## Seminars in 2016

Seminars from April 2016 through March 2017.

EHQG Seminar

- Title
- Canonical Tensor Model and its relation to general relativity
- Speaker
- Naoki Sasakura (YITP, Kyoto Univ.)
- Date & Time
- Tuesday, February 28, 2017, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- First, I briefly review the outcomes of a few discretized approaches to quantum gravity, such as Dynamical Triangulation, Causal Dynamical Triangulation, and Tensor Models, and argue the essential importance of causality for viable theories of quantum gravity with emergence of classical spacetimes. I also argue that “time” must be a sort of gauge parameter rather than a real entity in such theories for the consistency with general relativity. Then, I introduce Canonical Tensor Model (CTM) as a possible realization of such a viable theory. In fact, by taking a formal continuum limit and a derivative expansion up to the fourth order, CTM is shown to agree with general relativity coupled with a scalar field. The system has a critical dimension, six, with a conformal symmetry. Higher spin gauge fields are also present, which should in principle be derived by employing higher order derivative expansions. The contents are mainly based on arXiv:1609.01946 to appear in PRD.

QG Seminar

- Title
- 回転ブラックホール近傍における高エネルギー粒子衝突と、エネルギー引き抜き過程について
- Speaker
- Kota Kogasawara (Rikkyo Univ.)
- Date & Time
- Monday, February 27, 2017, 5:00 p.m.
- Place
- QG colloquim(ES744)
- Abstract
- 回転ブラックホール近傍において2粒子衝突を考えた場合、任意に大きな重心系が実現されることが知られている。これはBañados-Silk-West効果（BSW効果）と呼ばれている。また、回転ブラックホールにはエルゴ領域と呼ばれる負のエネルギー状態が可能な領域が存在し、エルゴ領域内で2粒子衝突を考えると衝突で生成された粒子の一方は衝突前の2粒子のエネルギーの総和より大きなエネルギーをもち、無限遠まで脱出できる。この過程は回転ブラックホールの回転エネルギーを引き抜く過程であり、collisional Penrose processと呼ばれている。 本講演では、これらの回転ブラックホール特有の粒子衝突に注目し、高エネルギー粒子衝突の結果生成される高エネルギー粒子がどの程度の割合で無限遠まで脱出できるか評価した結果について議論する

Colloquium

- Title
- Application of AdS/CFT Correspondence to Non-equilibrium Physics -- Analog Black Holes and Non-equilibriun Steady States --
- Speaker
- Shin Nakamura (Chuo Univ.)
- Date & Time
- Tuesday, February 21, 2017, 2:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract

Special Lecture(for DC)

- Title
- ゲージ・重力対応で探る非平衡物理学
- Speaker
- Shin Nakamura (Chuo Univ.)
- Date & Time
- Monday, February 20–Wednesday, February 22, 2017
- Place
- Science Symposia (ES635)
- Abstract

EHQG-KMI joint Seminar

- Title
- Dense Matter Physics with Rare Isotopes
- Speaker
- Youngman Kim (Rare Isotope Science Project, Institute for Basic Science,Korea)
- Date & Time
- Tuesday, February 14, 2017, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Dense nuclear matter is important to understand heavy ion collisions, nuclear structure, and neutron stars. In this seminar, opportunities and challenges in dense matter physics with upcoming rare isotope facilities will be discussed.

EHQG Seminar

- Title
- Introduction to General Probabilistic Theories and its Applications to information theory
- Speaker
- Gen Kimura (Shibaura Institute of Technology)
- Date & Time
- Tuesday, January 31, 2017, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- General probabilistic theories (GPT) are designed to provide operationally the most general probabilistic theories including both classical and quantum probability theory. In this seminar, I will give a brief introduction of GPT with the emphasis of applications to foundations of quantum mechanics and information theory. In particular, we will introduce the inductive method to construct entropies and prove the general upper bound of information gain in any probabilistic model. This result generalizes the famous Holevo theorem in quantum mechanics.

QG Seminar

- Title
- Stability of Wormholes with Singular Hypersurfaces in Einstein and Gauss-Bonnet theories of gravity
- Speaker
- Takafumi Kokubu (Rikkyo Univ.)
- Date & Time
- Monday, January 30, 2017, 3:30 p.m.
- Place
- QG colloquim(ES744)
- Abstract
- We introduce a way to a spacetime short-cut, ``wormholes", that might be realized in theoretical physics. Wormhole is a spacetime structure which connects two different universes or even two points of our universe. General relativity, the most successful and the simplest theory of classical gravitational theories, predicts a wormhole spacetime. In this seminar, we pursue the possibility for eternal existence of such objects. First, we introduce properties of wormholes with its history of discoveries. Next, we review thin-shell wormholes that are categorized into a class of wormhole solutions. After that, negative tension branes as stable thin-shell wormholes in Reissner-Nordstr\"{o}m-(anti) de Sitter spacetimes in $d$ -dimensional Einstein gravity is investigated. Imposing $Z_2$ symmetry, we construct and classify traversable static thin shell wormholes in spherical, planar (or cylindrical) and hyperbolic symmetries. In spherical geometry, we find wormholes which are stable against spherically symmetric perturbations. We also find the classes of stable thin shell wormholes in planar and hyperbolic symmetries with a negative cosmological constant. In most cases, stable wormholes are found with the appropriate combination of an electric charge and a negative cosmological constant. Finally, the effect of the Gauss-Bonnet term on the existence and dynamical stability of thin-shell wormholes as negative tension branes is studied in the arbitrary dimensional spherically, planar, and hyperbolically symmetric spacetimes with a cosmological constant.

EHQG Seminar

- Title
- Hadron-hadorn interaction form two-particle momentum correlation in heavy ion collisions
- Speaker
- Kenji MORITA (YITP.)
- Date & Time
- Tuesday, January 24, 2017, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- I will talk about recently developping approach to extract hadron-hadron interactions from particle momentum correlations in heavy ion collisions. I will mainly focus on the correlations due to the final state interaction and the identical particle effect (also known as HBT effect). Then I will give a brief account of our recent works on proton-Omega correlations and Lambda-Lambda correlations which have some implications for the possible existence of S=-3 and -2 dibaryon states.

EHQG Seminar

- Title
- Phenomenology of non-standard interactions of neutrinos
- Speaker
- Osamu Yasuda (Tokyo Metropolitan University)
- Date & Time
- Tuesday, January 17, 2017, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Thanks to the successful experimental results in the past, we now know the three mixing angles and the two mass squared differences of neutrinos. In the future experiments with huge detectors such as Hyperkamiokande, it is expected that we can study not only the unknown quantities (the mass hierarchy and the CP phase) in the standard scenario but also physics beyond the standard model with massive neutrinos. In the mean time, it has been pointed out that there is a tension between the solar neutrino and KamLAND data, and that the tension can be solved by assuming the flavor dependent non-standard interactions. In this talk, I will briefly review the constraints on the non-standard interactions of neutrinos, and discuss the prospect of discovering the effects of such interactions.

EHQG Seminar

- Title
- Turbulent strings in AdS/CFT
- Speaker
- Keiju Murata (Keio Univ.)
- Date & Time
- Tuesday, January 10, 2017, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- We study nonlinear dynamics of the flux tube between an external quark-antiquark pair in N=4 super Yang-Mills theory using the AdS/CFT duality. In the gravity side, the flux tube is realized by a fundamental string whose endpoints are attached to the AdS boundary. We perturb the endpoints in various ways and numerically compute the time evolution of the nonlinearly oscillating string. As a result, cusps can form on the string, accompanied by weak turbulence and power law behavior in the energy spectrum. We also find that, with sufficiently strong perturbations, the string continues extending and plunges into the Poincare horizon. In the evolution, effective horizons are also dynamically created on the string worldsheet. The quark and antiquark are thus causally disconnected, and the string transitions to two straight strings.

KMI-TH-QG-C-Tagen joint seminar

- Title
- eLISA science in the era of first detections
- Speaker
- Enrico Barausse (IAP Paris)
- Date & Time
- Tuesday, January 10, 2017, 3:30 p.m.
- Place
- ES621
- Abstract
- I will provide a review of the latest (~1 yr) progress toward a space-based gravitational-wave detector. The eLISA space-based interferometer is the main candidate for ESA’s Cosmic Vision theme "The Gravitational Universe", for which the L3 launch slot in 2034 has been reserved. ESA’s final decision on the mission will happen in 2017 so as to allow sufficient time for industrial production. It is therefore urgent to assess the science return of the eLISA mission vs cost-saving measures. In more detail, I will consider different eLISA mission designs, including four-link (two-arm) and six-link (three-arm) configurations with different lengths, low-frequency noise sensitivities and mission duration, and explore their science capabilities, focusing on massive black-hole binaries, extreme mass-ratio inspirals, tests of General Relativity and cosmology, as well as possible synergies with ground based detectors.

EHQG Seminar

- Title
- Infrared supersymmetry enhancement in 4d QFT
- Speaker
- Kazunobu Maruyoshi (Seikei Univ.)
- Date & Time
- Tuesday, December 20, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- We study certain N=1 preserving deformations of four-dimensional N=2 superconformal field theories (SCFTs) with non-Abelian flavor symmetry. The deformation is described by adding an N=1 chiral multiplet transforming in the adjoint representation of the flavor symmetry with a superpotential coupling, and giving the nilpotent vacuum expectation value to the chiral multiplet. Remarkably, we find classes of theories flow to N=2 supersymmetric fixed points in the infrared under the deformation. Namely the supersymmetry is enhanced in the infrared. In particular, we find renormalization group flows from the deformed conformal SQCDs with gauge group SU(N) and Sp(N) to N=2 SCFTs of Argyres-Douglas type. From these ``Lagrangian descriptions," we compute the full superconformal indices and find agreements with the previous results. This talk is based on arXiv:1606.05632, arXiv:1607.04281, arXiv:1610.05311.

QG Seminar

- Title
- Informational Theory of Relativity
- Speaker
- Akio Hosoya (Tokyo Institute of Technology)
- Date & Time
- Monday, December 12, 2016, 3:30 p.m.
- Place
- QG colloquim(ES744)
- Abstract
- Assuming the minimal time to send a bit of information in the Einstein synchronization of the two clocks located at different positions, we introduce the extended metric to the information space. This modification of relativity changes the red shift formula keeping the geodesic equation intact. Extending the gauge symmetry to the 5 dimensional general invariance, we start with the Einstein-Hilbert action in the 5 dimensional space. After 4+1 decomposition, we arrive at the effective action which includes the Einstein-Hilbert action for gravity, Maxwell action for the velocity field and the Lagrange multiplier term which ensures the normalization of the unit time-like velocity field. As an application, we investigate a solution of the field equations in the case that a 4 dimensional part of the extended metric is spherically symmetric.Relation to the Einstein-Aether theory is briefly discussed.

EHQG Seminar

- Title
- Electroweak-Skyrmion as Topological Dark Matter
- Speaker
- Masafumi Kurachi (KEK)
- Date & Time
- Tuesday, December 6, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- We show the existence of a nontrivial topological configuration of the Higgs field in the Standard Model with the Skyrme term. It is shown that the current upper bound of the mass of the topological object is about 34 TeV. We discuss the impact of the existence of the topological object on cosmology.

QG Seminar

- Title
- AdS Black Hole as a Leaking Chaotic Billiard System
- Speaker
- Yuichiro Hoshino ( Waseda Univ.)
- Date & Time
- Monday, December 5, 2016, 3:30 p.m.
- Place
- QG colloquim(ES744)
- Abstract
- Two-dimensional chaotic billiard system has been widely studied for a long time. In particular, its quantum system is analytically and numerically discussed for the purpose of understanding the quantum counterpart. In this seminar, I will give you a brief review of its chaotic property. Then we see that a classical cohomogeneity-one string in five-dimensional AdS Schwarzschild BH exhibits chaos, Lyapunov exponents depend on BH mass, and its survival probability includes the stage obeying the power-low. This behavior is known in two-dimensional open billiard system as well. Finally, I talk about quantum version of the string with respect to level-spacing distribution and its application.

EHQG Seminar

- Title
- Search for wino dark matter
- Speaker
- Satoshi Shirai (IPMU)
- Date & Time
- Tuesday, November 29, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Wino is one of the most attractive candidates for the dark matter. I will talk about characteristic signatures of the wino at the colliders and in the sky, and discuss the possibility of further improvement of the wino search.

QG Seminar

- Title
- A Smolin-like branching multiverse from multiscalar-tensor theory
- Speaker
- Kevin Croker ( University of Hawai’i)
- Date & Time
- Monday, November 28, 2016, 3:30 p.m.
- Place
- QG colloquim(ES744)
- Abstract
- We implement a Smolin-like branching multiverse through a directed, acyclic graph of N metrics defined on a common manifold. Our gravitational and matter actions are indistinguishable from N decoupled statements of General Relativity, if one varies with respect to metric degrees of freedom. We replace N−1 metrics with scalar fields by conformally relating each metric to its unique graph predecessor. Varying with respect to the N−1 scalar fields gives a multiscalar-tensor model with novel gravitational radiation signatures and dark matter candidates. Following Chapline and Laughlin, branching is phenomenological and accomplished with the emergence of an order parameter during gravitational collapse: we initialize a suitably defined N scalar field model with final data from an N−1 field model. We focus on the nearest-neighbour approximation, determine conditions for dynamical stability, and discuss the equations of motion. Given a Robertson-Walker ansatz, the model naturally features an initial singularity. Further, the equations of motion may exhibit a novel screening property where the scalar fields seek to decouple from the stress. Present challenges and future directions will be discussed.

EHQG Seminar

- Title
- Tree-unitarity and renormalizability in Lifshitz-scaling theory
- Speaker
- Keisuke Izumi ( Nagoya Univ.)
- Date & Time
- Tuesday, November 22, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- I investigate a conjecture; the conditions for tree-unitarity and for renormalizability are identical. If this property stems from purely quantum origin, even in the theory without Lorentz symmetry the relation is expected to hold true. In my talk, I show the conditions for tree-unitarity and renormalizability in Lifshitz-scalar field theory. The theory is characterized by an anisotropic scaling between the space and time directions. Without the Lorentz symmetry, both the tree-unitarity and the renormalizability conditions are modified from those in relativistic theories. For renormalizability, an extended version of the power counting condition is required in addition to the conventional one. The unitarity bound for S-matrix elements also gives stronger constraints on interaction terms because of the reference frame dependence of scattering amplitudes. I show that both tree-unitarity and renormalizability require identical conditions as in the case of conventional relativistic theories.

EHQG Seminar

- Title
- A supersymmetric two-field relaxion model
- Speaker
- Natsumi Nagata ( Tokyo Univ.)
- Date & Time
- Tuesday, November 15, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- We discuss a supersymmetric version of a two-field relaxion model that naturalizes supersymmetric models with high SUSY-breaking. This exploits a relaxion mechanism that does not depend on QCD dynamics and where the relaxion potential barrier height is controlled by a second axion-like field. During the cosmological evolution, the relaxion rolls down with a nonzero value that breaks supersymmetry and scans the soft supersymmetric mass terms. Electroweak symmetry is broken after the soft masses become of order the supersymmetric Higgs mass term and causes the relaxion to stop rolling. This can explain the tuning in supersymmetric models, while preserving the QCD axion solution to the strong CP problem. We will also consider possible inflation models compatible with this framework.

EHQG Seminar

- Title
- Structure of Y(4260)
- Speaker
- Makoto TAKIZAWA ( Showa Pharmaceutial uni.)
- Date & Time
- Tuesday, November 1, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- First, I start with the brief introduction of the present situation of the exotic hadrons including heavy quarks. Next, I explain our recent results of X(3872), Pc(4380) and Pc(4450). Then, I discuss our very recent result of Y(4260). We performed full coupled channel calculations of the J^{PC} = 1^{—} states in the framework of the quark potential model and we found a sharp resonance. We consider our result shed light on understanding rather complicated situation of Y-type exotic hadrons.

EHQG Seminar

- Title
- Non-perturbative Contributions from Complexified Solutions in CP^{N-1} Models
- Speaker
- Norisuke SAKAI ( Keio Univ.)
- Date & Time
- Tuesday, October 25, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Starting from how to make sense of divergent perturbation series in quantum mechanics and field theories, I will give a brief introduction of resurgence : intimate relations exist between the sum of perturbation series and nonperturbative contributions, both of which conspire to give a well-defined result. The nonperturbative contributions come from composite solitons called bions. Although bions have been given as only approximate solutions so far, it has been noted recently that bions become exact solutions of complexification of simple quantum mechanics such as sine-Gordon model. I will describe our recent study of nonperturbative contributions in the CP^1 quantum mechanics with fermionic degrees of freedom. We find bion solutions, which correspond to (complexified) instanton-antiinstanton configurations stabilized in the presence of the fermonic degrees of freedom. By computing the one-loop determinants in the bion backgrounds, we obtain the leading order contributions from both the real and complex bion solutions. The quasi zero modes are evaluated using the Lefschetz thimble formalism. The non-perturbative contributions from the real and complex bions are shown to cancel out in the supersymmetric case and give an (expected) ambiguity in the non-supersymmetric case, which plays a vital role in the resurgent trans-series. For nearly supersymmetric situation, evaluation of the Lefschetz thimble gives results in precise agreement with those of the direct evaluation of the Schr\"odinger equation. We also perform the same analysis for the sine-Gordon quantum mechanics and point out some important differences showing that the sine-Gordon quantum mechanics does not correctly describe the 1d limit of the CP^{N-1} field theory on RxS^1.(arXiv:1607.04205)

EHQG Seminar

- Title
- Non-Gaussian fluctuations in relativistic heavy-ion collisions
- Speaker
- Masakiyo KITAZAWA ( Osaka Univ.)
- Date & Time
- Tuesday, October 18, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Relativistic heavy-ion collisions are unique experiments to create extremely hot and dense medium on the Earth. Exploring the onset of deconfinement phase transitions and properties of the quark-gluon plasma (QGP) is one of the main purposes of these experiments. Recently, fluctuations of conserved charges observed in these experiments acquire much attention as experimental observables sensitive to thermal propeties in the early stage of the collisions. Both experimental measurements and theoretical studies have been done actively last ten years. In particular, non-Gaussianity of the fluctuations characterized by higher-order cumulants has been investigated in these studies. In this talk, I overview recent developments in this field, and discuss our recent ideas to understand nature of the experimentally-observed fluctuations further and to exploit them for the search of the QCD critical point.

EHQG Seminar

- Title
- Gauge Coupling Unification with Hidden Photon, and Minicharged Dark Matter
- Speaker
- Norimi Yokozaki ( Tohoku Univ.)
- Date & Time
- Tuesday, October 11, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- We show that gauge coupling unification is realized with a greater accuracy in the presence of a massless hidden photon which has a large kinetic mixing with hypercharge. We solve the renormalization group equations at two-loop level and find that the GUT unification scale is around $10^{16.5}$ GeV which sufficiently suppresses the proton decay rate, and that the unification depends only on the kinetic mixing, but not on the hidden gauge coupling nor the presence of vector-like matter fields charged under U(1)$_H$ and/or SU(5). Matter fields charged under the unbroken hidden U(1)$_H$ are stable and they contribute to dark matter. Interestingly, they become minicharged dark matter which carries a small but non-zero electric charge, if the hidden gauge coupling is tiny. The minicharged dark matter is a natural outcome of the gauge coupling unification with a hidden photon.

Colloquium

- Title
- 重力の量子論へのアプローチ
- Speaker
- Nobuyoshi Ohta (Kinki Univ.)
- Date & Time
- Tuesday, October 4, 2016, 2:00 p.m.
- Place
- 第6講義室 (A421)
- Abstract

Special Lecture(for MC)

- Title
- 重力の量子論 -- 漸近的安全性入門 --
- Speaker
- Nobuyoshi Ohta (Kinki Univ.)
- Date & Time
- Monday, October 3–Wednesday, October 5, 2016
- Place
- 第6講義室 (A421)
- Abstract

QG informal Seminar

- Title
- Gravitational Memory Charges of Supertranslation and Superrotation on Rindler Horizons
- Speaker
- Masahiro Hotta ( Tohoku Univ.)
- Date & Time
- Tuesday, August 9, 2016, 2:00 p.m.
- Place
- QG colloquim (ES744)

EHQG Seminar

- Title
- Particle-Vortex Duality from 3d Bosonization
- Speaker
- Andreas Karch ( Univ. of Washington, Seattle)
- Date & Time
- Tuesday, July 19, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- We provide a simple derivation of particle-vortex duality in d = 2 + 1 dimensions. Our starting point is a relativistic form of flux attachment, designed to transmute the statistics of particles. From this seed, we derive a web of new dualities. These include particle-vortex duality for bosons as well as the recently discovered counterpart for fermions.

EHQG Seminar

- Title
- Search for Sphalerons: LHC vs. IceCube
- Speaker
- Kazuki Sakurai ( Darrum Univ.)
- Date & Time
- Tuesday, July 12, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- In a recent paper, Tye and Wong (TW) have argued that sphaleron-induced transitions in high-energy interactions should be enhanced compared to previous calculations, based on a construction of a Bloch wave function in the periodic sphaleron potential and the corresponding pass band structure. In this talk, I present our resent work studying future prospects of observing sphaleron transitions at high energy hadron colliders and IceCube, based on TW results. I first discuss the production rate and possible signatures of the sphaleron-induced processes at high energy hadron colliders. We recast the early ATLAS Run-2 search for microscopic black holes to constrain the rate of sphaleron transitions at 13 TeV LHC. In the second half of the talk, I will discuss the possibility of observing sphaleron transitions induced by cosmogenic neutrinos at IceCube. I calculate the sphaleron event rate at IceCube and discuss the signature of such events. Finally I compare the performance of the sphaleron searches at the LHC and IceCube and find complementarity of these experiments.

QG Seminar

- Title
- The geometry of gravitational lensing
- Speaker
- Marcus C. Werner ( YITP)
- Date & Time
- Monday, July 11, 2016, 3:30 p.m.
- Place
- QG colloquim(ES744)
- Abstract
- Geometrical optics in gravity can be approached from different points of view: the quasi-Newtonian impulse (or thin lens) approximation of gravitational lensing as used in astronomy; optical (or Fermat) geometry, defined by the 3-space whose geodesics are the spatial light rays; and, of course, null geodesics in spacetime. In this talk, I give an introduction to the theory, focusing on the rich geometrical properties exhibited by these approaches. In particular, I discuss image counting and Morse theory; magnification invariants and Lefschetz fixed point theory; the Gauss-Bonnet method for the Riemannian optical geometry of static spacetimes, as well as the Finslerian optical geometry of stationary spacetimes; and finally, an extension of the standard definition of lensing magnification to spacetime, with its geometrical interpretation in terms of the van Vleck determinant and the exponential map. In this context, I also mention a recent observational development, namely the discovery of the first strongly lensed type Ia supernovae.

EHQG Seminar

- Title
- Constraint on ghost-free bigravity from gravitational Cherenkov radiation
- Speaker
- Ranpei Kimura ( Tokyo Institute of Technology)
- Date & Time
- Tuesday, July 5, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- I will briefly review the ghost-free bigravity model, which is a simple extension of dRGT massive gravity. Then I discuss gravitational Cherenkov radiation in a healthy branch of background solutions in the ghost-free bigravity model. In this model, because of the modification of dispersion relations, each polarization mode can possess subluminal phase velocities, and the gravitational Cherenkov radiation could be potentially emitted from a relativistic particle. I will discuss conditions for the process of the gravitational Cherenkov radiation to occur and estimate the energy emission rate for each polarization mode. I will show that the gravitational Cherenkov radiation emitted even from an ultrahigh energy cosmic ray is sufficiently suppressed for the graviton's effective mass less than 100 eV.

EHQG Seminar

- Title
- Stochastic approach for Infrared effects in de Sitter space
- Speaker
- Hiroyuki Kitamoto ( Kyouto Univ.)
- Date & Time
- Tuesday, June 28, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- I talk about quantum field theories in de Sitter space, especially infrared dynamics of them. In the presence of massless and minimally coupled scalar fields, quantum fluctuations at super-horizon scales make physical quantities growing with time. These infrared effects spoil perturbation theories if the cosmic expansion continues long enough. In models without derivative interactions, it has been known that these infrared effects can be described nonperturbatively by a Langevin equation. In fact, the stochastic approach is equivalent to the resummation of the leading infrared effects to all-orders. We generalize the stochastic approach as it is applicable also in models with derivative interactions. The outline of my talk is as follows. First I make a brief review of the standard stochastic approach, which is available only if the nonlinear term has no derivative couplings. Next I explain how to modify the stochastic approach if some derivative couplings exist.

EHQG Seminar

- Title
- Complete action for open superstring field theory
- Speaker
- Yuji Okawa ( Tokyo Univ.)
- Date & Time
- Tuesday, June 21, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- In formulating superstring field theory, construction of an action including the Ramond sector has not been successful for about thirty years, and this has been a major obstacle. Last year we finally succeeded in constructing a gauge-invariant action for open superstring field theory including both the Neveu-Schwarz sector and the Ramond sector. This is the first construction of a complete formulation of superstring field theory. In this talk, we explain the construction of the complete action without assuming any background on string field theory. The talk is based on the paper arXiv:1508.00366 in collaboration with Kunitomo.

EHQG Seminar

- Title
- A many-body extension of the LLP theory and its applications
- Speaker
- EIJI Nakano ( Kochi Univ)
- Date & Time
- Tuesday, June 14, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Froehlich type (continuous) polaron is an elementary excitation composed of electron entailing phonon cloud in polar crystals,where the electron-phonon interaction is of a Yukawa type originating from a dielectric interaction.For weak/intermediate interaction regimes,the Lee Low Pines (LLP) theory describes the dressed electron (polaron) by an unitary transformation (LLP transformation),which is though applicable only to single polaron systems.Recently we have proposed an extention of LLP (eLLP) for many-body polaron systems, and applied it toa BEC-polaron gas in Bose-condensed boson-fermion mixture of ultra cold atoms.The effective Haminltonian of this system is analogous to the electron polaron. We show the ground state properties obtained in eLLP, comparing with conventional methods.

EHQG Seminar

- Title
- Precision Higgs Analysis
- Speaker
- James D. Wells ( Michigan Univ)
- Date & Time
- Tuesday, June 7, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- After the Higgs boson discovery we are able to refocus our efforts on precision analysis in search of new physics contributions now that the Standard Model and its parameters are known well. Some questions I will address concern self consistent precision analysis frameworks, new physics expectations for deviations, and comparisons with experimental sensitivities for currently running and future facilities.

EHQG Seminar

- Title
- What can we learn from GW150914?
- Speaker
- Hiroyuki Nakano (Kyoto Univ.)
- Date & Time
- Tuesday, May 31, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- GW150914 detected by advanced LIGO detectors in the US has been considered as gravitational waves emitted from a binary black hole merger. The total signal-to-noise ratio of the gravitational waves from the inspiral, merger and ringdown phases was 24, and the waveform was consistent with that expected from Einstein's general relativity. But, when we focus only on the ringdown phase, the signal-to-noise ratio was 7 or less. In this talk, especially focusing on the quasinormal modes of the remnant black hole after merger, we discuss what we can conclude from the ringdown phase of gravitational waves in the current situation.

EHQG Seminar

- Title
- A study of spin-1 particles at the LHC
- Speaker
- Tomohiro Abe (KMI)
- Date & Time
- Tuesday, May 24, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Although a Higgs boson was discovered, the origin of the electroweak symmetry breaking is still mysterious. By the naturalness argument, we can expect strong dynamics at TeV scale which is the trigger of the electroweak symmetry breaking. In such a scenario, spin-1 new particles (W’ and Z’) generally exist. In this talk, I would like to discuss phenomenology of the W’ and Z’ at the LHC.

QG Seminar

- Title
- A Self-consistent Description of the Interior of Black Holes
- Speaker
- Yuki Yokokura (RIKEN)
- Date & Time
- Monday, May 23, 2016, 3:30 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- We analyze time evolution of a spherically symmetric collapsing matter taking the back reaction from evaporation into account, and find that the collapsing matter evaporates without forming a horizon. Nevertheless, a Hawking-like radiation is created in the metric, and the object looks the same as a conventional black hole from the outside. We then discuss how the information of the matter is recovered. We also consider a black hole that is adiabatically grown in the heat bath and obtain the interior metric. We show that it is the self-consistent solution of the semi-classical Einstein equation, and that the 4-dimensional Weyl anomaly induces the radiation and a strong angular pressure. Using the solution we reproduce the area law by summing up the entropy of the interior. [Phys. Rev. D 93, 044011 (2016)]

EHQG Seminar

- Title
- Baryon interactions from Lattice QCD with physical masses
- Speaker
- Takumi Doi ( Riken)
- Date & Time
- Tuesday, May 17, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Baryon interactions are one of the most basic quantities in nuclear physics. They are also crucial input to understand astrophysical phenomena such as supernovae, structures and mergers of neutron stars, and nucleosynthesis. In this talk, I present first-principles calculations of baryon interactions from lattice QCD. I first review the theoretical formulation, HAL QCD method, to obtain baryon forces which are faithful to the scattering phase shifts. After giving a brief look at lattice results at (unphysically) heavy quark masses, I will present the latest results at physical quark masses, calculated by K-supercomputer and others. Various interactions from nuclear forces to hyperon forces are shown, and their impacts on physical phenomena are discussed. Future prospects toward post-K exascale computing are given as well.

QG Seminar

- Title
- Gauged Nambu-Jona-Lasinio inflation
- Speaker
- Tomohiro Inagaki ( Hiroshima Univ.)
- Date & Time
- Friday, May 13, 2016, 5:00 p.m.
- Place
- QG colloquim (ES744)
- Abstract
- We investigate the gauged Nambu-Jona-Lasinio model in curved spacetime at the large Nc limit and in slow-roll approximation. The model can be described by the renormalization group corrected gauge- Higgs-Yukawa theory with the corresponding compositeness conditions. Evaluating the renormalization group (RG) improved effective action, we show that such model can produce CMB fluctuations and find inflationary parameters: spectral index, tensor-to-scalar-ratio and running of the spectral index. We demonstrate that the model can naturally satisfy the Planck 2015 data and maybe considered as an alternative candidate for Higgs inflation.

EHQG Seminar

- Title
- Topological insulator edge state and D-branes
- Speaker
- Taro Kimura ( Keio Univ.)
- Date & Time
- Tuesday, May 10, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Topological insulator and superconductor (topological phases of matter) provide an interesting opportunity to see how non-perturbative natures of quantum field theory play a role in physical phenomena both for theoretical and experimental studies. One of the most important aspects of them is the renowned relation between bulk and edge states, called the bulk/edge correspon- dence. In this talk, we start with our proposal to connect electron band structure of topological systems and D-branes in superstring theory, and then discuss how it works especially in the study of edge states. We also show generic argument to deal with boundary conditions and its implications for characterization of edge states. This talk is based on a collaboration with K. Hashimoto (Osaka Univ.) arXiv:1509.04676, arXiv:1602.05577 and work in progress.

EHQG Seminar

- Title
- Gravitational waves from second-order scalar perturbations
- Speaker
- Sachiko Kuroyanagi ( C-Lab Nagoya Univ.)
- Date & Time
- Tuesday, April 26, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Inflation is now widely considered to be the most attractive scenario for describing the early evolution of the Universe. One of the reasons why inflation succeeds as a standard paradigm is that it not only solves problems in the big bang theory but also predicts an almost scale-invariant spectrum of scalar (density) perturbations originating from quantum fluctuations. It has been suggested that the scalar perturbations generate gravitational waves at second order. Previous works have shown that gravitational waves are generated efficiently in matter-dominated era due to the growth of density perturbations on sub-Hubble scales. If the Universe have experienced reheating with inflaton oscillations where the Universe behaves like matter-dominated era, large enhancement of gravitational waves is possible in the frequency range of direct detection experiments. We numerically solve the evolution of gravitational waves from second -order scalar perturbations and investigate the effect of the potential decays due to the sound speed at the end of the early matter era. We also discuss about the detectability of the gravitational waves by future experiments.

EHQG Seminar

- Title
- Mesic atoms and mesic nuclei
- Speaker
- Satoru Hirenzaki ( Nara Women's Univ.)
- Date & Time
- Tuesday, April 19, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- Mesic atoms and mesic nuclei are meson-nucleus bound systems, which have been studied for a long time and provided us information on meson properties at finite nuclear density. The study of these hadron exotic systems are one of the natural extension of the traditional nuclear physics to new frontier. And meson properties at finite density are believed to have close connection to the aspects of the symmetry of the strong interaction. In this talk, we will study recent research activities of mesic atoms and mesic nuclei such as pionic atoms, eta(958) mesic nuclei and so on .

EHQG Seminar

- Title
- Self-consistent Calculation of the Sommerfeld Enhancement
- Speaker
- Ryosuke Sato ( Weizmann Institute of Science)
- Date & Time
- Tuesday, April 12, 2016, 5:00 p.m.
- Place
- Science Symposia (ES635)
- Abstract
- The annihilation cross section of the dark matter is one of the most important quantity for the phenomenology of the dark matter. If the dark matter couples with a light force carrier, non-perturbative resummation is required in non-relativistic regime due to so-called Sommerfeld enhancement. A commonly used formula of this cross section is a product of the hard (short-range) scattering cross section and the enhancement factor which is calculated by dark matter two-body wave function. However, it is known that this formula violates the unitarity bound for small velocity if there is zero energy bound state. In this talk, I will discuss the calculation of the dark matter annihilation cross section in non-relativistic quantum mechanics. In our framework, both short-range and long-range effect is treated in a non-perturbative way, and the cross section satisfies the unitarity bound.

C-QG Joint Seminar

- Title
- Cosmology with nonminimal kinetic coupling and a Higgs-like potential
- Speaker
- Jiro Matsumoto ( Kazan Federal University)
- Date & Time
- Thursday, April 7, 2016, 1:00 p.m.
- Place
- ES606
- Abstract
- We consider cosmological dynamics in the theory of gravity with the scalar field possessing the nonminimal kinetic coupling to curvature given as $\kappa G^{\mu\nu}\phi_{,\mu}\phi_{,\nu}$, and the Higgs-like potential $V(\phi)=\frac{\lambda}{4}(\phi^2-\phi_0^2)^2$. Using the dynamical system method, we analyze stationary points, their stability, and all possible asymptotical regimes of the model under consideration. We show that the Higgs field with the kinetic coupling provides an existence of accelerated regimes of the Universe evolution. There are three possible cosmological scenarios with acceleration: (i) {\it The late-time de Sitter epoch} when the Hubble parameter tends to the constant value, $H(t)\to H_\infty=(\frac23 \pi G\lambda\phi_0^4)^{1/2}$ as $t\to\infty$, while the scalar field tends to zero, $\phi(t)\to 0$, so that the Higgs potential reaches its local maximum $V(0)=\frac14 \lambda\phi_0^4$. (ii) {\it The Big Rip} when $H(t)\sim(t_*-t)^{-1}\to\infty$ and $\phi(t)\sim(t_*-t)^{-2}\to\infty$ as $t\to t_*$. (iii) {\it The Little Rip} when $H(t)\sim t^{1/2}\to\infty$ and $\phi(t)\sim t^{1/4}\to\infty$ as $t\to\infty$. Also, we derive modified slow-roll conditions for the Higgs field and demonstrate that they lead to the Little Rip scenario.