-α emitters (LAEs) through machine learning. We apply conditional Generative Adversarial Network (cGAN) trained with the results of our numerical simulations for cosmic reionization. As a result, we find that 21cm-line brightness temperature maps and the neutral fraction maps can be well predicted by using the distribution of LAEs at large scales. We also show that the cross correlation between observed 21cm-line data and the generated 21cm-line image is detectable at k < 0.2 Mpc^-1 by combing 400 hours of MWA Phase II observation and LAE deep survey of the Subaru Hyper Suprime Camera.

発表者
宮武広直

日程/場所
6月01日(月)13:00-

題名
Enlightening the Dark Universe with Weak Gravitational Lensing

概要
Weak gravitational lensing, the coherent distortion of distant galaxy images caused by massive structures in the Universe, is one of the powerful probes of cosmic acceleration. I will start my talk with basics of weak lensing, highlight cosmology results from the Subaru Hyper Suprime-Cam (HSC) survey, and show the current status of the HSC survey. I will then introduce my ongoing projects; cosmological constraints from galaxy-galaxy lensing and clustering using the Baryon Oscillation Spectroscopic Survey (BOSS) spectroscopic sample at z~0.55 and LBG Lyman Break Galaxies (LBGs) at z~4. I will also discuss Japanese participation plan for upcoming weak lensing surveys.

発表者
横山修一郎

日程/場所
5月28日(木)13:00-

題名
Are redshift-space distortions (RSDs) actually a probe of growth of structure?
~equivalent principle in dark sector~

概要
We present an impact of coupling between dark matter and a scalar field, which might be responsible for dark energy, on measurements of redshift-space distortions (RSDs). We point out that, in the presence of conformal and/or disformal coupling, linearized continuity and Euler equations for total matter fluid significantly deviate from the standard ones even in the sub-horizon scales. In such a case, a standard relation between a peculiar velocity of total matter field and growth of matter density field would be modified, and then RSDs are not a direct probe of growth of structure any longer. As a result, we’d like to stress the importance of the direct measurement of the time-evolution of structure.

発表者
阿部 智広

日程/場所
5月21日(木)13:00-

題名
The effect of the early kinetic decoupling in a fermionic dark matter model

概要
We study the effect of the early kinetic decoupling in a model of fermionic dark matter (DM) that interacts with the standard model particles only by exchanging the Higgs boson. There are two DM-Higgs couplings, namely CP-conserving and CP-violating couplings. If the mass of the DM is slightly below half of the Higgs boson mass, then the couplings are suppressed to obtain the measured value of the DM energy density by the freeze-out mechanism. In addition, the scattering processes of DM off particles in the thermal bath are suppressed by the small momentum transfer if the CP-violating DM-Higgs coupling is larger than the CP-conserving one. Due to the suppression, the temperature of the DM can differ from the temperature of the thermal bath. By solving coupled equations for the number density and temperature of the DM, we calculate the DM-Higgs couplings that reproduce the right amount of the DM relic abundance. We find that the couplings have to be larger than the one obtained without taking into account the difference in the temperatures. A consequence of the enhancement of the DM-Higgs couplings is the enhancement of the Higgs invisible decay branching ratio. The enhancement is testable at current and future collider experiments.

発表者
田代寛之

日程/場所
5月14日(木)13:00-

題名
Gravitational waves and small-scale magnetic fields

概要
Gravitational waves can be used as powerful probes of magnetic fields in the early universe. In this talk, considering the anisotropic stress of magnetic fields as a source of gravitational waves, we show that pulsar timing arrays have a potential to provide a strong constraint on magnetic fields in the early universe. We also demonstrate that the turbulent motion due to magnetic fields could be an interesting source of gravitational waves.

発表者
市來淨與

日程/場所
5月7日(木)13:00-

題名
Observing cosmological density fluctuation twice- A new test of dark energy using CMB quadrupoles.

概要
Scattering of cosmic microwave background (CMB) radiation in galaxy clusters induces polarization signals according to the quadrupole anisotropy in the photon distribution at the location of clusters. This `remote quadrupole' derived from the measurements of the induced polarization in galaxy clusters provides an opportunity to reconstruct primordial fluctuations on large scales. Here we discuss that comparing the CMB quadrupoles predicted by these reconstructed primordial fluctuations and the direct measurements done by the CMB satellites may enable us to test dark energy beyond cosmic variance limits.