ATセミナー 2007

Japanese ver. only

4月 | 5月 | 6月 | 7月 | 8月 | 9月 | 10月 | 11月 | 12月 | 1月 | 2月 | 3月

＊プレゼンテーションファイルは研究室内部ネットワークのみで閲覧可能です。

## 4月のセミナー

4月17日(火)16:30-＠B404

4月24日(火)16:30- @B404

MOND(MOdified Newtonian Dynamics)を用いた銀河団でのweak lens の話をします。 あと、こちらでやってみたい今後の話もします

4月26日(木)14:00- @B404

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## 5月のセミナー

Bartosz Lew

5月1日(火)16:30- @B404

A full sky and regional (directional) one-point, real space (mean,variance, skewness and kurtosis) statistics of the three year coadded WMAP temperature data is performed. The sky regionalization is defined by two different sky pixalization schemes based on Equidistant Cylindrical Projection (LB) and HEALPIX (HP) sphere pixelization scheme. Residual, knwon foregrounds are masked out by the third year release of Kp0 sky mask (kp).
Full resolution (n_s = 512) Monte-Carlo simulaitons (Nsim = 104) of random, Gaussain, (signal and noice) CMB sky realizations are performed for estimation of uncertainties and confidence levels (CL) of deviations from Gaussianity and/or statistical isotropy (SI). Directional analysis is performed at three different resolutions in two regionalization schemes, giving total number 280 000 regions of different shapes and sizes and testing different angular scales, ranging from (~5 degree, ~29 degree). Number of random orientations of regionalizations schemes have been used to enhance different data sampling for different regions. Individual region and full covariance matrix analysis is performed and results compared. Our analysis is is sensitive both to non-Gaussianity (NG) and super-Gaussianity (SG) via skewness and kurtosis and to super-Statistical Isotropy (SSI) and Statistical non-Isotropy (SNI) via mean and variance sky distributions.
We find the WMAP data well consistent with the random, Gaussian simulations in the full sky analysis. The full covariance matrix regional analysis finds the data well consistent with the simulations (i.e. with the Gaussianity and SI) at all scales and at relatively small confidence levels (lesssim99%). However, few very strong, yet unreported, NG detections have been found. We present maps of these detections, list their directions, and compare our results with other reports on NG/SNI detections, and revisit their statistical importance.

5月7日(月)13:00- @B404

Further simulations of primordial star formation

5月15日(火)13:00- @B404

5月22日(火)16:30- @B404

SDSSのクェーサーカタログから、重力レンズ効果を受けたクェーサーを探すプロジェクト"SQLS"を紹介します。SQLSは、稲田直久さん(理研)と大栗真宗さん(ス タンフォード大)により進められているプロジェクトです。このプロジェクトで は追観測が決定的に重要ですが、私も２年前から追観測に参加しています。実際 の観測・解析例を挙げながら解説します。

5月29日(火)16:30- @B404

## 6月のセミナー

6月5日(火)16:30- @B404

We have examined how the gravitational potential(GP) evolves with redshift in its non-linear stage. Within the linear theory, GP is stationary in the EdS Universe, but is always decaying because of the accelerated expansion caused by dark energy in the case for LCDM. So time derivative of GP has no significant linear contribution at high-z, which can be considered as EdS universe. Then the leading order becomes higher order.
In this seminar, I introduce some calculations of 2nd order PT for GP, and show how the nonlinear effect becomes important in the cross correlation between GP and its time derivative. Some technical details may be included.

6月12日(火)16:30- @B404

Big bang nucleosynthesis (BBN) can be used to constrain the strength of primordial magnetic fields and gravitational waves separately. Moreover, we can obtain much stronger limits using BBN bound on gravitational waves induced by anisotropic stress of stochastic magnetic fields, especially for spectral indices n>-3. I introduce briefly about BBN constraints and review the article "Gravitational wave production: A strong constraint on primordial magnetic fields." C.Caprini and R.Durrer, Phys.Rev. D65 (2002) 023517.

6月19日(火)16:30- @B404

Optimization when distinguishing dark energy models and modified gravity models

6月26日(火)16:30- @B404

From recent observations, it is inferred that cosmic reionization started at z > 10 and ended at z ~ 6. Atomic hydrogen 21cm line is a useful way probe of the reionization era. It is produced via the transition between sublevels of the hyperfine structure of neutral hydrogen. Neutral and ionized IGM are seen either as absroption or emission against the cosmic microwave background radiation.
I first present how an early HII bubble around a radiation source evolves. Then I describe the way I calculate the 21cm signature of them prior to global ionization. Finally I show the evolution of the ionized region in a 21cm map using cosmological simulations outputs on the assumption that Lyman alpha coupling is unimportant. My ongoing work is to study the evolution of an ionized region, when Lyman alpha photons affect the level population of the ground state hydrogen - the so-called Woutheuysen-Field effect.

## 7月のセミナー

7月3日(火)18:00- @B404

Consistency Relation in Cosmology

Kentaro Nagamine (ネバダ大学)

7月12日(木) 10:30- @B404

Today, theorists are challenged by the overwhelming wealth of observational data on galaxies, which　must　be analyzed and interpreted in a cosmological context. The goal of our work is to bridge the gap　between　the observation and theory of galaxy formation using cosmological hydrodynamic simulations.　The concordance Lambda cold dark matter (CDM) model, which has been very successful in explaining various observations, is currently challenged by two major issues in galaxy formation: one is the existence of massive galaxies at z~6, and the other is the existence of dead & red'' extremely red objects (EROs) at z=1-3. Using two different types of cosmological simulations (smoothed particle hydrodynamics [SPH] and total variation diminishing [TVD]), I will discuss our current understanding of these population of galaxies and issues with simulations. Turning to a purely analytic model of cosmic SF history, we recently developed the two-component `Fossil' model based on the observed colors and luminosity densities of SDSS galaxies at z~0. This model exhibits roughly constant SFR density at z=3-6. These two models (i.e. the hydro simulations and the Fossil model) both predict that 60-70% of stellar masses in the Universe were already in place by z=2, in contrast with current observational constraints. The Fossil model also predicts that the bulge component mostly formed at z>1.5.

7月17日(火) 10:30- @B404

## 9月のセミナー

9月25日(火)16:30- @B404

## 10月のセミナー

10月9日(火)16:30- @B404

10月16日(火)16:30- @B404

Inflationary models generally predict a stochastic background of gravitational waves. The shape of its spectrum is important because it will provide us with information about the early universe. To make some prediction about that, we calculated the evolution of the primordial gravitational waves with considering the process of inflaton decay during reheating. We also took into account the change of the effective number of degree of freedom which causes the expansion rate of the universe to change suddenly during radiation era. In this seminar, I'll introduce the phenomena which relate to the evolution of the gravitational waves and show our result of the calculation.

10月30日(火)16:30- @B404

I have worked in this 3 years on CMB temperature fluctuation that is caused by the time variation of gravitational potentials of large scale structure of Universe. The gravitational potentials decay with time at large scale due to the accelarating expansion of the background spacetime(ISW), and evolve on small scale where the gravitational attracting force is dominant(RS): the sign of temperature flucuation exchanges. To describe such a cross-over, we should trace the evolution of matter to the non-linear scale. We find the very reasonable theory to predict the non-linear evolutions of gravitational potentials, and temperature fluctuation induced by them.
We then estimate the possibility of detecting this non-linear effect, and find that PLANCK/LSST can achive 2 \sigma detection. While the significance of detection is poor with a next decade facilities, statistically 50 \sigma detection is potential. We also explore the ability of ISW,RS effect to constraint dark energy parameters.
The orientation of degeneracy between w0 and w1, a time varying equation of state of dark energy is different from that of baryon acoustic oscillation and super novae luminosity distance. Hence the ISW,RS is expected to impose tighter constraints on w combining BAO and SNe observation.

This is a summary report of my works as a PhD student.

## 11月のセミナー

11月6日(火)16:30- @B404

I will give a summary talk of my PhD study, about a clustering analysis of the SDSS Luminous Red Galaxy (LRG) sample. We measure the correlation function of the LRGs as a function of separations parallel and perpendicular to the line-of-sight in order to take account of anisotropy of the large-scale structure in redshift space. We find a slight signal of baryonic features in the anisotropic correlation function which we call a "baryon ridge". Because the baryon ridge forms an isotropic structure in comoving space, it enables us to divide the redshift distortion effects into dynamical and geometrical components. With an assumption of a flat Lambda cosmology, we give constraints not only on the fundamental cosmological parameters (the mass and baryon density parameters and the hubble constant) but also on the dark energy equation-of-state. Our constraints agree quite well with those from the other observations. With the CMB prior from the WMAP results, we give stronger constraints on those parameters. This is the first cosmological application of the two-dimensional acoustic features to observational data.

11月13日(火)16:30- @B404

no title

no abstract

11月22日(木)16:30- @B404

Acceleration expansion of the universe was implied from various observations. The characteristic of the dark energy considered to be the origin is calculated from the galaxy distribution of a large scale. It is estimated using Fisher matrix whether photometric redshift survey can restrict how much w(z).

11月27日(火)16:30- @B404

Cosmic reionization is a landmark epoch in the history of the universe. Recent obserevations suggest that reionization began some early time at z>10 and ended by z~6.
Previously at At seminar, I presented preliminary results of the evolution of HII regions. I made 21cm differential temperature maps using cosmological simulation outputs on the assumption that the effect of Lyman-alpha coupling (the Wouthuysen-Field effect) can be ignored.
I will show that the effect is indeed important and the 21 cm spin temperatures in low density regions need to be calculated by including the term which account for the Lyman-alpha coupling. My ongoing work is on how to estimate this contribution using three-dimensional simulations. I summarize recent progress. In future work, I will make high-redshift 21 cm maps and study the detectability of early reionization epoch by future radio telescope arrays.

## 12月のセミナー

12月11日(火)16:30- @B404

I will provide a review of the recent development in modeling and observations of the galaxy biasing particularly at large-scale, where the baryon acoustic oscillation features are prominent.

12月18日(火)16:00- @B404

Formation of Primordial Stars in a LCDM Universe - The Final Chapter -

コールドダークマターモデルに基づく初期条件を設定し、重力、流体力学、非平衡化学反応、および放射輸送過程を取り入れた初代天体形成の大規模宇宙論的シミュレーションをおこなった。これまでの計算コードを大幅に改良し、新たに高密度領域での化学反応、連続光吸収によるガス冷却率の低下率を計算し、始原ガスの熱化学進化を密度にしておよそ２５桁以上、10$^{22} {\rm cm}^{-3}$まで追えるようになった。高密度での化学種分率の計算には化学平衡を過程し、分子解離による熱吸収と他の加熱冷却過程と整合的にとりあつかった。ガス雲中心コアまわりの連続光に対するオパシティには、LenzuniやDuschlの研究により得られたプランクオパシティの計算結果を利用し、３次元シミュレーションで得られる密度、温度分布から直接計算した。
シミュレーションの結果を用いて、始原ガス雲の分裂可能性とガス雲内の質量降着率をあらためて調べた。さらに原始星形成過程の詳細、降着衝撃波の形成の結果を示す。第一世代連星系の形成可能性についても議論し、この過程で形成される星と初期極超新星、ガンマ線バーストとの関連について言及する。

12月19日(水) 11:30- @B404, 16:00- @B402

fNL(11:30-)
BAO: 現在の理論的到達点と今後やるべき事、および観測計画と将来の展望(16:00-)

なぜ宇宙は加速膨張しているのだろうか。ダークエネルギーのせいなのか？ならば、ダークエネルギーは宇宙定数か？真空のエネルギーか？スカラー場か？あるいは、実はダークエネルギーなど存在せず、加速膨張は重力理論が一般相対論でないために生じているのだろうか？この問題は、宇宙論屋にとって文句なしにNo.1の重大問題であり、天文屋と物理屋をも巻き込んでえらい事になっているのはご承知の通りである。では、どのようにして加速膨張のメカニズムを探れば良いのだろう？
BAO (=Baryon Acoustic Oscillation)は、Dark Energy Task Forceにより、系統的誤差の最も少ない観測手法として位置づけられている。そのため、BAOは加速機構を解明するのに大きな役割を果たすと期待されている。しかし、系統的誤差が完全に払拭されているわけではない。最も重大な系統的誤差は、その理論計算にある。BAOの測定には銀河の分布を使うが、観測データと理論を比較する際、銀河の分布は線形理論では記述できないため、線形理論を超えたものが必要とされる。この分野は、８０年代から９０年代にかけて精力的に理論研究がされてきたが、２１世紀に入って急激に衰退してしまった。しかし近年、BAOが脚光を浴びる事により、再びこの分野が活気づきつつある。
このセミナーでは、そんなBAOを取り巻く現在の到達点をレビューした後、日本、アメリカ、ヨーロッパで考えられている観測計画に触れ、さらに時間があれば今後の日本の宇宙論業界のあり方に関して少し議論したい。

## 1月のセミナー

M2学生3名

1月8日(火)16:30- @B404

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Bartosz Lew

1月15日(火)16:30- @B404

Tests of Isotropy and Gaussianity of the CMB WMAP data

In my talk I will give a summary and present the results from the projects. I was and still am involved in during my PhD course, all of which are related to the tests of isotropy and Gaussianity (stationarity) of the CMB fluctuations, based on the temperature WMAP data. I will also discuss the prospects for future developments in the field of testing Gaussianity as well as constraining degree of non-Gaussianity and detail a bit on the currently ongoing projects that open up a best promice of short having a long sought breakthrough.

1月22日(火)16:30- @B404

Consistency test for DGP model and general relativity

DGP model is one of the modified gravity models which explains accelerated expansion of the universe without introducing the conception of dark energy. In this seminar, I will present a method which distinguishes between ordinary general relativity and DGP model.

1月29日(火)16:30- @B404 中止

## 2月のセミナー

2月5日(火)16:30- @B404

We develop a new approach to study the nonlinear evolution in the large-scale structure of the universe both in real space and in redshift space, extending the standard perturbation theory of gravitational instability. Infinite series of terms in standard Eulerian perturbation theory are resummed as a result of our starting from a Lagrangian description of perturbations. Our approach provides a unique opportunity to analytically investigate the nonlinear effects on baryon acoustic scales in observable redshift space, which is requisite in constraining the nature of dark energy, the curvature of the universe, etc., by redshift surveys.

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