Cセミナー 2017
English発表者
Purnendu Karmakar (Universita degli Studi di Padova)
日程/場所
3月12日(月)16:00-@ES635
題名
Cosmic structures
and gravitational waves in ghost-free scalar-tensor theories of gravity
概要
We study cosmic structures in the quadratic Degenerate Higher Order Scalar Tensor
(qDHOST) model, which has been proposed as the most general scalar-tensor theory (up to
quadratic dependence on the covariant derivatives of the scalar field), which is not
plagued by the presence of ghost instabilities. We then study a static, spherically sym-
metric object embedded in de Sitter space-time for the qDHOST model. This model exhibits
breaking of the Vainshtein mechanism inside the cosmic structure and Schwarzschild-de
Sitter space-time outside, where General Relativity (GR) can be recovered within the
Vainshtein radius. We then look for the conditions on the parameters on the considered
qDHOST scenario which ensure the validity of the Vainshtein screening mechanism inside
the object and the fulfilment of the recent GW170817/GRB170817A constraint on the speed
of propagation of gravitational waves. We find that these two constraints rule out the
same set of parameters, corresponding to the Lagrangians that are quadratic in
second-order derivatives of the scalar field, for the shift symmetric qDHOST.
発表者
Victor Bonjean
日程/場所
3月8日(木)11:00-@ES606
題名
Galaxy properties
from WISE with machine learning
概要
The star formation rates (SFR) and the stellar masses (Mstar) of galaxies hold a lot of
information about the evolution and the history of the cosmic structures they belong to.
These quantities are well estimated for star-forming galaxies, but not so much for
passive galaxies, which are of particular interest to study and characterise the galaxy
clusters and the nature of cosmic filaments. Recently, machine learning algorithms have
been more and more developed and have now become reliable tools to classify or estimate
physical properties of astrophysical objects. I will present a machine-learning based
estimation of SFR and Mstar for any types of galaxies in the all sky.
発表者
Nadege Lemarchand
日程/場所
3月1日(木)11:00-@ES606
題名
Generalized
Faraday rotation power spectra: from CMB to large scale structures
概要
A cluster of galaxies is both a magnetized relativistic and non relativistic plasma.
Thus, it acts as a birefringent medium for the light that goes through this kind of
structures. In particular, CMB photons cross clusters of galaxies on their way to us.
Depending on the relativistic nature or not of the free electrons in the plasma, the
effect on the CMB polarization will be different. In the case of a cold plasma, the
polarization plane is rotated after going through a cluster of galaxies (Faraday
Rotation). On the contrary, when the plasma is relativistic, CMB photons experience
Faraday Conversion which transfers linear polarization into circular polarization. I
looked at a statistical study of this effect, by first focusing on predicting the
angular power spectra of such effects due to clusters, using a line-of-sight approach
and the halo model, implementing the cosmological principle for the statistics of the
directions of the magnetic fields inside clusters. These effects are both sensitive to
the cosmology through the mass function of the clusters and so parameters such as σ8,
and to the distribution of the magnetic field and electrons inside a cluster, and can be
used as a probe both for cosmology and for clusters of galaxies. Then I looked at the
consequences of these effects on the angular power spectra of the CMB polarized
anisotropies: the Faraday rotation effect mixes the E and B modes (creating secondary B
modes in addition to the primordial and lensing ones), whereas the Faraday conversion
effect transfers E and B anisotropies into the V mode, creating circular polarization
which has no primordial origin in the standard cosmological scenario. Finally, I will
sketch how polarized CMB anisotropies can be used for reconstructing the Faraday
rotation and conversion fields.
発表者
橋本大輝
日程/場所
2月22日(木)10:00-@ES606
題名
Proving the
Cross-Correlation Signal with Fermi Gamma-Ray Sky and CAMIRA Clusters Catalog
概要
Almost isotropic gamma-ray background(EGB) is observed by Fermi gamma-ray sky survey.
Good understandings of its origin are helpful for clarifying astronomical objects
radiating gamma-rays. the EGB is thought to originate from objects such as blazars and
star-forming galaxies or from exotic components such as annihilating or decaying dark
matters. These gamma-ray sources are concentrated on halos. Therefore researches have
been performed to probe the cross correlation signals with the gamma-ray sky map and the
matter distributions of sky in the EGB. In this research, we focus on the red shift
evolution of signals. Actually, each gamma-ray source candidate has a different red
shift dependence on the gamma-ray intensity. Therefore, the clusters catalog with
clusters of the wide red shift distribution is expected to arrow us to clarify the red
shift evolution of the cross correlation signal and we can approach the properties of
the EGB itself and the gamma-ray sources in the EGB by comparing the red shift
dependence of each gamma-ray source.
In my presentation, I present the cross correlation signal with Fermi gamma-ray sky
survey and HSC clusters catalog(CAMIRA) from the two point cross correlation analysis
and the stacking analysis with introductions for how to analyze.
発表者
榊原日菜子
日程/場所
2月22日(木)10:00-@ES606
題名
Impact of
gravitational lensing on the constraint of cosmological parameters from type Ia
supernovae
概要
Type Ia supernova (SN Ia) is a well-known standard candle, and is useful for the
constraining cosmological parameters. The cosmological parameters can be obtained from
the distance moduli of SNe Ia only after the precise measurement of photometry (e.g.
Suzuki et al., 2012). However, the current observations do not correct for the
magnification of SNe flux caused by gravitational lensing due to large-scale structure.
The aim of this work is to study the effect of gravitational lensing on the constraint
of cosmological parameters. First, we estimate the effect of the magnification on the
distance modulus by N-body simulation (Takahashi et al., 2017) and find it is less than
3%. Second, we estimate the magnification by two estimators using HSC galaxy catalogs;
one is convergence map reconstructed from HSC shear catalog, and the other is mass
distribution anticipating the profile of galaxies and stellar to halo mass relation
combined with photometric redshift of galaxies. Although it is naively expected that
scatter of distance modulus around the best fit theoretical curve can partly be
explained by the gravitational magnification, we find no significant signature of it.
Last, we show the result of the measurement of cosmological parameters by Markov Chain
Monte Carlo (MCMC) method and rest of the time will be devoted for the discussion about
the lensing effect on the cosmological parameters.
発表者
加藤健太
日程/場所
2月22日(木)10:00-@ES606
題名
The test for
statistical isotropy of CMB temperature anisotropy
概要
The existence of CMB is considered to be one of the most powerful evidences that support
Big Bang theory. The CMB temperature field has about 0.01% fluctuations and it results
from the primordial density perturbations predicted by the inflation theory. The
inflation theory predicts that the perturbations obey the statistically isotropic
Gaussian. In this study, I compared the CMB Monte Carlo simulation maps and the real CMB
map, and tested the statistical anisotropy of the mean of the CMB temperature
fluctuations in spherical harmonics space.
発表者
並河俊弥 (国立台湾大学)
日程/場所
2月21日(水)10:30-@ES606
題名
Cosmology from cosmic microwave background polarization
概要
One of the promising cosmological probes in the next decades is the CMB polarization.
While CMB temperature anisotropies have been already measured very precisely, CMB
polarization, in particular a twisting pattern in the polarization map (B mode) is not
well measured. The detection of B mode at more than degree angular scale opens new
window into the inflationary universe and high energy physics beyond the standard model.
Precise polarization data also enables us to measure gravitational lensing of CMB which
is a key probe to understand the properties of neutrinos, dark matter and dark energy.
In this talk, I will first present my analysis works within the BICEP2/Keck Array
collaborations. I will also talk about synergy between CMB experiments and galaxy
surveys such as the galaxy-lensing cross correlation with Subaru-Hyper Suprime Cam and
CMB experiments, and delensing B mode with mass tracers.
発表者
田中雅臣 (国立天文台)
日程/場所
2月13日(火)15:00-@ES606
題名
Electromagnetic Wave Observations of GW170817
概要
The first gravitational wave (GW) observationfrom a neutron star merger was successfully
made for GW170817. The detection triggered electromagnetic (EM) wave observations over
the entire wavelength range, which enabled the first identification of an EM counterpart
of a GW source. Observed properties of optical and near-infrared emission are similar to
those of theoretically-expected “kilonova” which is powered by radioactive decays of
r-process nuclei. In this seminar, I review EM observations of GW170817 and discuss
implications for the origin of heavy elements in the Universe.
発表者
松井由佳
日程/場所
2月1日(木)13:00-@ES606
題名
Gravitational wave
background from kinks on cosmic superstrings with different tensions
概要
It is proposed that there are one dimensional high energy objects called cosmic strings
and cosmic superstrings in the universe. Cosmic strings are formed at the GUT phase
transition and some inflation models and cosmic superstrings are suggested by
superstring theory. Cosmic superstrings have Y-junctions in the configuration and low
reconnection probability.
It is difficult to observe these strings directly, but we know that they make the
gravitational wave background from the sharp structure called kinks. However, it is
complex to calculate the gravitational wave background of cosmic superstrings because
there are Y-junctions in the cosmic superstrings, so it has not been clarified properly.
Therefore, we focus on the specific tensions of cosmic superstrings, and calculate the
number of kinks and the power spectrum of the gravitational wave background. Then, we
discuss the observational probability of the gravitational wave background.
発表者
遠藤隆夫
日程/場所
1月25日(木)13:00-@ES606
題名
Identifying cosmic
voids in the 21cm line
概要
Underdense regions in the large scale structure of the universe, namely voids, are
expected to be a probe of cosmology. Recent works have reported that the evolution of
voids represents differences of dark energy or gravity models. To identify the void
structure, we need tracers of dark matter because we do not observe it directly. In
Stark et al.,(2015) they present a method to identify voids by using Lyα flux. In this
work we consider the neutral hydrogen (HI) gas to be one of tracers of dark matter. The
HI gas emit the 21cm line which is expected to be detected by Square Kilometer Array.
Our goal is to identify void structures in the distribution of HI gas provided by the
ILLUSTRIS simulation and inspect whether HI voids are consistent with dark matter voids.
In this seminar I explain our procedure in this work via reviewing previous researches.
発表者
Patel Teerthal
日程/場所
1月18日(木)10:00-@ES606
題名
Magnetogenesis in Axion Monodromy Inflation
概要
Magnetic fields are ubiquitous in the Universe and are present at various scales. Recent
observations has suggested the presence of cosmological magnetic fields in the inter
galactic medium and indicate that the magnetic fields were generated in the Early
Universe. The ambiguity surrounding the high energy physics fundamental to inflation has
motivated us to explore a string theory inspired inflation model, namely, Axion
Monodromy. We quantitatively compute, not only the primordial field strength generated
in this inflation model, but also the corresponding scale dependence. The magnetic
fields are generated in this setup via a helical interaction term between the scalar
inflaton and the electromagnetic vector field. Quantitative comparison is conducted
between the magnetic fields generated with an inflationary background driven by a
quadratic scalar potential and the ones generated with an oscillatory contribution to
the inflaton potential. This suggests that the oscillating background does not
contribute any significant changes to the generated magnetic fields over the plain
quadratic potential case and a qualitative analysis will be performed.
発表者
小粥一寛
日程/場所
1月18日(木)10:00-@ES606
題名
Exploring primordial
anisotropic non-Gaussianity from galaxy alignment
概要
Non-linear effects during inflation can generate primordial non-Gaussianities.
Arkani-Hamed & Maldacena showed that an interaction between the inflation and higher
spin fields, which may be predicted in string theory, can generate angular dependent
non-Gaussianities, while preserving the global isotropy. As was argued by Schmidt et
al., this anisotropy can be explored by observing galaxy alignments. In this talk, we
study whether the angular dependent non-Gaussianity from massive spin 2 fields can be
observationally distinguished from the anisotropic non-Gaussianity with a violation of
the global isotropy, which can be generated e.g., by a vector field. As a result, we
found that the violation of the global anisotropy leads to non-vanishing off-diagonal
components of multipole moment ell and B mode, which cannot be generated from the
angular dependent non-Gaussianity with the global isotropy. In addition, if possible,
the previous study will be shown with more precisely.
発表者
安藤梨花
日程/場所
1月18日(木)10:00-@ES606
題名
HI bias modeling for
21-cm line observations
概要
Dark energy is considered as a strong candidate that causes accelerating expansion of
the universe. By constraining the parameters of the equation of state of dark energy, it
is possible to constrain the properties of dark energy. By using baryon acoustic
oscillation(BAO), we can constrain the models of dark energy from the expansion history
of the universe.
Square Kilometre Array (SKA) which is a large-scale radio interferometer will observe
the 21-cm line emitted from neutral hydrogen(HI). By Intensity mapping survey, SKA will
measure the intensity from unspecified sources. Therefore, we can obtain the information
of BAO from HI.
In the previous research (Bull et al 2015), they predicted the constraint on the
parameters of dark energy by SKA. The parameters are constrained by comparing the power
spectra obtained by observations with that calculated using the model. They forecasted
using a model where the HI bias is linear. For modeling the HI bias, we used the
illustris simulation and osaka model simulation.
発表者
大場淳平
日程/場所
12月21日(木)13:00-@ES606
題名
Planck constraints on
the non-flat ΛCDM inflation model
概要
We study Planck 2015 cosmic microwave background anisotropy data using the energy
density inhomogeneity power spectrum generated by quantum fluctuations during an early
epoch of inflation in the non-flat ΛCDM model.
Unlike earlier analyses of non-flat models, which assumed an inconsistent power-law
power spectrum of energy density inhomogeneities, we find that the Planck 2015 data
alone, and also in conjunction with baryon acoustic oscillation measurements, are
reasonably well fit by a closed ΛCDM model in which spatial curvature contributes a few
percent of the current cosmological energy density budget.
発表者
Tanmay Vachaspati (Arizona State University)
日程/場所
12月19日(火)16:00-@ES606
題名
Search for
Intergalactic Magnetic Fields and Implications
概要
The ongoing search for intergalactic magnetic fields using blazar observations suggests
field strength in the 10^(-14) to 10^{-17} G range on tens of Mpc length scales. Such
fields can have important implications for the early universe and also raises some
puzzles.
発表者
箕田鉄兵
日程/場所
12月7日(火)9:00-@ES606
題名
The Primordial
Magnetic Fields and the CMB anisotropies
概要
The existence of the primordial magnetic fields (PMFs) is suggested for the origin of
the cosmic magnetic fields, but there are no direct evidence for the PMFs. Now the upper
limit of the strength for the PMFs is about 4.4 nano-Gauss obtained by the CMB
anisotropies (Planck 2015 results XIX). On the other hand, (Marinacci & Vogelsberger,
2016) has claimed that the PMF stronger than 1 nano-Gauss can dramatically impact the
cosmic star formation and the galaxy formation history based on the cosmological MHD
simulation. Therefore the above constraint on the PMFs with CMB observation is not
strong enough with respect to the cosmological structure formation. In addition, the
current upper limit of the PMFs with CMB observation is obtained with only the primary
component of the CMB anisotropy at large-angle, where $\ell \lesssim 3 \times 10^3$.
Therefore, we investigated the two different works on the PMFs and the CMB anisotropies:
(1)The constraint on PMFs with primary component of the CMB anisotropy at small-angle,
$\ell \lesssim 10^4$. (2)The constraint on PMFs with secondary component of the CMB
anisotropy, especially thermal Sunyaev-Zel’dovich effect. Consequently, we obtained the
tighter constraint on the PMFs of $\mathcal{O}(0.1)$ nano-Gauss with work (1). Also, we
concluded that the constraint with work (2) is much weaker than that with (1), but we
found that the non-linear evolution in the high-z universe can affect the results of (2)
even with the $\mathcal{O}(0.1)$ nano-Gauss PMF. The numerical calculation including the
non-liner structure formation with the PMFs is beyond the scope of our works, so we put
this on the future work.
発表者
簑口睦美
日程/場所
12月7日(火)9:00-@ES606
題名
Redshift
evolution of cosmic voids
概要
Owing to resent redshift surveys, we now have a lot amount of data on galaxy clusters’
positions. Accordingly, the number of voids between galaxy clusters also can be treated
statistically. This means voids also can be one of the important prove for testing
cosmological models. So it is important to construct model for describing the evolution
of void’s quantities such as sizes and shapes. Icke 1984 reported voids tend to be
expand and be spherical in very simple case as isolated top-hat model, whereas it seems
not necessarily the case in cosmological circumstances, as shown by Nadathur 2016, for
example. I found out that individual void can grows to be either spherical or distorted
in cosmological case using N-body simulation. Because we distinguish the void from
density peaks around it, the model with density peaks, rather than top-hat model, is
worth examining. In this talk, I will show the methods and results on cosmological
simulation and isolated void simulation, and discuss on the evolution of individual
voids.
発表者
田中俊行
日程/場所
12月7日(火)9:00-@ES606
題名
The Impact of the
Halo Gas on the 21-cm Signal within the Vicinity of the First Stars
概要
The first stars are the first luminous objects in the universe, which marked the end of
the dark ages. Although they are thought to have affected the following structure
formation, their mass spectrum has not been clarified very much as well as other
properties. Since the mass spectrum can be investigated through the 21-cm signature
emerged in the vicinity of the first stars, some radiative transfer simulations have
been done to predict the structure of the 21-cm signal in previous works. However, halos
are not resolved and the constant escape fraction of ionizing photons is assumed in
these previous works, nevertheless, the escape fraction changes with time so that the
ionization structure resulted from the time-varying escape fraction would give different
structures of the 21-cm signal from the case of constant escape fraction.
In order to investigate the impact of evolving escape fraction on the 21-cm signal, we
conduct one-dimensional Lagrangian hydrodynamics simulations incorporating radiative
transfer and non-equilibrium chemistry self-consistently, considering gas density
profile in a halo. In this talk, we will quantitatively show the impact of the
time-changing escape fraction on the signal. Also, we will discuss the dependences of
stellar masses, halo masses, and redshifts on the signal.
発表者
竹内太一
日程/場所
12月7日(火)9:00-@ES606
題名
The AGN luminosity
function from high-z 21-cm line observation
概要
Observations of quasars at z>6 reveal the existence of supermassive black holes (SMBHs)
with a few billion solar masses in 1 Gyr after the Big Bang. Because of the difficulty
in observing AGNs in higher redshifts, we have not yet got the details of their
formation process. However it can be expected that there exist a number of AGNs as the
seeds of SMBHs before the epoch of reionization.
In this talk, we focus on redshifted 21 cm lines originated from neutral hydrogen
hyperfine structure as a probe of seed AGNs in high redshifts. These signals depend on
the physical conditions of neutral hydrogen gas. Since AGNs emit UV and X-ray photons
which can ionize and heat surrounding neutral hydrogen gases, AGNs can produce the
specific spatial structures of 21 cm signals around them. Therefore, we can probe the
redshift evolution of AGN number count on redshifted 21 cm maps.
In our study, we assume a simple AGN luminosity function model based on the
Press-Schechter formalism. Then, we evaluate the AGN number count survey by the SKA
observation, and estimate parameter values in our model using Fisher analysis. I’m going
to talk about this result and potential of constraining the AGN luminosity function by
the future SKA observation.
発表者
角田匠
日程/場所
12月7日(火)9:00-@ES606
題名
Diversity of the
Lyman continuum escape fractions of high-z galaxies and its origins
概要
The Lyman continuum (LyC) escape fraction is a key quantity to determine the contri-
bution of galaxies to cosmic reionization. It has been known that the escape fractions
estimated by observations and numerical simulations show a large diversity. However, the
origins of the diversity are still uncertain. In this work, to understand what quan-
tities of galaxies are responsible for controlling the escape fraction, we numerically
evaluate the escape fraction by performing ray-tracing calculation with simplified disc
galaxy models. With a smooth disc model, we explore the dependence of the escape
fraction on the disposition of ionizing sources, and find that the escape fraction
varies up to ? 3 orders of magnitude. It is also found that the halo mass dependence of
disc scale height determines whether the escape fraction increases or decreases with
halo mass. With a clumpy disc model, it turns out that the escape fraction increases as
the clump mass fraction increases because the density in the inter-clump region
decreases. In addition, we find that clumpiness regulates the escape fraction via two
ways when the total clump mass dominates the total gas mass; the escape fraction is
controlled by the covering factor of clumps if the clumps are dense sufficient to block
LyC photons, otherwise the clumpiness works to reduce the escape fraction by increasing
the total number of recombination events in a galaxy.
発表者
飯田遼
日程/場所
12月7日(火)9:00-@ES606
題名
ポテンシャルに干渉項を持つaxion
inflation modelの観測的制限
概要
本研究では、ストリング理論において予言されるaxion
場が引き起こすinflationモデルを考える。axion場のポテンシャルは典型的には振動項を持つことが知られており、一般には複数の異なる振動数を持つことが知られている。スローロールポテンシャルに対する補正項として、単一の振動数を持つaxion
inflation
モデルを用いた結果では、べき乗則に従う初期の曲率揺らぎのパワースペクトルを用いた時よりも、CMBのデータによくあったいたことが報告されている。今回、補正項としてaxion場のポテンシャルに異なる2つの振動数を持ったインフレーションモデルを考える。このモデルからは、その特徴を反映し、干渉項を持つパワースペクトルが得られた。さらに、Planck2015のデータを用いて本モデルを検証した結果についても報告する。
発表者
原田知広(立教大学)
日程/場所
11月21日(火)17:00-@ES606
題名
Formation of primordial black holes from cosmological fluctuations
概要
After a brief introduction of primordial black holes, I will talk our recent results on
primordial black hole formation by primordial fluctuations both in the
radiation-dominated era and matter-dominated era. In the former, I will discuss the
formation threshold in several aspects, while in the latter, I will discuss nonspherical
effects in the formation probability and the spins of formed primordial black holes.
発表者
北嶋直弥
日程/場所
11月16日(木)13:00-@ES606
概要
My talk consists of two parts. First, I will discuss cosmological evolution of the QCD
axion dark matter coupled to (hidden) photons. The motion of the axion field leads to
explosive production of hidden photons by tachyonic instability. We find that the axion
abundance is suppressed compared to the case without the coupling. Next, I will discuss
the cosmological implications of the string axion whose potential has a pleateu region
far from the minimum. Depending on the parameters and the initial value, the axion self
interaction can cause strong parametric resonances and, as a result, a significant
amount of gravitational waves can be emitted followed by oscillon formations ? a
quasi-stable soliton-like object.
発表者
堀口晃一郎
日程/場所
11月9日(木)13:00-@ES606
題名
Weak lensing from
self-ordering scalar fields
概要
In the standard cosmology, there could be a lot of cosmological phase transitions in the
early universe and these phase transitions produce some kinds of cosmic defects. In this
talk, we investigate the cosmic defect called global textures by using weak lensing
signals, CMB lensing curl and cosmic shear B modes. Here we introduce the evolution of
vector and tensor modes perturbations of textures at first, and we will see the
generation of weak lensing signals by textures the next. Finally, we discuss the
detectability of textures using weak lensing signals.
発表者
Jean-Baptiste Durrive
日程/場所
11月2日(木)13:00-@ES606
題名
Gravitational
Fragmentation of Baryons in Cosmic Walls
概要
Gravitational instability is a key process in astrophysics and cosmology. Formally, the
study of gravitational instability is an eigenvalue problem, which is not easy to solve
because the corresponding system of equations is of fourth order, with complicated
coefficients. In this talk, I will focus on the relatively simple case of a static
self-gravitating planar structure, but with a general polytropic equation of state. This
problem has already been solved by other authors in the past, but in most part
numerically. Here I will present a way to solve it analytically. More precisely, I will
explicit the discrete part of the spectrum (eigenfunctions and eigenfrequencies), by
reformulating and decomposing the full fourth-order problem into a sequence of
second-order problems that can be solved separately. I will also mention how to
generalize these results in order to describe in a more realistic way the graviational
fragmentation of baryons in cosmic walls and filaments, in the context of the cosmic
web.
発表者
大栗真宗(東京大学)
日程/場所
10月31日(火)16:00-@ES606
題名
Toward understanding
clusters of galaxies
概要
Clusters of galaxies have been thought as a powerful cosmological probe, yet for
accurate cosmological studies it is important to understand selection effects inherent
to individual cluster finding methods. I will discuss possible selection biases in
various cluster samples selected in different wavelenths, and then talk about our
ongoing efforts to construct new cluster catalogs in the Subaru Hyper Suprime-Cam survey
発表者
小林将人
日程/場所
10月26日(木)13:00-@ES606
題名
Star Formation
Induced by Cloud-Cloud Collisions and Galactic Giant Molecular Cloud Evolution
概要
Recent radio observations show that giant molecular cloud (GMC) mass functions
noticeably vary across galactic disks (e.g., Colombo et al. 2014). High-resolution
magnetohydrodynamics simulations show that multiple episodes of compression are required
for creating a molecular cloud in the magnetized interstellar medium (e.g., Inoue et al.
2012). We formulate a semi-analytical time evolution equation for GMCs including
cloud-cloud collision process, which represents GMC populations in Milky Way and nearby
galaxies. Our analysis shows that large radio observations are capable of constraining
GMC formation timescale, self-dispersal timescale, and gas resurrecting factor in
different galactic environment by measuring GMC mass function slopes. Our results also
indicate that star formation triggered by cloud-cloud collision may amount to a few 10
percent of total star formation in galactic disks.
In addition, I am explaining some ongoing pilot study of galactic-scale simulations that
employ the GMC time evolution prescription as a sub-grid model. Lastly, I also briefly
mention some ongoing and upcoming observational collaboration both in Milky Way and in
external galaxies.
発表者
竹内太一
日程/場所
10月19日(木)13:00-@ES606
題名
High-z QSO number
count through redshifted 21cm line observation
概要
Observations of quasars at z>6 reveal the existence of supermassive black holes (SMBHs)
with a few billion solar masses in 1 Gyr after the Big Bang. Because of the difficulty
in observing quasars in higher redshifts, we have not yet got the details of their
formation process. However it can be expected that there exist a number of quasars as
the seeds of SMBHs before the epoch of reionization. In this talk, we focus on
redshifted 21 cm lines originated from neutral hydrogen hyperfine structure as a probe
of seed quasars in high redshifts. These signals depend on the physical conditions of
neutral hydrogen gas, e.g., density, temperature etc. Since quasars emit UV and X-ray
photons which can ionize and heat surrounding neutral hydrogen gases, quasars can
produce the specific spatial structures of 21 cm signals around them. Therefore, we can
probe the redshift evolution of quasar number count on redshifted 21 cm maps. Assuming a
simple model for the high redshift quasar distribution based on the Press-Shechter
formalism, we evaluate the feasibility of the quasar number count survey by the SKA
observation. We also discuss the potential of the SKA observation to probe the redshift
evolution of the quasar mass function which is deeply related to the formation of SMBH
in high redshifts.
発表者
飯田遼
日程/場所
10月19日(木)13:00-@ES606
題名
Axion inflation with
interference and CMB anomaly
概要
From the observation of Cosmic microwave background (CMB) by the Planck andWMAP ,they
indicate the CMB angular power-spectrum has CMB anomaly.
There are about 3sigma deviation between observational data sets and theoretical
prediction from simple inflation models at large scale.
This is CMB anomaly.
CMB anomaly may indicate that primordial power spectrum is differ from power law
primordial power spectrum.
In my work,I search the inflation model by axion field which comes from super string
theory.
Typically potential of axion field has oscillation and generally there are some
oscillations in the potential.
I use potential which has 2 oscillations . Then the potential has the interference .
And firstly I can get a primordial power spectrum which has the interference.
Second, I used the CosmoMC which is the MCMC analysis code and I researched how improved
chi^2 .Then we set a limit to the model's parameter region.
In this talk,I will talk about these results and problems.
発表者
西澤篤志
日程/場所
10月12日(木)13:00-@ES606
題名
Gravitational
Waves and Large-scale Structures
概要
Recent detections of gravitational waves (GW) emitted from binary black holes (BBH)
imply that a BBH is a dominant source in event rate for the second-generation GW
detectors like advanced LIGO and that they can be detected out to cosmological distance.
This opens up a new window to utilize BBH as a probe for cosmology. In particular, their
angular and distance distributions give information about large-scale structures of the
Universe. In this presentation, we propose new methods to measure the anisotropies of
source luminosity distance and the matter inhomogeneities in the Universe by
cross-correlating GW and galaxy observations. First, we show that the second-generation
GW detector network is able to measure the angular clustering of BBH and test how they
trace the matter density fluctuations. This information can be an important clue to
distinguish the possible origins of stellar-mass BBH. Second, we show that future GW
detectors such as Einstein Telescope are able to precisely measure source luminosity
distances out to high redshifts and extract cosmological information about the
large-scale structures around z~2 without any help of redshift information. The expected
constraints on the primordial non-Gaussianity with the Einstein Telescope would be
comparable to or even better than the other large-scale structure probes at the same
epoch. Also the cross-correlation with other cosmological observations is found to have
high-statistical significance, providing additional cosmological information at very
high redshifts.
発表者
新田大輔
日程/場所
10月5日(木)13:00-@ES606
題名
Equivalence principle
violation after reheating
概要
Gauge fields with non-minimally coupled gravities are often contained in the
Kaluza-Klein theory of higher dimensional gravity or a quantum effect of gravity. The
non-minimaly coupled fields cause some interesting phenomena such as an equivalence
principle violation.
We consider a Horndeski vecter-tensor theory, which is a non-minimal coupling theory, in
the radiation dominated universe. In the curved space time, on this theory, the
dispersion relation of the Gauge particles depend on the direction of travel, and
birefringence occurs when the metric perturbations have quadrupole moments. Due to these
effects, the gravitational waves are generated by the anisotropic stress of the gauge
particle in the thermal bath. We find that the equation of the gravitational wave is
non-linear. It shows the equations are significantly different from the minimal coupling
theory.
In this talk, I will introduce this model and show the parameter regime of this model
required to detect gravitational wave by future observations.
発表者
多田祐一郎(Institut d'Astrophysique de Paris)
日程/場所
9月20日(水)14:00-@ES606
題名
Stochastic Formalism in Curved Field Space
概要
In multi-field inflation scenarios, the scalar fields can span curved field spaces in
general.
Recently it was pointed out that the sufficiently large field curvature can make the
entropic degrees of freedom tachyonic during inflation and alter the inflation dynamics
[PRL117, 141301]. This geometrical destabilization can be applied to a large class of
inflationary models.
To analyze the destabilization, we formalize the stochastic approach in the general
curved field space from first principles.
Also I’ll briefly mention the slow-roll phase well after the geometrical
destabilization.
発表者
Jean Coupon (Geneva)
日程/場所
8月8日(木)11:00-@ES606
題名
Probing the
galaxy-mass connection in TeraByte-scale imaging surveys
概要
The past decade has seen the emergence of new techniques and exciting discoveries
powered by wide-field imaging surveys from the UV to the near-IR domain. Owing to
gravitational lensing, galaxy clustering and abundance matching (to name but a few),
coupled with advanced statistical interpretation, the informative power of astronomical
imaging surveys has significantly increased. In particular, the connection between
galaxies and dark matter, a keystone in cosmology and the study of galaxy evolution, has
widely gained from this "scale revolution" and the future is bright, as the next
experiments such as HSC, LSST, Euclid or WFIRST are dedicated "survey" machines that
will further increase imaging data by orders of magnitude (without mentioning the
tremendous gain in image resolution, time domain and deep near-IR imaging). I will focus
my talk on reviewing the main techniques to connect galaxies and dark matter in the
context of wide-field surveys and I will show some concrete examples of applied data
analysis in the CFHTLenS and COSMOS projects, showing that these techniques are now well
proven, although the challenges in reducing some critical systematic uncertainties are
ahead of us.
発表者
Victor Bonjean
日程/場所
7月26日(水)10:30-@ES606
題名
Multi-wavelength analysis of inter-cluster filaments
概要
I will present a multi-wavelength analysis of two galaxy-cluster pairs detected in SZ by
Planck with an excess of SZ signal between clusters. For the first time, we have
combined SZ and optical analysis, to derive gas pressure and galaxy properties such as
SFRs and stellar masses in the filamentary regions between the clusters. We propose a
possible scenario for the filament in the cluster pair A399-A401.
発表者
Bharat Ratra
日程/場所
7月25日(火)16:00-@ES606
題名
Dark Energy: constant or time variable? (... and other open questions)
概要
Experiments and observations over the two last decades have persuaded cosmologists that
(as yet undetected) dark energy is by far the main component of the energy budget of the
current universe. I review a few simple dark energy models and compare their predictions
to observational data, to derive dark energy model-parameter constraints and to test
consistency of different data sets. I conclude with a list of open cosmological
questions.
発表者
橋本大輝
日程/場所
7月19日(水)11:15-@ES606
題名
Proving Dark
Matter from HSC Catalog of Galaxy Cluster and the Gamma-ray Map from Fermi GRST
概要
As a way of proving dark matter, one can use the it’s property that gamma rays are
emmited when a dark matter annihilates (Dark Matter Annihilation (DMA)) or decays
(Decaying Dark Matter (DDM)). Therefore, as a method of indirectly searching dark
matter, there is a method of searching signals of these gamma rays in Extragalactic
Gamma-ray Background (EGB) . The properties of dark matter can be restricted from the
intensity distribution of EGB and the gamma ray intensity from dark matter predicted
theoretically.
In this study, I use the intensity distribution of EGB from observation of Fermi GRST
and the distribution of the galaxy clusters and the redshift of each cluster from
HSC.
These observation bring the intensity distribution of the EGB in the direction of the
cluster with information of the depth on the line of sight. On the other hand, In
theory, I obtain the total gamma ray intensity distribution from one cluster as a
function of the observed the gamma ray energy and the redshift of the gamma ray from DMA
and DDM.
In this presentation I will report current progress on the properties of DMA and DDM
using the cross-correlation signal obtained from observation and the gamma ray intensity
from dark matter predicted theoretically.
発表者
榊原日菜子
日程/場所
7月19日(水)11:15-@ES606
概要
Primordial black hole (PBH) is formed out of the high density region by the
gravitational collapse in the early Universe. There is no evidence indicating the
existence of PBH, but limiting the abundance of PBH may solve the cosmological problems
such as identifying the candidate of dark matter. A previous work (Carr et al. 2010)
calculated the flux of gamma-rays emitted from PBHs in the Universe, and imposed the
limit on the ratio of the density of the PBHs at their formation time to Universe’s
density by using the observation data of gamma-ray background radiation. In this work,
we focus on the dark matter halos of the galaxy clusters which are expected to have many
PBHs because of their high density. We examine whether we can update the constraint of
the PBH abundance more strongly by considering the gamma-ray from dark matter halos. As
a result, we impose stronger limit on the ratio of the PBH density parameter to the dark
matter density parameter. We discuss the result in comparison with that in the previous
work.
発表者
小粥一寛
日程/場所
7月19日(水)11:15-@ES606
題名
Limitations on
Cosmological Parameters using Gravitational Waves from BBH
概要
LIGO directly detected Gravitational waves (GWs) from Binary Black Holes (BBHs)
coalescence in 2015.This demonstrates that it is possible to observe the Universe using
GWs as an observation method independent of electromagnetic wave observation. GWs gives
us measurement of the cosmic expansion rate. I review the papers which estimated the
measurement precision of the cosmic expansion rate using GWs, (Holz & Hughes 2005) and
(Nishizawa 2016). In the former paper, the space GW telescope LISA determines the
luminosity distance up to the supermassive BBH. In addition, the electromagnetic
counterpart to the BBH GW event gives the redshift of the BBH. So it is possible to
restrict the state equation of dark energy independently of the observation the standard
candle. In the latter paper, GW detector networks detects GWs from stellar-mass BBHs and
the redshift of them is obtained from the host galaxy. This paper shows Hubble constant
can be determined with high accuracy, and it can be a means to resolve the discrepancy
of the Hubble constant from the observation of CMB and Cepheid variables. Through these
papers we discuss limitations on cosmological parameters by GWs.
発表者
加藤健太
日程/場所
7月19日(水)11:15-@ES606
題名
Estimate of
primordial non-Gaussianity using CMB spectral distortion anisotropies
概要
The existence of CMB is considered to be one of the most powerful evidences that support
Big Bang theory. In the early universe, the blackbody spectrum of CMB is held by
processes such as Compton scattering, bremsstrahlung, and double Compton scattering.
However, by cooling of the universe due to the expansion, these processes become
inefficient gradually. Then, if any energy is released at those epochs, the CMB
distortions are created. Anisotropies of CMB distortions can be created by spatially
varying heating processes. For example, the dissipation of small scale perturbations can
create distortion anisotropies. As Cross-correlation of distortion parameters and
temperature can be regarded as three-point correlation of temperature, we can estimate
primordial non-Gaussianity. In this talk, I review the paper that estimates primordial
non-Gaussianity using CMB spectral distortion anisotropies (Chluba et al, 2016). This
work describes the energy injections more factually than previous similar works, and
derives more factual conclusion.
発表者
安藤梨花
日程/場所
7月19日(水)11:15-@ES606
題名
Constraint on dark
energy models by future SKA BAO survey
概要
It is confirmed by observations that the expansion of the universe is accelerating.
However, we can not explain the cause. Dark energy is considered as a candidate which
causes the accelerating expansion. there are a lot of dark energy models. In order to
find the most suitable models for our universe, it is necessary to constrain the
parameters that characterize dark energy. Since the expansion history depends on the
value of the parameters of Equation of State of dark energy “w”, we can constrain the
models from the expansion rate of the universe.
Baryon acoustic oscillation (BAO) can be used as a standard ruler of the universe. It is
possible to measure the expansion rate of the universe by measuring BAO scale.
Information of BAO will be obtained by galaxy redshift survey and HI intensity mapping
survey by Square Kilometer Array (SKA). In previous research, Fisher forecast was used
to predict the constraint on parameters of dark energy based on expected specifications
of SKA. In this presentation, I explain the mechanism of the constraint on the
parameters ,and reproduce the previous results.
発表者
Surhud More (Kavli IPMU)
日程/場所
7月13日(木)11:00-@ES606
題名
On halo assembly
bias and the splashback radius of galaxy clusters
概要
Halo assembly bias -- the dependence of the large scale clustering amplitude of halos on
secondary parameters other than the halo mass -- is a well established prediction of the
standard structure formation model. However it has been notoriously hard to confirm,
observationally. I will present a 6.6 sigma detection of difference in the clustering of
redmapper galaxy clusters which share the same weak lensing mass. I will also present a
detection of the splashback radius or the edges of redmapper galaxy clusters in
observations. I will discuss some recent progress in understanding these observations in
light of selection effects induced by optical cluster finding.
発表者
Patel Teerthal
日程/場所
7月12日(水)10:30-@ES606
題名
Generation of
Magnetic Fields in Axion Monodromy Inflation
概要
Cosmological magnetic fields are ubiquitous in the Universe and are observed from
astronomical to the largest scales. Numerous studies involving the possible origin of
the magnetic fields span various epochs and employ a wide range of mechanisms, yet no
conclusive theory or model has been established. It has been shown that the standard
inflationary approach with generic coupling between the scalar(pseudo-scalar) fields
cannot produce the required magnetic field strength. In this study, the generation of
magnetic field in Axion Monodromy Inflation is explored. The axion driven inflaton field
in this scenario has a modulation term and can contribute significantly to primordial
field generation through resonant enhancement. The effects of the backreaction are
studied to constrain the modulation and coupling parameters but, it is assumed to have
insignificant impact on the evolution of the background inflaton field. The resulting
primordial magnetic field is used to perform order estimation of the present day
magnetic field strength. A thorough analysis can thus not only provide a way to generate
the required primordial magnetic field but also provide phenomenological constraints on
high energy physics models inspired by string theory.
発表者
Clément Walter
日程/場所
7月12日(水)10:30-@ES606
題名
Future prospect for
direct measurements of gravitational wave speed
概要
With a ground-based detector network composed of advanced LIGO, VIRGO, and KAGRA, we can
measure the speed of a gravitational wave directly. Currently gravitational wave speed
has been weakly constrained because there are only two detectors operating. But in the
next couple of years, we will be able to obtain a much better constraint from direct
measurements of gravitational waves. We resolve to what extent we can achieve in
measurement precision and how we can optimize the method.
発表者
角田匠
日程/場所
7月12日(水)10:30-@ES606
題名
Dependence of escape
fraction on properties of galaxies
概要
Escape fraction is a key quantity to determine the contribution of galaxies to cosmic
reionization. Though many numerical simulations have predicted the LyC escape fraction,
the predicted values are different for each study. Since characteristics of the
simulations, e.g., resolution, implemented physics and numerical algorithm, are quite
different each other, it is usually difficult to understand what causes the diversity.
In this work, to understand what quantities of a galaxy are responsible for controlling
the escape fraction, we numerically evaluate the escape fraction by performing
ray-tracing calculations with simplified disk galaxy models. With a smooth disk model,
we first explore the dependence of the escape fraction on the disposition of ionizing
sources, and find that the escape fraction varies up to ~ 3 orders of magnitude. With a
clumpy disk model, it turns out that clumps basically increase the escape fraction as
far as the total clump mass is less dominant, because LyC photons can effectively escape
through gaps among the clumps. We also find that the escape fraction is controlled by
the covering factor of clumps if the clumps are dense enough.
発表者
箕田鉄兵
日程/場所
7月5日(水)13:00-@ES606
題名
tSZ effect in the
IGM with primordial magnetic fields
概要
According to many previous observations, magnetic fields are found on various
astronomical objects in the universe, from asteroids to clusters of galaxies. One
possible origin of these cosmic magnetic fields is the magnetogenesis in the primordial
universe. Magnetic fields generated by such a cosmological mechanism are called
primordial magnetic field (PMFs), and are considered to affect the evolution of matter
density fluctuations due to the Lorentz force and the thermal history of the
intergalactic medium (IGM) gas due to
the so-called ambipolar diffusion. Hence the information of PMFs is expected to be
imprinted on the anisotropies of the cosmic microwave background through the thermal
Sunyaev-Zel’dovich (tSZ) effect in the IGM. In this talk, given an initial power
spectrum of PMFs, we show dynamical and thermal evolutions of the IGM with PMFs, and the
resultant tSZ angular power spectrum. As a result, we find that the tSZ angular power
spectrum induced by the PMFs becomes more remarkable on small scales than that by galaxy
clusters even with
PMFs below the current cosmological constraint (Minoda et al., 2017, arXiv:1705.10054).
The measurement of the tSZ angular power spectrum on small scales can provide the
stringent constraint on PMFs.
発表者
簑口睦美
日程/場所
7月5日(水)13:00-@ES606
題名
Redshift
evolution of the shape of isolated voids
概要
Cosmic voids can be used as a prove of the cosmological model and it has been studied
eagerly as we obtain statistically enough data about void structures from
observation.
I tried to explain the mechanical process of individual void using simplified isolated
void model, while there are many study about voids focusing on statistical profile and
using N-body simulation.
I analyzed the redshift evolution of individual voids in N-body simulation and compared
the result to that of isolated void models with numerically calculation.
発表者
田中俊行
日程/場所
7月5日(水)13:00-@ES606
題名
21-cm Signal
Originating within The Vicinity of The First Stars
概要
The first stars are the first luminous objects in our universe, which marked the end of
the dark age. They are thought to have formed as a result of growth of density
fluctuation, and have affected following structure formation such as galaxies. However,
its properties have not been clarified very much even though many previous studies
conducted numerical simulations on the first stars’ formation. Therefore, there are
still many theoretical models of the first stars. Some characteristics (e.g. its
masses), can be investigated through observations of 21-cm line emitted from the
vicinity of the first stars. The 21-cm line signals would be detected by forthcoming
radio interferometers such as Square Kilometre Array. In order to interpret those
observations’ data and extract the physical properties of the first stars, we need to
investigate what each model of the first stars looks like on the celestial sphere.
I conducted radiative hydrodynamics simulation to obtain the distribution of 21-cm
signals in various masses of the first stars and some different redshifts. We took gas
density profile into consideration and investigated spatial distribution of 21-cm line
signals. In this talk, I will compare my results with the radiative transfer simulation
of Yajima & Li (2014) in whose setup gas is treated as static and uniform intergalactic
medium. Also, we will discuss detectability of the first stars with SKA.
発表者
矢島秀伸(東北大)
日程/場所
6月26日(月)17:00-@ES606
概要
Lyman-alpha emitting galaxies (LAEs) are key objects to understand cosmic reionization
and galaxy formation in the early Universe. Combining cosmological hydrodynamics
simulations and multi-wavelength radiation transfer calculations, we investigate the
formation mechanism of LAEs and their contribution to cosmic reionization. Our findings
are as follows : (1) cold gas accretion produces bright LAEs via the excitation cooling
process; (2) observed LAEs can keep the ionization of IGM at z < 7; (3) some of high-z
LAEs evolve to local L* galaxies (Yajima et al. 2015, ApJ, 801, 52). We also study
impacts of star formation and stellar feedback on the galaxy formation. We find the
star formation efficiency affects the star formation history and galactic morphology
significantly (Yajima et al. 2017 arXiv:1704.03117). In addition, as galaxies
evolve, massive black holes are likely to form at galactic centers. I will introduce
our recent studies about the formation of massive black holes in high-redshift
galaxies.
発表者
長谷川賢二
日程/場所
6月21日(水)13:00-@ES606
題名
Detectability of
21cm-signal during the Epoch of Reionization with 21cm-LAE cross-correlation
概要
The redshifted 21cm signal from neutral hydrogen in the intergalactic medium (IGM)
during the Epoch of Reionization (EoR) is difficult to detect due to intense foreground
radiation. Taking cross-correlation between the 21cm signal and Lyman Alpha Emitters
(LAEs) is one of the ways to reduce the foreground effects because the spatial
distribution of high-z LAEs is not correlated with the foreground emission. In this
work, we investigate the detectability of the 21cm- signal with the 21cm-LAE
cross-correlation by using our state-of-the-art reionization simulation data. As a
result, we find that the combination of Murchison Widefield Array(MWA) and Subaru Hyper
Suprime-Cam (HSC) has the ability to detect the cross-power spectrum signal on large
scales. It is also found that the sensitivity on small scales is dramatically improved
by the spectroscopic observations with the Prime Focus Spectrograph (PFS) because the
redshifts of LAEs are accurately determined. Finally, we find that upcoming observations
with the Square Kilometre Array(SKA) and PFS has a potential to accurately determine the
typical size of ionized bubbles by measuring the turnover scale of the cross-power
spectrum.
発表者
浦川優子
日程/場所
6月14日(水)13:00-@ES606
題名
Cosmological
implications of ultra-light axion
概要
The Lambda CDM model, which provides a consistent prediction at larger scales than
~10kpc, has not succeeded to match the observational data at smaller scales. While this
is usually attributed to the computational issue of baryon physics, the discrepancy from
the Lambda CDM model below kpc scales may suggest the presence of an ultra-light axion
whose mass scale is of O(10^{-22}eV). In this talk, I will review a recent progress on
the cosmological consequences of the ultra-light axion. Then, I will explore another
cosmological consequence on cosmic microwave background and large scale structures.
発表者
西澤淳
日程/場所
5月24日(水)13:00-@ES606
題名
The HSC first
year data release ? a compilation of various results ?
概要
The first data release of the HSC survey has been public since Feb 2017. The data covers
more than 100 square degrees of sky. I will briefly describe the HSC survey and data
products of the HSC DR1.
On the last half of the seminar, I will give a summary of the collection of various
results including, cluster evolution, photometric redshift and synergy with CMB
observations, Planck and ACTPol.
発表者
杉山尚徳(IPMU)
日程/場所
5月22日(月)13:30-@ES606
題名
Kinematic Sunyaev-Zel'dovich effect
概要
Over the past few years, cosmologists have been able to make the first detections of the
kinematic Snuyaev-Zel'dovich (kSZ) effect by combining galaxy data with measurements
from CMB experiments. The kSZ effect is well-suited for studying properties of the
optical depth of halos hosting galaxies or galaxy clusters. As the measured optical
depth via the kSZ effect is insensitive to gas temperature and redshift, the kSZ effect
can be used to detect ionized gas that is difficult to observe through its emission,
so-called "missing baryons". This work presents the first measurement of the kSZ effect
in Fourier space. While the current analysis results in the kSZ signals with only
evidence for a detection, the combination of future CMB and spectroscopic galaxy surveys
should enable precision measurements. This talk emphasizes the potential scientific
return from these future measurements.
発表者
黒柳幸子
日程/場所
5月17日(水)13:00-@ES606
概要
We discuss a new detection method for ultra-low frequency gravitational waves (GWs) with
a frequency much lower than the observational range of pulsar timing arrays. Ultra-low
frequency GWs (< 10^-10 Hz) are not detectable with the conventional method of pulsar
timing arrays, because the effect of the GWs is exactly the same as the pulsar
spin-down rate, and it is absorbed when we fit the pulsar spin-down rate for
individual pulsars. However, the GWs from a single source should leave the effect
with a quadrupole pattern in the sky, which depends on relative direction of a
pulsar and GW source, while the spin-down rate of pulsars is randomly distributed.
Thus, in principle, ultra-low frequency GWs can be detected by looking for a
quadrupole pattern in all-sky distribution of the pulsar spin-down rates. We
evaluate the potential of this method by employing Monte-Carlo simulations and
estimate the sensitivity of pulsar observations by the Square Kilometre Array.
発表者
田代寛之
日程/場所
5月10日(水)13:00-@ES606
概要
The energy injection in the early universe (before the redshift $z \sim 10^6$) heat up
the CMB. If the energy injection is inhomogeneous, the additional temperature
fluctuations are generated. In this talk, we consider the dissipation of the primordial
magnetic fields in the early universe as the energy injection. We show that the
measurement of the CMB temperature anisotropy can provide the constraint on the
primordial magnetic fields on small scales ($10^4 Mpc^-1 < k < 10^8 Mpc^-1$).
発表者
市來淨與
日程/場所
4月27日(木)10:00-@ES606
題名
Developing a new
template foreground cleaning method for the LiteBIRD experiment
概要
Detecting gravitational wave background generated during inflation through B-mode
polarization of the cosmic microwave background (CMB) is one of the main scientific
goals of future CMB experiments. However, it has already become clear that synchrotron
and thermal dust emissions from our galaxy hinder the cosmological B-mode signal across
the sky. Here, assuming only Gaussianity and statistical isotropy and homogeneity of the
CMB map, we develop a new template cleaning method taking into account spatial
variations of spectral indices of the foreground emissions, and apply it to various
foreground models using Monte-Carlo simulation technique. We find that the method
successfully remove the unwanted bias in determining the tensor-to-scalar ratio $r$ that
was found in the simple template cleaning method presented in Katayama and Komatsu 2011.
In this poster, we present how small $r$ we will be able to reach according to the
frequency bands and noise specification proposed for the LiteBIRD experiment.
発表者
大場淳平
日程/場所
4月20日(木)10:00-@ES606
題名
Cosmological
constraints on scalar-tensor gravity and the variation of the gravitational
constant
概要
The existance of scalar fields whose vacuum expectation values determine the physical
constants is generically predicted
by the recent attempts toward unifying all elementary forces in nature based on string
theory.
In scalar-tensor theories of gravity, a scalar field couples to the Ricci scalar, which
provides a natural framework
for realizing the time variation of the gravitational constant via the dynamics of the
scalar field.
I present cosmological constraints on the scalar-tensor theory of gravity by analyzing
the angular power spectrum data of the cosmic microwave background (CMB) obtained from
the Planck 2015 results together with the baryon acoustic oscillations (BAO) data. We
find that the inclusion of the BAO data makes more than 10% improvement on the
constraints on the time variation of the effective gravitational constant.
発表者
榊原日菜子
日程/場所
4月13日(木)10:00-@ES606
題名
Impact of
gravitational lensing on the distance modulus of type Ia supernovae
概要
The distance modulus is defined as a difference between apparent magnitude and absolute
magnitude of the celestial object, and is related to the luminosity distance. The
distance modulus from type Ia supernovae surveys has been compared with the theoretical
prediction which depends on cosmological parameters (e.g. J. Guy et al., 2010). It is
known that there is a discrepancy between the distance modulus from observation and
LambdaCDM prediction. The discrepancy can partly be accounted for by a flux
magnification due to gravitational lensing. In this work, first we estimate the effect
of the magnification on the distance modulus using N-body simulation and analytic
calculation. We find the effect of the magnification is less than 3%. Second, from
Supernova Legacy Survey (SNLS) data, we impose constraints on the cosmological
parameters by Markov chain Monte Carlo (MCMC) method and obtain a consistent result with
the previous work. Finally, we reconstruct the projected mass distribution from Canada
France Hawaii Telescope Lensing Survey (CFHTLenS) data and find no significant cross
correlation between the distance modulus.
発表者
小粥一寛
日程/場所
4月13日(木)10:00-@ES606
題名
Anisotropic
primordial bi-spectrum through an observation of galaxy shapes
概要
Arkani-Hamed and Maldacena showed that massive higher spin fields, whose presence may be
predicted in string theory, can generate angular dependent primordial non-Gaussianity,
while the global isotropy is still preserved.
As was argued by F.Schmidt et al., such an angular dependent non-Gaussianity can be
explored through an observation of galaxy shapes.
Meanwhile, an angular dependent non-Gaussianity can be generated also in case the global
isotropy is broken, e.g., by a vector field.
We studied whether the anisotropic bi-spectrum generated in a setup with the global
isotropy can be distinguished from the one in another setup without the global isotropy
by observing galaxy shapes.
Then, we found that the B-mode of the galaxy lensing and the off-diagonal component of
ell can be generated only in the latter case. This can provide a crucial difference
between these two cases.
発表者
加藤健太
日程/場所
4月13日(木)10:00-@ES606
概要
The existence of CMB is considered to be one of the most powerful evidences that support
Big Bang theory. The CMB temperature field has about 0.01% fluctuations and it results
from the primordial density perturbations predicted by the inflation theory. The
inflation theory predicts that the perturbations obey the statically isotropic Gaussian.
In this study, I compared the CMB Monte Carlo simulation maps and the real CMB map, and
tested the statical anisotropy of the mean of the CMB temperature fluctuations in
spherical harmonics space.
発表者
安藤梨花
日程/場所
4月13日(木)10:00-@ES606
題名
Nonlinear growth of
ellipsoidal collapse
概要
Dark matter is one of the most important factors in considering the evolution of the
universe, and accounts for 90 % or more of the mass of the cluster of galaxies. If we
know how density perturbations of dark matter evolve, we can determine perturbations in
early universe from the structure of the present universe. I assumed that the
perturbations in ellipsoids are all uniform. I derived differential equations of the
time evolution about their shapes, and solved them numerically. I calculated them for
various axis ratios using the probability distribution of the axial ratio around the
peak of the random gaussian field.
発表者
杉山直
日程/場所
4月13日(木)10:00-@ES606
題名
所信表明
概要
所信表明