University of Crete HEP Seminars
Experimental measurement of von Neumann entropy and mutual information in a quantum field simulator
| Speaker: | Spiros Sotiriadis |
| Institution: | Crete U. |
| Time: | Tuesday 26 September 2023, 13:15 |
| Venue: | Webinar |
| Abstract: | Ultracold atom experiments have demonstrated their potential as quantum simulators of QFT models. Tunnel-coupled one-dimensional Bose gases, in particular, have been successfully used to implement strongly interacting models of QFT and explore their equilibrium and dynamical properties. I will discuss how this platform can be used to study measures of quantum information in QFT and their scaling with size, dubbed as volume and area law. Based on a version of quantum tomography suitable for continuous fields, we achieve a detailed reconstruction of the system’s quantum state, allowing measurements of the von Neumann entropy and mutual information in thermal equilibrium states. |
| Recording: | The recorded talk can be found here. |
Lanczos and all that
| Speaker: | Xenophon Zotos |
| Institution: | Crete U. |
| Time: | Thursday 28 September 2023, 13:15 |
| Venue: | Webinar |
| Abstract: | I will discuss the numerical implementation of the Lanczos method, the evaluation of zero temperature spectral functions,the extension to finite temperatures by the microcanonical Lanczos method and recent ideas about Lanczos coefficients, operator growth and complexity. |
| Recording: | The recorded talk can be found here. |
Fixed Points and Defects in the ε Expansion
| Speaker: | Andreas Stergiou |
| Institution: | King's Coll |
| Time: | Tuesday 28 September 2023, 13:15 |
| Venue: | Webinar |
| Abstract: | The ε expansion was invented more than 50 years ago and has been used extensively ever since to study aspects of renormalisation group flows and critical phenomena. In the first part of this talk we will discuss the structure of the ε expansion and the fixed points that can be obtained within it, focusing mostly on scalar theories in 4−ε dimensions. In the second part we will consider line defect deformations of various ε expansion fixed points and discuss aspects of the infrared defect conformal field theories that arise |
| Recording: | The recorded talk can be found here. |
Localization improved gluon amplitudes in AdS
| Speaker: | Connor Behan |
| Institution: | Oxford U. |
| Time: | Tuesday 17 October 2023, 14:15 |
| Venue: | WebinarCFTs with type IIB string theory duals have correlation functions which are tractable in a double expansion. For maximally supersymmetric Yang-Mills, one parameter is 1/N^2 representing the number of loops in supergravity. The other parameter is the 'tHooft coupling which keeps track of stringy corrections away from supergravity. I will discuss the first example of this analysis being done for a less supersymmetric CFT where the bulk dual includes not just super-gravitons but super-gluons as well. This will be a USp(2N) gauge theory with eight supercharges which has received attention in F-theory, To obtain high spin CFT data in this theory, it is enough to impose superconformal symmetry, crossing symmetry and Regge boundedness. The low spin data requires extra information which can be supplied with supersymmetric localization. I will explain this procedure and how it sheds light on the Veneziano amplitude in AdS. I will also show how some observables can be understood at finite gauge coupling by combining localization with instanton counting |
| Abstract: | The recorded talk can be found here. |
Relativistic Hydrodynamics and Causality
| Speaker: | Michal Heller |
| Institution: | Ghent U. |
| Time: | Tuesday 24 October 2023, 13:15 |
| Venue: | Webinar In my talk I will discuss recently discovered implications of relativistic causality on transport. In particular, I will explain how causality in holographic QFTs explains the presence of short-lived quasinormal modes of dual black branes and, similarly, how causality forces upon us the known ways of formulating effective equations of motion for relativistic fluids. Finally, I will discuss a new way of thinking about relativistic transport by adopting a bootstrap perspective based on relativistic causality. Based on 2007.05524, 2212.07434 and 2305.07703. |
| Abstract: | The recorded talk can be found here. |
A simple model, extracted using holography, of a domain wall between a confining and a de-confining phases and its velocity
| Speaker: | Jacob Sonnenschein |
| Institution: | Tel Aviv U. |
| Time: | Thursday 26 October 2023, 13:15 |
| Venue: | Webinar In the context of theories with a first order phase transition, we propose a general covariant description of coexisting phases separated by domain walls using an additional order parameter-like degree of freedom. In the case of a holographic dual to a confining and a de-confing phases, the resulting model extends hydrodynamics and has a simple formulation in terms of an action and a corresponding energy-momentum tensor. The proposed description leads to simple analytic profiles of domain walls, including the surface tension density, which agree nicely with holographic numerical solutions. We show that for such systems, the domain wall or bubble velocity can be expressed in a simple way in terms of a perfect fluid hydrodynamic formula, and thus in terms of the equation of state. We test the predictions for various holographic domain walls . |
| Abstract: | The recorded talk can be found here. |
Defects, RG flows and C-theorems in scalar field theory
| Speaker: | Jorge Russo |
| Institution: | ICREA, Barcelona U. |
| Time: | Tuesday 31 October 2023, 13:15 |
| Venue: | Webinar Theories with defects and boundaries have multiple applications in condensed matter and high energy physics. Here we will discuss general scalar CFT's with a linear defect in four and six dimensions. Using holography and the Hamilton-Jacobi formalism, we will show that the beta functions for the defect RG flow are the gradient of the entropy function. This enables the proof that the relevant C-functions decrease monotonically throughout the RG flow. We will also obtain closed formulas for the dimension of scalar operators and discuss possible instabilities . |
| Abstract: | The recorded talk can be found here. |
Explaining nonlinearities in black hole ringdowns from symmetries
| Speaker: | Antonio Riotto |
| Institution: | Geneva U., INFN, CERN |
| Time: | Tuesday 7 November 2023, 13:15 |
| Venue: | Webinar It has been recently pointed out that nonlinear effects are necessary to model the ringdown stage of the gravitational waveform produced by the merger of two black holes giving rise to a remnant Kerr black hole. We show that this nonlinear behavior is explained, both on the qualitative and quantitative level, by near-horizon symmetries of the Kerr black hole within the Kerr/CFT correspondence. |
| Abstract: | The recorded talk can be found here. |
Bootstrapping Dual Resonance
| Speaker: | Grant Remmen |
| Institution: | New York U. |
| Time: | Tuesday 14 November 2023, 17:15 |
| Venue: | Webinar String amplitudes famously accomplish several extraordinary and interrelated mathematical feats, including an infinite spin tower, tame UV behavior, and dual resonance: the ability of the amplitude to be represented as a sum over a single scattering channel. But how unique are these properties to string amplitudes? In this talk, I will demonstrate that it is possible to construct infinite new classes of tree-level, dual resonant amplitudes with customizable, non-Regge mass spectra. Crucial ingredients are Galois theory and a particular dlog transformation of the Veneziano amplitude. The formalism generalizes naturally to n-point scattering and allows for a worldsheet-like integral representation. In the case of a Regge spectrum, I will investigate whether the structure of the Veneziano amplitude can be bootstrapped from first principles. Even there, we will find that there is extra freedom in the dynamics, allowing for a new class of dual resonant hypergeometric amplitudes with a linear spectrum . |
| Abstract: | The recorded talk can be found here. |
Macrostates and microstates of the cosmic horizon: developments in de Sitter quantum gravity
| Speaker: | Eva Silverstein |
| Institution: | Stanford U. |
| Time: | Tuesday 21 November 2023, 18:15 |
| Venue: | Webinar The accelerated expansion of the universe leads to a horizon beyond which we cannot see. Structure arises from the quantum variance of early universe fields stretched across the horizon, according to the simplest theory fitting observations. In concrete new models in string- (or `M-’) theory, the accelerating universe itself relies on the variance of extra dimensional fields, analogously to the quantum stability of atoms, stars and materials. We derive these models starting from several favorable properties of hyperbolic compactifications, combined with magnetic flux and the automatically generated Casimir energy from internal fields. Theoretical calculations also suggest an enormous unobserved entropy associated with the de Sitter horizon. Recent and ongoing work of multiple research groups has refined and sharpened the meaning of this entropy along with other thermodynamic quantities such as energy and temperature. Timelike features – such as a fixed-metric boundary or an observer within the system – play a key role, as do novel deformations of (2d) field theories defining a family of quantum systems with a finite Hilbert space. These structures combine naturally into a new proposal for holography of a bounded patch of (3d) de Sitter (at large radius and with matter included), realizing the finite entropy as a microstate count in a non-gravitational boundary theory . |
| Abstract: | The recorded talk can be found here. |
Reflection and Transmission coefficients in T\bar{T} deformed ICFT
| Speaker: | Avik Banerjee |
| Institution: | Crete U. |
| Time: | Thursday 23 November 2023, 13:15 |
| Venue: | Webinar Scattering of matter against a conformal interface in two-dimensional CFTs exhibits a broad universality in terms of the reflection and transmission coefficients, which get completely determined by the central charges of the underlying theories (and an additional central charge-like parameter, to be explained). This is rather counterintuitive in generic quantum field theories, where these coefficients are expected to depend on the nature of incident excitation as well as the momentum it carries. It thus remains to be an interesting question to understand how is the universality modified as we depart the CFT fixed point along some RG flow. In this talk, I shall first give a brief derivation of the universality. both from the field theory as well as a (bottom-up) holographic point of view. Then I shall introduce the T\bar{T} deformation of 2d CFTs, which generates an integrable flow in the space of field theories, and outline how can one adopt the techniques in the holographic dual of the deformed ICFT to compute these coefficients . |
| Abstract: | The recorded talk can be found here. |
Renormalizing diffusion models
| Speaker: | Jordan Cotler |
| Institution: | Harvard U. |
| Time: | Tuesday 28 November 2023, 17:15 |
| Venue: | Webinar We derive an equivalence between exact renormalization group (RG) flow equations and stochastic Langevin PDEs. After reviewing latent diffusion models, a prominent machine learning method, we show that a certain class of latent diffusion models are based on Langevin equations taking the precise form of lattice RG flow equations. We leverage our findings to construct ML-based models for studying field theories, in which the models learn the inverse process to an explicitly specified RG scheme. We detail how these models define a class of adaptive bridge samplers for lattice field theories and provide numerical demonstrations. |
| Abstract: | The recorded talk can be found here. |
A loophole in the proofs of quantum triviality and asymptotic freedom
| Speaker: | Paul Romatschke |
| Institution: | Colorado U. |
| Time: | Tuesday 5 December 2023, 17:15 |
| Venue: | Webinar Back in 1973, Sidney Coleman and Nobel Prize winner David Gross proved that only non-abelian gauge theories can have asymptotic freedom. More recently, Michael Aizenman and Hugo Duminil-Copin (Field Medalist 2022) proved that scalar field theories are quantum trivial in four dimensions. Both of these important proofs have the same loophole: they assume that the coupling constant in the UV is positive definite. While a reasonable physics assumption, the results obtained in non-Hermitian (PT-symmetric) quantum mechanics indicate that certain field theories with negative coupling exist and fulfill the basic requirements of unitarity and stability. I will show an explicit calculation on how a particular field theory (the O(N) model) in 3+1 dimensions exploits this loophole, leading to a candidate for an asymptotically free interacting scalar field theory, and a potential alternative to the Standard Model Higgs sector. |
| Abstract: | The recorded talk can be found here. |
A dS S-matrix
| Speaker: | Guilherme Leite Pimentel |
| Institution: | Pisa, Scuola Normale Superiore |
| Time: | Thursday 7 December 2023, 13:15 |
| Venue: | Webinar I’ll define and explain how to compute a cosmological S matrix in de sitter. I’ll also mostly advertise some upcoming work on a new set of techniques to compute cosmological correlators using boundary differential equations. |
| Abstract: | The recorded talk can be found here. |
String Thermodynamics
| Speaker: | Andrew Frey |
| Institution: | Winnipeg U. |
| Time: | Tuesday 12 December 2023, 18:15 |
| Venue: | Webinar The high-energy regime of string theory has long been of great interest. Both the interactions of highly-excited strings and string thermodynamics provide an approach to study this topic. We explore the connection between the two approaches, using interaction rates to find Boltzmann equations for gases of strings and detailed balance to conjecture the form of unknown interaction rates. We then use the Boltzmann equations to study the approach to equilibrium for gases of strings and discuss some applications. |
| Abstract: | The recorded talk can be found here. |
Confinement in 1+1 dimension from I-branes
| Speaker: | Ricardo Stuardo |
| Institution: | Swansea U. |
| Time: | Thursday 14 December 2023, 13:15 |
| Venue: | Webinar We holographically study the strongly coupled dynamics of the field theory on I-branes (D5 branes intersecting on a line). In this regime, the field theory becomes (2+1) dimensional with 16 supercharges. The dual background has an IR singularity. We resolve this singularity by compactifying the theory on a circle, preserving 4 supercharges. We study various aspects: confinement, symmetry breaking and Entanglement Entropy |
| Abstract: | The recorded talk can be found here. |
On the stability and deformability of top stars
| Speaker: | Massimo Bianchi |
| Institution: | Tor Vergata U. |
| Time: | Tuesday 21 December 2023, 13:15 |
| Venue: | Webinar Top(ological) stars are smooth horizonless static solutions of Einstein-Maxwell theory in 5-d that reduce to spherically symmetric solutions of Einstein-Maxwell-Dilaton theory in 4-d. We study their scalar perturbations at linear order with different techniques and identify three classes of quasi-normal modes, all having negative imaginary parts. This suggests linear stability of top stars. Moreover we determine the tidal Love and dissipation numbers encoding the response to tidal deformations and, similarly to black holes, we find zero value in the static limit but, contrary to black holes, we find non-trivial dynamical Love numbers and vanishing dissipative effects at linear order |
| Abstract: | The recorded talk can be found here. |