2017年度のセミナー

Date/Place Nov. 28th (Tues.) 15:30-16:30 / H711
Name Jnanadeva Maharana (Bhubaneswar, India)
Title T-duality and Scattering of String States (Slides)
Abstract I shall briefly recall the salient features of T-duality for a closed bosonic string compactified on a d-dimensional torus. The vertex operators associated with the closed compactified bosonic string in the massless sector will be introduced. They are defined in the weak field approximation. The symmetry properties of the S-matrix elements under T-duality for the moduli will be discussed. The Kawai-Lewellyn-Tye approach will be utilzed to show transformations of S-matrix elements under T-duality.

 

Date/Place Nov. 21th (Tues.) 15:30-16:30 / H711
Name Nilay Kundu (YITP, Kyoto Univ.)
Title Second law of black-hole thermodynamics in Lovelock theories of gravity (Slides)
Abstract In this talk we will discuss the construction of an entropy function for dynamical black holes in a specific higher derivative theory of gravity, namely Lovelock theories. As is known, in classical general relativity described by Einstein-Hilbert gravity, black holes behave as thermodynamic objects. The first law of black hole mechanics extends to higher derivative theories via the Noether charge construction of Wald. In order to extend the second law (which in Einstein-Hilbert theory owes to Hawking's area theorem) to higher derivative theories one needs a notion of entropy for dynamical black holes beyond the Noether charge construction. We will discuss one such possible extension for the Lovelock theories of gravity, treating the higher derivative terms as perturbations to Einstein's gravity.

 

Date/Place Nov. 14th (Tues.) 15:30-16:30 / H711
Name Masafumi Fukuma (Kyoto Univ.)
Title Parallel tempering algorithm for integration over Lefschetz thimbles and distance between configurations in MCMC simulations
Abstract The algorithm based on integration over Lefschetz thimbles is a promising method to resolve the sign problem for complex actions. However, this algorithm often encounters a difficulty in actual Monte Carlo calculations because the configuration space is not easily explored due to the infinitely high potential barriers between different thimbles. In this talk, I would like to explain our proposal to use the flow time of the antiholomorphic gradient flow as a tempering parameter for the highly multimodal distribution. In this algorithm, we can take the maximum flow time to be sufficiently large such that the sign problem disappears there, and two separate modes are connected through configurations at small flow times. I present results for the (0+1)-dimensional massive Thirring model at finite density and show that analytic results are correctly reproduced. If there is time left, I also would like to discuss our recent proposal to define distances between configurations in Markov chain Monte Carlo simulations, and argue that an AdS-like geometry naturally emerges as a result of optimization on the tempering method.

 

Date/Place Nov. 7th (Tues.) 15:30-16:30 / H711
Name Haruki Watanabe (Univ. of Tokyo)
Title Symmetry-Based Indicator of Band Topology (Slides)
Abstract he interplay between symmetry and topology leads to a rich variety of electronic topological phases, protecting states such as the topological insulators and Dirac semimetals. Previous results, like the Fu-Kane parity criterion for inversion-symmetric topological insulators, demonstrate that symmetry labels can sometimes unambiguously indicate underlying band topology. In this talk we develop a systematic approach to expose all such symmetry-based indicators of band topology in all the 230 space groups. This talk is based on arXiv:1703.00911, 1707.01903, 1709.06551, 1710.07012.

 

Date/Place Oct. 31th (Tues.) 15:30-16:30 / H711
Name Takuya Kanazawa (RIKEN)
Title Random matrices for supersymmetric SYK models (Slides)
Abstract The Sachdev-Ye-Kitaev (SYK) model is a useful arena to study quantum chaos and holography. In this talk, I first review the SYK model with supersymmetry (SUSY) and then present its complete symmetry classification based on the ten-fold way of random matrix theory (RMT). I will also show numerical evidence that demonstrate precise agreement between energy level fluctuations of SYK models with N=1&2 SUSY and those of RMT. This work is based on my paper JHEP09(2017)050 (arXiv:1706.03044 [hep-th]).

 

Date/Place Oct. 24th (Tues.) 15:30-16:30 / H711
Name Minoru Tanaka (Osaka Univ.)
Title Towards atomic neutrino spectroscopy (Slides)
Abstract Radiative emission of neutrino pair (RENP) is a novel tool of neutrino physics. It turns out that the photon spectrum in the RENP provides us important information of neutrino properties to be unveiled, such as absolute mass, Dirac/Majorana nature and CP violating phases. Although the RENP process inevitably occurs in the standard model, a rate enhancement mechanism is mandatory to observe it and prove the nature of neutrinos. In this seminar, I explain the principle of the rate enhancement using quantum coherence in a macroscopic target and how the neutrino properties affect the RENP spectrum. I also present some experimental results that exhibit the enhancement mechanism.

 

Date/Place Oct. 17th (Tues.) 15:30-16:30 / H711
Name Tatsuhiro Misumi (Akita Univ.)
Title Exact Resurgent Trans-series and Complex Solutions to All Orders (Slides)
Abstract We discuss the full resurgence structure in quantum mechanical limit of CP^N‐1 and Sine-Gordon models on R^1 x S^1. We complexify the variables and consider the trans‐series composed of a perturbative series and non‐perturbative contributions from real and complex solutions. The perturbative series of the ground state energy is calculated by use of Bender‐Wu recursion relation and the associated Borel resummation is derived. The non‐perturbative contribution is derived via Lefschetz thimble integrals associated with all the real and complex multi-bion solutions. We show that the imaginary ambiguities arising from these contributions cancel out. We find out that the exact ground state energy agrees with the full trans‐series composed of the perturbative and non‐perturbative contributions. This is the first result in which the full resurgence structure in the trans‐series including contributions of complexified saddle points is clarified.

 

Date/Place Oct. 10th (Tues.) 15:30-16:30 / H711
Name Masahiro Takada (Kavli IPMU)
Title Microlensing constraints on 10^{-10}Msun-scale primordial black holes from high-cadence observation of M31 with Hyper Suprime-Cam(Slides)
Abstract We use the Subaru Hyper Suprime-Cam (HSC) to conduct a high-cadence (2 min sampling) 7~hour long observation of the Andromeda galaxy (M31) to search for the microlensing magnification of stars in M31 due to intervening primordial black holes (PBHs) in the halo regions of the Milky Way (MW) and M31. The combination of an aperture of 8.2m, a field-of-view of 1.5 degree diameter, and excellent image quality (~ 0.6'') yields an ideal dataset for the microlensing search. If PBHs in the mass range M_PBH=[10^{-13},10^{-6}]Msun make up a dominant contribution to dark matter (DM), the microlensing optical depth for a single star in M31 is tau~10^{4}-10^{-7}, owing to the enormous volume and large mass content between M31 and the Earth. The HSC observation allows us to monitor more than tens of millions of stars in M31 and in this scenario we should find many microlensing events. To test this hypothesis, we extensively use an image subtraction method to efficiently identify candidate variable objects, and then monitor the light curve of each candidate with the high cadence data. Although we successfully identify a number of real variable stars such as eclipse/contact binaries and stellar flares, we find only one possible candidate of PBH microlensing whose genuine nature is yet to be confirmed. We then use this result to derive the most stringent upper bounds on the abundance of PBHs in the mass range. When combined with other observational constraints, our constraint rules out almost all the mass scales for the PBH DM scenario where all PBHs share a single mass scale.

 

Date/Place Oct. 3rd (Tues.) 15:30-16:30 / H711
Name Kei. Yamamoto (Nagoya Univ.)
Title New Physics implications of direct CP violation of Kaon decay(Slides)
Abstract Flavor physics is one of the most powerful probes of physics beyond the standard model (SM), and sensitive to high scale new physics (NP). Recently, some discrepancies with the SM are reported in several observables in Kaon and B meson decays. One of the exciting topics is the anomaly in the direct CP violation of Kaon(epsilon'/epsilon). Current progress of lattice calculation enables us to predict epsilon'/epsilon accurately, and there was a discrepancy between the SM prediction and the experimental results at the 2.9 sigma level. In this talk, I will discuss the SUSY contributions on epsilon'/epsilon and show the correlations with other observables.

 

Date/Place Sep. 26th(Tue.) 15:30-16:30 / H711
Name Masashi Kimura (Univ. of Lisbon)
Title Mass Ladder Operators from Spacetime Conformal Symmetry (Slides)
Abstract We introduce a novel type of ladder operators, which map a solution to the massive Klein-Gordon equation into another solution with a different mass. It is shown that such operators are constructed from closed conformal Killing vector fields in arbitrary dimensions if the vector fields are eigen vectors of the Ricci tensor. As an example, we explicitly construct the ladder operators in AdS spacetime. It is shown that the ladder operators exist for masses above the Breitenlohner-Freedman bound. We also discuss their applications, the relation between supersymmetric quantum mechanics, some phenomenon around extremal black holes whose near horizon geometry is AdS2 and possible applications to AdS/CFT correspondence.

 

Date/Place Jul. 18th(Tue.) 15:30-16:30 / H711
Name Yukio Kaneko (Tohoku University)
Title Gravity theory based on Poisson geometry
Abstract Gravity on a noncommutative space would give an effective description of quantum gravity. The semi-classical approximation of the noncommutativity space is described by the Poisson structure. Since the Poisson geometry is a geometric framework which contains both Riemann and Poisson structures, gravity based on the Poisson geometry would be a semi-classical approximation of quantum gravity. We formulated the contravariant gravity which is given by the Einstein-Hilbert type action based on the Poisson geometry. In this talk, I will explain basics of the Poisson geometry and the contravariant gravity at first, then I will discuss relations to the noncommutative gauge theory and string theory.

 

Date/Place Jul. 11th(Tue.) 15:30-16:30 / H711
Name Ya-Juan Zheng (Osaka University)
Title Probing Higgs CP properties with htt at the e+e− collider
Abstract We study consequences of CP violation in the htt Yukawa coupling in the process e+e− → h(125) tt. The helicity amplitudes are calculated in the ttbar rest frame, where the initial ee current and the final Higgs boson have the same three-momentum. CP violating asymmetries appear not only in the azimuthal angle between the e+e− plane and the tt ̄plane about the Higgs momentum direction, but also in the correlated decay angular distributions of t and t. Complete description of the production and decay angular distributions are obtained analytically, and we study the ultimate sensitivity to the CP violating htt ̄ coupling at the ILC in its various running scenarios. Our analysis shows that the possibility of discovering CP violating htt coupling improves significantly by studying tt ̄ decay angular correlations, and more importantly by increasing the energy from √s = 500 GeV to 550 GeV. Beam polarization does not affect much the sensitivity to CP violation, but it is useful to determine the relative sign between the htt coupling and the hZZ coupling.

 

Date/Place Jul. 4th(Tue.) 15:30-17:00 / Nambu Hall
Name Masatoshi Sato (YITP, Kyoto University)
Title K理論とトポロジカル結晶物質 (Slides)
Abstract 多数の自由度が集まることによって元の構成要素がもち得なかった性質が生じる。場の量子論における重要な問題の一つはこのような「相」としてどのようなものがあるかを明らかにすることである。トポロジカル相とは、そのような相の一つであり、絶縁体や超伝導体のようなギャップのある系だけでなく、電子系でワイルフェルミンやディラックフェルミオンを実現する半金属などギャップのない系でも実現されていることが知られている。本講演では、K理論を用いたトポロジカル物質の定式化および分類理論を紹介する。

 

Date/Place June. 27th(Tue.) 15:30-16:30 / H711
Name Tsuyoshi Yokoya
Title Entanglement Entropy for 2D Gauge Theories with Matters (Slides)
Abstract We investigate the entanglement entropy in 1+1-dimensional SU(N) gauge theories with matter fields using the lattice regularization. Here we use extended Hilbert space definition for entanglement entropy, which contains three contributions; (1) classical Shannon entropy associated with superselection sector distribution, where sectors are labelled by irreducible representations of boundary penetrating fluxes, (2) logarithm of the dimensions of their representations, which is associated with “color entanglement”, and (3) EPR Bell pairs, which give “genuine” entanglement. We explicitly show that entanglement entropies (1) and (2) above indeed appear for various multiple “meson” states in gauge theories with matter fields. Furthermore, we employ transfer matrix formalism for gauge theory with fundamental matter field and analyze its ground state using hopping parameter expansion (HPE). We evaluate the entanglement entropy for the ground state and show that all (1), (2), (3) above appear in the HPE, though the Bell pair part (3) appears in higher order than (1) and (2) do. With these results, we discuss how the ground state entanglement entropy in the continuum limit can be understood from the lattice ground state obtained in the HPE.

 

Date/Place June. 20th(Tue.) 15:30-16:30 / H711
Name Seiji Terashima(YITP, Kyoto University)
Title A Note on Sachdev-Ye-Kitaev Like Model without Random Coupling
Abstract We study a description of the large N limit of the Sachdev-Ye-Kitaev (SYK) model in terms of quantum mechanics without quenched disorder. Instead of random couplings, we introduce massive scalar fields coupled to fermions, and study a small mass limit of the theory. We show that, under a certain condition, the correlation functions of fermions reproduce those of the SYK model with a temperature dependent coupling constant in the large N limit. We also discuss a supersymmetric generalization of our quantum mechanical model. As a byproduct, we develop an efficient way of estimating the large N behavior of correlators in the SYK model.

 

Date/Place Jun. 13th(Tue.) 15:30-16:30 / H711
Name Takashi Shimomura (University of Miyazaki)
Title Search for Lmu-Ltau gauge boson at Belle-II and neutrino beam experiment(Slides)
Abstract Recently, some anomalies have been reported by IceCube collaboration on cosmic neutrino flux and Atomki collaboration on electron-positron emission in Beryllium decay. There is also long-standing discrepancy in muon g-2. These anomalies and discrepancy can be regarded as suggestion of MeV-scale new particle. In this seminar, I show that the gauge boson associated with U(1)_{Lmu-Ltau} gauge symmetry can explain the IceCube anomaly as well as muon g-2. Then, such a gauge boson can be searched at Belle-II through one-photon + missing event and at neutrino beam experiments through neutrino trident production processes.

 

Date/Place June. 6th(Tue.) 15:30-16:30 / H711
Name Hiroshi Ohki(Nara Women's University)
Title Lattice calculation of the nucleon EDM
Abstract High-Precision nuclear physics is a vital part of searches for new physics. In particular, observation of permanent electric dipole moments (EDMs) of nucleons (and nuclei) would be direct evidence for violation of CP symmetry. We discuss the methodology for computing the nucleon form factors and EDM on a lattice, and find that in previous lattice calculations they lead to spurious contributions from the Pauli form factor due to inadequate definition of the form factors when parity mixing of nucleon fields is involved. We perform lattice calculations of nucleon EDM induced by CP-odd quark-gluon (chromo EDM) interactions using two different methods: from the form factor and the energy shift in the background electric field in the presence of the CP-odd interaction, and show that two results are consistent if the new formula is used. We also discuss some implications for the lattice results of the theta-induced EDM.

 

Date/Place June. 2nd(Fri.) 13:00-14:00 / Communication space on 7th floor
Name Akio Tomiya(Central China Normal University)
Title 物理学科ならわかる機械学習(Slides)
Abstract 近年話題の機械学習は、実は線形代数と微積分、最小二乗法から理解できる。 本講義では、微分の応用である、最小二乗法から始め、深層学習などの外観を説明する。

 

Date/Place May. 30th(Tue.) 15:30-16:30 / H711
Name Norihiro Tanahashi (Osaka University)
Title Wave propagation and shock formation in the most general scalar-tensor theory(Slides)
Abstract We study the wave propagation in the most general scalar-tensor theory focusing on the shock formation caused by nonlinear effects. For this study we use the Horndeski theory, which is the most general scalar-tensor theory that gives second order equations of motion. The propagation speeds of the scalar field wave and gravitational wave depend on the environment and also their own amplitudes in this theory, and it causes various phenomena which cannot be seen in GR. To study the shock formation, we focus on transport of weak discontinuity in the metric and scalar field. We find that amplitude of the discontinuity generically diverges within finite time, which corresponds to shock formation. It turns out that the canonical scalar field and the scalar DBI model, among the theories described by the Horndeski theory, are free from such shock formation even on nontrivial background. We also observe that gravitational wave is protected against shock formation when the background has some symmetries at least. We will discuss implications of these findings.

 

Date/Place May. 23th(Tue.) 15:30-16:30 / H711
Name Takaki Matsumoto (University of Tsukuba)
Title Information metric for the matrix geometry(Slides)
Abstract Noncommutative geometry is a promising candidate for the quantum geometry of space-time. Matrix geometry is known as a typical example of noncommutative geometry and defined by a sequence of some Hermitian matrices. Matrix geometry also appears naturally in describing the fundamental objects in the string/M theory and plays an important role in formulating these theories. However, the relation between the matrix geometry and Riemannian geometry, which plays a crucial role in describing theories of classical gravity, has not been fully understood so far. In order to understand this relation, we introduce a recently proposed method, which is based on the notion of the coherent states. This method makes it possible to relate matrix geometry to smooth differential geometry. In this formulation, we introduce the information metric and show that the information metric works as a Riemannian metric on the corresponding smooth geometry. The information metric is expressed in terms of given matrices and therefore regarded as a new object that characterize the matrix geometry.

 

Date/Place May. 16th(Tue.) 15:30-16:30 / H711
Name Akihiro Ishibashi (Kindai University)
Title BMS Supertranslations and Gravitational Memory(Slides)
Abstract The “memory effect” is the permanent displacement of test particles near infinity produced by radiation burst and is, in principle, a measurable effect. The memory effect has been an active topic of study, particularly with regard to the relationship between the memory, BMS asymptotic symmetry, and soft gravitons. In this talk I will show how BMS supertranslation characterizes the memory effect in 4-dimension, and why they vanish in higher dimensions, by showing explicit calculations of linear perturbation in a simple example, as well as providing a general, nonlinear analysis.

 

Date/Place May. 9th(Tue.) 15:30-16:30 / H711
Name Shinya Kanemura(Osaka University)
Title Higgs as a probe of new physics(Slides)
Abstract The Higgs boson was discovered and its measured property turned out to be consistent with that in the standard model within the current experimental uncertainty. However, the nature of the Higgs boson, the multiplet structure of the Higgs sector and the physics behind the electroweak symmetry breaking remain unknown. On the other hand, there are many reasons to consider new physics beyond the standard model. Details of the Higgs sector are expected to be strongly related to new physics. In this talk, we discuss various aspects of "non-minimal" Higgs sectors and their relation to new physics scenarios. We then discuss how the structure of the Higgs sector can be explored by current and future experiments. We emphasize that the Higgs sector is an important probe of the new physics beyond the standard model.

 

Date/Place Apr. 27th(Thu.) 11:00-12:00 / H711
Name Ryusuke Jinno(IBS-CTPU)
Title Hillclimbing inflation(Slides)
Abstract We propose a new class of inflationary models in which inflation takes place while the inflaton is climbing up a potential hill due to a gravity effect. This mechanism is applicable to inflaton potentials with multiple vacua, and such models typically predict the most preferred region in CMB observations. We discuss possible realizations with the natural inflation potential and the Higgs potential (when the multiple point principle holds). Reference : 1703.09020 (in collaboration with Kunio Kaneta)

 

Date/Place Apr. 26th(Wed.) 14:30-15:30 / H711
Name Masazumi Honda(Weizmann Institute)
Title How to resum perturbative series in supersymmetric gauge theories(Slides)
Abstract Perturbative series in quantum field theory is typically divergent. There is a standard method to resum divergent series called Borel resummation. While perturbative series in typical field theory is expected to be non-Borel summable, it is important to ask when perturbative series is Borel summable and if it is non-Borel summable, what is a correct way to resum the perturbative series. In my talk I will first discuss that we can prove Borel summability of perturbative series in 4d N=2 and 5d N=1 supersymmetric gauge theories with Lagrangians for various observables. It turns out that exact results in these theories can be obtained by summing over the Borel resummations with every instanton number. I also discuss perturbative series in general 3d N=2 supersymmetric Chern-Simons matter theory, which is given by a power series expansion of inverse Chern-Simons levels. We prove that the perturbative series are always Borel summable along imaginary axis. It turns out that the Borel resummations along this direction are the same as exact results. [PRL116,no.21,211601(2016), PRD94, no.2, 025039 (2016) and upcoming paper(s)]

 

Date/Place Apr. 25th(Tue.) 15:30-16:30 / H711
Name Hiromasa Takaura(Tohoku University)
Title Hidden (Λ_QCD)^n structure in perturbative QCD(Slides)
Abstract Perturbative series, which appear in predictions of quantum field theories, are generally divergent. Especially in QCD, this problem causes non-negligible size of uncertainties in perturbative predictions. We formulate a way to remove such uncertainties according to the OPE framework. As a result, we find a non-trivial power dependence on Lambda_QCD inherent in a perturbative prediction. I also argue that such a power behavior is favored from the viewpoint of the analyticity of an observable.

 

Date/Place Apr. 18th(Tue.) 15:30-16:30 / H711
Name Tsukasa Tada(RIKEN)
Title The use of unconventional quantizations for CFT(Slides)
Abstract It is conventionally thought that different time foliations for the quantum field theory lead merely physically equivalent quantizations. Therefore, one may choose whichever time-foliation that suits one's purpose best. There is a caveat, though. In the case of conformal field theories, there exists a singular time-foliation which corresponds to the vanishing point of the Casimir operator, or the “light-cone” for the inherent SL(2, R) symmetry. We show that this singular time-foliation for 2d CFT yields continuous Virasoro algebra implying the continuous spectrum for the system. The phenomenon known as the sine-square deformation in the study of quantum many body systems can be understood in this context. Further, we argue the change of the time foliation poses a very useful perspective on the nature of conformal field theories.

 

Date/Place Apr. 11th(Tue.) 15:30-16:30 / H711
Name Tokiro Numasawa(Osaka University)
Title Projection measurements in CFTs and their gravity duals(Slides)
Abstract In this paper we analyze three quantum operations in two dimensional conformal field theories (CFTs): local projection measurements, creations of partial entanglement between two CFTs, and swapping of subsystems between two CFTs. We also give their holographic duals and study time evolutions of entanglement entropy.

 

過去のセミナー