The talk files can be downloaded from the Seminar files (for member login required). 2018 †Apr. 27Room/Time  Room 907 / 16:0017:30  Speaker  Munekazu Horikoshi (University of Tokyo)  Title  Fundamental physics for quantum manybody systems investigated by cold atom experiments  Abstract  In a lowenergy quantum system, particles behave as matter wave with quantum statistics, and the influence of the interparticle interactions appears as the symmetry and the phase shift of the scattering wave. While the scattering length is a parameter describing the phase shift, it is an important physical quantity giving the coupling constant between two particles. Since the scattering length is controllable in cold atomic systems by using Feshbach resonances, we can study various interacting quantum manybody systems experimentally in a wide range of coupling constants. Especially, the unitary regime, where the scattering length diverges, are interested in various quantum fields from quark matter to neutron matter, since they have similar lowenergy scattering conditions. In this seminar, we deal with the spin1/2 Fermi particle system interacting with tunable swave scattering length. Firstly, we confirm the physical meaning of the scattering length and various universal physical laws described by swave scattering length. Secondly, we will introduce an experiment that investigated the equation of state (EOS) of fermions from the BCS regime to the unitary regime using ultracold 6Li atomic gases [1]. Finally, we show application of the EOS to dilute neutron matter. [1] Munekazu Horikoshi, Masato Koashi, Hiroyuki Tajima, Yoji Ohashi, and Makoto KuwataGonokami, Phys. Rev. X 7, 041004 (2017). 
2017 †Dec. 15Room/Time  Room 907 / 15:3017:00  Speaker  Keiju Murata (Keio University)  Title  Outoftimeorder correlators in quantum mechanics  Abstract  The outoftimeorder correlator (OTOC) is considered as a measure of quantum chaos. We formulate how to calculate the OTOC for quantum mechanics with a general Hamiltonian. We demonstrate explicit calculations of OTOCs for a harmonic oscillator, a particle in a onedimensional box, a circle billiard and stadium billiards. For the first two cases, OTOCs are periodic in time because of their commensurable energy spectra. For the circle and stadium billiards, they are not recursive but saturate to constant values which are linear in temperature. Although the stadium billiard is a typical example of the classical chaos, an expected exponential growth of the OTOC is not found. We also discuss the classical limit of the OTOC. Analysis of a time evolution of a wavepacket in a box shows that the OTOC can deviate from its classical value at a time much earlier than the Ehrenfest time. 

Dec. 5 †Room/Time  Room 907 / 16:0017:30  Speaker  Nobuyuki Yoshioka (University of Tokyo)  Title  Learning Disordered Topological Phases by Statistical Recovery of Symmetry  Abstract  In machine learning, computational algorithms are constructed and executed to optimize the quantified objective of the problem to be solved. The surging development of the stateoftheart techniques has led condensed matter physicists to realize the effectiveness of the tools in their own research field, such as phase classification [1,2], solving quantum manybody problem [3,4] and speeding up the Monte Carlo simulation [5]. Firstly we start with basic information to understand the classification by the artificial neural network (ANN), which maps out in our work the quantum phase diagram of disordered topological superconductor in class DIII. Given the disorder that keeps the discrete symmetries of the ensemble as a whole, translational symmetry which is broken in the quasiparticle distribution individually is recovered statistically by taking an ensemble average. By using this, we classify the phases by the ANN that learned the quasiparticle distribution in the clean limit and show that the result is totally consistent with the calculation by another independent approach. If all three phases, namely the Z2, trivial, and the thermal metal phases appear in the clean limit, the machine can classify them with high confidence over the entire phase diagram. If only the former two phases are present, we find that the machine remains confused in the certain region, leading us to conclude the detection of the unknown phase which is eventually identified as the thermal metal phase. [1] J. Carrasquilla and R. G. Melko, Nat. Phys. 13, 431 (2017). [2] N. Yoshioka, Y. Akagi, and H. Katsura, arXiv:1709.05970. [3] G. Carleo and M. Troyer, Science 355, 602 (2017). [4] Y. Nomura, A. Darmawan, Y. Yamaji, and M. Imada, arXiv:1709.06475 (2017). [5] L. Huang and L. Wang, Phys. Rev. B 95, 035105 (2017). 
Nov. 28Room/Time  Room 907 / 16:0017:30  Speaker  Haruki Watanabe (University of Tokyo)  Title  Filling and SymmetryBased Indicator of ManyBody Chern Number  Abstract  The topology of quantum manybody systems are deeply related to the average number of particles of the system and/or the symmetry representation of the ground state. One of the most established example of this relation is the socalled (HasingsOshikawa) LiebSchultzMattis theorem, a theorem that applies to a very wide class of Hamiltonian regardless of the interaction strength or the spatial dimension of the system. In this talk, I will first overview the HOLSM theorem and then discuss recent advances concerning the manybody Chern number. The talk will be based on A. Matsugatani, Y. Ishiguro, K. Shiozaki, and H. Watanabe, arXiv:1710.07012. 
Nov. 24 †Room/Time  Room 907 / 16:0017:30  Speaker  Zebin Qiu (University of Tokyo)  Title  Electrodynamics of Chiral Matter  Abstract  A manybody system with chiral fermions can
exhibit novel transport phenomena that violate parity and timereversal
symmetries, such as the chiral magnetic effect, the anomalous Hall effect, and
the anomalous electric charge. We study the electromagnetic and optical properties
of such systems by examining the electromagnetic sector of the ChernSimons
theory. Based on the MaxwellChernSimons equations, we derive modified laws
for the generation of static electromagnetic fields, and the propagation of
electromagnetic waves. 
Oct. 20 †Room/Time  Room 907 / 16:0017:30  Speaker  Arata Yamamoto (University of Tokyo)  Title  Condensed Matter Application of Lattice QCD  Abstract 

Oct. 6 †Room/Time  Room 907 / 16:0017:30  Speaker  Toshiaki Fujimori (Keio University)  Title  Exact resurgent transseries and allorder multibion contributions in CP^N quantum mechanics  Abstract  I will discuss resurgence structures in CP^N quantum mechanics derived from a supersymmetric model with a small SUSY breaking deformation parameter. By using the standard RayleighSchrodinger perturbation theory, we exactly determine how the ground state energy respond to the deformation. The full resurgent transseries expressions for the expansion coefficients of the ground state energy are found exactly in CP^1 quantum mechanics. We then discuss the semiclassical bion contributions in the complexified path integral formalism and compare them with the exact results. We determine all exact saddle point solutions corresponding to multibion configurations in the complexified theory. By evaluating the complexified quasimoduli integral, we obtain all order multibion contributions which are consistent with the exact results. 
June 23 †Room/Time  Room 907 / 16:0017:30  Speaker  Shun Furusawa (RIKEN)  Title  Nuclear Equation of State for CoreCollapse Supernovae  Abstract  The corecollapse supernovae are one of the most fascinating phenomena in astrophysics. The mechanism of these events is not clearly understood yet because of their intricacies. One of the underlying problems is uncertainties in the equations of state of hot and dense matter. In this talk, I will give an overview about the nuclear equation of state and its roles in the numerical simulations of supernovae. If time permits, I also introduce a recent study about transitions of hadronic matter to threeflavor quark matter, which may be realized during or after corecollapse supernovae. 
June 9 †Room/Time  Room 907 / 16:0017:30  Speaker  Noriyuki Sogabe (Keio University)  Title  New dynamic critical phenomena in nuclear and quark superfluids  Abstract  We study the static and dynamic critical phenomena near the possible highdensity QCD critical point in the superfluid phase of nuclear and quark matter. In particular, we find that its dynamic universality class is different from those studied in QCD and condensed matter systems so far. We argue that this novelty stems from the interplay between the chiral criticality and the presence of the superfluid phonona feature specific for highdensity QCD critical point. 
May 8 †Room/Time  Room 907 / 16:0017:30  Speaker  Daisuke Satow (Goethe Universität)  Title  Transport coefficients of QGP in strong magnetic fields  Abstract  We compute the transport coefficients in magnetohydrodynamics at finite temperature, in strong magnetic fields (B), which is expected to be generated in heavy ion collision. We use the lowest Landau level approximation, in which the 1to2 scattering process is kinematically allowed in contrast to the B=0 case. We find that this effect of the magnetic field is significant in the electrical conductivity and the bulk viscosity: These quantities become sensitive to the current quark mass, and we discuss its physical origin in terms of the chirality conservation and the conformal invariance. This presentation is partially based on Phys. Rev. D 94, 114032 (2016) and arXiv:1610.06839 [hepph]. 
April 7 †Room/Time  Room 907 / 16:0017:30  Speaker  Takuya Kanazawa (RIKEN)  Title  Phases of circlecompactified QCD with adjoint fermions at finite density  Abstract  We study chemicalpotential dependence of confinement and mass gap in QCD with adjoint fermions in spacetime with one spatial compact direction. By calculating the oneloop effective potential for the Wilson line in the presence of chemical potential, we show that a centersymmetric phase and a centerbroken phase alternate when the chemical potential in unit of the compactification scale is increased. In the centersymmetric phase we use semiclassical methods to show that photons in the magnetic bion plasma acquire a mass gap that grows with the chemical potential as a result of anisotropic interactions between monopoleinstantons. For the neutral fermionic sector which remains gapless perturbatively, there are two possibilities at nonperturbative level. Either to remain gapless (unbroken global symmetry), or to undergo a novel superfluid transition through a fourfermion interaction (broken global symmetry). If the latter is the case, there exists a new type of BECBCS crossover of the diquark pairing across 3 and 4 dimensions. 
March 27 †Room/Time  Room 907 / 16:0017:30  Speaker  Tomoya Hayata (Chuo University)  Title  Chiral magnetic effect in multiWeyl semimatals  Abstract  New topological phase of matters named Weyl semimetal has attracted growing attention in recent years. In a Weyl semimetal, Weyl fermions are realized as lowenergy excitations near band touching points called Weyl points. The Weyl points act as monopoles in momentum space, and lead to topological transport phenomena such as the chiral magnetic effect. Since condensed matter system does not have Lorentz and rotational symmetries, there appear Weyl excitations with nonrelativistic dispersion relations, which results in the exotic chiral magnetic effect. In this talk, our recent work on such an exotic chiral magnetic effect in multiWeyl semimetals is presented [1]. MultiWeyl semimetal is a Weyl semimetal with multiplemonopole charge. We show that in static magnetic fields, the CME is manifestly topological, and given by the straightforward extension of that for conventional WSMs with unit monopole charge to multiple case. On the other hand, the dynamic CME with timedependent magnetic field is not manifestly topological, but we found the topological feature hidden there. We propose an experimental setup to measure the multiple monopole charge via the topological nature hidden in the dynamic CME. [1] Tomoya Hayata, Yuta Kikuchi, Yuya Tanizaki, arXiv:1703.02040 [condmat.meshall] 
March 16 †Room/Time  Room 907 / 14:0015:30  Speaker  York Schroder (UBB Chillan)  Title  Fiveloop Beta function and anomalous dimensions in QCD  Abstract  I provide an update on a longterm project that aims at evaluating massive vacuum Feynman integrals at the fiveloop frontier, with high precision and in various spacetime dimensions. A number of applications are sketched, mainly concerning the determination of anomalous dimensions, for quantum field theories in four, three and two dimensions. 
20142016 †
