TALKS

Boundaries and corners in supersymmetric gauge theories

Tadashi Okazaki (KIAS)

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I will discuss recent studies of boundary and corner configurations in supersymmetric gauge theories. They involve various dualities across the dimensions of spacetime and potential applications to twisted holography from their brane constructions in the context of twisted M-theory.

Wilson loops in 5d supersymmetric gauge theories 

Xin Wang (KIAS)

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In the supersymmetric version of gauge theories in 5d, the insertion of half-BPS Wilson loop operators provides interesting physical observables. In this talk, I will review the recent progress in calculating the 5d Wilson loop expectation values in supersymmetric gauge theories.

Kite and Triangle diagrams through Symmetries of Feynman Integrals

Subhajit Mazumdar (SNU)

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The Symmetries of Feynman Integrals (SFI) is a method for evaluating Feynman Integrals which exposes a novel continuous group associated with the diagram which depends only on its topology and acts on its parameters. Using this method we study the kite diagram (a two-loop diagram with two external legs) and the most general triangle diagram (one-loop diagram with three external legs) with arbitrary masses and space-time dimensions. Generically, this method reduces a Feynman integral into a line integral over simpler diagrams. We identify the locus/loci in parameter space where the integrals further reduce to a mere linear combination of simpler diagrams. We generalize and revisit some known results.

Lecture: Schwinger-Keldysh formalism and open field theories

Akhil Sivakumar (ICTS)

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Schwinger-Keldysh path integral is a technique to study evolution of mixed states. In this lecture, I will introduce this formalism and explain how it can be used to compute the effective action of a quantum system interacting with a bath. Such a system will undergo non-unitary evolution and is an open quantum system. Using the toy model of a Brownian particle, I will show how the data contained in the SK description can be mapped to the more familiar form of a Langevin equation.

Real-time gravitational replicas

Mukund Rangamani (UC Davis)

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I will discuss real-time path integrals in gravitational theories. As applications we will describe the general structure of replica wormhole saddles and exemplify them with some low dimensional examples. Time permitting, I will also mention,  some aspects of effective dynamics of open quantum systems with long-term memory.

Analyticity and Unitarity for Cosmological Correlators

Shota Komatsu (CERN)

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I will discuss the fundamentals of quantum field theory on a rigid de Sitter space. First, I will show that the perturbative expansion of late-time correlation functions to all orders can be equivalently generated by a non-unitary Lagrangian on a Euclidean AdS geometry. This finding simplifies dramatically perturbative computations, as well as allows us to establish basic properties of these correlators, which comprise a Euclidean CFT. Second, I use this to infer the analytic structure of the spectral density that captures the conformal partial wave expansion of a late-time four-point function, to derive an OPE expansion, and to constrain the operator spectrum. Third, I will prove that unitarity of the de Sitter theory manifests itself as the positivity of the spectral density. This statement does not rely on the use of Euclidean AdS Lagrangians and holds non-perturbatively.

Hydrodynamics beyond hydrodynamics

Pavel Kovtun (University of Victoria)

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In this talk, I will discuss two questions. First, do the equations of relativistic hydrodynamics make sense? And second, are the long-distance, late-time predictions of classical hydrodynamics universal?

Strong coupling models for dense and hot QCD

Matti Jarvinen (APCTP)

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Gauge/gravity duality can be useful to model QCD at intermediate temperatures and densities, where first-principles results are not available. This region is relevant for core-collapse supernovae and binary neutron star mergers. I present a new framework for the QCD equation of state which combines the holographic V-QCD model with traditional nuclear theory models, and covers all relevant temperatures and densities. I use V-QCD to describe both nuclear and quark matter at high densities, with temperature dependence estimated by employing a simple van der Waals hadron gas model. At low densities, I use DD2 Hempel-Schaffner-Bielich model, i.e., a statistical model for nuclear matter with relativistic mean field interactions. The resulting "hybrid" model gives predictions, among other things, for the mixed quark-hadron phase and the location of the critical endpoint of the quark-hadron transition. I will also discuss preliminary results from neutron star merger simulations which use this model.

Quantum Perturbiner Method

Kanghoon Lee (APCTP)

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We construct the off-shell recursion relation for arbitrary loop-level scattering amplitudes beyond the tree-level Berends-Giele recursion relation for any quantum field theory. We define the quantum perturbiner expansion from the quantum effective action formalism, including the perturbative quantum corrections. Instead of the classical EoM in the conventional perturbiner method, we exploit the Dyson-Schwinger equation to derive the recursion relation for arbitrary order of loop-level scattering amplitudes. Furthermore, we extend this technique to compute the loop-level correlation functions.

Identifying Riemannian singularities with regular non-Riemannian geometry

Miok Park (IBS-CTPU)

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Admitting non-Riemannian geometries, Double Field Theory extends the notion of spacetime beyond the Riemannian paradigm. We identify a class of singular spacetimes known in General Relativity with regular non-Riemannian geometries. The former divergences merely correspond to coordinate singularities of the generalised metric for the latter. Computed in string frame, they feature an impenetrable non-Riemannian sphere outside of which geodesics are complete with no singular deviation. Approaching the non-Riemannian points, particles freeze and strings become (anti-)chiral.

Breakdown of hydrodynamics in fracton fluids below four dimensions

Paolo Glorioso (Stanford University)

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Fracton phases are characterized by that their elementary excitations have restricted mobility. In the context of hydrodynamics it has been shown theoretically, and confirmed experimentally, that such restricted mobility leads to novel emergent scaling laws. In this talk, I will introduce the hydrodynamics of fractons with translation symmetry, focusing on the simplest case where dipole moment is the only additional conserved quantity. This hydrodynamics turns out to have rather exotic properties, owing to the fact that translation invariance leads to a non-trivial extension of spacetime symmetries. Using an effective field theory approach that allows to account for stochastic fluctuations, I will show that this hydrodynamics contains relevant nonlinearities that lead to the emergence of a non-Gaussian "fractonic" universality class, thus constituting a breakdown of its local hydrodynamic description.

Fractons, geometrically

Stephen Angus (APCTP)

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I will discuss how fracton physics can be studied systematically within the geometric framework of Double Field Theory (DFT).  Following an introductory review of fractons, I will argue that their restricted mobility and large degeneracy of quantum states can be attributed to the generalized geodesics and infinite-dimensional isometries present in non-Riemannian backgrounds of DFT.  Furthermore, we find that a doubled pure Yang-Mills or Maxwell theory reduces to an ordinary one interacting with a strain tensor theory, giving a unifying description of photons and phonons.  I will show how this photon-phonon theory, when minimally coupled to a charged particle in a non-Riemannian background, lifts the particle immobility to a saturation velocity and gives a modified dispersion relation.

Holographic teleportation with conservation laws: diffusion on traversable wormholes

Viktor Jahnke (GIST)

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We study the effects of conservation laws on wormholes that are made traversable by a double trace deformation. After coupling the two asymptotic boundaries of an eternal AdS-Schwarzschild black hole with U(1) conserved current operators, we find that the corresponding quantum matter stress-energy tensor violates the averaged null energy condition (ANEC) in the bulk, rendering the wormhole traversable. We discuss how the wormhole opening depends on the charge diffusion constant and how this affects the amount of information that can be sent through the wormhole.

New  dualities between 2d rational CFTs

Kaiwen Sun (KIAS)

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I discuss some interesting new developments on 2d rational CFTs, which are basic tools for both string theory and condensed matter theory. For the last a few years, holomorphic modular bootstrap has become a powerful approach to classify 2d rational CFTs with given number of characters. A large number of new CFTs have been revealed. Benefited from the recent results on the classification, a new pattern of duality emerges for pairs of two CFTs with sumation of their central charge as 24. The characters of the dual CFTs satisfy certain universal bilinear relations. We systemically study such duality among 2d rational CFTs with less than six characters. This is based on a recent work with Zhihao Duan and Kimyeong Lee.

How fast do open quantum systems relax?

Taiki Haga (Osaka Metropolitan University)

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Quantum systems coupled to environments relax to a highly mixed steady state after a sufficiently long time. This process is called decoherence. In recent years, with the progress of quantum control and quantum information technology, decoherence in quantum many-body systems has attracted much attention. A fundamental question here is what determines the timescale for an open quantum system to reach a steady state. In isolated quantum systems, the spectral gap of a Hamiltonian determines the timescale of low-energy excitations. Similarly, it has been postulated in many studies that the relaxation time of open quantum systems is given by the inverse of the spectral gap of a Liouvillian that governs the time evolution of the density matrix [1]. Recently, however, several examples have been reported in which the relaxation time and the inverse of the Liouvillian gap scale with different exponents with respect to the system size [2]. The mechanism of such discrepancy between the relaxation time and Liouvillian gap is not yet understood. In this presentation, I propose one scenario that leads to divergence of the relaxation time without closing the Liouvillian gap [3]. A key phenomenon is the Liouvillian skin effect, which means that the eigenmodes of the Liouvillian are localized exponentially near the boundary of the system. We show that, if the Liouvillian skin effect takes place, the conventional relationship between the relaxation time and the Liouvillian gap breaks down. Instead, we find a novel relation connecting the relaxation time with the Liouvillian gap and the localization length of eigenmodes. This result implies that the relationship between relaxation of open quantum systems and structure of the Liouvillian spectrum is far more subtle than usually expected.  

 

[1] M. Znidaric, Phys. Rev. E 92, 042143 (2015)

[2] T. Mori and T. Shirai, Phys. Rev. Lett. 125, 230604 (2020)

[3] T. Haga, M. Nakagawa, R. Hamazaki, and M. Ueda, Phys. Rev. Lett. 127, 070402 (2021)

Operator delocalization in quantum networks

Dario Rosa (PCS-IBS)

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I will introduce the notion of operator delocalization, to be contrasted with the more conventional notion of operator growth. I will show that even free quantum mechanical systems, once defined on sufficiently connected networks, can exhibit non-trivial delocalization properties. Some preliminary results on the connection between operator delocalization and quantum many-body chaos will be discussed.
As an application, I will show that the notion of operator delocalization is at the core of the observed quantum charging advantage of a class of quantum batteries based on SYK-like models.

Janus Interfaces, S-Folds, and Conformal Manifolds

Jesse Van Muiden (SISSA)

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In this talk I will present some recent holographic studies on Janus interfaces in four-dimensional N=4 SYM, and the CFTs living on these interfaces. Interestingly, these theories can be compactified on S^1, with an S-duality twist, resulting in a new class of three-dimensional CFTs, known as S-folds. Finally, I will discuss the conformal manifolds on which these S-fold CFTs lie, which preserve either three-dimensional N=1 or N=2 supersymmetry.

Defect black hole horizons and new SCFT twists

Chris Couzens (Kyunghee University)

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In this talk we will give a pedagogical review of new (supersymmetric) black hole horizons containing defects, that have appeared recently in the literature. These 2d horizons are topologically punctured two-spheres, with at least two punctures, and are equipped with non-constant curvature metrics. They arise when considering the near-horizon limit of extremal asymptotically AdS accelerating black holes. Interestingly, despite the black hole solutions having singularities, by uplifting the solutions to string theory the solution can be made singularity free in certain cases. By using AdS/CFT we have a complimentary dual field theory perspective. The near-horizon geometry corresponds to the fixed point of an RG-flow across dimensions, triggered by wrapping a parent theory  on the 2d horizon. As we will show, in order for the fixed point to preserve supersymmetry, the introduction of new and novel twists of the theory is required. We will make some comments on performing a microstate computation of the entropy of the black hole.