2017年度のセミナー

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