University of Crete HEP Seminars
QFT in AdS instead of LSZ
| Speaker: | Balt van Rees |
| Institution: | Ecole Polytechnique |
| Time: | 4 February 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | Consider a conformally covariant four-point function of identical scalar operators with a discrete spectrum, a twist gap, and compatible with the unitarity conditions. We give a mathematical proof confirming that the spectrum and OPE coefficients at large spin and fixed twist always become that of a generalized free field theory. |
| Recording: | The recorded talk can be found here. |
A microscopic description of ds3
| Speaker: | Lorenz Eberhardt |
| Institution: | Amsterdam U. |
| Time: | 11 February 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | I will explain a proposal for relating pure Einstein gravity with positive cosmological constant in 2+1d to a matrix model. The matrix model is capable of reproducing all the integrated cosmological correlators in the bulk as well as the exact de Sitter entropy. Based on 2501.01486 in collaboration with Scott Collier and Beatrix Mühlmann. |
| Recording: | The recorded talk can be found here. |
Exploring Boundary Effects in TTbar-deformed Quantum Field Theories
| Speaker: | Roberto Tateo |
| Institution: | Turin U. |
| Time: | 18 February 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | In this seminar, we will explore the properties of the TTbar deformation --a distinctive integrable deformation built from components of the stress-energy tensor -- in the context of two-dimensional quantum field theories. While the bulk properties of TTbar-deformed theories are now well understood, thanks to their connections with coordinate transformations and topological gravity models, their behavior in the presence of boundaries and defects remains a largely uncharted territory. We will review recent analytical advancements, focusing on the exact g-function of TTbar deformed theories, derived using the Thermodynamic Bethe Ansatz (TBA) and verified through solutions to a Burgers-type flow equation. This comparison highlights a remarkable consistency between different approaches. The talk will conclude with a discussion of open problems and promising directions for future research in this evolving field. |
| Recording: | The recorded talk can be found here. |
Gravitational Collapse at the Boundary
| Speaker: | David Mateos |
| Institution: | Barcelona U. |
| Time: | 20 February 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | Holography has provided valuable insights into the time evolution of strongly coupled gauge theories in a fixed spacetime. However, this framework is insufficient if this spacetime is dynamical. We present a scheme to evolve a four-dimensional, strongly interacting gauge theory coupled to four-dimensional dynamical gravity in the semiclassical regime. We apply this framework to the description of the gravitational collapse and the subsequent formation of a black hole at the boundary. In the bulk, this corresponds to the formation of a black funnel. If time permits, we will also use holography to study the so-called BKL dynamics near the singularity behind the black hole horizon. |
| Recording: | The recorded talk can be found here. |
Quasinormal ringdown of chaotic systems
| Speaker: | Matthew Dodelson |
| Institution: | CERN |
| Time: | 25 February 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | I will discuss the late time behavior of thermal correlators in chaotic systems. Under certain assumptions, the thermal two point function exhibits exponential decay, with a discrete spectrum of complex frequencies. I will explain how these frequencies can be thought of as quasinormal modes of a black hole whose radial direction is identified with complexity. This perspective leads to an efficient method for computing the spectrum, and also a better understanding of the analytic structure. I will give various examples, mostly in the context of holography or the SYK model, where explicit computations can be done. |
| Recording: | The recorded talk can be found here. |
Looking at extremal black holes from far away
| Speaker: | Gustavo Joaquin Turiaci |
| Institution: | Washington U. |
| Time: | 4 March 2025, 17:15 |
| Venue: | Webinar |
| Abstract: | In the first part of this talk I review recent progress clarifying some physical aspects of the extremal limit of black holes. I describe two puzzles that arise from a semiclassical treatment of near-extremal black hole thermodynamics. Both puzzles are resolved by realizing that quantum gravity effects become arbitrarily large at low temperatures. In the second part, I will describe some recent work clarifying the origin of these quantum effects from the gravitational path integral. Finally, I will describe ongoing work on identifying similar effects in certain cosmological setups. |
| Recording: | The recorded talk can be found here. |
String Theory in a Pinch : Resoving the Gregory-Laflamme Singularity
| Speaker: | Roberto Emparan |
| Institution: | ICREA, Barcelona U. |
| Time: | 11 March 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | Thin enough black strings are unstable to growing ripples along their length, eventually pinching and forming a naked singularity on the horizon. We investigate how string theory can resolve this singularity. First, we study the string-scale version of the static non-uniform black strings that branch off at the instability threshold: "string-ball strings", which are linearly extended, self-gravitating configurations of string balls obtained in the Horowitz-Polchinski (HP) approach to near-Hagedorn string states. We construct non-uniform HP strings and show that, as the inhomogeneity increases, they approach localized HP balls. We also examine the thermodynamic properties of the different phases in the canonical and microcanonical ensembles. We find that, for a sufficiently small mass, the uniform HP string will be stable and not evolve into a non-uniform or localized configuration. Building on these results and independent evidence from the evolution of the black string instability with α′ corrections, we propose that, at least in d=4,5 spatial dimensions, string theory slows and eventually halts the pinching evolution at a classically stable stringy neck. The system then enters a slower phase in which the neck gradually evaporates into radiation. We discuss this scenario as a framework for understanding how string theory resolves the formation of naked singularities. |
| Recording: | The recorded talk can be found here. |
The defective origin of spindles and disks
| Speaker: | Pieter Bomans |
| Institution: | Oxford U. |
| Time: | 18 March 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | Spindle and disc solutions have recently attracted substantial interest, though their physical interpretation remained somewhat elusive. In this talk, I will present a compelling interpretation of these solutions as arising from co-dimension two disorder defects positioned at the sphere’s poles. To support this perspective, I constructed explicit supergravity solutions and calculated corresponding holographic observables, offering robust evidence for our interpretation. I will illustrate this with various examples including the (2,0) theory compactified on a spindle as well as Gukov-Witten type defects in N=4 SYM. Additionally, I will introduce a bulk-to-defect inflow formalism, facilitating the extraction of diverse defect data. |
| Recording: | The recorded talk can be found here. |
(S)QCD meets (PM) gravity
| Speaker: | Jung-Wook Kim |
| Institution: | Postdam, Max Planck Inst. |
| Time: | 23 March 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | Since the first direct detection of gravitational waves, the interest in perturbative approaches to gravitational dynamics has been steadily growing within the hep-th community. I will give a brief overview on how the tools developed for theoretical particle physics, such as Feynman integrals and Seiberg-Witten theory, are being applied to post-Minkowskian (PM) gravitational dynamics. |
| Recording: | The recorded talk can be found here. |
Where is tree level string theory?
| Speaker: | Leonardo Rastelli |
| Institution: | SUNY, Stony Brook |
| Time: | 2 April 2025, 15:15 |
| Venue: | Webinar |
| Abstract: | Tree-level string theory extends Einstein gravity by an infinite set of massive higher spin particles. From a purely spacetime perspective (if we didn't know about the worldsheet picture) the consistency of string amplitudes would appear truly miraculous. This prompts the question: is string theory the unique framework for a higher spin extension of gravity? We investigate this question by bootstrap methods, focussing on maximal 10D supergravity. We parametrize theory space by the first few EFT coefficients and by the on-shell coupling of the lightest massive state, and impose on these data causality and positivity constraints. While Type II string theory lives strictly inside the allowed region, we uncover a novel extremal solution of the bootstrap problem, which appears to contain a single linear Regge trajectory. We repeat a similar analysis for supergluon scattering. |
| Recording: | The recorded talk can be found here. |
Quantum Criticality in Black Hole Scattering
| Speaker: | Uri Kol |
| Institution: | Harvard U. |
| Time: | 8 April 2025, 16:15 |
| Venue: | Webinar |
| Abstract: | Black hole perturbation theory captures a few important effects in the dynamics of binary mergers, such as tidal deformations and the decay of ringdown modes, as well as the physics of the photon ring. However, deriving qualitative results that lead to robust predictions in this theory remains a challenging problem, despite a rich scientific history. |
| Recording: | The recorded talk can be found here. |
Cosmic Topological Defects from Holography
| Speaker: | Aldo Cotrone |
| Institution: | Leuven U. |
| Time: | 15 April 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | In this talk I will consider a QCD-like theory with a flavor condensing at a large scale, with distinct confining and chiral symmetry breaking transitions. The theory, admitting a holographic dual, can have a rich cosmological history, with a number of defects such as strings, domain walls, vortons, etc. I will show how the holographic description allows to derived their physics beyond the effective field theory approach. |
| Recording: | The recorded talk can be found here. |
The evaporation of charged black holes
| Speaker: | Luca Iliesiu |
| Institution: | Stanford U. |
| Time: | 29 April 2025, 14:15 |
| Venue: | Webinar |
| Abstract: | I will describe the dynamical evolution of a universe containing a single black hole. If the black hole has sufficiently large initial charge, it will be driven very close to extremality by the emission of neutral Hawking radiation, while charged particle emission is exponentially suppressed. At low enough temperatures, quantum gravity becomes important and Hawking-style quantum field theory in curved spacetime calculations give completely incorrect answers, even for simply questions like the energy spectrum of emitted radiation. This leads to interesting new physics, e.g. in certain regimes the dominant radiation channel becomes entangled pairs of photons, as in the "forbidden'' 2s->1s hydrogen atom transition. By careful analysis of the relevant metric fluctuations, we can calculate the quantum gravity effects in a controlled manner and tell the complete story of the black hole evaporation in both a universe with a matter content similar to ours and in a supersymmetric universe described by supergravity. |
| Recording: | The recorded talk can be found here. |
Quantum Corrections in Near-Extremal Black Holes, Thermodynamics, Dynamics and Applications
| Speaker: | Leopoldo A. Pando Zayas |
| Institution: | Michigan U. |
| Time: | 6 May 2025, 17:15 |
| Venue: | Webinar |
| Abstract: | I will revisit the low-temperature thermodynamics of near-extremal rotating black holes that has recently been shown to incorporate one-loop contributions that are dominant in this regime. I will review these quantum corrections to the gravitational path integral for asymptotically Anti de-Sitter black holes in four and five dimensions. I will also revisit how the above quantum corrections affect the holographic approach to the strange metal phase which is known to rely on near-extremal asymptotically AdS4 electrically charged black branes with important input from their AdS2 near-horizon throat geometry. |
| Recording: | The recorded talk can be found here. |
Tensions in Cosmology: Are we Approaching New Physics ?
| Speaker: | Emmanuel Saridakis |
| Institution: | National Observatory of Athens |
| Time: | 8 May 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | We summarize the famous tensions between various observational datasets and theoretical predictions of the Standard Model of Cosmology, such as the H0 and S8 tensions, that could be a sign that we are approaching New Physics. Then we provide possible solutions, arising from modifications /extensions of the standard lore, focusing on (late-time) modified gravity solutions, and in particular on geometric theories such as torsional and non-metricity gravities. |
| Recording: |
The Finite Temperature Matrix Quantum Mechanics
| Speaker: | Barak Gabai |
| Institution: | EPFL |
| Time: | 13 May 2025, 13:15 |
| Venue: | Webinar |
| Abstract: | The MQM bootstrap formulates the Hamiltonian equations of motion together with Norm positivity as a semi-definite programing problem. This allows for a rigorous numerical determination of the low lying spectrum as well as the first moments of the matrices (for polynomial potentials). In this talk I will explain how to extend this to finite temperature moments, and show some numerical results. Finally I will present some advancements towards bootstrapping time separated 2 point functions. |
| Recording: | The recorded talk can be found here. |