# abstracts

Tue 30 May

0930-1015 talk: Niels Obers

Title: Carroll symmetry in field theory, gravity and string theory

Abstract: Carroll symmetry arises from Lorentzian symmetry when sending the speed of light to zero, which is also called an ultra-local limit. I will start with a brief overview of

the relevance of Carroll symmetry and Carroll geometry. I will then review some essential features of Carroll symmetry which will be illustrated by discussing some properties of Carroll particles as well as some simple field theory models of scalars and electrodynamics. I will then discuss how Carroll geometry and Carroll gravity arises from the small speed of light expansion of General Relativity, and also present some simple solutions of what is known as electric and magnetic Carroll gravity respectively. Finally, I will briefly comment on the appearance of Carroll symmetry

in novel worldsheet models arising in non-relativistic corners of string theory.

1045-1130 talk: Charlotte Kristjansen

Title: Integrable Monopoles

Abstract: We consider the defect CFT defined by a ’t Hooft line embedded in N = 4 super Yang-Mills theory. By explicitly quantizing around the given background we exactly reproduce a prediction from S-duality for the correlators between the ’t Hooft line and chiral primaries in the bulk and pave the way for higher loop analyses for non-protected operators. Furthermore, we demonstrate at the leading perturbative order that correlators between the ’t Hooft line and non-protected bulk operators can be efficiently computed using integrability.

1130-1215 talk: Suddhasattwa Brahma

Title: Entanglement, non-equilibrium dynamics & complexity in de Sitter

Abstract: I will show why momentum-space entanglement is an essential concept in early universe cosmology and derive quantum corrections to cosmological observables. This will demonstrate explicitly why it is important to go beyond standard (Wilsonian) effective field theory in cosmology. Going beyond entanglement entropy, I will discuss complexity in de Sitter space and, time permitting, briefly highlight why this quantum informatic measure is pivotal for establishing cosmic ER=EPR.

1345-1430 talk: Niko Jokela

Title: Precision Holography

Abstract: Gauge/gravity duality is a great vehicle to guide one's path when strongly coupled. We show that this duality will explain many unusual scaling laws for bipartite entanglement entropy and quark-anti-quark potentials present in the numerical data we obtain from the lattice Yang-Mills theory in three- and four dimensions. We also discuss their dual gravity descriptions.

1430-1515 talk: Ashish Shukla

Title: Entanglement and complexity for CFTs dual to AdS3 black holes with end of the world branes

Abstract: In the talk, I will discuss planar AdS3 black hole geometries with an end of the world (ETW) brane embedded in them, cutting off the second asymptotic region of the maximally extended spacetime. I will consider the ETW brane to have possible gravitational dynamics localized on it, the simplest possibility for which is to have JT gravity on the brane. Interestingly, as I will illustrate, bounds on the allowed rate of growth of entanglement in the CFT state dual to this geometry constrain the allowed values for the JT coupling on the brane. Also, by looking at the asymptotic growth of entanglement in the CFT state, one can read-off the brane parameters in the dual geometry, such as its location in the bulk and the value of the JT coupling. I will also comment about the holographic volume complexity and its time dependence for these geometries.

1545-1630 talk: Nima Lashkari

Title: Information loss, black holes, and algebras in time

Abstract: A manifestation of the black hole information loss problem is that the two-point function of probe operators in an eternal AdS black hole decays exponentially fast in time, whereas, on the boundary, it is expected to be an almost periodic function of time. We point out that the decay of the two-point function (clustering in time) holds important clues to the nature of observable algebras, states, and dynamics in quantum gravity. In the thermodynamic limit of infinite entropy (infinite volume or large N), the operators that cluster in time are expected to form an algebra. We prove that this algebra is a unique and very special infinite dimensional algebra called the III factor. This has implications for the emergence of a local bulk in holography.

An important example is N = 4 SYM, above the Hawking-Page phase transition. The clustering of the single trace operators implies that the algebra is a type III factor. We prove a generalization of a conjecture of Leutheusser and Liu to arbitrary out-of-equilibrium states. We explicitly construct the C-algebra and von Neumann subalgebras associated with time bands and more generally, arbitrary open sets of the bulk spacetime in the strict N\to\infty limit. The emergence of time algebras is intimately tied to the second law of thermodynamics and the emergence of an arrow of time.

1630-1715 talk: Jelle Hartong

Title: On the 1/c expansion of GR for a radiating source

Abstract: I will discuss the covariant non-relativistic expansion of GR in powers of 1/c for the case of a compact perfect fluid matter source that can radiate gravitational waves. This is a well-studied scenario in the literature and is nowadays conventionally studied using the approach developed amongst others by Blanchet and Damour. This approach uses the harmonic gauge and a rather strong set of boundary conditions. Our aim is to modify their methods so as to make them more covariant and to investigate the consequences of working with the weakest possible boundary condition that ensures that there is no incoming radiation at past null infinity. Another motivation was to make contact between the literature on post-Newtonian expansions and the literature on the covariant 1/c expansion. The final motivation was to pave the way to consider 1/c expansions around non-flat backgrounds. It is well-known that the covariant 1/c expansion works outside the context of a weak field expansion around flat space and so we would like to see if this can be used as an approximation scheme to study radiating sources.

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Wed 31 May

0930-1015 talk: Juan F. Pedraza

Title: Gravitation from optimized computation

Abstract: Inspired by the universality of computation, I advocate for

a notion of spacetime complexity, where gravity arises as a

consequence of spacetime optimizing the computational cost of its

quantum dynamics. This principle is realized in the context of

holography, where complexity is understood in terms of state

preparation via Euclidean path integrals, and the linearized equations

of motion, for any theory of gravity, emerge from the first law of

complexity. This suggests gravity has a computational origin. When the

leading 1/N bulk quantum corrections are included, the holographic

first law is modified by an additional term which could be interpreted

as `bulk complexity’. This leads to a derivation of semi-classical

gravitational equations of motion.

1045-1130 talk: Dimitrios Patramanis

Title: The Krylov Panopticon

Abstract: In recent years the notion of computational complexity has become the object of intensive study for physicists despite the fact that it is a concept originating from computer science. So why is the physics community so interested in this particular topic and what can we hope to learn from it? In my talk I will briefly address these questions in a general context and then proceed to discuss the measure called Krylov complexity in particular. This measure, although one of many, has become very popular because of its wide range of applicability and computability. I will elaborate on these qualities by reviewing its construction and highlighting certain aspects that in principle make it an interesting probe for any quantum system. Hence, it can be likened to a panopticon from which one can gain access to information about systems ranging from condensed matter to exotic QFTs and possibly holography. Finally, I will present some of the latest advancements and discuss how they shape our current understanding of Krylov complexity and its place in the “zoo” of complexity measures.

1130-1215 talk: Victoria Martin

Title: Lessons from the quotient structure of spacetime: flat space cosmology edition

Abstract: In this talk we revisit the quotient structure of flat space cosmologies (FSCs) (also known as symmetric boost orbifolds) to independently determine the quasinormal modes (QNMs) on these backgrounds, which in principle require non-trivial boundary conditions due to the timelike horizon. We construct a Selberg-like zeta function for FSCs, and claim its zeros are mapped to the QNMs. This extends previous zeta function constructions from hyperbolic quotients to flat space quotients. The relevance to the QNM method of Denef, Hartnoll and Sachdev is discussed.

1345-1430 talk: Jørgen Musaeus

Title: A Covariant Approach to the Post-Newtonian Approximation

Abstract: In this talk I present the covariant 1/c-expansion of general relativity and how it relates to the well-known post-Newtonian expansion. The 1/c-expansion is an expansion of general relativity around the limit in which the tangent space lightcone flattens. This differentiates the 1/c-expansion from the post-Newtonian expansion, as it does not assume the gravitational field strength to be weak a priori. Thus, the 1/c-expansion is able to capture strong gravitational effects, such as gravitational time dilation at leading order, giving rise to a new approximation of general relativity. However, this talk is going to be focused on how to filter out the strong field effects and make contact with the post-Newtonian approximation. This is an important step in understanding the 1/c-expansion as a whole, and it gives us a new framework for post-Newtonian gravity based on Newton-Cartan geometry, the novel feature of which is covariance. Furthermore, due to the limited region of validity of the post-Newtonian approximation, the 1/c-expansion cannot stand alone. Thus, we are forced to use the methods matched asymptotic expansions with a post-Minkowskian expansion far away from the matter source. I will explain how this work in our framework. Then making use of the covariance, I will consider post-Newtonian gravity in a new gauge, different to the standard harmonic gauge that much of the modern theory relies on. Finally, I will give an outlook on other potential uses of this new framework and summarise what we have learned about the covariant 1/c-expansion.

1430-1515 talk: Andrew Svesko

Title: The minus sign in the first law of de Sitter horizons

Abstract: While formally analogous, the thermodynamics of the de Sitter cosmological horizon is more subtle than its black hole counterpart. For example, the first law of de Sitter horizons has a minus sign indicating the entropy of a cosmological horizon is reduced by the addition of matter Killing energy. Even more, there is no asymptotic boundary in de Sitter space where thermodynamic data may be fixed to sensibly define a thermal ensemble. In this talk, I will discuss how both of these issues can be clarified by introducing a finite timelike boundary inside the de Sitter static patch. In particular, I will argue the confusion about the minus sign in the first law is due to a mistaken interpretation of the added Killing energy as the total internal energy. Rather, the total energy of the canonical ensemble is given by the quasi-local Brown-York energy. In the limit the boundary shrinks to zero size, the standard Gibbons-Hawking result is recovered. If the Killing matter is in global equilibrium at the de Sitter temperature, the first law becomes the statement that the generalized entropy is stationary. With time permitting, I will discuss how de Sitter thermodynamics with timelike boundaries relates to various proposals of de Sitter holography.

1545-1630 talk: Rahul Poddar

Title: TTbar deformations of Holographic Warped CFTs

Abstract: We explore TTbar deformations of Warped Conformal Field Theories (WCFTs) in two dimensions, which are quantum field theories with a Virasoro×U(1) Kac-Moody symmetry, as examples of TTbar deformed non-relativistic quantum field theories. We compute the deformed symmetry algebra of a TTbar deformed holographic WCFT, using the asymptotic symmetries of AdS3 with TTbar deformed Compére, Song and Strominger (CSS) boundary conditions. The U(1) Kac-Moody symmetry survives provided one allows the boundary metric to transform under the asymptotic symmetry. The Virasoro sector remains but is now deformed and no longer chiral.

1630-1715 talk: Friðrik Gautason

Title: Worldsheet instantons in holography

Abstract: I will discuss worldsheet instanton corrections to holographic observables in type IIA string theory. I will focus on two holographic backgrounds dual to supersymmetric Yang-Mills theory in five dimensions and ABJM. We will compute the one-loop string partition function for a tower of worldsheet instantons and show that they reproduce non-perturbative corrections to the sphere partition function of the QFT which can be computed directly in field theory using supersymmetric localization.

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Thu 01 June

0930-1015 talk: Troels Harmark

Title: The Panorama of Spin Matrix Theory

Abstract: TBA

1045-1130 talk: Eleni Alexandra Kontou

Title: Non-minimal coupling and negative null energies

Abstract: Even classical non-minimally coupled scalar fields can violate energy conditions such as the NEC. In the context of QFT, non-minimally coupled scalars can obey lower bounds, known as quantum energy inequalities, but these are always state dependent. In this talk I will discuss classical and quantum bounds on the null energy and consider possible violations. Further, I will examine the conformal transformation between Jordan and Einstein frames both classically and semiclassically. Finally, I will comment on extensions of this work on self-interacting fields.

1130-1215 talk: Sergio Aguilar

Title: Complexity = Anything Can Grow Forever in de Sitter

Abstract: Recent developments in anti-de Sitter holography point towards the association of an infinite class of covariant objects, the simplest one being codimension-one extremal volumes, with quantum computational complexity in the microscopic description. One of the defining features of these gravitational complexity proposals is describing the persistent growth of black hole interior in classical gravity. It is tempting to assume that the gravitational complexity proposals apply also to gravity outside their native anti-de Sitter setting in which case they may reveal new truths about these cases with much less understood microscopics. Recent first steps in this direction in de Sitter static patch demonstrated a very different behavior from anti-de Sitter holography deemed hyperfast growth: diverging complexification rate after a finite time. We show that this feature is not a necessity and among gravitational complexity proposals there are ones, which predict linear or exponential late-time growth behaviors for complexity in de Sitter static patches persisting classically forever.

1345-1430 talk: Oscar Henriksson

Title: First order phase transitions and holography

Abstract: First order phase transitions typically proceed through the nucleation and expansion of bubbles. This talk will focus on the study of such nucleation at strong coupling using holographic duality. I will show, in a simple toy model, how to compute quantities of interest in (for example) early-universe cosmology. I will also touch on alternative ways in which a first order transition might proceed.

1430-1515 talk: Pieter Bomans

Title: On the class S origin of spindles and discs.

Abstract: In this talk I will discuss various aspects of the supergravity solutions obtained by wrapping N M5 branes on a topological disk or so-called spindle. In particular, I will discuss how the smeared branes arising in the former can be localized by explicitly breaking one of the symmetries of the supergravity solution and how the latter gives rise to a new type of puncture in class S.

1545-1630 talk: Stefan Vandoren

Title: Spontaneous supersymmetry breaking in string theory and black holes

Abstract: TBA

1630-1715 talk: Jeremy van der Heijden

Title: Modular Berry phases and the bulk symplectic form

Abstract: In this talk I will present a new perspective on bulk reconstruction using Berry phases in the boundary CFT. I will set up a parallel transport of modular Hamiltonians based on a change of state that is prepared via the Euclidean path integral. The main result is that the expectation value of the modular Berry curvature on the boundary agrees with an appropriately defined bulk symplectic form associated to the entanglement wedge. Moreover, I will derive a quantum information metric from the Berry curvature, and consider the case where a state change reduces to a shape change, uncovering the coadjoint orbit structure of kinematic space in higher dimensions.

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Fri 02 June

0930-1015 talk: Claire Zukowski

Title: Wilson Loops and de Sitter Quantum Gravity

Abstract: I will propose a mechanism, based on the Chern-Simons formulation of three-dimensional Euclidean gravity, that couples matter fields to three-dimensional de Sitter quantum gravity. First, I will derive novel su(2) representations that differ in Hermiticity choice from the usual unitary representations; these are important for gravitational applications of Chern-Simons theory. I will then introduce the concept of a “Wilson spool” constructed from a collection of Wilson loops winding around Euclidean de Sitter space. In the classical limit, this spool correctly reproduces the one-loop determinant of a free massive scalar field on the three-sphere. I will end with a prediction for quantum gravity: allowing for quantum metric fluctuations, the spool can be systematically evaluated to any order in perturbation theory.

1045-1130 talk: Jorge da Rocha

Title: Black hole-wormhole collisions and the emergence of islands

Abstract: We use ray-tracing techniques to determine the evolution of the event horizon of a large black hole that "gobbles" a tiny, traversable wormhole. Our calculation is exact in the strict extreme mass ratio limit. The wormhole considered is described by the simple Ellis-Bronnikov spacetime, but the analysis can be reproduced for any desired spacetime for which one has the exact solution. Two setups are considered: a single-mouth wormhole connecting two otherwise independent universes, and a double-mouth wormhole within the same universe. In the first setting it turns out that, at early times, there exist two disconnected horizons —one in each universe— which then merge as the wormhole falls into the large black hole. In the second setup, we observe the appearance of an “island", a region of spacetime that is spatially disconnected from the exterior of the black hole, but in causal contact with future null infinity. The island shrinks as time evolves and eventually disappears, providing a communication channel with the interior of the large black hole for a certain duration. We compute numerically the lifetime of the island and verify that it grows linearly with the inter-mouth distance, to very good approximation.

1130-1215 talk: Antonia Micol

Title: Higher-dimensional origin of extended black hole thermodynamics

Abstract: In this seminar, a new approach to understanding the varying cosmological constant in holographic braneworlds will be presented. By tuning the brane tension, a dynamic cosmological constant can be achieved on the brane. Therefore, the braneworld holography approach is a natural framework for exploring extended black hole thermodynamics. I will use the quantum black hole (quBTZ) as a case study, emphasizing its distinguishing features in comparison to its classical counterpart.

1345-1430 talk: Gerben Oling

Title: Carroll limits and flat space holography

Abstract: I will discuss recent advances in Carroll limits of field theories and their relation to celestial holography. Motivated by asymptotic symmetries and their relation to soft theorems, celestial holography maps four-dimensional scattering amplitudes to correlators in a two-dimensional CFT. However, such celestial CFTs have several nonstandard features, and only few explicit examples are known. On the other hand, one can consider flat space limits of AdS/CFT which naturally lead to three-dimensional CFTs with Carroll symmetry. After giving a brief overview overview of both of these approaches to flat space holography, I will construct two explicit examples of Carroll CFTs from a limit of Lorentzian CFT.

1430-1515 talk: Emil Have

Title: Carrollian spaces at infinity, the gauging procedure and Carrollian gravity

Abstract: I will demonstrate that the geometry of the blow-ups (in the sense of Ashtekar-Hansen) of the asymptotic infinities of Minkowski space are described by Carrollian geometries that arise as homogeneous spaces of the Poincaré group. I will then discuss a gauging procedure which amounts to the construction of a Cartan geometry modelled on a Klein geometry corresponding to a given Klein pair. This geometry is endowed with dynamics via a Lagrangian that consists of all gauge-invariant top-forms built from the Cartan geometry. To demonstrate the procedure in action, I will gauge the Klein pair corresponding to Minkowski space to obtain General Relativity, as well as the Klein pair that corresponds to Carrollian spacetime to obtain a theory of (magnetic) Carrollian gravity.

1545-1630 talk: Diego Hidalgo

Title: TBA

Abstract: TBA

1630-1715 talk: Ro Jefferson

Title: Crossed product algebras and generalized entropy for subregions

Abstract: An early result of algebraic quantum field theory is that the algebra of any subregion in a QFT is a von Neumann factor of type III, in which entropy cannot be well-defined because such algebras do not admit a trace or density states. However, associated to the algebra is a modular group of automorphisms characterizing the local dynamics of degrees of freedom in the region, and the crossed product of the algebra with its modular group yields a type II factor, in which traces and hence von Neumann entropy can be well-defined. In this talk, I will generalize recent constructions of the crossed product algebra for the TFD to, in principle, arbitrary spacetime regions in arbitrary QFTs, paving the way to the study of entanglement entropy without UV divergences. If time permits, I will discuss the application of this construction in both flat space and AdS/CFT. In the latter case, the algebraic perspective also provides a simple argument for why the bulk dual of a boundary subregion must be the entanglement wedge.