MathPhys Seminar
11 events

Seminar
Vortex Reconnection in Classical and Quantum Fluids
November 10 (Fri) at 15:00  16:30, 2023
Yoshifumi Kimura (Professor, Graduate School of Mathematics, Nagoya University)
As a fundamental process in turbulence, vortex reconnection has been studied widely not only in classical fluids but also in quantum fluids. For the latter, the first real observation of vortex reconnection was rather recent, and since then active analyses have been continued. On the other hand, vortex reconnection in the former has a long history, and it is now studied intensively as a candidate for a solution to the problem of the regularity/Singularity of the NavierStokes equations, which is one of the seven millennium prize problems of the Clay Mathematical Institute. In this talk, after introducing the problem, we will present some results of analysis and simulations of the dynamical system which has been proposed to describe a vortex reconnection of two vortex rings located symmetrically on two tilted planes [1], [2], [3]. Then it will be shown that this dynamical system can be written in noncanonical Hamiltonian form with Hamiltonian, H, and a Casimir invariant, C in the limit of zero viscosity [4].
Venue: Seminar Room #359 (Main Venue) / via Zoom
Event Official Language: English

Seminar
Feynman’s proof of integrability of Calogero system from a modern point of view
March 10 (Fri) at 10:00  11:30, 2023
Yehao Zhou (Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), The University of Tokyo)
In his last year of life Feynman was interested in integrable system, and in his study of Calogero models he came up with his own proof of the commutativity of integrals of motions of these models, which remains unpublished until it was transcribed by Polychronakos in 2018. His idea is to organize integrals of motions of a Calogero model into a generating function of differential operators which look like a correlation function in a certain free theory, then he showed that the generating function of differential operators commute for all spectral values, which leads to a proof of commutativity of integrals of motions. He commented on his proof “I learn nothing, no real clue as to why all this works, and what it means”. Recently in a joint work with Davide Gaiotto and Miroslav Rapcek we identify Feynman’s generating function as the correlation function of Miura operators in a Walgebra of type A, and in the rational and trigonometric cases we show that they equal to certain elements in the Dunkl representation of corresponding spherical Cherednik algebras in type A, which make the commutativity selfevident. This progress is a byproduct of a project in the study of M2M5 brane junction in the Mtheory.
Venue: Common Room #246248 / via Zoom
Event Official Language: English

String theory, N=4 SYM and Riemann hypothesis
February 16 (Thu) at 14:00  16:10, 2023
Masazumi Honda (Assistant Professor, Yukawa Institute for Theoretical Physics, Kyoto University)
We discuss new relations among string theory, fourdimensional N=4 supersymmetric YangMills theory (SYM) and the Riemann hypothesis. It is known that the Riemann hypothesis is equivalent to an inequality for the sum of divisors function σ(n). Based on previous results in literature, we focus on the fact that σ(n) appears in a problem of counting supersymmetric states in the N=4 SYM with SU(3) gauge group: the Schur limit of the superconformal index plays a role of a generating function of σ(n). Then assuming the Riemann hypothesis gives bounds on information on the 1/8BPS states in the N=4 SYM. The AdS/CFT correspondence further connects the Riemann hypothesis to the type IIB superstring theory on AdS5×S5. In particular, the Riemann hypothesis implies a miraculous cancellation among KaluzaKlein modes of the supergravity multiplet and D3branes wrapping supersymmetric cycles in the string theory. We also discuss possibilities to gain new insights on the Riemann hypothesis from the physics side. This talk is based on a collaboration with Takuya Yoda (arXiv:220317091).
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

An Introduction to Rough Geometry (with a view to Euclidean Gravity)
October 14 (Fri) at 14:00  16:30, 2022
Christy Koji Kelly (Special Postdoctoral Researcher, iTHEMS)
The mathematical formulation of Einstein gravity typically utilises differentiable manifolds as models of smooth spacetimes. In many scenarios, however, it is desirable to have coarser models of spacetime and a correspondingly rough theory of geometry applicable to these coarser spacetime structures. In 2D Euclidean quantum gravity, for instance, the use of Regge calculus allows one to treat triangulations as regularisations of smooth spacetimes. There has been much recent progress in the mathematical (rigorous) understanding of this theory which we briefly review. We also introduce a rich alternative framework for the study coarse Euclidean geometry in the form of metric geometry augmented by optimal transport theory. In particular we introduce several optimal transport theoretic curvatures and demonstrate that these recover the familiar smooth notions under suitable limits.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
Implications of singularity theorem for nonsingular universe
June 16 (Thu) at 13:30  15:00, 2022
Daisuke Yoshida (Designated Assistant Professor, Graduate School of Mathematics, Nagoya University)
The singularity theorem by Penrose shows that a spacetime singularity arises in certain universal situations. The existence of a spacetime singularity is thought to represent a breakdown in the validity of theories such as general relativity and the phenomenological models of the universe. Thus, if we could build a correct model that describes the beginning of the universe, the universe predicted by that model should be nonsingular. In this talk, we will discuss general properties that a nonsingular universe must satisfy in order to avoid the singularity theorem. In particular, we will see that the universe must be, in some sense, smaller than the corresponding closed de Sitter spacetime.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
Recent Progress in the Swampland Program
May 19 (Thu) at 14:00  15:30, 2022
Toshifumi Noumi (Associate Professor, Institute of Cosmophysics, Department of Physics, Graduate School of Science, Kobe University)
In the past years, it has become increasingly clear that there exist nontrivial consistency conditions on symmetries in quantum gravity, that are invisible in classical gravity. The Swampland program aims at identifying such quantum gravity constraints and their implications for particle physics and cosmology, toward quantum gravity phenomenology. In this talk, I will review recent progress in this program, including my own works.
Venue: Hybrid Format (Common Room 246248 and Zoom)
Event Official Language: English

Seminar
Selfadjoint extension in quantum mechanics and nonRydberg spectra of onedimensional hydrogen atom
April 13 (Tue) at 16:00  18:10, 2021
Takuju Zen (Professor, School of Environmental Science and Engineering, Kochi University of Technology)
We offer a beginner’s guide to the functionalanalytical techniques in quantum mechanics, and cover its application to the 1D Coulomb problem. It is shown that the wave function at the diverging point of the Coulomb potential is mathematically described by threeparameter family of generalized connection conditions. A scheme is devised to physically implement the generalized conditions, which provides the way to experimentally realize nonRydberg spectra in 1D Hydrogen atom. Schedule: Part 1, Selfadjoint extension of Hilbert space operator Part 2, 1D Coulomb problem
Venue: via Zoom
Event Official Language: English

Seminar
Nonperturbative tests of duality cascades in three dimensional supersymmetric gauge theories
December 14 (Mon) at 16:00  18:10, 2020
Naotaka Kubo (Postdoctoral Researcher, Yukawa Institute for Theoretical Physics, Kyoto University)
M2brane is an interesting object in Mtheory and string theory. A threedimensional 𝒩=6 super conformal Chern Simons theory with gauge group U(𝑁1)×𝑈(𝑁2), called ABJ theory, describes the low energy behavior of M2brane On the one hand, it has been considered that when 𝑁1−𝑁2 is larger than the absolute value of Chern Simons level, the supersymmetry is broken. On the other hand, it was predicted that an interesting phenomenon called duality cascade occurs, and supersymmetry is not broken in some cases. Motivated by this situation, we performed nonperturbative tests by focusing on the partitionfunction on 𝑆3. The result strongly suggests that the duality cascade indeed occurs. We also proposed that the duality cascade occurs in theories with more general gauge groups and we performed nonperturbative tests in the same way. I will review and explain our physical prediction in the first half of my talk. In the second half of my talk , I will explain the nonperturbative tests . This part is mathematical because the partition function reduces to a matrix model by using the supersymmetric localization technique.
Venue: via Zoom
Event Official Language: English

Seminar
Mathematics of thermalization in isolated quantum systems
November 10 (Tue) at 16:00  18:10, 2020
Naoto Shiraishi (Assistant Professor, Faculty of Science Department of Physics, Gakushuin University)
If an isolated macroscopic quantum system is left at a nonequilibrium state, then this system will relax to the unique equilibrium state, which is called thermalization. Most of quantum manybody systems thermalize, while some manybody systems including integrable systems do not thermalize. What determines the presence/absence of thermalization and how to understand thermalization from microscopic quantum mechanics are profound longstanding problems. In the first part of my talk, I briefly review some established results of quantum thermalization. I first clarify the problem of thermalization in a mathematical manner, and then introduce several important results and insights: typicality of equilibrium states [1], relaxation caused by large effective dimension [2], and eigenstate thermalization hypothesis (ETH) [3,4] and weakETH [5]. In the second part of my talk, I explain some of my results. First, I introduce a model which is nonintegrable and thermalizes but does not satisfy the ETH [6,7]. This finding disproves the conjectures that all nonintegrable systems satisfy the ETH and that the ETH is a necessary condition for thermalization. I also discuss the hardness of the problem of thermalization from the viewpoint of computational science [8]. Then, I move to an analytical approach to a concrete model, and prove that S=1/2 XYZ chain with a magnetic field is nonintegrable [9]. This is the first example of proof of nonintegrability in a concrete quantum manybody system, which will help a mathematical approach to thermalization.
Venue: via Zoom
Event Official Language: English

TQFT, integrable lattice model, and quiver gauge theories
October 2 (Fri) at 16:00  18:00, 2020
Toshihiro Ota (Student Trainee, iTHEMS / Graduate School of Science, Osaka University School of Science)
1st part (math): In physics literature, “lattice models” appear quite often as mathematical models of physical systems, e.g. Ising model, vertex models, lattice gauge theory. The aim of the 1st part is to introduce ‘what is (T)QFT,’ ‘what is lattice model,’ and ‘what does integrability mean’ in the language of mathematics. In turn, they will play a crucial role in the 2nd part of my talk. I also hope that this will lead to a good exchange among us, especially between physicists and mathematicians. 2nd part (physics): In the 2nd part, I would like to explain where an integrable lattice model may come from, especially for people in the physics background. I will show a certain class of integrable lattice models is realized by Wilson’t Hooft lines in 4d quiver gauge theories. I will also explain a bit how these gauge theories are constructed from brane configurations in string theory. String dualities allow us to relate the original 4d setups to 4d partially topological ChernSimons theory, which is a partial TQFT and generates integrable lattice models. Please contact Keita Mikami's mail address to get access to the Zoom meeting room.
Venue: via Zoom
Event Official Language: English

Seminar
Geometric Perspective for the Theory of Hydrodynamic Limits
August 31 (Mon)  September 1 (Tue), 2020
Makiko Sasada
Kenichi Bannai (Professor, Faculty of Science and Technology Department of Mathematics, Keio University)This is a series of lectures on "Geometric Perspectives for Fluid Dynamic Limit Theory" by the following speakers: [DAY 1: Aug 31] Dr. Makiko Sasada (University of Tokyo) [DAY 2: Sept 1] Prof. Kenichi Bannai (Keio University) Abstract: One of the fundamental problems in the natural and social sciences is to explain macroscopic phenomena that we can observe from the rules governing the microscopic system giving rise to the phenomena. Hydrodynamic limit provides a rigorous mathematical method to derive the deterministic partial differential equations describing the time evolution of macroscopic parameters, from the stochastic dynamics of a microscopic large scale interacting system. In the article "Topological Structures of Large Scale Interacting Systems via Uniform Locality" joint with Yukio Kametani, we introduce a general framework encompassing a wide variety of interacting systems in order to systematically investigate various microscopic stochastic large scale interacting systems in a unified fashion. In particular, we introduced a new cohomology theory called the uniformly local cohomology to investigate the underlying geometry of the interacting system. Our theory gives a new interpretation of the macroscopic parameters, the role played by the group action on the microscopic system, and the origin of the diffusion matrix associated to the macroscopic deterministic partial differential equation obtained via the spacetime scaling limit of the microscopic system. The purpose of the series of lectures is to introduce to the audience the theory of hydrodynamic limits, especially the relation between the macroscopic observables and the microscopic interacting system. We then explain our new perspective of how geometry comes into play in investigating the interacting system, and introduce the ideas and results of our article. *Detailed information about the seminar refer to the email.
Venue: via Zoom
Event Official Language: English
11 events