Cosmophysics Group Seminar (2014)
26-Feb-2015
吉野 裕高「Simulating a BH-axion system」
アブストラクト：Stringy axions with ultralight mass may cause interesting astrophysical phenomena around a rotating black hole through formation and growth of an axion cloud by the super-radiant instability. I am now trying to study the axionic bosenova in more detail (compared to our previous work) and developing a method to simulate gravitational wave emission from this system. In this seminar, I explain the current status on our numerical studies on this system system. 参考文献：
12-Feb-2015
大橋 勢樹「Multipole moments in Einstein-scalar system」
アブストラクト：In this presentation, I review the definition of multipole moments of gravitational fields in curved space time. After that I explain the extension of multipole moment in Einstein-scalar system. I also discuss whether the multipole moments uniquely characterize the spacetime. 参考文献：
5-Feb-2015
高見 一「Source candidates of ultrahigh-energy cosmic rays from the interpretation of the latest cosmic -ray data」
アブストラクト：The origin of ultrahigh-energy cosmic rays (UHECRs; > $10^{19}$ eV), as well as their composition, has been one of the biggest mystery in modern astrophysics. Expected anisotropy at small angular scale has been expected to be a hint of their sources, no strong anisotropy has not been observed even by the gigantic detector such as Pierre Auger Observatory (~ 3000 km^2 in the area of surface detectors). Recently, the Telescope Array collaboration reports anisotropy in medium angular scale (~20 deg), called a hotspot. This hotspot reached 5 sigma in (unpenalized) statistical significance and is expected to be a hint of UHECR sources and cosmic magnetic fields in local universe. In this talk, the candidates of UHECR sources and their location are discussed through the interpretation of "isotropy" and the Telescope Array hotspot. On-axis known blazars , which have been discussed as plausible sources of the hotspot, are ruled out. Also, the hotspot (and other theoretical implications) allows for proton-dominated composition only in limited cases. Future observations of cosmic magnetic fields in local universe can test these possibilities and are expected to conclude whether proton-dominated composition is realized in the highest energy range, independently of composition inference through the profile of extensive air showers. Interestingly, the hotspot does not necessarily disfavor heavy-nucleus-dominated composition. 参考文献：
22-Jan-2015
蘇 垠成「Detecting the relic gravitational wave from the electroweak phase transition at SKA」
アブストラクト：We discuss possibilities to observe stochastic gravitational wave backgrounds produced by the electroweak phase transition in the early universe. Once the first-order phase transition occurs, which is still predicted in a lot of theories beyond the standard model, collisions of nucleated vacuum bubbles and induced turbulent motions can become significant sources of the gravitational waves. Detections of such gravitational wave backgrounds are expected to reveal the Higgs sector physics. In particular, through pulsar timing experiments planned in Square Kilometre Array (SKA) under construction, we will be able to detect the gravitational wave in near future and distinguish particle physics models by comparing the theoretical predictions to the observations. 参考文献：
15-Jan-2015
大山 祥彦「Constraints on the neutrino parameters by future cosmo logical 21cm line and precise CMB polarization observations」
アブストラクト：We focus on future observations of both the 21 cm line radiation coming from epoch of the reionization, and the CMB polarization produced by gravitational lensing, and study their sensitivities to the neutrino properties such as the total neutrino mass, the neutrino mass hierarchy, the effective number of neutrino species (extra radiation), and the lepton asymmetry of our Universe. We find that by combining the precise CMB polarization observations with Square Kilometer Array (SKA). we can detect the non zero neutrino mass, and determine the neutrino mass hierarchy at 2 sigma level if the total neutrino mass is smaller than 0.1 eV. Additionally, we also show that by using these combinations\x{00a0} we can constrain the lepton asymmetry better than big-bang nucleosynthesis (BBN). Besides we discuss constraints on it i n the presence of some extra radiation, and show that the 21 cm line observations can substantially improve the constraints obtained by CMB alone, and allow us to distinguish the effects of the lepton asymmetry from the ones of extra radiation. 参考文献：
8-Jan-2015
田邉健太朗「soft graviton theorem and BMS symmetry」
アブストラクト：最近 Strominger らにより議論されている soft graviton theoremとnull infinity の漸近的対称性（BMS対称性）との関係についてレビュー をする。 参考文献：
18-Dec-2014
木坂 将大「ショートガンマ線バーストの長時間放射成分」
アブストラクト：ショートガンマ線バーストにおいて、中心エンジンの活動が ~10^4s 程度の継続時間を持つという示唆が観測から得られている。中性子星連星合体後にブラックホールが形成する(もしくは大質量中性子星が形成するが寿命が短い)場合で、観測されたような長時間の活動性を持つ可能性について議論する。 参考文献： Gompertz, O'Brien & Wynn (2014) Rowlinson et al. (2013)
4-Dec-2014
井岡 邦仁「On Magnetically Arrested Disk (MAD)」
アブストラクト：We review the magnetically arrested disk (MAD). MAD may be the most efficient accretion disk in the Universe, which may explain the recent observations of high-energy emission from black holes. We also discuss the implications of MAD for the short gamma-ray bursts from neutron star mergers. 参考文献： Tchekhovskoy, Narayan & McKinney (2010)
20-Nov-2014
郡 和範「Coleman-Weinberg Inflation」
アブストラクト：We revisit the small field Coleman-Weinberg (CW) inflation, which has two problems, the smallness of the slow roll parameter, and the smallness of the spectral index. We show that the fermion condenate can solve the above problems. 参考文献： Iso, Kohri & Shimada arXiv:1408.2339
13-Nov-2014
小玉 英雄「Supergravity Version of the Starobinsky Influm and its String Uplift」
アブストラクト：理論のスケール不変性という統一的観点に基づいて，Starobinsky R^2 理論の超重力理論への拡張とその超弦理論への埋め込みを議論したKounnas, Lust, Toumbasの最近の論文を紹介する. 参考文献： C. Kounnas, D. Lust, N. Toumbas: arXiv: 1409.7076
30-Oct-2014
大山 祥彦「Constraints on the neutrino mass by future precise CMB polarization and 21cm line observations」
アブストラクト：Super-Kamiokande discovered the neutrino oscillation, hence it is confirmed that neutrinos have small but non-zero masses. However, their absolute values have not been determined yet. On the other hand, we can also use cosmological observations to determine the mass of neutrino. In the universe, the matter distribution has density fluctuations and the growth of them is affected by relic neutrinos. Therefore we focus on the future precise observations of both the CMB polarization (e.g. POLARBEAR2 and Simons Array) and the 21 cm line (e.g. SKA: Square kilometer Array), and study their sensitivities to the sum of the neutrino masses. In this talk, I will talk about the results of our analysis and show that combinations of CMB polarization experiments and SKA can strongly improve errors of the bounds on the sum of the neutrino masses. 参考文献：
25-Sep-2014
吉野 裕高「ブラックホール・スカラー場系の研究の最近の進展」
アブストラクト：ブラックホール・スカラー場系の研究の現状認識を目的として 最近の研究をいくつかピックアップしてレビューします。また、 自分が現在行っているブラックホール・有質量スカラー場系の 重力波の計算の現状報告をします。 参考文献：
Benone et al, arXiv:1409.1593
Okawa and Cardoso, arXiv:1405.4861
11-Sep-2014
大橋 勢樹「Progress on Bi-Horndeski Theory」
アブストラクト：Horndeski Theory is the most general single scalar+tensor theory with 2nd order field equations. This theory has a wide range of application,e.g. inflationary model. In the previous talk, I discussed on the construction of two-scalar version of Horndeski (Bi-Horndeski) theory. In this talk, I will report on the recent progress of the Bi-Horndeski theory construction. \ 参考文献：
4-Sep-2014
高見 一「Recent review of ultrahigh-energy cosmic-ray physics」
アブストラクト：The origin of ultrahigh-energy cosmic rays (UHECRs; typically > 10^7 GeV), especially the highest energy cosmic rays (> 10^{10} GeV) has been a longstanding mystery in astrophysics and astroparticle physics. In order to overcome their extremely small flux (~ 1 event yr^{-1} millennium^{-1} @ 10^{11} GeV!), cosmic-ray experimentalists have build gigantic cosmic-ray detectors to unveil their origin. Thanks to the Pierre Auger Observatory (detector area ~ 3000 km^2) at the southern hemisphere from 2004 and the Telescope Array (~ 600 km^2) at the northern hemisphere from 2009, we are now approaching their origin. We review the latest decadal progress on the understanding of UHECR physics and UHECR origin as well as multi-particle approaches to the origin with high-energy gamma rays and neutrinos. This is a detailed review part of a talk which will be presented in the UHECR symposium scheduled in the next JPS meeting. In addition to the review, I will present the future prospects of UHECR physics in that symposium. \ 参考文献：
24-July-2014
蘇 垠成「The effective potential theory and gravitational waves from first order phase transition」
アブストラクト：有限温度での有効ポテンシャル理論と電弱相転移について復習する。また、1次相転移による重力波のスペクトルについて詳しく論じる。 \ 参考文献：
17-July-2014
郡 和範「Consistency relations in large-field inflation models」
アブストラクト： I am going to give a talk on consistency relations between the tensor to scalar ratio and the running of the spectral index in various large-filed inflation models such as chaotic, natural, or extranatural inflation models, In particular, I discuss how to distinguish a model from the others by using future 21cm observations.\ 参考文献：
Consistency Relations for Large Field Inflation
Takeshi Chiba, Kazunori Kohri.
KEK-COSMO-149, KEK-TH-1747
e-Print: arXiv:1406.6117 [astro-ph.CO]
Distinguishing between Extra Natural Inflation and Natural Inflation after BICEP2
Kazunori Kohri, C.S. Lim, Chia-Min Lin
KEK-COSMO-144, KEK-TH-1733
e-Print: arXiv:1405.0772 [hep-ph]
Ambiguity in running spectral index with an extra light field during inflation
Kazunori Kohri, Tomohiro Matsuda
KEK-COSMO-147, KEK-TH-1738
e-Print: arXiv:1405.6769 [astro-ph.CO]
12-Jun-2014
井岡 邦仁「Blandford-Znajek Mechanism Revisited」
アブストラクト： ブラックホールは高エネルギー宇宙現象を引き起こす中心エンジンになる。今回は、ブラックホールの回転エネルギーを引き抜く最も有力な機構であるブランドフォード-ツナジェック機構を再考する。\ 参考文献： Blandford & Znajek 1977
Thorne et al. 1986
Punsly 2008
Komissarov 2004
Komissarov et al. 2009
McKinney 2006
24-Apr-2014
木坂 将大「Structure of pulsar magnetosphere」
アブストラクト： 強磁場をもち高速で自転する中性子星、パルサーはその周囲に磁気圏を形成する。この磁気圏では、単極誘導により誘起される電位差の一部を使って粒子加速が起きている。これらの粒子はガンマ線を放出して電磁カスケードが発展し、磁気圏の大部分は大量の電子・陽電子で満たされていると考えられている。しかし、その具体的な描像はあまりわかっていない。今回は、パルサー磁気圏構造の理解の進展を紹介した後、パルサーの磁極領域近傍におけるプラズマのダイナミクスについて議論を行う。 参考文献：
17-Apr-2014
田邉 健太朗「The large D limit of general relativity」
アブストラクト： 重力理論は理論のパラメータとして次元Dをもち、この次元Dが 大きいとき重力理論は非常にシンプルかつ非自明な構造となる。 今回はこの性質を生かした large D による重力理論の近似法を 紹介し、また large D limit における重力理論の有効理論について議論する。 参考文献：
10-Apr-2014
蘇 垠成「Detection possibility of the gravitational wave from the electroweak phase transition at the SKA」
アブストラクト： 電弱相転移による重力波をSKAで観測する可能性について論じた。 結果として、重力波のパラメータβ/Hが小さいところで観測可能性があることを明らかにした。 その際にvacuum energyがあることで生じるinflationの効果も議論したが、 この影響は小さいことが分かった。 参考文献：