## 2014年度セミナー

2014年4月から2015年3月までのセミナーです。

EHQG セミナー

Search for Muon to Electron Conversion at J-PARC - COMET Experiment

2015年2月17日（火） 17:00

Muon to electron conversion in a muonic atom is a process of charged lepton flavor violation (CLFV). The COMET experiment aims to search for muon to electron conversion at J-PARC with single-event sensitivity of 3x10^{-17}. which is about 10,000 improvement over the current limit. Recently the COMET experiment has taken a staged approach. COMET Phase-I. as the first phase, aims at a single-event sensitivity of 3x10^{-15} with a partial part of the full muon beam line and a Phase-I dedicated detector. The funds for COMET Phase-I facility has been approved as the supplemental budget in 2012, and the construction has started in 2013. The physics run is expected to start in 2017. The COMET Phase-II is planed to follow immediately after Phase-I. In this talk, I will describe physics motivation of CLFV, and the details of COMET Phase-I / Phase-II together with the current experimental status.

QG セミナー

Statistics for Physicists

2015年2月16日（月） 14:00

QG研コロキウム室（ES744）

Statistics is a fundamental quantitative tool to analyze data and extract objective conclusions from them. Many people misunderstand that the statistics is already established and stable, say, "dead" methodology, but it is not true at all. In this seminar, we try to introduce the fundamental concept of statistics and some useful methods for the data analysis.

EHQG セミナー

Interplay of kaon condensation and hyperons in high-density hadronic matter and its implications for neutron-star phenomena

2015年2月10日（火） 17:00

Neutron stars are expected to have highly dense matter in the inner core region with baryon density several times larger than that of usual atomic nuclei. It is an important issue to understand the equation of state (EOS) of highly dense matter and properties of various hadronic phases. In such highly dense matter, mesons and baryons having the strangeness'' quantum number can appear as well as nucleons (neutrons and protons) and leptons. We consider possible coexistence of antikaons in Bose-Einstein condensation and hyperons in highly dense matter and discuss the effects of such multi-strangeness system on the structure of neutron stars through analyzing mass-radius relations. On the basis of the relativistic mean-field theory for baryon-baryon interaction, combined with the effective chiral Lagrangian incorporating $\bar K$-baryon and nonlinear $\bar K-\bar K$ interactions, we obtain onset density of kaon condensation in the hyperon-mixed matter and the EOS of the developed phase. It is shown that coexistence of kaon condensation and hyperon-mixed matter is plausible, but it necessarily leads to significant softening of the EOS, which should be reconciled with recent observations of massive neutron stars.

QG セミナー

Geodesics in Myers-Perry black holes and in Emparan-Reall black rings

2015年2月9日（月） 15:30

QG研コロキウム室（ES744）

Geodesics in various black holes have been extensively studied to gain new insights into background geometries and to understand physical phenomena related to test particles. In this talk, we focus on geodesics in Myers-Perry black holes and Emparan-Reall black rings in higher-dimensional spacetimes. We discuss non-trivial physics of the geodesics system such as integrability relevant to hidden symmetries, stable bound particle orbits, and the Newtonian limit.

EHQG セミナー

Massive gravity and supergravity

2015年2月3日（火） 17:00

In the massive gravity theory proposed in 2011 by de Rham, Gabadadze and Tolley, we give an explicit proof for the absence of the Boulware-Deser ghost on arbitrary admissible background. We also discuss the possibility for supersymmetrizing this dRGT theory, and report the massive supergravity action at the linearlized level.

EHQG セミナー

Hybrid Monte Carlo on Lefschetz thimbles

2015年1月27日（火） 17:00

We formulate a hybrid Monte Carlo algorithm which is applicable to lattice theories defined on Lefschetz thimbles. In the algorithm, any point (field configuration) on a thimble is parametrized uniquely by the flow-direction and the flow-time defined at a certain asymptotic region close to the critical point, and it is generated by solving the gradient flow equation downward. Molecular dynamics is then formulated as a constrained dynamical system, where the equations of motion with Lagrange multipliers are solved by the second-order constraint-preserving symmetric integrator. The algorithm is tested in the lambda $\phi^4$ model and chiral random matrix model at finite density.

EHQG セミナー

Conjectures on physics behind the standard model

2015年1月27日（火） 15:00

We reconsider naturalness and the gauge hierarchy problem from the viewpoint of a high-energy physics or a fundamental theory, motivated by the alternative scenario that the standard model holds up to a high-energy scale such as the Planck scale. For naturalness, we propose a calculation scheme of radiative corrections utilizing a hidden duality relating integration variables, that justifies the subtraction of quadratic divergences. For the gauge hierarchy problem, we give a conjecture that theories with hidden fermionic symmetries can be free from the problem and become a candidate of physics behind and/or beyond the standard model, and present a prototype model for the grand unification.

EHQG セミナー

(p,q) webs, the T_N theory and Higgsing

2015年1月13日（火） 17:00

We study the 5d T_N theory, which is a non-Lagrangian theory with three SU(N) flavor symmetries, by using a web of (p, q) 5-branes. Due to its web diagram realization, we can make use of the refined topological vertex to compute the exact partition functions of the 5d T_N theory as well as the Higgsed 5d T_N theories. In order to obtain the correct partition functions, we need to eliminate the contributions that are decoupled from the theories from the refined topological vertex computation. The decoupled factors can be easily identified from the web diagrams.We exemplified our method by calculating the partition functions of the E6, E7 and E8 theories. The computation also uncovers the relation between the mass-deformation of the T_N theory with a Lagrangian linear quiver theory.

EHQG セミナー

New Physics at SuperKEKB/Belle II

2014年12月16日（火） 17:00

After a brief review of the physics achievement at B factories and the plan of the SuperKEKB/Belle II experiment, I will discuss the following new physics possibilities at SuperKEKB/Belle II: semitauonic B decays, right-handed b to u current and lepton flavor violation in tau decays.

EHQG セミナー

Effective field theory for spacetime symmetry breaking

2014年12月9日（火） 17:00

The effective field theory approach based on the underlying symmetry structures provides a powerful framework for low-energy dynamics in the symmetry broken phase. Just as the internal symmetry case, one standard approach for spacetime symmetry breaking is the coset construction. It is based on the breaking pattern of global spacetime symmetries and contains additional Nambu-Goldstone (NG) fields (the number of broken global spacetime symmetries does not coincide with that of physical NG fields in general). Correspondingly, it has to be implemented with the so-called inverse Higgs constraints to remove such redundant NG fields. Although the coset construction captures a certain aspects of spacetime symmetry breaking, its understanding seems to be still incomplete compared to the internal symmetry case and a lot of attention has been paid recently for further understanding. In this talk, I would like to revisit the effective action construction for spacetime symmetry breaking from the local symmetry point of view. Since NG fields are generated by local transformations of order parameters, such a local picture provides a correct identification of physical NG fields. I will first illustrate that the local picture becomes important when we take into account massive modes associated with symmetry breaking. I will then revisit the coset construction form the local symmetry point of view. (based on a work with Yoshimasa Hidaka and Gary Shiu)

EHQG セミナー

Exotic Five-branes

2014年11月25日（火） 17:00

In this seminar I discuss exotic branes in string theory. First, I briefly mention the emergence of exotic branes via string dualities. Here I introduce various exotic five-branes in type II, type I and heterotic string theories. Next, I focus on the exotic 522-brane. The exotic 522-brane can be obtained from NS5-brane via T-duality. Though its supergravity description is not globally well-defined, I can construct it from the perspective of 2D supersymmetric gauge theory, called the gauged linear sigma model (GLSM). In particular, I show that the exotic'' strcuture of the 522-brane indeed originates from the string winding modes. Finally, I try to discuss the importance of the stringy spacetime picture beyond the Einstein gravity.

EHQG セミナー

Turbulent meson condensation in quark deconfinement

2014年11月18日（火） 17:00

In a QCD-like strongly coupled gauge theory at large Nc, using the AdS/CFT correspondence, we find that heavy quark deconfinement is accompanied by a coherent condensation of higher meson resonances. This is revealed in non-equilibrium deconfinement transitions triggered by static, as well as, quenched electric fields even below the Schwinger limit. There, we observe a "turbulent" energy flow to higher meson modes, which finally results in the quark deconfinement. Our observation is consistent with seeing deconfinement as a condensation of long QCD strings. (ArXiv:1408.6293)

EHQG セミナー

Dynamical generation of fermion mass hierarchy in an extra dimension

2014年11月11日（火） 17:00

We first discuss that extra dimensions may naturally explain the flavor structures of quarks and leptons in the standard model, in particular, the origin of the fermion generation and the fermion mass hierarchy. We then propose a five-dimensional gauge theory on an interval, and discuss the possibility of a dynamical generation of a fermion mass hierarchy. By introducing point interactions, we can produce triply-degenerated chiral zero modes and each zero mode localizes at a different position of the extra dimension. We find that the 4d masses of the zero mode fermions crucially depend on the positions of the point interactions, and that the positions of the point interactions can be determined by minimizing the 1-loop effective potential. Then, we will show that the configuration of the point interactions, which are determined dynamically, naturally leads to a fermion mass hierarchy.

EHQG セミナー

dS/CFT and prospects on cosmology

2014年11月4日（火） 17:00

We address the possibility that the inflationary universe may be holographically described by means of a quantum field theory which lives in one fewer dimension. For this purpose, we compute the correlation functions of the curvature perturbation holographically and compare the result to the one obtained from the standard cosmological perturbation theory. We also discuss the prospect of holographic inflation scenario on the observational cosmology.

EHQG セミナー

Boosted Higgs shapes at LHC

2014年10月28日（火） 17:00

The inclusive Higgs production rate through gluon fusion has been measured to be in agreement with the SM. We show that even if the inclusive Higgs production rate is very SM like, a precise determination of the boosted Higgs transverse momentum shape offers the opportunity to see effects of natural new physics. We show in detail how a measurement at high pT higgs via H to tautau mode could be performed and demonstrate that it offers a compelling alternative to the ttH channel.

EHQG セミナー

Dark energy and dark matter in the ghost-free bigravity theory

2014年10月21日（火） 17:00

We study dynamics of Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime based on the ghost-free bigravity theory. We find two stable attractors for spacetime with “twin” dust matter fields: One is de Sitter accelerating universe and the other is matter dominated universe. A considerable number of initial data leads to de Sitter universe, although we also find matter dominated universe or spacetime with a future singularity for some initial data. The cosmic no-hair conjecture does not exactly hold, but the Lambda-CDM model is found naturally as an attractor. We also analyze the possibility for the twin matter fluid to be dark matter in “our world". Dark matter appears as the galactic missing mass, is required in the cosmic structure formation and is found in the cosmic pie (the content of the Universe). We show the bigravity theory can also explain those facts by twin matter fluid when the Compton wavelength of the massive graviton is about kpc.

アンルー放射に関する理論予言

2014年10月16日（木） 14:00

2014年10月15日（水）〜17日（金）

EHQG セミナー

Lattice energy-momentum tensor from the Yang-Mills gradient flow

2014年10月14日（火） 17:00

Since lattice regularization explicitly breaks the translational invariance, the construction of a lattice operator that reproduces the correctly normalized conserved energy-momentum tensor in the continuum limit has been an awkward problem. In this talk, I point out that the Yang-Mills/Wilson gradient flow---its applications in lattice QCD have intensively been studied in recent years---can be useful also in this context. I present what has been done, what is currently investigated and some open problems.

EHQG セミナー

Entanglement entropy and renormalization group flow

2014年9月30日（火） 17:00

Entanglement entropy is a useful order parameter charactering phases in quantum field theories in various dimensions. For example, it can capture confinement/deconfinement and quantum phase transitions. The analytic computations, however, are limited to special cases such as conformal and free field theories. In this talk, I would like to elucidate various properties of entanglement entropy in gapped systems by using both field theoretic and holographic approaches. I will also discuss how entanglement entropy behaves under a perturbation of CFT by a relevant operator and point out that the perturbative calculation may fail depending on the conformal dimension

EHQG セミナー

CP-safe Gravity Mediation and Muon g-2

2014年7月22日（火） 17:00

We propose a CP-safe gravity mediation model, where the phases of the Higgs B parameter, scalar trilinear couplings and gaugino mass parameters are all aligned. Since all dangerous CP violating phases are suppressed, we are now safe to consider low-energy SUSY scenarios. For an application, we consider a gravity mediation model explaining the observed muon g-2 anomaly. It is also shown that the CP-safe gravity mediation model is consistent with a sequestered Kahler potential.The CP-safe property originates from two simple assumptions: the SUSY breaking in the Kahler potential and a shift symmetry of a SUSY breaking field Z. Consequently, the imaginary part of Z behaves as a QCD axion, leading to an intriguing possibility; the strong CP problem in QCD and the SUSY CP problem are solved simultaneously.

QG セミナー

Causality and Hyperbolicity of Lovelock Theories

2014年7月22日（火） 14:00

QGコロキウム室（ES744）

In Lovelock theories, gravity can travel faster or slower than light. The causal structure is determined by the characteristic hypersurfaces. We generalise a recent result of Izumi to prove that any Killing horizon is a characteristic hypersurface for all gravitational degrees of freedom of a Lovelock theory. Hence gravitational signals cannot escape from the region inside such a horizon. We investigate the hyperbolicity of Lovelock theories by determining the characteristic hypersurfaces for various backgrounds. First we consider Ricci flat type N spacetimes. We show that characteristic hypersurfaces are generically all non-null and that Lovelock theories are hyperbolic in any such spacetime. Next we consider static, maximally symmetric black hole solutions of Lovelock theories. Again, characteristic surfaces are generically non-null. For some small black holes, hyperbolicity is violated near the horizon. This implies that the stability of such black holes is not a well- posed problem.

EHQGセミナー

Quantum Entanglement in de Sitter Space

2014年7月15日（火） 17:00

We consider the entanglement entropy of a free massive scalar field in the one parameter family of α-vacua in de Sitter space by using a method developed by Maldacena and Pimentel. An α-vacuum can be thought of as a state filled with particles from the point of view of the Bunch-Davies vacuum. Of all the α-vacua we find that the entanglement entropy takes the minimal value in the Bunch-Davies solution. We also calculate the asymptotic value of the R\'enyi entropy and find that it increases as α increases. We argue these features stem from pair condensation within the non-trivial α-vacua where the pairs have an intrinsic quantum correlation.

EHQGセミナー

Tensor Renormalization Group Study of Lattice Schwinger Model

2014年7月8日（火） 17:00

The tensor renormalization group is one of the successful methods to avoid the numerical sign problem, though the practical calculations in higher dimensions are beyond the reach of current computer facilities. As a first step toward lattice QCD, we apply it to two-dimensional lattice QED (lattice-regularized Schwinger model). In this talk, I would like to show its validity through the numerical investigation on the phase structure with the theta vacuum term.

QGセミナー

Twistorial models for spinning particles

2014年7月7日（月） 16:00

QGコロキウム室（ES744）

Twistor theory was proposed by Penrose in 1967. It is known that twistor theory is a useful framework for describing massless particles. As for massive particles, they can be described by N($\geq$ 2) twistor variables entailing a SU(N) internal symmetry. In this talk, we first study a twistorial model for massless spinning particles. This model can be regarded as a modification of an earlier model studied by Shirafuji. Carrying out the canonical quantization, we show that our model describes massless particles with integer or half-integer spins. Furthermore, we systematically derive equations of motion for higher spin fields within the framework of the model. Next, as an extension of the massless model, we construct a massive spinning particle model with SU(2) gauge symmetry, which provides a realization of the SU(2) internal symmetry. We examine properties of the SU(2) symmetry. Reference: S. Deguchi, S. Negishi, S. Okano and T. Suzuki, Int. J. Mod. Phys. A 29 (2014) 1450044, [arXiv:1309.4169]

EHQGセミナー

M5-branes and Wilson surfaces in AdS_7/CFT_6 correspondence

2014年7月1日（火） 17:00

We consider the correspondence between M-theory on AdS_7 x S^4 and 6d (2,0) theory. We focus on the expectation values of Wilson surfaces of anti-symmetric representations and symmetric representations. In the M-theory side they correspond to M5-branes wrapping on AdS_3 x S^3. Recently it have been shown that these expectation values are expressed in terms of the Chern-Simons matrix model by localization in 5d maximally supersymmetric Yang-Mills theory. We use this result and evaluate the expectation values in the M-theory side and the CFT side, and find the perfect agreement.

EHQGセミナー

Higgs inflation at string scale

2014年6月24日（火） 17:00

The Higgs boson discovered at LHC has been very much Standard-Model-like. Its observed mass indicates that, if we extrapolate the SM towards very high scales, the Higgs potential becomes nearly flat around the string scale. I will discuss implications of this fact on an inflation scenario in which the Higgs field plays a role of inflaton. I will also disscuss the recent claim by BICEP2 of the discovery of large tensor mode in the cosmic microwave background, and show its possible realization in the Higgs inflation scenario.

EHQGセミナー

Universal physics of three bosons with isospin

2014年6月17日（火） 17:00

We show that there exist two types of universal phenomena for three-boson systems with isospin degrees of freedom. In the isospin symmetric limit, there is only one universal three-boson bound state with the total isospin one, whose binding energy is proportional to that of the two-boson bound state. With large isospin symmetry breaking, the standard Efimov states of three identical bosons appear at low energies. Both phenomena can be realized by three pions with the pion mass appropriately tuned in lattice QCD simulations, or by spin-one bosons in cold atom experiments. Implication to the in-medium softening of multi-pion states is also discussed.

EHQGセミナー

Realizing the Standard Model particles in the IIB matrix model

2014年6月10日（火） 17:00

We discuss how the Standard Model particles appear from the IIB matrix model, which is considered to be a nonperturbative formulation of superstring theory. We point out that introduction of a matrix version of the warp factor is needed to realize chiral fermions in the model. Based on this new insight, we show that two generations of the Standard Model fermions can be realized by considering a rather generic configuration of fuzzy S^2 and fuzzy S^2×S^2 in the extra dimensions. We also show that three generations can be obtained by squashing one of the S^2's that appear in the configuration. Chiral fermions appear at the intersections of the fuzzy manifolds with nontrivial Yukawa couplings to the Higgs field, which can be calculated from the overlap of their wave functions.

EHQGセミナー

Holographic superconductivity in the large D expansion

2014年6月3日（火） 17:00

We consider holographic superconductivity by using the expansion in the inverse of the spacetime dimensions, D. Large D expansion method gives simple analytic expressions for the critical temperature in good accuracy compared with numerical results. From this result we can find the universal features of holographic superconductivity in the large D limit and easily compute the backreaction effects of the gravity on the critical temperature.

EHQGセミナー

ATOM/Fastlim: Recasting LHC constraints on new physics models

2014年5月27日（火） 17:00

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.

QGセミナー

The effective field theory of inflation/dark energy and the Horndeski theory

2014年5月26日（月） 14:00

QG研コロキウム室（ES744）

The effective field theory (EFT) of cosmological perturbations is a useful framework to deal with the low-energy degrees of freedom present for inflation and dark energy. We review the EFT for modified gravitational theories by starting from the most general action in unitary gauge that involves the lapse function and the three-dimensional geometric scalar quantities appearing in the Arnowitt-Deser-Misner (ADM) formalism. Expanding the action up to quadratic order in the perturbations and imposing conditions for the elimination of spatial derivatives higher than second order, we obtain the Lagrangian of curvature perturbations and gravitational waves with a single scalar degree of freedom. The resulting second-order Lagrangian is exploited for computing the scalar and tensor power spectra generated during inflation. We also show that the most general scalar-tensor theory with second-order equations of motion-Horndeski theory-belongs to the action of our general EFT framework and that the background equations of motion in Horndeski theory can be conveniently expressed in terms of three EFT parameters. Finally we study the equations of matter density perturbations and the effective gravitational coupling for dark energy models based on Horndeski theory, to confront the models with the observations of large-scale structures and weak lensing.

EHQGセミナー

Beyond the SM with Scale Invariance and NG Dark Matter

2014年5月20日（火） 17:00

We consider a classically scale invariant extension of the standard model, in which the scale invariance is broken by dynamical chiral symmetry breaking in a QCD-like hidden sector. Because of the unbroken SU(3) flavor symmetry, the quasi Nambu-Goldstone bosons are stable so that they can become dark matter particles. We study their properties with the Nambu-Jona-Lasinio method and also discuss the phase transition in the dark sector as well as in the electroweak sector.

EHQGセミナー

QCD inhomogeneity favored or disfavored by the magnetic field?

2014年5月13日（火） 17:00

I will summarize recent progress in the understanding of QCD matter in extreme environments such as high baryon density, strong magnetic field, and strong gravity. I will put my emphasis on the possibility of inhomogeneous states induced by density, which should be more favored with strong magnetic field due to the dimensional reduction. However, our holographic QCD model analysis implies a tendency opposite to this expectation. I will explain how to understand this result in analogy to the pion condensation in nuclear matter. If I have time, I will briefly mention on a new direction of QCD research in curved space-time.

EHQGセミナー

BICEP2 implications for particle physics and cosmology

2014年4月22日（火） 17:30

I will discuss implications of the recent BICEP2 results for particle physics and cosmology, after giving a brief review on the inflation, scalar and tensor mode perturbations and CMB.

EHQGセミナー

General relativity, cosmology and geometry

2014年4月15日（火） 17:00

Using the basics of geometry, we can have some implications for cosmology/astrophysics in elegant way. In this seminar, I will review a part of my research. In particular, I will focus on the four topics (shortly for each): Size of black holes in inflationary universe. Basic equation in Randall-Sundrum braneworld, DGP bubble. Uniqueness/non-uniqueness of higher dimensional black holes. Looking for models consistent with positive mass. For non-expert audience, I will give a brief introduction of general relativity too.

EHQGセミナー

Two-Higgs-doublet models with gauged U(1) Higgs symmetry

2014年4月8日（火） 17:00

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 Type-I and Type-II 2HDMs with the U(1)_H symmetry. We investigate the constraints on the scalars and U(1)_H gauge interactions in the both types. Then we discuss the dark matter physics: the thermal relic density, direct and indirect detections. The additional gauge interaction plays a crucial role in reducing the relic density, and we find that O(10) GeV dark matter scenario, which is disfavored in the ordinary Inert Doublet Model with Z_2 Higgs symmetry, is revived in our type-I 2HDM. One of the ways to prove our model may be the indirect astrophysical observations, so that we calculate the velocity-averaged cross section for the dark matter annihilation in the dwarf spheroidal galaxies, and consider the constraints on our scenario from the Fermi-LAT by observing the γ-ray flux in the type-I 2HDM. We also comment on our recent results in our type-II 2HDM.