The NITEP Theoretical Physics Seminar Series delves into quantum field theory and its related disciplines.
This series aims to explore specialized topics, including the latest advancements in gauge fields, contemporary issues in string theory, and quantum gravity, while also touching on some phenomenological and observational aspects.

All seminars are conducted online, with Zoom links sent to registered participants via email shortly before each session.

To participate, please register through this Google Form. Detailed information for each seminar will be provided via email.

**M2-M5 giant graviton expansions indico link**

Date: November 29 (Fri), 17:30 (JST)

Speaker: Tadashi Okazaki (Yau Center of Southeast University)

Title: M2-M5 giant graviton expansions

Abstract: We investigate exact closed-forms for supersymmetric indices of the theories describing a stack of N M2-branes and their giant graviton expansions. We demonstrate that M2-branes can hold a lesson for M5-branes and vice versa via the reversible giant graviton expansions of the indices. Consequently, we obtain several exact closed-form expressions for the indices of 6d (2,0) theory describing a stack of N M5-branes. The talk will be based on the collaborative work with Hirotaka Hayashi and Tomoki Nosaka [arXiv: 2409.13239].

**Islands in black hole spacetimes indico link**

Date: November 5 (Tue), 9:00(JST)

Speaker: Yoshinori Matsuo (Kindai Univerisity)

Title: Islands in black hole spacetimes

Abstract: Recently, it was proposed that the Page curve is reproduced by using the prescription of islands. The island prescription is first proposed in the framework of holography. By using the formula of the quantum extremal surface, it turns out that there is a region which is not covered by the entanglement wedge of the CFT after a sufficient amount of Hawking radiation has got outside of the AdS spacetime. This region, which is called the island, is interpreted as a part of the entanglement wedge of (a dual of) the Hawking radiation. The same formula can be obtained by using the replica trick for theories with gravity, and hence, can be applied for any black holes without relying on holography. In this talk, we discuss islands in general black holes with non-degenerate horizons.

**Black Hole from Entropy Maximization indico link**

Date: October 8 (Tue), 9:00(JST)

Speaker: Yuki Yokokura (RIKEN)

Title: Black Hole from Entropy Maximization

Abstract: The identity of a black hole is still mysterious theoretically and observationally. It has the thermodynamic entropy (the Bekenstein-Hawking entropy). According to quantum theory and thermodynamics, the origin of thermodynamic entropy is quantum mechanical. Therefore, a black hole should be essentially a quantum object. So, what is the quantum definition/characterization of black holes? One candidate motivated by (local) holography and thermodynamics is that a black hole maximizes thermodynamic entropy for a given (expectation value of) surface area. As a step toward exploring this possibility, we study the entropy of various highly-excited spherical static configurations in the 4D semi-classical Einstein equation with many matter fields, and reach uniquely the entropy-maximizing configuration. That is, self-gravitating quanta condensate into a radially-uniform dense configuration with no horizon, where the self-gravity and a large quantum pressure induced by the curvatures are balanced and no singularity appears. The interior metric is a self-consistent and non-perturbative solution for Planck's constant. The maximum entropy, given by the volume integral of the entropy density, agrees exactly with the Bekenstein-Hawking formula through the self-gravity, leading to the Bousso bound for thermodynamic entropy. Finally, we see a speculative view that the configuration represents semi-classically a quantum-gravitational condensate. [arXiv:2309.00602]

**Magnetic Quivers and Phase Diagrams indico link**

Date: 17 September (Tue) 17:30 (JST)

Speaker: Amihay Hanany(Imperial Coll.)

Title: Magnetic Quivers and Phase Diagrams

Abstract: Higgs branches in theories with 8 supercharges change as one tunes the gauge coupling to critical values. This talk will focus on six dimensional (0,1) supersymmetric theories in studying the different phenomena associated with such a change. Based on a Type IIA brane system, involving NS5 branes, D6 branes and D8 branes, one can derive a "magnetic quiver” which enables the construction of the Higgs branch using a “magnetic construction” or as a more commonly known object “3d N=4 Coulomb branch”. Interestingly enough, the magnetic construction opens a window to a new set of Higgs branches which were not available using the well studied method of hyperkähler quotient. It turns out that exceptional global symmetries are fairly common in the magnetic construction, and few examples will be shown. In all such cases there are strongly coupled theories where Lagrangian description fails, and the magnetic construction is helpful in finding properties of the theory. Each Higgs branch can be characterized by a phase diagram which describes the different sets of massless fields around vacua. We will use such diagrams to study how Higgs branches change. If time permits we will show an interesting exceptional sequence consisting of SU(3) — G2 — SO(7).

**Asymptotically Safe Quantum Gravity and Essential RG indico link**

Date: 27 August (Tue) 17:30 (JST)

Speaker: Nobuyoshi Ohta (Kindai U./APCTP)

Title: Asymptotically Safe Quantum Gravity and Essential RG

Abstract: We first explain one of the approaches to quantum gravity based on the Functional Renormalization Group, what is called asymptotic safety. The main issue is how to control the high energy behavior of the gravity theory, keeping predictability without ghosts (negative metric states). Asymptotic safety tries to achieve this goal by finding UV fixed points of the finite number of the gravitational couplings. We discuss how to deal with the wave function renormalization, which is one of the inessential couplings, which do not affect physical quantities. We find that higher derivative operators are necessary but with Gaussian fixed point. This leads to negative metric states. We suggest that a possible resolution of this conflict may be the essential RG which deals with only the essential couplings.

**Eigenvalue method for multi-matrix invariants indico link**

Date: July 30th (Tue), 17:30 (JST)

Speaker: Ryo Suzuki (Shing-Tung Yau Center of Southeast University)

Title: Eigenvalue method for multi-matrix invariants

Abstract: Multi-matrix invariants, or equivalently the scalar multi-trace operators of N=4 super Yang-Mills with U(N) gauge symmetry, are in one-to-one correspondence with the elements of the permutation centralizer algebra (PCA), which is a generalisation of the symmetric group algebra. We develop a new method to explicitly construct all the irreducible representations of PCA up to a modest value of the operator length. The main idea is to consider the eigensystem of the commuting subalgebras of PCA, and to identify the eigenvectors with the orthonormal bases of operators of N=4 SYM, known as the restricted Schur basis and covariant basis. Furthermore, we find that all the coefficients of these operator bases, or equivalently eigenvector elements, can be integer.

This talk is based on arXiv:2408.nnnnn, done in collaboration with S. Ramgoolam (QMUL) and Adrian Padellaro (Bielefeld).

**Field theory for branes and higher-form symmetry indico link**

Date: July 18th (Thu), 9:00(JST)

Speaker: Kiyoharu Kawana (KIAS)

Title: Field theory for branes and higher-form symmetry

Abstract: We propose field theory for branes with higher-form symmetry. The field \psi is no longer a mere function of spacetime point but a functional of p-dimensional closed brane C_p embedded in a spacetime. We show that it is possible to construct an action that is invariant under higher-form transformation by utilizing the “area derivative”, which is a generalization of ordinary derivative \partial/\partial X^\mu. Then, we discuss various fundamental properties of this theory. The classical solution exhibits the area law in the unbroken phase of p-form symmetry, while it indicates a constant behavior (Perimeter law) in the broken phase. In the latter case, the low-energy effective theory is described by the p-form Maxwell theory.

When time permits, I will also discuss gauged version of the brane-field theory and show that it is indeed a generalization of the Ginzburg-Landau theory for superconductivity.

**Toward quantitative Swampland physics indico link**

Date: June 27 (Thr), 9:00(JST)

Speaker: Yuta Hamada (KEK)

Title: Toward quantitative Swampland physics

Abstract: The Swampland bounds are quantum gravity constraints on the low-energy physics. In this talk, I will focus on recent efforts towards developing quantitative Swampland physics. After reviewing the recent progress in this field, I will talk about my recent works on 6d supergravity. I will enumerate the consistent supergravity theories, and then discuss the Swampland bounds on them. I will also discuss the universality of F-theory constructions.

**Universal Spectrum of Superconformal Field Theory and Holography indico link**

Date: June 11 (Tue), 17:30 (JST)

Speaker: Jaewon Song (KAIST)

Title: Universal Spectrum of Superconformal Field Theory and Holography

Abstract: In the celebrated work of Cardy, he derived universal formula for the density of states at high-temperature in two-dimensional CFT. We study an analog of Cardy’s formula of in four-dimensional superconformal theory (SCFT). We also find that large N limit of the 4d supersymmetric index agrees with the Cardy limit when underlying theory is ‘holographic,’ meaning that it admits a dual AdS5 description. We apply the large N formula for the supersymmetric index to model an information loss problem in quantum gravity. Here we find that non-perturbative saddles that correspond to orbifolded Euclidean black holes play a crucial role to cure the “information loss.”