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

Coming Seminars

Seminars in February

Speaker
Yuma Matsui

Date/Place
10:30-, 8(Wed), February. @ES635

Abstract
The Big Bang scenario has many problems. Inflation theory solves some problems due to sustained long accelerating expansion. But the initial singularity problem is not solved even in inflation theory. To answer this problem, bouncing cosmology is considered. In bouncing cosmology, we assume a contraction phase before an expansion phase to avoid the initial singularity. However, it is difficult to achieve bounce because Null Energy Condition (NEC) must be violated near bounce. In this talk, I discuss how bouncing cosmology solves horizon and flatness problems and how some models violate NEC based on [1]. [1]Diana Battefeld and Patrick Peter, Phys.Rept. 571 (2015) 1-66, arXiv:1406.2790.

Speaker
Yurino Mizuguchi

Date/Place
10:30-, 8(Wed), February. @ES635

Title
Lattice simulation of stochastic inflation

Abstract
Our motivation is the accurate estimation of PBH(primordial black hole) abundance, which is made by the large perturbation in Inflation. In the early universe, it is the big problem to estimate accurately its abundance. Typically, one adopts the linear perturbation theory for the growth of the fluctuation. However, this theory can not be used in the case where the curvature perturbation is large enough to make PBH. Then we introduce stochastic formalism to resolve this problem. Moreover, numerical simulation can get the growth of accurate initial density fluctuation. We hence execute the lattice simulation which is excellent with stochastic formalism, confirm the growth of perturbation in Inflation, and make the map of the Inflation end. Additionally, the large perturbation is at the tail of the curvature perturbation’s PDF(probability density function) and is unlikely to happen stochastically. We try to use “Importance sampling” in the tail so that we make the PDF of the region that has the large perturbation. At this time we mainly explain the growth of perturbation in Inflation and the map at end of Inflation and touch on roughly the process that is from general “Importance sampling” to stochastic inflation, and the conventional method of the PBH abundance.

Speaker
Genki Naruse

Date/Place
10:30-, 1(Wed), February. @ES635

Title
Can subhalos affect the 21cm absorption line in the pre-reionization epoch?

Abstract
The 21 cm forest is a promising tool to trace the structure of the universe before the reionization epoch. In that epoch, a promising source of 21cm forest is the minihalo. In the previous study, it was found that the 21 cm optical depth could be enhanced due to subhalos in a minihalo if such subhalos could survive and keep a low temperature. In our work, using hydro simulation, we investigated how much mass of the subhalos can survive during their dynamic motion such as dynamical friction and tidal force, and estimated that the subhalos whose mass is 0.1% of their host halo can survive. Now we are investigating the evolution of temperature, and I will talk about my progress till now.

Speaker
Keitaro Ishikawa

Date/Place
10:30-, 1(Wed), February. @ES635

Title
BAO measurement of the three-dimensional correlation function for photometric surveys

Abstract
There are two main types of galaxy observation methods: spectroscopic and photometric. In contrast to spectroscopic observations, photometric observations have the advantage of being able to reach faint galaxies. However, photometric observations have a large uncertainty in estimating the redshift of galaxies. In this study, we consider baryon acoustic oscillations (BAO) using photometric observations. We also discuss the allowed level of systematics due to the photometric redshift uncertainties that should be achieved in future observations. For this purpose, we modeled the photo-z effect by incorporating the photo-z distribution assuming a Gaussian distribution in the three-dimensional two-point correlation function and verified the effect using mock simulations in redshift space. As a result, we found the following three things. Firstly, if the magnitude of the photo-z error associated with the data is known, the three-dimensional two-point correlation function can constrain the BAO peak location up to a photo-z error of σ = 0.01(1+z). If the magnitude of the photo-z error is unknown, a photo-z 1% template can be used (although the statistical error will be larger), and the BAO peak location will not be biased. Secondly, up to a photo-z error equivalent to about 50 Mpc/h, the three-dimensional two-point correlation function can be used for unbiased cosmological tests. Finally, even if the photo-z distribution is skewed non-Gaussian, skewness does not affect the BAO measurement as long as the mean and variance of the distribution are reproduced correctly. We will summarize the conditions for robust measurements using BAO and discuss the required level of photometric observation accuracy.

Speaker
Koki Tanida

Date/Place
10:30-, 1(Wed), February. @ES635

Title
Testing general relativity with the joint analysis of weak lensing and galaxy clustering from HSC-Y3 and BOSS

Abstract
Einstein’s theory of general relativity has been successful in describing various phenomena caused by gravity, such as black holes and gravitational lensing. It has been confirmed that general relativity is consistent with t he experiments in the Solar System, whereas it has not been exclusively examined on cosmological scales. In particular, the discovery of cosmic acceleration has recently motivated the investigation of a number of proposals for modified gravity models. Such alternative models can produce the late-time acceleration without the cosmological constant involved in the standard \Lambda CDM model. In our study, we aim to test the modified gravity models by combining the three two-point correlation functions (3×2pt) of the large-scale structure: cosmic shear, galaxy-galaxy lensing, and galaxy clustering. We use measurements from the third-year HSC (HSC-Y3) weak lensing sample and SDSS spectroscopic galaxy catalog.a. We employ a phenomenological model of gravity for structure formation, covering broad types of modified gravity models. In this presentation , as the first step of our study, we report the development of a software pipeline to compute the theoretical model of the correlation functions in \Lambda CDM case and confirm whether it can reproduce input cosmological parameters through analyzing mock data with the two correlation functions; galaxy-galaxy lensing and galaxy clustering.

Seminars in January

Speaker
Jason Kristiano(University of Tokyo)

Date/Place
14:00-, 18(Wed), January. @ES606

Title
Ruling out primordial black hole formation from single-field inflation

Abstract
The most widely studied formation mechanism of a primordial black hole (PBH) is collapse of large-amplitude perturbation on small scales generated in single-field inflation. In this talk, we will present the one-loop correction to the large-scale power spectrum in such a model. We find models producing appreciable amount of PBHs generically induce too large one-loop correction on large scale probed by cosmic microwave background radiation. We therefore conclude that PBH formation from single-field inflation is ruled out. Reference: arXiv:2211.03395

Speaker
Yusuke Mikura

Date/Place
10:30-, 11(Wed), January. @ES635

Title
Palatini-Higgs Inflation

Abstract
Among a plethora of inflation models, Higgs inflation is one of the most attractive candidates because an observationally confirmed particle is responsible for the accelerated expansion in the early universe. Even though one assumes the Higgs particle to be the inflaton, inflationary phenomenology is not unique due to a choice of gravitational formulations, such as metric and Palatini formalisms. In this talk, I review a basic framework of Palatini formalism and its application to Higgs inflation. I also introduce the remaining questions on the Palatini-Higgs inflation.

Seminars in December

Speaker
Koya Murakami

Date/Place
10:30-, 21(Wed), December. @ES635

Title
Constraints on WDM mass using machine learning

Abstract
The distribution of matter in the universe can be the probe of the mass of dark matter because dark matter mass affects the matter distribution at small scale. In our work, we test that the machine learning algorithm can constrain the dark matter mass better than power spectrum by using the map of 21 cm radiation from the hydrodynamic simulation. In addition, we discuss the effect of astrophysical process such as self-shielding of HI gas, star formation and UV background, and the system noise of SKA.

Speaker
Shintaro Hayashi

Date/Place
10:30-, 7(Wed), December. @ES635

Title
Constraints on the phase transition of Early Dark Energy with the CMB anisotropies

Abstract
Early dark energy (EDE) is the one of the solutions to Hubble tension. Introducing the EDE reduces the sound horizon at the last scattering. On the other hand, the Hubble constant becomes larger to keep the consistency with the CMB data. This is the basic idea. However, it is not enough to keep the consistency because of the constraints from the CMB high-l region. This motivates the study of EDE perturbation. We focus on the phase transition (PT) of EDE. In this case, the EDE decay happens stochastically. This means the additional density fluctuations are generated by the PT of EDE. We calculate the generation and growth of this perturbation, and the effects on the CMB spectra. In conclusion, we show such a perturbation is not preferred to appear in the CMB spectra by the MCMC analysis although we need more careful analysis.

Speaker
Gonzalo Morras (Autonomous University of Madrid)

Date/Place
15:00-, 2(Fri), December. @ES635

Title
The search for Primordial Black Holes at current Gravitational Wave Detectors

Abstract
Primordial Black Holes are black holes formed in the early universe which could originate from the gravitational collapse of large (order one) density perturbations from inflation. If black holes of this kind exist, they could make up a part, possibly all, of the dark matter. Even if they don't explain the totality of Dark Matter, the discovery of such black holes would have far reaching implications for the study of Dark Matter and Inflation. In this seminar I will explain different methods by which current Gravitational Wave Detectors such as LIGO-Virgo-KAGRA can and are used to look for these Primordial Black Holes.

Speaker
Seongwhan Yoon

Date/Place
10:30-, 1(Thu), December. @ES635

Title
A study on the relation between formation history and observables of galaxy clusters

Abstract
Since galaxy clusters are the most massive self-gravitating system in the Universe, the halo number density per unit volume per unit mass is one of the most powerful probes to constrain cosmological models. However, to estimate the halo number density as a function of halo mass, one should understand systematics stemming from the relationship between halo properties and cluster observables. Otherwise, model ingredients of the halo number density, such as selection function and mass-observable relations, will be biased. In this presentation, I report the connection between one of the halo properties, i.e., the halo mass accretion history, and the baryonic physics inside of the halo based on IllustrisTNG hydrodynamical simulation. By adopting two parametrized models (Diffmah & Baryon Pasting model) and studying the model parameters, the connection can be understood well. Since this connection is quite complicated, machine learning played a key role in establishing the connection.

Seminars in November

Speaker
Koichiro Nakashima

Date/Place
10:30-, 30(Wed), November. @ES635

Title
RSD analysis with Lyman alpha forest including non-linearities

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 and analyze the full shape to measure the growth rate of the structure through redshift space distortions. Looking ahead to future observations, we tested the validity of the models presented in previous research under different maximum wavenumbers used in the fit. In addition, I’ll discuss the requirements of survey parameters in the assumption of Subaru Prime Focus Spectrograph.

Speaker
Ryoto Inui

Date/Place
10:30-, 16(Wed), November. @ES635

Title
Primordial black holes as whole dark matter explored by the scalar-induced gravitational waves.

Abstract
In recent years, primordial black hole (PBH) has been attracting much attention as a candidate for dark matter (DM). PBHs are produced by the gravitational collapse of the large primordial density perturbations in the radiation dominated universe. PBH has a wide mass range in [10^{-18}M_{\solar}, 10^3M_{\solar}] and there are many observational constraints (Hawking radiation, microlensing, GWs…etc). However, there is a possibility that PBHs account for 100% of DM in the mass range between 10^{-15}M_{\solar} and 10^{-11}M_{\solar}. The large primordial density perturbations required for PBH production can also induce the primordial stochastic gravitational waves (GWs) through a second-order interaction between tensor and scalar metric perturbations. Previous studies have shown that the 2nd-order scalar-induced GWs would be detectable in the foreseeable space-based GW interferometer called LISA when PBHs exist as the whole DM. Stochastic GWs can be utilized as indirect evidence that PBHs account for 100% of DM. The primordial perturbations statistically follow almost the Gaussian distribution, however, the primordial perturbations which have a heavier tail probability distribution function (PDF) have been investigated. The PBH abundance is quite sensitive to the tail behavior of PDF and much enhanced by such heavy tail distribution as discussed in several previous works. In this work, we focus on the exponential tail curvature perturbations which are well-motivated in the ultra-slow-roll inflation models. Then we investigated the 2nd-order scalar-induced GWs associated with PBH as the whole DM. We have found that the GWs would still be detectable in LISA sensitivity though the amplitude is slightly lower than that induced by the Gaussian curvature perturbations. We also found that the footprints of the non-Gaussianity appear in the high-frequency region. Although this feature emerges under the LISA sensitivity, it might be possible to obtain information about the non-Gaussianity from GW observation with a deeper sensitivity such as the DECIGO mission.

Speaker
Seiya Imoto

Date/Place
10:30-, 10(Thu), November. @ES635

Title
A new LW feedback model for first star formation and photon supply to IGM.

Abstract
First star(population III star) is the stellar population formed in early universe at pristine gas cloud and play vital roles for providing metals to next generation star formation. Unfortunately, their physical properties are highly unknown, such as the IMF or SFRD. Recent studies have shown that self-feedback that UV photon emitted by other stars (11.2-13.6 eV range, called Lyman Werner band) destroys the coolant affects the formation of first stars and changes these properties. I introduce a new way in which feedback affects the SFRD of the first stars and their photon supply to IGM in the form of the evolution of ionizing escape fraction evidenced by simulations. This presentation will discuss how this new handling of feedback affects the first star formation in cosmic scale.

Speaker
Noriaki Nakasawa

Date/Place
10:30-, 9(Wed), November. @ES635

Title
Testing gravity by combining weak lensing, clustering and RSD

Abstract
In this presentation, I will talk about testing gravity using gravitational lensing, redshift space distortion (RSD), and projected galaxy clustering. Accelerated expansion of the universe is one of the most mysterious problems in the field of cosmology. The standard cosmological model assumes the existence of unknown energy, called dark energy, to explain the cosmic acceleration. Another approach is to modify general relativity to explain cosmic acceleration. RSD records the motion of individual galaxies as a ratio of linear growth rate and galaxy bias. The galaxy bias of a sample used for the Red measurement can be estimated by combining galaxy-galaxy clustering and lensing. Thus, the combination of these three probes, the so-called E_G, enables us to extract the linear growth rate, which is sensitive to the properties of gravity. In this work, we will constrain E_G with the BOSS CMASS sample and the HSC S19A data.

Speaker
Hiroto Kondo

Date/Place
10:30-, 2(Wed), November. @ES635

Title
Testing dark energy by combining galaxy cluster polarization and CMB temperature and E-mode polarization multipoles

Abstract
The polarization of the galaxy clusters is induced by Thomson scattering of CMB photons and depends on the quadrupole anisotropy. This CMB photon scattered by galaxy clusters comes from inside our last scattering surface(LSS). Therefore we can get the information inside of our LSS by the cluster polarization and estimate the density fluctuations through CMB polarization observation. By comparing the CMB temperature quadrupoles reconstructed from estimated fluctuation, we test the cosmology (dark energy). In this work, we improve this estimation by combining the polarization of galaxy clusters and CMB temperature and E-mode polarization multipoles.

Seminars in Octobar

Speaker
Anupreeta More (IUCAA)

Date/Place
15:00-, 21(Fri), Octobar. @ES635

Title
Detection of Gravitational wave sources and gravitational lensing effects

Abstract
Detection of gravitational wave sources consisting of massive binary black holes (BBH), in particular, is still a challenge due to contamination from noise transients called glitches. I will discuss our efforts to distinguish BBH from specific kinds of glitches. Gravitational lensing of gravitational waves is expected to be detected in the near future. I will present an improved statistic which will help identify candidate lensed GW events. The stellar population located within lensing galaxies are thought to produce distortions in the gravitational wave signals referred to as microlensing. I will also discuss how severe such microlensing effects are going to be and how they may affect detection of strongly lensed GW events.

Speaker
Divya Rana (IUCAA)

Date/Place
13:30-, 20(Thu), Octobar. @ES635

Title
Subaru Hyper Suprime-Cam view of the Universe: Galaxy-dark matter connection and the boundaries of dark matter halos

Abstract
Dark matter forms the backbone of the cosmic web, in which galaxies form and evolve over cosmic time and assemble to form groups and the massive clusters of galaxies we see today. The Hyper Suprime-Cam (HSC) survey provides high-quality imaging data at an unprecedented depth spanning a wide sky area which is well suited to carry out weak lensing studies. We will use these techniques to probe the dark matter distribution and explore its connection with the observable universe. These correlations will be discussed with the help of weak lensing calibrated halo masses for GAMA galaxies and groups obtained using the first year HSC shape catalog. I will present the scaling relations between the dark matter masses of galaxy groups and their observable properties such as the group luminosity and velocity dispersion, as well as those between the sizes of galaxies and their dark matter halos. Finally I will also present the tightest constraints on the location of the splashback radius using X-ray clusters selected from the eROSITA eFEDS. I will then talk about the agreement with expectations from the ΛCDM model and compare it with previous works in the literature.

Speaker
Surhud More (IUCAA)

Date/Place
10:30-, 20(Thu), Octobar. @ES635

Title
Status of Planet Nine Search using the Subaru

Abstract
Planet Nine has been primarily proposed to explain the observed structure of the Kuiper belt objects with semi-major axes beyond 200 AU. In this talk, I will report on our multi-year observational program to search for Planet Nine with the Hyper Suprime-Cam instrument on the 8 meter Subaru telescope. Our survey area covers the sky region near the apocenters of the proposed path of Planet Nine. I will describe the challenges involved with the data reduction using the bleeding edge of the Rubin LSST pipeline, its management over computing clusters separated over multiple continents and having to deal with a large number of false positive detections in difference images. I will summarize the current best constraints on the existence of Planet Nine.

Speaker
Katsuya Abe

Date/Place
10:30-, 19(Wed), Octobar. @ES635

Title
Free-free emission from dark matter halos and small-scale perturbations

概要
The diffuse background free-free emission has already been studied for example, as one of the important foreground components in the CMB analysis. Although most of the observed free-free emission is the observed free-free emissions are believed to be Galactic origin, a lot of cosmological free-free emitters can be considered, and DM halos are one of them. In this presentation, we talk about our estimation of the intensity and the anisotropy induced by the DM halos and also discuss features of them. While the observation data for the free-free emission are still limited, we show the possibility that the future observation might be probe for the cosmology.

Speaker
Maxime Paillassa

Date/Place
10:30-, 12(Wed), Octobar. @ES635

Title
Investigation of the HSC unrecognized blends with new simulations and machine learning.

Abstract
A serious issue for astronomical imaging surveys is blending, the phenomenon of apparent source image overlap. In the image analysis process, a blend is referred as unrecognized when it is considered as a single object. Leveraging the Hubble Space Telescope (HST) observations, we suspect that a significant fraction of the COSMOS field sources in the Hyper Suprime Cam (HSC) survey are unrecognized blends. Though, their impact on important cosmological probes such as source shapes and photometric redshifts is still unclear, and their identification is not trivial. In this talk, I introduce a new GalSim COSMOS data set that can be used throughout the LSST DESC BlendingToolKit (BTK) software to simulate realistic HSC multiband blend images. We demonstrate the correctness of the dataset and simulations through a comprehensive validation process and use them to train a machine learning based unrecognized identifier that can outperform the HSC pipeline.

Speaker
Hironao Miyatake

Date/Place
10:30-, 05(Wed), Octobar. @ES635

Title
Weak Lensing Cosmology with Subaru Hyper Suprime-Cam

Abstract
The accelerating expansion of the Universe is one of the biggest problems in modern physics. Weak lensing is a powerful probe of cosmic acceleration because it can directly measure dark matter distributions. The primary goal of the Subaru Hyper Suprime-Cam (HSC) survey is to constrain the nature of cosmic acceleration through weak lensing measurements. In this talk, I will introduce the basics of weak lensing cosmology. I will then report the first-year cosmology results of the HSC survey and the current status of the third-year cosmology analyses.

Seminars in July

Speaker
Yuma Matsui

Date/Place
13:00-, 27(Wed), July. @ES635

Title
Phenomenology of α-attractors in hybrid inflation

Abstract
Inflation theory is considered as solution of some problems for the initial conditions of the standard Big Bang theory. Inflation has a freedom to choose parameter which makes model property. In particular, slow-roll inflation is a typical model which have many possibilities of potential and interaction terms. On the other hand, supergravity model is featured as a physical model exceeds the current standard model. In this talk, I discuss about α-attractors inflation model that corresponds to this supergravity model. Among them, some α-attractors models inspired by string theory may have many interacting scalar fields. So that I investigate mechanism how this model cause inflation and difference between single field and two-field based on [1]. I will use only black board in this time. [1] Renata Kallosh and Andrei Linde, (2022), arXiv:2204.02425

Speaker
Yurino Mizuguchi

Date/Place
13:00-, 27(Wed), July. @ES635

Title
The distinction of potential by predictions of Reheating nd primordial gravitational waves

Abstract
Inflation theory can resolve problems of Big-bang theory, horizon problem and flatness problem. In this theory, one of the most important models is slow-roll Inflation. In many slow-roll inflation models, we respect that matching CMB observables and conformal symmetry thought presumably significant for constructing theory in high-energy regions. Now, we focus on two models, T-model and E-model. These models' potentials describe different potentials by model parameters. However, on each model, respectively, {ns,r} observables can't be distinguished in the CMB observable, independently of exactly model parameters. Here, we think that distinguish these by the two ways. Firstly, we consider that CMB observables and energy scales happen during Reheating, so we decide the possible range of {ns,r}. Secondly, relic gravitational waves from Inflation can constitute directly model parameters. In this presentation, I review the paper [1] treated at summer school and confirm that they can distinguish actually. [1]Swagat S.Mishra et al., JCAP, 40, 2021

Speaker
Keitaro Ishikawa

Date/Place
13:00-, 20(Wed), July. @ES635

Title
BAO measurement of three-dimensional correlation function for photometric surveys

Abstract
Galaxy surveys are of two types: spectroscopic survey and photometric. Spectroscopic observations provide the exact redshift of galaxies, but only bright galaxies can be observed. On the other hand, photometric observations have the advantage which could image faint galaxies at the same time, so we can expect statistical accuracy because we can secure an adequate number of samples. However, photometry has a large degree of uncertainty in estimating the redshift to galaxies. For this reason, some people who research ahead have performed analysis using statistics without line-of-sight information in galaxy clustering analysis for photometry. In general, we can confirm a gain of characteristic correlation when the separation between two galaxies is about 100 Mpc/h in two-point statistics of the galaxy distribution. This is a trace that baryons and photons oscillated until they decouple (Baryon Acoustic Oscillation) when the age of the Universe was about 380 thousand years. Because the position of BAO peak doesn't evolute in time in the comoving coordinate system, this scale is a predictable quantity exactly using linear theory, and we can utilize it for cosmology test as a standard ruler of the Universe. In this study, we aim at BAO measurement at photometry retaining three-dimensional information. Due to this aim, we adopted an effect of photometric redshift uncertainty to a two-point correlation model of three-dimensional distributions of galaxies. To check this model's correctness, we simulated photometric observation using galaxy positions and estimated the BAO scale. Then we try to show an acceptable magnitude of photometric redshift uncertainty by measuring a divergence from fiducial cosmology. As a result, we showed that when photometric redshift uncertainty is 1% at redshift z~1 which current photometric survey like HSC could be able to reach there, we could tolerate the measurement. Also, in this speech, we will discuss the magnitude of photometric redshift uncertainty that future photometric observation will implement.

Speaker
Koki Tanida

Date/Place
13:00-, 20(Wed), July. @ES635

Title
The possibility to restrict gravity through splashback

Abstract
Currently, the general relativity is used to describe gravity. However, while this theory explains observational facts such as in the solar system without contradiction, it has not yet been verified with good accuracy whether it is valid on cosmological scales as well. In this situation, we consider many models of modified gravity theory, which extends general relativity on cosmological scales. One of the observables considered to restrict the modified gravity theory is the splashback radius, which characterizes the physical boundary of a galaxy or cluster of galaxies. It is observed as the location where the density gradient value drops sharply to its minimum. In this presentation, we will discuss the splashback radius that characterizes the galaxy cluster scale (about a few Mpc) based on [1]. In this paper, we calculate the splashback radius by simulations in general relativity and the f(R)-gravity theory, which is one of the modified gravity theories. Specifically, we investigate the difference in the behavior of the positional change of the splashback radius as a function of the mass of the material accreting into the galaxy cluster in each gravity theory. We found that if we take into account the difference in the mass of the material falling into the cluster, there is a good chance that we can actually observe the splashback radius through future observations such as LSST to constrain the gravity theory based on the difference in the behavior of the splashback radius.

Speaker
Genki Naruse

Date/Place
13:00-, 20(Wed), July. @ES635

Title
Calculation of the contribution of star-forming galaxies and AGN to reionization

Abstract
The detailed process of cosmic reionization has yet to be revealed. It is considered that the star-forming galaxies are the plausible candidates for ionizing sources by most previous studies. However, it is claimed that there are a lot of faint active galactic nuclei (AGNs) that have not been found yet at high redshift[1], so that AGNs are also considered as another type of ionizing sources. How much they contribute to reionization is under debate. In the first half of this talk, I will introduce the previous study[2] which constrains the contribution of galaxies and AGNs to reionization with parameters such as the escape fraction of ionizing photons and the faint-end slope of the AGN luminosity function at high redshift. The latter part, I will talk about reproduced results by my calculations and future works for summer school. For the purpose of this talk, it includes the preparation of the summer school, so that I will start from some basic things to some extent. 1.Giallongo E. et al., 2015, A&A, 578, A83 2.Yoshiura, S., Hasegawa;, K., Ichiki, K., et al. 2017, MNRAS, 471, 3713

Speaker
Takahiro Yamamoto

Date/Place
13:00-, 6(Wed)&13(Wed), July. @ES635

Title
Deep learning and its application to popcorn GW signal

Abstract
From the milestone work by George&Huerta, the deep learning (DL) application to gravitational wave (GW) astronomy is actively studied. There are many works in which DL is used for the detection of GW signals, parameter estimation, waveform modeling, and burst-like noise classification. It is becoming a promising method for GW data analysis. I will give a brief review of deep learning in the former half of my talk. In the latter half of my talk, I show the application of DL to popcorn GW background; the superposition of burst GWs emitted from a bunch of sources. Popcorn GW background is characterized by its non-Gaussianity. If bursts frequently overlap, it is almost Gaussian. On the other hand, if bursts rarely overlap, the popcorn signal exhibits non-Gaussianity. Because the strength of the non-Gaussianity depends on the event rate history of burst signals, measuring the non-Gaussianity is one of the keys to inferring the events rate history. For the case of binary black hole (BBH) coalescence, the non-Gaussianity will reveal the source of BBH. Recently, we apply DL to detect popcorn signals and estimate the non-Gaussianity of popcorn signals. We demonstrate our method by using a toy model of a popcorn signal. We show that our method can detect popcorn signals with comparable sensitivity as the maximum likelihood statistic, while the DL method is computationally more efficient than the likelihood-based method. Also, we show that our method can well estimate the signal-to-noise ratio and the non-Gaussianity of the popcorn signal. I will use the blackboard in my first half while the latter topic is presented by slide.

Seminars in June

Speaker
Tomomi Sunayama

Date/Place
13:00-, 29(Wed), June. @ES635

Title
Toward an accurate optical cluster cosmology

Abstract
In this talk, we present a novel analysis for cluster cosmology which combines abundances, weak lensing, and the clustering of galaxy clusters. Optical clusters are susceptible to projection effects and the distribution of the optical clusters becomes anisotropic due to the preferential selection of filamentary structure along the line-of-sight. This causes the anisotropic boost on the lensing and clustering signals of the clusters. By modeling this anisotropic boost, we ait to constrain cosmological parameters more accurately. However, the result using the SDSS redMaPPer clusters favored a small Omega_m, which is consistent with DES Y1 cluster cosmology. Using HSC data, we find out the cause of the problem.

Speaker
Laura Herold(MPA, Max Planck Institute for Astrophysics)

Date/Place
13:00-, 22(Wed), June. @ES635

Title
Early Dark Energy: a status update and a new constraint using the profile likelihood

Abstract
A dark energy-like component in the early universe, known as early dark energy (EDE), is a proposed solution to the Hubble tension. Currently, there is no consensus in the literature as to whether EDE can simultaneously solve the Hubble tension and provide an adequate fit to the data from the cosmic microwave background (CMB) and large-scale structure of the universe. In this talk, I will give a brief overview on the status of EDE and describe the disagreement about EDE in the literature. To explore the origin of this disagreement, we deconstruct the current constraints on EDE: We use two different methods, a grid sampling and a profile likelihood, and find evidence that the current constraints on EDE might suffer from (prior) volume effects upon marginalization and are possibly biased towards small values of the EDE fraction. Using the profile likelihood, we construct a new constraint that is not subject to volume effects.

Speaker
Viraj Nistane(University of Geneva)

Date/Place
13:00-, 15(Wed), June. @ES635

Title
Research overview: (1) CMB lensing in inhomogeneous universe (2) Lensing estimation from galaxy number countsa>

Abstract
I will talk briefly about my overall work until now in the field of large-scale structure and CMB and gravitational lensing. (1) In one half of the seminar, I shall talk about a possibility that we occupy a special position in our universe (breaking the Copernican principle) close to the center of a local underdense region (spherical large-scale void) that can be modelled using LTB spacetime metric. The CMB sky measured by an off-center observer in this void is not statistically isotropic. In addition to the non-stochastic CMB anisotropies due to the geometry of the model, we also observe a lensing-like distortion of the CMB anisotropies. We will have a look at a framework to forecast the precision with which we can measure the amplitude of the lensing-like deformation of the CMB temperature anisotropies. (Ref: arXiv:1908.05484) (2) In the other half, I shall talk about an estimator for the lensing potential from galaxy number counts, which contains a linear and a quadratic term. In our work, we show that this estimator has a much larger signal-to-noise ratio than the corresponding (quadratic) estimator from intensity mapping. This is due to the additional lensing term in the number count angular power spectrum which is present already at linear order. We estimate the signal-to-noise ratio for future photometric surveys. We find that particularly at high redshifts, z ≳ 1.5, the signal to noise ratio can become of order 30. We therefore claim that number counts in photometric surveys are an excellent means to measure tomographic lensing spectra. (Ref: arXiv:2201.04129)

Speaker
Xiaolin Liu

Date/Place
13:00-, 8(Wed), June. @ES635

Title
Gravitational waves model and memory from coalescing binary black holes systems

Abstract
The first detection of gravitational waves (GWs) marked the beginning of the era of gravitational wave astronomy. Binary black hole systems are among the most common sources of gravitational waves. The modeling of gravitational waves is important for detection and data analysis. Here we focus on the template of gravitational radiation and gravitational memory effects. The main contents of this talk include the following aspects. Firstly, the effective-one-body (EOB) numerical-relativity (NR) waveform models, known as the SEOBNR waveform models, are based on the EOB theoretical framework and NR simulations. We study the SEOBNRE model which was extended by SEOBNRv1 model and validated for spin-aligned binary black holes (BBH) coalescence along eccentric orbits. We validate this theoretical waveform model by comparing them against the NR simulating bank, and 278 NR waveforms are investigated in total. We find that SEOBNRE can model the NR waveform quite well. The fitting factor for most of the 278 waveforms are larger than 99%. Then, based on the validation analysis of SEOBNRE model, we update it to SEOBNREHM model in the following three respects. We update the EOB conservative dynamics from SEOBNRv1 to SEOBNRv4, and we properly treat the Schott term which has been ignored in SEOBNRE to improve radiation reaction force. Besides, we construct a new factorized waveform including (l,m)=(2,2),(2,1),(3,3),(4,4) modes based on EOB formalism. We have also validated SEOBNREHM waveform model through comparing the waveform against SXS catalog.The comparison is done for BBH with total mass in (20,200) solar mass using Advanced LIGO designed sensitivity. We have compared our (2,2) mode waveforms and gravitational polarization waveforms via combinations of the inclination angle and orbit phase angle to the results of NR and SEOBNRv4HM. Finally, we apply the Bondi-Metzner-Sachs method to calculate the gravitational wave memory. Our method can accurately calculate the memory if the nonmemory waveform is known. We combine our method with the matured NR results of a nonmemory waveform for BBH systems, which was compared with the results of post-Newtonian method and NR simulation. Our calculation results are consistent with the NR results of memory. We also determine the dependence of the memory amplitude on the mass ratio and the spins of the two spin-aligned black holes.

Speaker
Yuichiro Tada

Date/Place
13:00-, 1(Wed), June. @ES635

Title
Effective treatment of U(1) gauge field and charged particles in axion inflation

Abstract
The axionic inflaton with the Chern–Simons coupling may generate U(1) gauge fields and charged particles simultaneously.In order to incorporate the backreaction from the charged particles on the gauge fields, we develop a procedure to obtain an equilibrium solution for the gauge fields by treating the induced current as effective electric and magnetic conductivities.Introducing mean field approximation, and numerically solving self-consistency equations, we find that the gauge field amplitudes are drastically suppressed. Interestingly, as the production becomes more efficient, the charged particles gain a larger part of the transferred energy from the inflaton and eventually dominate it.Our formalism offers a basis to connect this class of inflationary models to a rich phenomenology such as baryogenesis and magnetogenesis.

Seminars in May

Speaker
Daichi Kashino

Date/Place
13:00-, 25(Wed), May. @ES635

Title
The EIGER project

Abstract
We introduce our JWST GTO program, EIGER (Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization). Our EIGER project aims to understand the process of cosmic reionization, the evolution of young galaxies, and the formation of supermassive black holes in the Epoch of Reionization. Using NIRCam, we carry out slitless spectroscopy of z∼6 star-forming galaxies in the fields of six z > 6 bright quasars and correlate the distribution and properties of these galaxies with the conditions of the inter/circumgalactic media along the lines of sight, which are provided from the spectra of the background quasars. Our team is also carrying out complementary observations in our target fields from space and ground. In particular, we conducted ALMA observations to blindly search for [CII]-emitting star-forming galaxies along the quasars' line of sight at z~5--6. In the latter half of the talk, we present two significant detections of [CII]158um-emitting galaxies revealed with ALMA to be associated to high-ionization absorving clouds. They are uniquely characterized by their compact size and narrow emission line profiles. These suggest that they are tracing cold neutral phase in the complex multiphase interstellar or circumgalactic media and unlikely to be mature galaxies that have often been detected in [CII] at high redshifts.

Speaker
Tomohiro Fujita (Waseda University)

Date/Place
13:00-, 18(Wed), May. @ES635

Title
SU(N)-natural inflation

Abstract
Inflation is widely accepted as a part of the standard cosmology, while its mechanism is still unknown. Among many proposed models, natural inflation have attracted much attention, because this class of inflation models offers not only natural realization of inflation but also rich phenomenology such as magnetogenesis, baryogenesis, gravitational wave production, etc. In this context, we constructed a new model where the axionic inflation is coupled to general SU(N) gauge fields. After briefly reviewing natural inflation, I will introduce our model and discuss recent developments and open questions.

Speaker
Koki Kakiichi (University of California)

Date/Place
13:00-, 11(Wed), May. @ES635

Title
IGM Tomography with Subaru/HSC: implications to reionization and SMBH

Abstract
The art of cosmography, i.e. map-making of the Universe, is essential for the progress in astronomy. In this talk, I present a new technique to reconstruct a large-scale structure of the intergalactic medium (IGM) using a unique combination of the narrow-band filters with Subaru/HSC. The technique is applicable to high redshifts across z~4-6 and is perfectly suited to examine the ionizing radiation and the gaseous environment of galaxies and quasars. I demonstrate the method using the public release of HSC data and present the first co-spatial, large-scale map of the Lyman-alpha emitters and the IGM in the COSMOS field at z~5. I also discuss the potential applications of IGM tomography and the implications for our understanding of reionization and the growth of supermassive black holes.