KEK Theory Workshop 2021

7 Dec 2021, 09:00 → 9 Dec 2021, 18:00 Asia/Tokyo

Online (Zoom)

KEK Theory Workshop is an annual workshop on string theory and quantum field theory. Since KEK Theory Workshop 2014, it has been held as an international workshop. Speakers are invited from abroad as well as from Japan, and all talks are given in English.

We hope the workshop provides a valuable opportunity to have active discussions and inspiration on various fundamental problems in theoretical physics related to superstrings, supersymmetric gauge theories, black hole physics, quantum field theories, condensed matter physics, and so on.

This year, in the light of COVID-19, we have decided to hold the workshop ONLINE from Dec. 7 (Tue.) to Dec. 9 (Thu.) in JST (UTC+9). This year, we plan to have a variety of talks on string theory looking ahead to the post-LHC era.

The tentative list of invited speakers is:

• Lara Anderson (Virginia Tech.)
• Ignatios Antoniadis (LPTHE)
• Jonathan Mboyo Esole (Northeastern U.)
• Hiroshi Itoyama (Osaka City U.)
• Tatsuo Kobayashi (Hokkaido U.)
• Susha Parameswaran (U. of Liverpool)
• Stuart Raby (Ohio State U.)

We will also have short talks with (15+5) minutes. Participants can apply for the talk at the registration. The topics to be discussed in the short talks can be chosen from field theory and string theory, and need not be related to the topic of invited talks. If there are too many applicants, we will have to make some selection. Some of the talks may be given in parallel sessions. 

Registration deadline

Those who wish to apply for a short talk: Nov. 7 (Sun.)
Other participants: Nov. 30 (Tue.)

The registration will be closed when the number of the applicants exceeds 300, which is the capacity of our Zoom meeting room.

NOTE: We will use the virtual meeting rooms on Zoom. The necessary information (links, IDs, and passcodes) will be sent to the participants by E-mail before the workshop starts.

 

We are looking forward to your participation.

 

Organizers:
Yu Hamada, Kohta Hatakeyama, Machiko Hatsuda, Yoshimasa Hidaka, Mitsuaki Hirasawa,
Satoshi Iso, Yusuke Kimura, Yoshihisa Kitazawa, Shun'ya Mizoguchi, Makoto Natsuume,
Jun Nishimura, Hajime Otsuka, Katsuta Sakai, Kengo Shimada, Ryo Yokokura

Secretary:
Yuko Ohno (Ms.)  yukoohno[at]post.kek.jp
(Please replace [at] with @.)

Tuesday, 7 December

10:00 → 10:10 Opening address

Convener: Prof. Shun'ya Mizoguchi (KEK)

10:10 → 11:00 Invited talk: Hiroshi Itoyama (Osaka City U.) "Enhanced gauge symmetry and suppressed cosmological constant in non-supersymmetric heterotic string"

Convener: Prof. Satoru Odake (Shinshu U.)

10:10 Enhanced gauge symmetry and suppressed cosmological constant in non-supersymmetric heterotic string

Speaker: Prof. Hiroshi Itoyama (Osaka City University)

KEK-TH2021_Itoyama.pdf

11:00 → 11:10 Break

11:10 → 12:00 Invited talk: Tatsuo Kobayashi (Hokkaido U.) "Modular flavor symmetries from string compactification"

Convener: Prof. Tetsutaro Higaki (Keio U.)

11:10 Modular flavor symmetries from string compactification

Speaker: Prof. Tatsuo Kobayashi (Hokkaido University)

KEK-TH2021_Kobayashi.pdf

12:00 → 14:00 Lunch break

14:00 → 14:20 Short talk: Hikaru Uchida (Hokkaido U.) "Anomaly structure of finite discrete symmetries"

Convener: Prof. Yutaka Sakamura (KEK)

14:00 Anomaly structure of finite discrete symmetries

Finite discrete symmetries are attractive especially for flavor symmetry of quarks and leptons. However, some classical symmetries can be broken by quantum anomaly effects. I will discuss anomaly free and anomalous structure of a finite discrete group $G$ generally.

Speaker: Mr Hikaru Uchida (Hokkaido University)

14:20 → 14:40 Short talk: Tetsutaro Higaki (Keio U.) "New 4D EFT from 10D non-Abelian DBI action in magnetic compactifications"

Convener: Prof. Yutaka Sakamura (KEK)

14:20 New 4D EFT from 10D non-Abelian DBI action in magnetic compactifications

We study a systematic derivation of four dimensional N = 1 supersymmetric effective theory
(EFT) from ten dimensional non-Abelian Dirac-Born-Infeld (DBI) action compactified on
a six dimensional torus with magnetic fluxes on the D9-branes. We find a new type of
matter Kahler metric while gauge kinetic function and superpotential are consistent with
previous studies. For the ten dimensional action, we use a symmetrized trace prescription
and focus on the bosonic part up to O(F^4). In the presence of the supersymmetry, four
dimensional chiral fermions can be obtained via index theorem. The new matter Kahler
metric is independent of flavor but depends on the fluxes, 4D dilaton, Kahler moduli and
complex structure moduli, and will be always positive definite if an induced RR charge of the
D-branes on which matters are living are positive. We read the superpotential from an F-term
scalar quartic interaction derived from the ten dimensional action and the contribution
of the new matter Kahler metric to the scalar potential which we derive turns out to be
consistent with the supergravity formulation.

Speaker: Prof. Tetsutaro Higaki (Keio University)

14:40 → 15:00 Short talk: Takuya Hirose (Osaka City U.) "Nonvanishing finite scalar mass in flux compactification"

Convener: Prof. Yutaka Sakamura (KEK)

14:40 Nonvanishing finite scalar mass in flux compactification

We study possibilities to realize a nonvanishing finite Wilson line (WL) scalar mass in flux compactification. Generalizing loop integrals in the quantum correction to WL mass at one-loop, we derive the conditions for the loop integrals and mode sums in one-loop corrections to WL scalar mass to be finite. We further guess and classify the four-point and three-point interaction terms satisfying these conditions. As an illustration, the nonvanishing finite WL scalar mass is explicitly shown in a six dimensional scalar QED by diagrammatic computation and effective potential analysis. This is the first example of finite WL scalar mass in flux compactification.

Speaker: Mr Takuya Hirose (Osaka City University)

15:00 → 15:20 Short talk: Ryo Yokokura (KEK) "Topological axion electrodynamics and 4-group symmetry"

Convener: Prof. Yutaka Sakamura (KEK)

15:00 Topological axion electrodynamics and 4-group symmetry

We study higher-form symmetries and a higher group in the low energy limit of a $(3+1)$-dimensional axion electrodynamics with a massive axion and a massive photon. A topological field theory describing topological excitations with the axion-photon coupling, which we call a topological axion electrodynamics, is obtained in the low energy limit. Higher-form symmetries of the topological axion electrodynamics are specified by equations of motion and Bianchi identities. We find that there are induced anyons on the intersections of symmetry generators. By a link of worldlines of the anyons, we show that the worldvolume of an axionic domain wall is topologically ordered. We further specify the underlying mathematical structure elegantly describing all salient features of the theory to be a 4-group.

Speaker: Dr Ryo Yokokura (KEK)

15:20 → 16:00 Break

16:00 → 16:20 Short talk: Hiroyuki Kitamoto (YITP) "Semiclassical analysis of axion-assisted and axion-driven pair production"

Convener: Dr Kiyoharu Kawana (SNU)

16:00 Semiclassical analysis of axion-assisted and axion-driven pair production

We study the pair production of fermions in a time dependent axion background with and without an electric background. We construct the adiabatic mode functions which incorporate the gauge field and the axion velocity dependence of the dispersion relation. The semiclassical approach using this adiabatic basis shows two types of pair production. One is axion-assisted pair production: the presence of the axion velocity gives enhancement and interference effects on the pair production driven by the electric field. The other is axion-driven pair production: the time variation of the axion velocity causes the pair production even though the electric field is absent.

Speaker: Dr Hiroyuki Kitamoto (Yukawa Institute for Theoretical Physics)

16:20 → 16:40 Short talk: Yugo Abe (Miyakonojo KOSEN) "Perturbative S-matrix unitarity（S† S＝１）in R^2_{μν} gravity"

Convener: Dr Kiyoharu Kawana (SNU)

16:20 Perturbative S-matrix unitarity（$S^\dagger S =1$）in $R^2_{μν}$ gravity

We investigate the relation perturbative unitarity and renormalizablility in quantum gravity. In particle theories point of view, Llewellyn Smith conjectured that renormalizablility and tree-unitarity at high energy give the same conditions for theories. If we apply this conjecture to gravity theory, it is shown that Einstein gravity is not renormalizable and does not hold perturbative unitarity at high energy. One candidate of quantum gravity, the quadratic gravity ($R_{\mu\nu}^2$ gravity or higher derivative gravity), is a renormalizable theory, but it contains negative norm states and hence does not satisfy tree-unitarity. This gives that the quadratic gravity is one of a counterexample of Llewellyn Smith's conjecture. In this talk, I introduce that Llewellyn Smith's conjecture and our contribution. Especially, we show that in a higher derivative theory, the unitarity bound at tree level (tree unitarity) is violated but $S$-matrix unitarity ($S^{\dagger}S=1$ or often called pseudo-unitarity) is satisfied. The point is our new conjecture that renormalizablility and $S$-matrix unitarity at high energy give the same conditions for theories.

Speaker: Dr Yugo Abe (Miyakonojo KOSEN)

16:40 → 17:00 Short talk: Takahiro Terada (IBS) "Constrained Superfields in Dynamical Background"

Convener: Dr Kiyoharu Kawana (SNU)

16:40 Constrained Superfields in Dynamical Background

We study nonlinear realization of supersymmetry in a dynamical/cosmological background in which derivative terms like kinetic terms are finite. Starting from a linearly realized theory, we integrate out heavy modes without neglecting derivative terms to obtain constraints on superfields. Thanks to the supersymmetry breaking contribution by the kinetic energy, the validity of constrained superfields can be extended to cosmological regimes and phenomena such as reheating after inflation, kinetic-energy domination, and (kinetic) misalignment of axion. (based on a paper with S. Aoki, to appear on arXiv: 2111.XXXXX [hep-th].)

Speaker: Dr Takahiro Terada (Institute for Basic Science)

17:00 → 17:40 Break

17:40 → 18:00 Short talk: Osmin Lacombe (YITP) "Hybrid inflation and waterfall field in string theory from D7-branes"

Convener: Prof. Satoshi Iso (KEK)

17:40 Hybrid inflation and waterfall field in string theory from D7-branes

We present an explicit string realisation of the hybrid inflation scenario within the framework of type IIB flux compactifications in the presence of three magnetised D7-brane stacks. The inflaton is identified with the total internal volume modulus and inflation takes place around a metastable de Sitter vacuum, obtained at the very shallow local minimum of the volume modulus scalar potential. Inflation ends due to the presence of ``waterfall" fields, realized by open string states, that drive the evolution of the Universe from a nearby saddle point towards a global minimum. The vacuum energy can be tuned so as to describe the present state of our Universe.

Speaker: Dr Osmin Lacombe (Yukawa Institute for Theoretical Physics)

18:00 → 18:50 Invited talk: Ignatios Antoniadis (LPTHE) "Challenges for an accelerating universe in string theory"

Convener: Prof. Satoshi Iso (KEK)

18:00 Challenges for an accelerating universe in string theory

Speaker: Prof. Ignatios Antoniadis (Laboratoire de Physique Théorique et Hautes Energies)

KEK-TH2021_Antoniadis.pdf

Wednesday, 8 December

10:00 → 10:50 Invited talk: Jonathan Mboyo Esole (Northeastern U.) "Under the spell of Dynkin"

Convener: Dr Katsuta Sakai (KEK)

10:00 Under the spell of Dynkin

I will explain how the Dynkin index of an embedding gives a unique perspective on the type of representations that appear in generic constructions in F-theory and how it provides a new point of view on the relationship between representation theory and crepant resolutions of singularities of elliptic fibrations.

Speaker: Prof. Jonathan Mboyo Esole (Northeastern University)

10:50 → 11:00 Break

11:00 → 11:20 Short talk: Hajime Otsuka (IBS) "Small flux superpotential in F-theory compactifications"

Convener: Prof. Kazunobu Maruyoshi (Seikei U.)

11:00 Small flux superpotential in F-theory compactifications

We investigate whether a class of models describing F-theory compactifications admits a specific type of flux vacua with an exponentially small vacuum expectation value of the superpotential, by generalizing a method recently developed in Type IIB flux compactifications. First we clarify that a restricted choice of G4-flux components reduces a general flux superpotential into a simple form, which promotes the existence of supersymmetric vacua with one flat direction at the perturbative level. Then we utilize the techniques of mirror symmetry to determine one-instanton corrections to the potential and investigate in detail the vacuum solutions of a particular model.

Speaker: Dr Hajime Otsuka (Institute for Basic Science)

11:20 → 11:40 Short talk: Rinto Kuramochi (SOKENDAI) "Non-split singularities and conifold transitions in F-theory"

Convener: Prof. Kazunobu Maruyoshi (Seikei U.)

11:20 Non-split singularities and conifold transitions in F-theory

In F-theory, if a fiber type of an elliptic fibration involves a condition that requires an exceptional curve to split into two irreducible components, it is called “split” or “non-split” type depending on whether it is globally possible or not. In the latter case, the gauge symmetry is reduced to a non-simply-laced Lie algebra due to monodromy. We show that the transition from a split to a non-split model is, except in certain exceptional cases, a conifold transition from the resolved to the deformed side, associated with the conifold singularities emerging at the codimension-two loci where the codimension-one singularity is enhanced to $D_{2k+2} (k ¥geq 1)$ or $E_7$. This clarifies the origin of non-local matter in the non-split case, which has been a mystery for many years. Reference: arXiv:2108.10136 [hep-th]

Speaker: Mr Rinto Kuramochi (SOKENDAI)

11:40 → 12:00 Short talk: Shuichi Murayama (Tokyo Inst. of Tech.) "Holographic index calculation for Argyres-Douglas and Minahan-Nemeschansky theories"

Convener: Prof. Kazunobu Maruyoshi (Seikei U.)

11:40 Holographic index calculation for Argyres-Douglas and Minahan-Nemeschansky theories

We calculate the superconformal indices of the $¥mathcal N=2$ superconformal field theories realized on $N$ coincident D3-branes in 7-brane backgrounds with constant axiodilaton via the AdS/CFT correspondence. We include the finite-$N$ corrections as the contribution of D3-branes wrapped around 3-cycles in the internal space. We take only single-wrapping contributions into account for simplicity. We also determine the orders of the next-to-leading corrections which we do not calculate. The orders are relatively high, and we obtain many trustable terms. We give the results for $N=1,2,3$ explicitly, and find nice agreement with known results.

Speaker: Mr Shuichi Murayama (Tokyo Institute of technology)

12:00 → 14:00 Lunch break

14:00 → 14:20 Short talk: Katsuta Sakai (KEK) "Entanglement entropy and two-point functions of operators"

Convener: Prof. Takeshi Morita (Shizuoka U.)

14:00 Entanglement entropy and two-point functions of operators

Entanglement entropy (EE) is one of the basic measure of the quantum entanglement between the subsystem we see and the other. In order to establish the relation between such an entanglement and realistic observable, it is inevitable to study EE in general interacting field theory. In this talk, I will present our analysis in the case where the subsystem is a half-space, and give a formula for would-be-dominant contribution to EE in terms of renormalized two-point functions of various operators. Then, in attempt to generalize the result and to grasp the underlying structure, I will reconsider EE for a general subsystem in the free theory case, which is expressed with two-point function of the fundamental fields.

Speaker: Dr Katsuta Sakai (KEK)

14:20 → 14:40 Short talk: Shoichi Kawamoto (NTHU) "Momentum-space entanglement in scalar field theory on noncommutative spaces"

Convener: Prof. Takeshi Morita (Shizuoka U.)

14:20 Momentum-space entanglement in scalar field theory on noncommutative spaces

In this talk, I consider the quantum entanglement in the momentum space for scalar field theory on noncommutative spaces. In an interacting quantum field theory, the degrees of freedom in momentum space show entanglement; it quantifies the correlation between the high/low momentum modes. In noncommutative spaces, it is known that the UV and IR degrees of freedom show a characteristic correlation known as UV/IR mixing. I thus study the entanglement entropy in the momentum space for quantum field theory defined on noncommutative spaces, in particular on the fuzzy sphere, and examine the difference from the theory on the commutative counterpart.

Speaker: Dr Shoichi Kawamoto (National Tsing Hua Universiry)

14:40 → 15:00 Short talk: Yasuhiro Sekino (Takushoku U.) "Rotating strings and particles in AdS: Holography at weak gauge coupling and without conformal symmetry"

Convener: Prof. Takeshi Morita (Shizuoka U.)

14:40 Rotating strings and particles in AdS: Holography at weak gauge coupling and without conformal symmetry

We consider gauge/gravity correspondence between maximally supersymmetric Yang-Mills theory in (p+1) dimensions and superstring theory on the near-horizon limit of the Dp-brane solution. The string-frame metric is AdS_{p+1}\times S^{8-p} times a Weyl factor, and there is no conformal symmetry except for p=3. We consider states which have angular momenta in the AdS directions. We first show that Gubser, Klebanov and Polyakov's solution, in which a folded string is rotating near the center of AdS, can be recast into a form which connects two points on the boundary. Transition amplitudes of such strings can be interpreted as gauge theory correlators, whether or not there is conformal symmetry. Then, we consider the case of zero gauge coupling, assuming the string worldsheet consists of discrete bits. We reproduce the free-field correlators from string theory, extending the previous result obtained for a special operator. (Based on 2109.12091 [hep-th])

Speaker: Prof. Yasuhiro Sekino (Takushoku University)

15:00 → 15:20 Short talk: Ken Kikuchi (YMSC) "Symmetry enhancement in RCFT"

Convener: Prof. Takeshi Morita (Shizuoka U.)

15:00 Symmetry enhancement in RCFT

We propose when and why symmetry enhancements happen in massless renormalization group (RG) flows to two-dimensional rational conformal field theories (RCFTs). We test our proposal against known RG flows from unitary minimal models. We also suggest which sign of the relevant coupling triggers the massless RG flow. The other sign triggers massive RG flows to topological quantum field theories (TQFTs). We comment on their ground state degeneracies.

Speaker: Dr Ken Kikuchi (Yau Mathematical Sciences Center)

15:20 → 16:00 Break

16:00 → 16:20 Short talk: Mitsuyo Suzuki (Osaka City U.) "UV divergent structure of supersymmetric gradient flow in N = 1 SQCD"

Convener: Dr Katsuta Sakai (KEK)

16:00 UV divergent structure of supersymmetric gradient flow in N=1 SQCD

I will discuss perturbation theory of supersymmetric gradient flow in four-dimensional N = 1 SQCD and show one-loop calculations to the flowed fields. In flow theory, the perturbation theory consists of a perturbative expansion of the 4D gauge theory and an iterative expansion of the flow equations. We apply the same technique to SQCD in the Wess-Zumino gauge. Once the boundary theory is renormalized in the standard way, flowed two-point functions for the gauge multiplet are UV finite. The matter multiplets require extra renormalization, and its renormalization factor is the same for all component fields.

Speaker: Mr Mitsuyo Suzuki (Osaka City University)

16:20 → 16:40 Short talk: Junichi Haruna (Kyoto U.) "Fixed Point Structure of Gradient Flow Exact Renormalization Group"

Convener: Dr Katsuta Sakai (KEK)

16:20 Fixed Point Structure of Gradient Flow Exact Renormalization Group

Gradient Flow Exact Renormalization Group (GFERG) is a framework of Exact Renormalization
Group and defines the Wilson action via Gradient Flow equation. We study the fixed
point structure of the GFERG equation associated with the general Gradient Flow equation
for scalar fields and show that it is almost the same as that of the Wilson-Polchinski
(WP) equation. Furthermore, we discuss that the GFERG equation has a similar RG flow
structure around a fixed point to the WP equation. We illustrate these results with O(N)
non-linear sigma model in 4-epsilon dimensions and the Wilson-Fisher fixed point.

Speaker: Mr Junichi Haruna (Kyoto University)

16:40 → 17:00 Short talk: Gota Tanaka (Shizuoka U.) "Higher derivative extension of the functional renormalization group"

Convener: Dr Katsuta Sakai (KEK)

16:40 Higher derivative extension of the functional renormalization group

We study higher derivative extension of the functional renormalization group (FRG).We consider the general form of the FRG equations for a scalar field that include higher functional derivatives with respect to the field. We show that the epsilon expansion around the Wilson-Fisher fixed point is indeed reproduced by the local potential approximation of the general FRG equations.

Speaker: Mr Gota Tanaka (Shizuoka University)

17:00 → 18:00 Break

18:00 → 18:50 Invited talk: Susha Parameswaran (U. of Liverpool) "The Remarkable Properties of Non-Supersymmetric String Theories"

Convener: Dr Hajime Otsuka (IBS)

18:00 The Remarkable Properties of Non-Supersymmetric String Theories

TBA

Speaker: Prof. Susha Parameswaran (University of Liverpool)

Thursday, 9 December

10:00 → 10:50 Invited talk: Stuart Raby (Ohio State U.) "Heterotic/F theory dual SU(5) model"

Convener: Prof. Shun'ya Mizoguchi (KEK)

10:00 "Heterotic/F theory dual SU(5) model"

Speaker: Prof. Stuart Raby (Ohio State University)

KEK-TH2021_Raby.pdf

10:50 → 11:00 Break

11:00 → 11:50 Invited talk: Lara Anderson (Virginia Tech.) "Progress in heterotic string compactification and phenomenology"

Convener: Dr Hajime Otsuka (IBS)

11:00 Progress in heterotic string compactification and phenomenology

TBA

Speaker: Prof. Lara Anderson (Virginia Polytechnic Institute and State University)

KEK-TH2021_Anderson.pdf

11:50 → 14:00 Lunch break

14:00 → 14:20 Short talk: Hidenori Fukaya (Osaka U.) "What is chiral susceptibility probing?"

Convener: Prof. Shinsuke Nishigaki (Shimane U.)

14:00 What is chiral susceptibility probing?

In the early days of QCD, the axial U(1) anomaly was considered to trigger the breaking of the SU(2)_L ×SU(2)_R symmetry through topological excitations of gluon fields. However, it has been a challenge for lattice QCD to quantify the effect. In this work, we simulate QCD at high temperatures with the overlap Dirac operator. The exact chiral symmetry enables us to separate the contribution from the axial U(1) breaking from others among the susceptibilities in the scalar and pseudoscalar channels. Our result in two-flavor QCD indicates that the chiral susceptibility, which is conventionally used as a probe for SU(2)_L×SU(2)_R breaking, is actually dominated by the axial U(1) anomaly at temperatures T ≥ 165 MeV.

Speaker: Prof. Hidenori Fukaya (Osaka University)

14:20 → 14:40 Short talk: Shoto Aoki (Osaka U.) "Chiral fermion on curved domain-wall"

Convener: Prof. Shinsuke Nishigaki (Shimane U.)

14:20 Chiral fermion on curved domain-wall

We consider a massive fermion system having a curved domain-wall embedded in a square
lattice. As already reported in condensed matter physics, the massless chiral edge modes
appearing at the domain-wall feel “gravity” through the induced spin connections. In this
work, we embed S^1 and S^2 domain-wall into a Euclidean space and show how the gravity is
detected from the spectrum of the Dirac operator.

Speaker: Mr Shoto Aoki (Osaka University)

14:40 → 15:00 Short talk: Akira Matsumoto (SOKENDAI) "Complex Langevin simulation of 4D SU(2) gauge theory with a theta term"

Convener: Prof. Shinsuke Nishigaki (Shimane U.)

14:40 Complex Langevin simulation of 4D SU(2) gauge theory with a theta term

The Monte Carlo simulation of the gauge theory with a theta term is extremely difficult due to the sign problem. The complex Langevin method (CLM) is one of the approaches which allow us to avoid the problem. Recently the analytic study of 't Hooft anomaly matching condition predicted some nontrivial phase structures around θ=π. We use CLM to study 4D SU(2) gauge theory with a theta term. Since the topological charge on the lattice is contaminated by short-range fluctuations, we apply the stout smearing to recover the topological property. In this method, the effect of the smearing can be included dynamically. We discuss the relation between the validity of CLM and the behavior of the topological charge.

Speaker: Mr Akira Matsumoto (SOKENDAI)

15:00 → 15:20 Short talk: Atis Yosprakob (SOKENDAI) "Tensor renormalization group and the volume independence in 2D U(N) and SU(N) gauge theories"

Convener: Prof. Shinsuke Nishigaki (Shimane U.)

15:00 Tensor renormalization group and the volume independence in 2D U(N) and SU(N) gauge theories

The tensor renormalization group method is a promising approach to lattice field theories, which is free from the sign problem unlike standard Monte Carlo methods. In this work, we apply the method to two dimensional U(N) and SU(N) gauge theories, where we propose a practical strategy to restrict the number of representations in the character expansion when constructing the fundamental tensor. Using this, we investigate the behaviour of singular values in the large-N limit and propose a novel interpretation of the Eguchi-Kawai reduction in the context of TRG. Additionally, with the presence of a theta term, we find a new type of volume independence in the strong-coupling phase, which goes beyond the Eguchi-Kawai reduction.

Speaker: Mr Atis Yosprakob (SOKENDAI)

15:20 → 16:00 Break

16:00 → 16:20 Short talk: Naoki Fukushima (Chiba U.) "Color confinement due to restoration of the residual local gauge symmetry"

Convener: Prof. Asato Tsuchiya (Shizuoka U.)

16:00 Color confinement due to restoration of the residual local gauge symmetry

All colored particles including dynamical quarks and gluons are confined if the color confinement
criterion proposed by Kugo and Ojima is satisfied. The criterion was obtained under
the gauge fixing of the Lorenz type. However, it was pointed out that the Kugo-Ojima criterion
breaks down for the Maximal Abelian gauge, which is quite strange in view of the fact
that quark confinement has been verified according to the dual superconductivity caused
by magnetic monopole condensations. In order to make a bridge between color confinement
due to Kugo and Ojima and the dual superconductor picture for quark confinement, we
reconsider the color confinement criterion to obtain the unified picture for confinement. We
show that the restoration of the residual local gauge symmetry which was shown by Hata to
be equivalent to the Kugo-Ojima criterion in the Lorenz gauge occurs also in the Maximal
Abelian gauge for the SU(N) Yang-Mills theory in two-, three- and four-dimensional Euclidean
spacetime once the singular topological configurations of gauge fields are taken into
account. This result indicates that the color confinement phase is a disordered phase caused
by non-trivial topological configurations irrespective of the gauge choice. As a byproduct,
we show that the compact U(1) gauge theory can have the disordered confinement phase,
while the non-compact U(1) gauge theory has the deconfined Coulomb phase.

Speaker: Mr Naoki Fukushima (Chiba University)

16:20 → 16:40 Short talk: Yusuke Kimura (KEK) "4D N = 1 SCFTs on S-folds with T-branes"

Convener: Prof. Asato Tsuchiya (Shizuoka U.)

16:20 4D N=1 SCFTs on S-folds with T-branes

We discuss four-dimensional (4d) N=1 superconformal field theories (SCFTs) obtained as deformations of 4d N=2 SCFTs on S-folds by tilting 7-branes. Geometric compatibility with the structures of S-folds constrains the forms of T-branes.

Speaker: Dr Yusuke Kimura (KEK)

16:40 → 17:00 Short talk: Kohta Hatakeyama (KEK) "Signature change of the space-time in the type IIB matrix model"

Convener: Prof. Asato Tsuchiya (Shizuoka U.)

16:40 Signature change of the space-time in the type IIB matrix model

We perform numerical studies of the type IIB matrix model, which was proposed as a
nonperturbative formulation of superstring theory in 1996. In our study, we apply the
complex Langevin method in order to overcome the sign problem, which occurs in Monte
Carlo simulations. In particular, we investigate a scenario on how the signature of space-time
could be determined dynamically in this model and discuss the possibility of the emergence
of the (3+1)D expanding universe.

Speaker: Dr Kohta Hatakeyama (KEK)

17:00 → 17:20 Short talk: Matsuo Sato (Hirosaki U.) "Perturbative Strings on Various Curved Backgrounds from String Geometry Theory"

Convener: Prof. Asato Tsuchiya (Shizuoka U.)

17:00 Perturbative Strings on Various Curved Backgrounds from String Geometry Theory

One perturbative string theory is defined on one fixed background. On the other hand, it is necessary that a non-perturbative formulation of string theory includes all the perturbatively stable vacuum and perturbative string theories on various curved backgrounds are derived from the single theory. In this talk, we derive perturbative string theories on various curved backgrounds from the fluctuations around fixed backgrounds in a single string geometry theory, which is one of the candidates of the non-perturbative formulation of string theory.

Speaker: Prof. Matsuo Sato (Hirosaki University)

17:20 → 17:30 Closing adress

Convener: Prof. Shun'ya Mizoguchi (KEK)