Yu Sang, Institute of Theoretical Physics, Chinese Academy of Sciences
Stochastic gravitational wave background from reheating
Seminar room, Kenkyu honkan 3F
In preheating stage after inflation, fluctuations of inflaton field may be enhanced exponentially by parametric resonance. The large and time dependent density inhomogeneity will produce stochastic gravitational wave background. We use lattice simulation to study the non-perturbative evolution of the inflaton field and the production of gravitational waves. We focus on axion monodromy inflation model and find that significant single-peak stochastic gravitational wave backgrounds are generated during preheating.
Junsei Tokuda, Department of Physics, Kyoto University
IR obstruction to Lorentz invariant UV completion
Seminar room, Kenkyu honkan 3F Recently, it has been recognized that low energy effective field theory must satisfy an infinite number of positivity bounds when UV completion is local, analytic, unitary, and Lorentz invariant. In this talk, I will firstly review the derivation of positivity bounds and their importance. Then, I will introduce our recent work in which we show that the locality assumption is not necessary to derive some of positivity bounds obtained in the literature. Such bounds may provide IR obstructions to analytic, unitary, and Lorentz invariant UV completion.
Recently, it has been recognized that low energy effective field theory must satisfy an infinite number of positivity bounds when UV completion is local, analytic, unitary, and Lorentz invariant. In this talk, I will firstly review the derivation of positivity bounds and their importance. Then, I will introduce our recent work in which we show that the locality assumption is not necessary to derive some of positivity bounds obtained in the literature. Such bounds may provide IR obstructions to analytic, unitary, and Lorentz invariant UV completion.
References :
Junsei Tokuda, arXiv:1902.10039
全卓樹, 高知工科大学
世論力学：数理的な政治社会学の試み
Seminar room, Kenkyu honkan 3F
多数決は生物社会の集団的意思決定における遍在的な原理であり、人類の民主主義社会もその一例である。民主主義な多数決には、その単純な見かけとは裏腹ないくつかの「逆理」が知られていて、少数ながら強い影響力を振るう利益団体の存在、冷笑的反対派が既存優越派の補完勢力となる事象、などがいたるところで観察されるのである。われわれは社会集団における多数派の形成を、スピン・モデルに範をとって数理物理学の枠組みに載せてモデル化した理論、「世論力学」を発展させた。このモデルが「多数決民主主義の実態」を、諸逆理を含めて、よく記述している様子を解説する。
Hidenori Fukaya, Osaka University
Atiyah-Patodi-Singer index theorem and domain-wall fermions
Meeting Room 1, Kenkyu honkan 1F, slides (kek.jp only)
The Atiyah-Patodi-Singer index theorem describes the bulk-edge correspondence of symmetry protected topological insulators. The mathematical set-up for this theorem is, however, not directly related to the physical fermion system, as it imposes on the fermion fields a non-local boundary condition known as the “APS boundary condition” by hand, which is unlikely to be realized in the materials. In 2017, we showed that the same integer as the APS index can be obtained from the eta-invariant of the domain-wall Dirac operator. In this work, we invite three mathematicians to our group and prove that this correspondence is not a coincidence but generally true.
Naoki Yamamoto, Department of Physics, Keio University
Chiral Soliton Lattice in QCD
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
The Chiral Soliton Lattice (CSL) is a state with a periodic array of topological solitons that spontaneously breaks parity and translational symmetries. Such a state is known to appear in chiral magnets. We show, based on a systematic low-energy effective theory, that the ground state of QCD becomes the CSL at finite chemical potential in a magnetic field or rotation due to the presence of the topological terms related to the chiral anomaly. We also discuss unusual electromagnetic properties of the CSL in QCD. In particular, we show the emergence of photons with the nonrelativistic dispersion relation that can be understood as a type-B Nambu-Goldstone mode of generalized global symmetries.
Takahiro Terada, KEK
Bouncing Universe from Nothing
Meeting room 1, Kenkyu honkan 1F We find a class of solutions for a homogeneous and isotropic universe in which the initially expanding universe stops expanding, experiences contraction, and then expands again (the “bounce”), in the framework of Einstein gravity with a real scalar field without violating the null energy condition nor encountering any singularities. Two essential ingredients for the bouncing universe are the positive spatial curvature and the scalar potential which becomes flatter at large field values. Depending on the initial condition, either the positive curvature or the negative potential stops the cosmic expansion and begins the contraction phase. The flat potential plays a crucial role in triggering the bounce. After the bounce, the flat potential naturally allows the universe to enter the slow-roll inflation regime, thereby making the bouncing universe compatible with observations. If the e-folding of the subsequent inflation is just enough, a positive spatial curvature may be found in the future observations. Our scenario nicely fits with the creation of the universe from nothing, which leads to the homogeneous and isotropic universe with positive curvature. As a variant of the mechanism, we also find solutions representing a cyclic universe.
We find a class of solutions for a homogeneous and isotropic universe in which the initially expanding universe stops expanding, experiences contraction, and then expands again (the “bounce”), in the framework of Einstein gravity with a real scalar field without violating the null energy condition nor encountering any singularities. Two essential ingredients for the bouncing universe are the positive spatial curvature and the scalar potential which becomes flatter at large field values. Depending on the initial condition, either the positive curvature or the negative potential stops the cosmic expansion and begins the contraction phase. The flat potential plays a crucial role in triggering the bounce. After the bounce, the flat potential naturally allows the universe to enter the slow-roll inflation regime, thereby making the bouncing universe compatible with observations. If the e-folding of the subsequent inflation is just enough, a positive spatial curvature may be found in the future observations. Our scenario nicely fits with the creation of the universe from nothing, which leads to the homogeneous and isotropic universe with positive curvature. As a variant of the mechanism, we also find solutions representing a cyclic universe.
Reference:
H. Matsui, F. Takahashi and T. Terada, “Bouncing Universe from Nothing,” arXiv:1904.12312 [gr-qc].
Yoshinori Matsuo, Osaka University
Vacuum energy and apparent horizon
Meeting room 1, Kenkyu honkan 1F
Effects of the negative vacuum energy plays a crucial role in a small neighborhood of the apparent horizon of evaporating black holes. We consider spherically symmetric configurations in which the collapsing star has already collapsed below the Schwarzschild radius. For static case, there are no divergences around the Schwarzschild radius even in the Boulware vacuum, if the back reaction from the negative vacuum energy is taken into account. The geometry around the Schwarzschild radius is modified by the effect of vacuum energy and has no event horizon. Instead, there is a local minimum in the radius, like the geometry around the neck of the wormhole. The local minimum of the radius becomes the apparent horizon when the black hole is evaporating by the Hawking radiation. Information can get away from the apparent horizon since it is time-like because of the negative vacuum energy.
Yoshitaka Hatta, Brookhaven National Laboratory
Unraveling the nucleon's mass and spin structure at an Electron-Ion Collider
Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
The US-based Electron-Ion Collider (EIC) is a future high-luminosity, polarized ep and eA collider dedicated to the physics of the nucleon/nucleus structure. I will give a theory overview of the science cases for the EIC. A special emphasis is placed on the partonic origin of the mass and spin of the nucleon, namely, how they can be understood in terms of quarks’ and gluons’ degrees of freedom. I will give a review of the mass and spin decompositions in QCD and discuss possible experimental observables
Masayuki Asakawa, Department of Physics, Graduate School of Science, Osaka University
Toward the understanding of strongly interacting quark-gluon plasma
Meeting room 1, Kenkyu honkan 1F, slides (kek.jp only)
It was discovered at RHIC that the quark-gluon plasma is very strongly interacting matter contrary to naive expectation. First I will explain how this conclusion was drawn with emphasis on the characteristics of the physics of high energy nuclear collisions. After the introduction, I will examine the interaction in the quark-gluon plasma in three ways: interaction measure, charmonia with finite momenta, and fluctuations of conserved quantities. In the presentation, I will mainly discuss physical implications rather than technical details.
Takeshi Morita, Shizuoka University
Nuclear physics and D-branes in string theory
Meeting room 3, Kenkyu honkan 1F, slides (kek.jp only), slides (kek.jp only)
