セミナー 2015年

Kai Schmitz, IPMU

Leptogenesis during Axion Relaxation after Inflation

Meeting Room ​322​, Kenkyu Honkan 3F
In this talk, I present a novel and minimal alternative to thermal leptogenesis, which builds upon the assumption that the electroweak gauge bosons are coupled to an axion-like scalar field, as it is, for instance, the case in certain string compactifications. The motion of this axion-like field after the end of inflation generates an effective chemical potential for leptons and antileptons, which, in the presence of lepton number-violating scatterings mediated by heavy Majorana neutrinos, provides an opportunity for baryogenesis via leptogenesis. In contrast to thermal leptogenesis, the final baryon asymmetry turns out to be insensitive to the masses and CP-violating phases in the heavy neutrino sector. Moreover, the proposed scenario requires a reheating temperature of at least O(10^12) GeV and it is, in particular, consistent with heavy neutrino masses close the scale of grand unification. This talk is based on recent work (Phys. Rev. Lett. 115 (2015) 1, 011302, 1412.2043 [hep-ph]) in collaboration with Alexander Kusenko from UCLA and Tsutomu T. Yanagida from Kavli IPMU.”

Emi Kou, Orsay, Laboratoire de l'Accélérateur Linéaire

B2TiP and highlight of Belle II physics

Meeting room 1, Kenkyu honkan 1F
For this occasion, I would like to present the activity of the Belle II physics working group, the B2TiP (Belle II Theory interface Platform) and the highlight of the current discussions in this working group. It will be an informal seminar targeted to experts and non-experts of B physics who are interested in B2TiP activity and want to know “what will be the main interests of Belle II physics?”.

Sayantan Sharma, Brookhaven

The origin of axial anomaly and the high temperature phase of QCD

Meeting Room 1, Kenkyu Honkan 1F ​
The axial U_A(1) though an anomalous symmetry is believed to affect the order of the chiral phase transition in QCD with two light quark flavours. In this talk I discuss about our study of the axial anomaly in finite temperature QCD using first principles lattice gauge theory technique. We use chiral overlap fermions to probe the underlying topology of dynamical QCD configurations with two light quark flavours generated with Highly improved staggered quarks. From the eigenvalue spectrum of the overlap operator we find no evidence of effective restoration of U_A(1) near the chiral transition temperature $T_c$. A pile up of the near-zero eigenmodes is observed to persist even at $1.5 T_c$ which is primarily responsible for its breaking . These eigenmodes are localized unlike those in the bulk, with a mobility edge similar to a Mott–Anderson like system. We find evidence in support of a dilute gas of instantons at the highest temperature studied, as the microscopic origin​ ​of the breaking of U_A(1) symmetry.

Ryosuke Hirai, Waseda

Ejecta-Companion Interaction in Massive Star Binaries

Meeting Room 1, Kenkyu Honkan 1F ​
Recent surveys show that almost all massive stars are born in binary systems. From the fact that these massive stars are the progenitors for core-collapse supernovae, the majority of these events should be occuring in binaries. When a star explodes in a binary, the companion may be affected by the supernova ejecta, possibly changing the further evolution of the binary. In this talk I will introduce results of hydrodynamical simulations of supernova ejecta hitting a star in massive binaries. We focus on the mass removed and its dependences on parameters. I will also show its application on a real supernova, iPTF13bvn, and our prediction on the possible observational features of the companion star.

Mariko Kikuchi, Toyama University


Meeting room 1, Kenkyu honkan 1F
新物理学模型におけるヒッグス結合定数の標準模型からのずれのパターンには 模型の特徴が表れる。よって、様々な模型においてそのズレのパターンを研究 することは模型の識別のために有効である。特に、高輝度LHC実験やILC実験 ではヒッグス結合定数の精密測定が期待されており、ヒッグス結合定数を輻射 補正の効果を含めて精密に計算することが必要である。 本セミナーでは、ヒッグス結合の将来精密測定を用いてヒッグスセクターを解明 し新物理学を決定することを目的に、様々な拡張ヒッグス模型におけるゲージ結合、 湯川結合、ヒッグス自己結合に対する輻射補正を系統的に計算した結果を示す。 そして、各模型ごとの結合定数のズレのパターンを1ループレベルで求め、将来の 精密測定でその特徴的なズレのパターンを観測することによる模型の識別・同定 可能性を示す。さらに、将来の精密測定と輻射補正を含めたヒッグス結合定数の 理論予言値の比較によって、模型の内部パラメーターの情報を引き出せる可能性 を議論する。
S. Kanemura, M. Kikuchi and K. Yagyu, Nucl. Phys. B896, 80 (2015)
S. Kanemura, M. Kikuchi and K. Yagyu, Phys. Lett. B731, 27 (2014)
S. Kanemura, M. Kikuchi and K. Yagyu, Phys. Rev. D88, 015020 (2013)
M. Aoki, S. Kanemura, M. Kikuchi and K. Yagyu, Phys. Rev. D87, 1, 015012 (2013)

Hiroyuki Ishida, Shimane University

Higgs inflation in a singlet extension of the standard model

Room 345, 4 go-kan 3F
Inflation is the most plausible mechanism to resolve several cosmological problems in the early universe. Higgs inflation is clearly the most economical possibility. The original Higgs inflation, however, requires quite a huge coupling between the Higgs field and the gravity, named the non-minimal coupling. We propose a model with a right-handed neutrino and a Z_2 odd real scalar field, which can account for tiny neutrino masses and the dark matter. We show that our model gives the non-minimal coupling of around 10, consistent with the recent Planck observation. Furthermore, we show that the masses of the right-handed neutrino and the dark matter are not seriously constrained by the observed value of the tensor-to-scalar ratio.

Shogo Tanimura, ​Graduate School of Information Science, Nagoya University

量子測定理論の数学的定式化・量子論と 確率の諸解釈

Seminar Room, Kenkyu Honkan 3F
量子測定理論は,素朴な「波束の収縮」仮説に訴えることなく,量子系の測定における確率と状態変化を記述する理論である.このセミナーでは、 量子測定理 論の基本概念である POVM (probability-operator valued measure), CP map (completely positive map), instrument と,間接測定モデル表現を解説する. また,量子論の解釈に関しては諸説あるが,波動関数の確率解釈を言うにしても,確率自体の解釈に関しても諸説ある.確率の解釈を吟味しないことには, 量子論の解釈を分析することもできないと思われるので,確率の解釈に関する議論を整理したいと思う.ちなみに,私は,波動関数や状態ベクトルやヒルベルト空間は,ミクロ系の内に宿った実体のようなものと捉えるべきではなく,ミク ロ系とマクロ系の間の橋渡し・窓口のようなものとみなすのがよいと考えている.そういう意味で,代数的量子論におけるヒルベルト空間のGNS構成が適切な数理だと考えている.
[1] M. Ozawa, “Uncertainty relations for noise and disturbance in generalized quantum measurements”, Ann. Phys. 311: 350-416 (2004). http://www.sciencedirect.com/science/article/pii/S0003491604000089
[2] 小澤正直「量子測定理論入門」(第56回物性若手夏の学校(2011年度) 講義ノート),物性研究 97巻 1031-1057 (2012). http://ci.nii.ac.jp/naid/110009327893
[3] D. ギリース(中山智香子 訳)「確率の哲学理論」日本経済評論社 (2004).
[4] 松原望「入門ベイズ統計 : 意思決定の理論と発展」東京図書 (2008).
[5] 谷村省吾「21世紀の量子論入門」 第15回:観測問題の基本概念(「理系への数学」(現代数学社)2011年7月号 pp.56-61), 第16回:測定における確率則と遷移則(「理系への数学」(現代数学社)2011年 8月号pp.56-61).
[6] 谷村省吾「波動関数は実在するか ― 物質的存在ではない.二つの世界をつなぐ窓口である」 数理科学2013年12月号 14-21.
[7] 谷村省吾「量子力学 ― 歴史・骨子・展開,そして基礎付け」 数理科学2015年2月号 26-32.

Kentaro Yoshida, Kyoto University

Towards the gravity/CYBE correspondence

Seminar room, Kenkyu honkan 3F
We present a systematic way to consider integrable deformations of the AdS5×S5 superstring. It is based on classical r-matrices satisfying classical Yang-Baxter equation (CYBE). Then a classical r-matrix gives rise to a gravitational solution that describes a deformed AdS5×S5 geometry. In this seminar, we provide some examples including the Lunin-Maldacena backgrounds for beta deformations of N=4 super Yang-Mills,the Maldacena-Russo backgrounds for non-commutative gauge theories,and Schrodinger spacetimes dual for cold atoms.We present a systematic way to consider integrable deformations of the AdS5×S5 superstring. It is based on classical r-matrices satisfying classical Yang-Baxter equation (CYBE). Then a classical r-matrix gives rise to a gravitational solution that describes a deformed AdS5×S5 geometry.In this seminar, we provide some examples including the Lunin-Maldacena backgrounds for beta deformations of N=4 super Yang-Mills, the Maldacena-Russo backgrounds for non-commutative gauge theories, and Schrodinger spacetimes dual for cold atoms.

Sakine Nishi, Rikkyo University

Generalized Galilean Genesis

Room 345, 4 go-kan 3F
The galilean genesis scenario is an alternative to inflation in which the universe starts expanding from Minkowski in the asymptotic past by violating the null energy condition stably. Several concrete models of galilean genesis have been constructed so far within the context of galileon-type scalar-field theories. We give a generic, unified description of the galilean genesis scenario in terms of the Horndeski theory, i.e., the most general scalar-tensor theory with second-order field equations. In doing so we generalize the previous models to have a new parameter (denoted by \alpha) which results in controlling the evolution of the Hubble rate. The background dynamics is investigated to show that the generalized galilean genesis solution is an attractor, similarly to the original model. We also study the nature of primordial perturbations in the generalized galilean genesis scenario. In all the models described by our generalized genesis Lagrangian, amplification of tensor perturbations does not occur as opposed to what happens in quasi-de Sitter inflation. We show that the spectral index of curvature perturbations is determined solely from the parameter \alpha and does not depend on the other details of the model. In contrast to the original model, a nearly scale-invariant spectrum of curvature perturbations is obtained for a specific choice of \alpha.

Kazuhiro Tobe, Nagoya University

Lepton-flavor-violating Higgs decay $h \rightarrow \mu \tau$ and muon anomalous magnetic moment in a general two Higgs doublet model

Meeting Room 3, Kenkyu Honkan 1F
A two Higgs doublet model (2HDM) is one of the minimal extensions of the standard model (SM), and it is well-known that the general setup predicts the flavor-violating phenomena, mediated by neutral Higgs interactions. Recently the CMS collaboration has reported an excess of the lepton-flavor-violating Higgs decay in $h \rightarrow \mu \tau$ channel with a significance of $2.4 \sigma$. We investigate the CMS excess in a general 2HDM with tree-level flavor changing neutral currents (FCNSs), and discuss its impact on the other physical observations. Especially, we see that the FCNCs relevant to the excess can enhance the neutral Higgs contributions to the muon anomalous magnetic moment (muon g-2), and can resolve the discrepancy between the measured value and the SM prediction. We also find that the couplings to be consistent with the muon g-2 anomaly as well as the CMS excess in $h \rightarrow \mu \tau$ predict the sizable rate of $\tau \rightarrow \mu \gamma$, which is with in the reach of future B factory.

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