Roberto Emparan, University of Barcelona, YITP
The large D limit of General Relativity
Meeting room 1, Kenkyu honkan 1F
General Relativity is an old theory but its dynamics remains difficult to solve and understand, in particular when strongly-gravitating objects such as black holes are involved. Although at first sight it may seem an odd idea, I will argue that it is actually quite natural to investigate the properties of this theory and its black holes in the limit in which the number of spacetime dimensions D grows to infinity. The gravitational field localizes very strongly near the black hole horizons, which simplifies dramatically the description of their interactions and allows efficient calculational approaches in an expansion in 1/D. There are also hints that this limit may lead to a reformulation of the theory in terms of low-dimensional strings.
Yuji Omura, Nagoya University
Study on two-Higgs-doublet models (with gauged U(1) symmetry)
Meeting room 1, Kenkyu honkan 1F
It is well known that generic two-Higgs-doublet models (2HDMs) suffer from potentially large Higgs-mediated flavor-changing neutral current (FCNC) problem, unless additional symmetries are imposed on the Higgs fields thereby respecting the Natural Flavor Conservation Criterion (NFC) by Glashow and Weinberg. A common way to respect the NFC is to impose Z_2 symmetry which is softly broken by a dim-2 operator. Another new way is to introduce local U(1)_H Higgs flavor symmetry that distinguishes one Higgs doublet from the other. In this talk, we discuss the phenomenology in 2HDMs with not only the Z_2 but also U(1)_H symmetry. We also study dark matter (DM) physics in the Type-I inert 2HDM with local U(1)_H Higgs gauge symmetry. The lightest neutral scalar component H of the U(1)_H-charged Higgs doublet, which does not have Yukawa couplings with the Standard-Model (SM) fermions, is stable because of the remnant discrete symmetry, and it interacts with the SM particles through the U(1)_H gauge boson (Z_H) exchange as well as the SM boson exchange. We investigate the constraints on DM: thermal relic density, and direct/indirect detections. The additional U(1)_H gauge interaction plays a crucial role in reducing the DM thermal relic density. The most important result within the inert DM model with local U(1)_H symmetry is that ~ O(10) GeV dark matter scenario, which is strongly disfavored in the usual Inert Doublet Model (IDM) with Z_2 symmetry, is revived in our model because of newly open channels, H H -> Z_H Z_H , Z_H Z. Exotic Higgs decays, h -> Z_H Z_H, Z Z_H, would be distinctive signatures of the inert 2HDM with local U(1)_H symmetry. I also give a comment on the type-II 2HDM inspired by E_6 GUT, and introduce some results on DM physics.
飯沼昌隆, 広島大学
非可換な偏光物理量の連続測定
Seminar room, Kenkyu honkan 3F
1988年にAharonovらによって提案された弱測定は、通常の量子測定とは異なり、状態をほぼ壊さずに測定する量子測定法である。初期状態をほぼ壊さずに情報を得られるため、これまで測定不可能とされた重ね合わせ状態などの中間状態での測定や、運動量と位置のような非可換な関係にある複数の物理量の連続測定を可能にする。これらの弱測定は、近年の量子測定技術の進展とともに従来では思考実験であった量子パラドックスの実験を可能しただけでなく、多くの場合、確率が負や複素数となる結果をもたらす。さらにこのとき弱測定で得られる実験値、すなわち弱値は、測定物理量の固有値の範囲を超えて大きく増大する。弱測定がもたらすこのような奇妙な結果は、従来の延長線上では考えにくいものであった。しかし近年行った偏光物理量の連続測定実験について、量子力学の数式に頼らず通常の確率論と統計的手法のみを使って、実験データから測定前の確率分布を推定したところ、量子力学や弱測定で予想される確率分布（Kirkwood-Dirac分布関数）と見事に一致した。この結果から弱値は直接得られない測定前の確率分布の平均値を表していること、測定前と測定後の確率分布は基本的に異なること、負や複素数の確率分布が本来の量子系の統計的性質である可能性が高いこと、さらに弱測定はその特性を見るきっかけを与えてくれたこと、などが分かってきた。これらは非可換な二つの偏光物理量の連続測定において初段の測定の強さを弱い領域だけでなく強い領域に至るまで行った測定からの帰結であり、量子状態は負や複素数の値を含む拡張された確率分布で記述できることを示唆する結果である。さらにこの確率分布は直接測定はできないが、その意味では密度行列と同じであり、しかも完全に１対１で対応している。セミナーでは、偏光を使った弱測定実験の結果と測定の強さの弱い領域から強い領域まで測定した連続測定実験の結果を紹介し、独立な両者の実験結果から上記の解釈ができる根拠を示す。
Yuan Qiang, IHEP
Millisecond pulsar interpretation of the Galactic center gamma-ray excess
Meeting room 2, Kenkyu honkan 1F
It was found in the Fermi-LAT data that there is an extended $gamma$-ray excess in the Galactic center region. The proposed sources to be responsible for the excess include the dark matter annihilation or an astrophysical alternative from a population of millisecond pulsars (MSPs). Whether or not the MSP scenario can explain the data self-consistently has very important implications for the detection of particle dark matter, which is however, subject to debate in the literature. In this work we study the MSP scenario in detail, based on the detected properties of the MSPs by Fermi-LAT. We build a model of the Milky Way MSPs which can reproduce the $gamma$-ray properties of the Fermi-LAT MSPs, and derive the intrinsic luminosity function of the MSPs. The model is then applied to a bulge population of MSPs. We find that the extended $gamma$-ray excess can be well explained by the bulge MSPs without violating the detectable flux distribution of MSPs by Fermi-LAT. The spatial distribution of the bulge MSPs as implied by the distribution of low mass X-ray binaries follows a $r^{-2.4}$ profile, which is also consistent with the $gamma$-ray excess data. We conclude that the MSP model can explain the Galactic center $gamma$-ray excess self-consistently, satisfying all the current observational constraints.
Yuta Hamada, Kyoto University
Naturalness and maximum entropy principle
Meeting room 3, Kenkyu honkan 1F
The theory of wormholes and multiverse suggests that the parameters of the Standard Model are fixed in such a way that the total entropy at the late stage of the universe is maximized, which we call the maximum entropy principle. In this talk, We show that Higgs vacuum expectation value is determined in order to satisfy maximum entropy principle. We assume that the baryon number is produced by the sphaleron process, and that the current quark masses, the gauge couplings and the Higgs self coupling are fixed when we vary Higgs vacuum expectation value. It turns out that the existence of the atomic nuclei plays a crucial role to maximize the entropy.
Yuki Yokokura, Yukawa Inst., Kyoto Univ.
Non-equilibrium thermodynamics of gravitational screens
Seminar room, Kenkyu honkan 3F
We study the Einstein gravity equations projected on a timelike surface, which represents the time evolution of what we call a gravitational screen. We show that such a screen possesses a surface tension and an internal energy, and that the Einstein equations reduce to the thermodynamic equations of a viscous bubble. We also provide a complete dictionary between gravitational and thermodynamical variables. In the non-viscous cases there are three thermodynamic equations which characterize a bubble dynamics: These are the first law, the Marangoni flow equation and the Young-Laplace equation. In all three equations the surface tension plays a central role: In the first law it appears as a work term per unit area, in the Marangoni flow its gradient drives a force, and in the Young-Laplace equation it contributes to a pressure proportional to the surface curvature. The gra vity equations appear as a natural generalization of these bubble equations when the bubble itself is viscous and dynamical. In particular, it shows that the mechanism of entropy production for the viscous bubble is mapped onto the production of gravitational waves. We also review the relationship between surface tension and temperature, and discuss the usual black-hole thermodynamics from this point of view. (This talk is based on [arXiv:1405.4881].)
Yu Nakayama, Kavli IPMU, Caltech
Understanding phase transitions and critical phenomena from conformal bootstrap
Meeting room 1, Kenkyu honkan 1F Conformal bootstrap has become an indispensable tool to understand the non-perturbative aspects of renormalization group fixed points in any space-time dimension. The recent “solution” of the d=3 critical Ising model is just one example.
Conformal bootstrap has become an indispensable tool to understand the non-perturbative aspects of renormalization group fixed points in any space-time dimension. The recent “solution” of the d=3 critical Ising model is just one example.
In this talk, I would like to discuss the real applications of conformal bootstrap to attack the long-standing controversies on the phase transitions and critical phenomena of the frustrated spin systems in non-collinear order and the finite temperature QCD chiral transition by determining the conformal windows of O(n)xO(m) CFTs in d=3 dimensions.
The talk is based on our recent paper arXiv:1404.0489 in collaboration with Tomoki Ohtsuki.
Kazuki Sakurai, King's College
ATOM/Fastlim: Recasting LHC constraints on new physics models
Meeting room 1, Kenkyu honkan 1F
The results of ATLAS and CMS beyond the Standard Model searches are very useful to constrain various new physics modes, yet they are originally designed to search for a particular model. Recasting existing analyses on to an arbitrary model involves various subtleties and one has to simulate detector responses and selection cuts as realistic as possible. For this task, we developed two programs: ATOM (Automated Testing Of Models) and Fastlim. ATOM takes event files as inputs and calculates the efficiencies of various analyses automatically, which can be used to calculate an exclusion p-value for an given model. Fastlim, on the other hand, takes spectrum files as inputs and immediately calculates an exclusion p-value using pre-calculated efficiencies of various simplified topologies. In this talk, I review the recent development of the attempt of recasting ATLAS and CMS searches on to general new physics models. I also discuss the methodology used and present performances of ATOM and Fastlim.
Masahide Yamaguchi, Tokyo Institute of Technology
Non-Gaussianities of primordial perturbations and tensor sound speed
Meeting room 1, Kenkyu honkan 1F
We investigate the relation between the non-Gaussianities of the primordial perturbations and the sound speed of the tensor perturbations, that is, the propagation speed of the gravitational waves. We find that the sound speed of the tensor perturbations is directly related not to the auto-bispectrum of the tensor perturbations but to the cross-bispectrum of the primordial perturbations, especially, the scalar-tensor-tensor bispectrum. This result is in sharp contrast with the case of the scalar (curvature) perturbations, where their reduced sound speed enhances their auto-bispectrum. Our findings indicate that the scalar-tensor-tensor bispectrum can be a powerful tool to probe the sound speed of the tensor perturbations.
Keisuke Harigaya, Kavli IPMU
Natural inflation with effective large decay constant by hierarchical charge
Meeting room 1, Kenkyu honkan 1F
