University of Crete HEP Seminars
Aspects of the black hole/string transition
| Speaker: | Yiming Chen |
| Institution: | Princeton |
| Time: | Tuesday 01 Febraury 2022, 16:00 |
| Venue: | Webinar |
| Abstract: | It has long been speculated that a black hole in string theory turns into highly excited strings close to the Hagedorn temperature. Gravitational attraction pulls different parts of the string together, forming a star-like configuration. In this talk, I will review the properties of a concrete solution of this kind, first discovered by Horowitz and Polchinski. I will discuss whether the Horowitz-Polchinski solution can be smoothly connected with the black hole as worldsheet CFTs. If time permits, I will discuss an ongoing work on the spectral form factor of a gas of strings, which probes the finer details of the spectrum. I will highlight the importance of a potential family of generalizations of the Horowitz-Polchinski solution. |
| Recording: | The recorded talk can be found here. |
Large N Fractons
| Speaker: | Kristan Jensen |
| Institution: | University of Victoria |
| Time: | Tuesday 08 February 2022, 19:00 |
| Venue: | Webinar |
| Abstract: | In this talk I will discuss two aspects of continuum field theories of fractons. These models have been of recent interest to condensed matter and high energy theorists. On the one hand they are candidates for new phases of quantum matter, and on the other, they have features which seem impossible to describe in continuum field theory, including quasiparticles of restricted mobility and a ground state degeneracy which depends sensitively on the ultraviolet. The two aspects I will discuss are (i.) some soluble interacting large N versions of these models, and (ii.) the coupling of these models to a spacetime background, useful for obtaining Ward identities for response functions. Our large N results show in detail the importance of interactions, and how a careful treatment of the path integral in continuum field theory can reproduce the exotic features mentioned above. |
| Recording: | The recorded talk can be found here. |
Conformal Surface Defects in Maxwell Theory are Trivial
| Speaker: | Chris Herzog |
| Institution: | Kings College London |
| Time: | Thursday 10 February 2022, 14:00 |
| Venue: | Webinar |
| Abstract: | I consider a free Maxwell field in four dimensions in the presence of a codimension two defect. Reflection positive, codimension two defects which preserve conformal symmetry in this context are very limited. Only generalized free fields can exist on the defect and interact with the free Maxwell field in the bulk. This result stands in stark contrast to the boundary case where interacting conformal boundary conditions can be found for free bulk fields, producing systems with physical relevance, for example for graphene. |
| Recording: | The recorded talk can be found here. |
Diagrammar of Physical and Fake Particles and Spectral Optical Theorem
| Speaker: | Damiano Anselmi |
| Institution: | Pisa U. |
| Time: | Tuesday 15 Febraury 2022, 13:00 |
| Venue: | Webinar |
| Abstract: | We prove spectral optical identities in quantum field theories of physical particles (defined by the Feynman iε prescription) and purely virtual particles (defined by the fakeon prescription). The identities are derived by means of purely algebraic operations and hold for every (multi)threshold separately and for arbitrary frequencies. Their major significance is that they offer a deeper understanding on the problem of unitarity in quantum field theory. In particular, they apply to "skeleton" diagrams, before integrating on the space components of the loop momenta and the phase spaces. In turn, the skeleton diagrams obey a spectral optical theorem, which gives the usual optical theorem for amplitudes, once the integrals on the space components of the loop momenta and the phase spaces are restored. The fakeon prescription/projection is implemented by dropping the thresholds that involve fakeon frequencies. We give examples at one loop (bubble, triangle, box, pentagon and hexagon), two loops (triangle with "diagonal", box with diagonal) and arbitrarily many loops. We also derive formulas for the loop integrals with fakeons and relate them to the known formulas for the loop integrals with physical particles. |
| Recording: | The recorded talk can be found here. |
OPE statistics from higher-point crossing
| Speaker: | Tarek Anous |
| Institution: | University of Amsterdam |
| Time: | Tuesday 01 March 2022, 13:00 |
| Venue: | Webinar |
| Abstract: | Crossing symmetry is responsible for a number of CFT constraints, including the famed Cardy density of states. In this talk I will review how crossing symmetry of four- and higher-point functions can be used to extract the density of products of OPE coefficients, deriving new universal formulas along the way. These formulas are theory independent, and therefore can be used e.g. to prove refined bounds using the conformal bootstrap. We will end with some comments on the dual interpretation of these results. |
| Recording: | The recorded talk can be found here. |
Black hole information transfer with a twist
| Speaker: | Christoph Uhlemann |
| Institution: | University of Michigan |
| Time: | Tuesday 08 March 2022, 16:00 |
| Venue: | Webinar |
| Abstract: | Recent years have seen remarkable progress in our understanding of black holes and the information paradox: for black holes in AdS coupled to a bath, Page curves consistent with unitarity have been obtained through semi-classical computations involving quantum extremal surfaces. These discussions have largely been based on two-dimensional models where gravity is solvable and on bottom-up models which may or may not make sense as consistent theories of quantum gravity. In this talk we will discuss simple top-down models for black hole information transfer based on twisted compactifications of concrete CFTs in various dimensions and their holographic duals. |
| Recording: | The recorded talk can be found here. |
Falling inside holographic black holes (Part 1)
| Speaker: | Lampros Lamprou |
| Institution: | University of British Columbia |
| Time: | Tuesday 15 March 2022, 19:00 |
| Venue: | Webinar |
| Abstract: | I will present a bulk reconstruction technique in AdS/CFT suitable for addressing a facet of the black hole information problem: how to unambiguously predict the results of measurements accessible to an infalling observer in the black hole interior. I will explicitly apply the method in the AdS_2/SYK correspondence and comment on its generalizations. |
| Recording: | The recorded talk can be found here. |
Exploring the QCD Phase Diagram with Neutron Star Mergers
| Speaker: | Tuna Demircik |
| Institution: | APCTP |
| Time: | Thursday 17 March 2022, 14:00 |
| Venue: | Webinar |
| Abstract: | Determining the phase structure of Quantum Chromodynamics (QCD) and its Equation of State (EoS) at densities and temperatures realised inside neutron stars and their mergers is a long-standing open problem. I will present a framework for the EoS of dense and hot QCD that describes the deconfinement phase transition between a dense baryonic and quark matter phase via the holographic V-QCD model. I will show some predictions of this model for the properties of isolated and binary neutron star systems and discuss the formation of quark matter in their post-merger stage. |
| Recording: | The recorded talk can be found here. |
Exactly marginal deformations of superconformal gauge theories and their supergravity duals
| Speaker: | Michela Petrini |
| Institution: | LPTHE |
| Time: | Tuesday 22 March 2022, 13:00 |
| Venue: | Webinar |
| Abstract: | In this talk we will discuss a class of AdS5 solutions of type IIB supergravity that are dual to marginal deformations of N = 1 conformal field theory. Using generalised geometry, we show how the geometry encodes the information about the holomorphic data of the dual SCFT and how this allows to count protected operators, Hilbert series etc. This construction generalises what is done for N=1 SCFT dual to Sasaki-Einstein manifolds. We apply the construction to the long-standing problem of finding the gravity dual of the generic N = 1 deformations of N = 4 conformal field theory. While we are not able to find the explicit supergravity backgrounds, continuity argument allow to proof its existence. |
| Recording: | The recorded talk can be found here. |
Topological solitons in gravity and stability of charged bubble
| Speaker: | Ibou Bah |
| Institution: | Johns Hopkins University |
| Time: | Tuesday 29 March 2022, 14:30 |
| Venue: | Webinar |
| Abstract: | In this talk I will discuss aspects of microscopic degrees of freedom of gravity as motivated by string theory. Although these are expected to be generically quantum mechanical, our goal is to understand a class of such states that are coherent enough to admit classical descriptions in Einstein gravity. The construction of such states corresponds to adding interesting topological structures in spacetime with the help of compact extra dimensions. The constructions manifestly behave like ultra compact objects, dubbed topological stars, which can also model black hole microstates. I will also discuss the classical and quantum mechanical stability of the spherically symmetric class. |
| Recording: | The recorded talk can be found here. |
Falling inside holographic black holes (Part 2)
| Speaker: | Lampros Lamprou |
| Institution: | University of British Columbia |
| Time: | Thursday 31 March 2022, 19:00 |
| Venue: | Webinar |
| Abstract: | I will present a bulk reconstruction technique in AdS/CFT suitable for addressing a facet of the black hole information problem: how to unambiguously predict the results of measurements accessible to an infalling observer in the black hole interior. I will explicitly apply the method in the AdS_2/SYK correspondence and comment on its generalizations. |
| Recording: | The recorded talk can be found here. |
Emergent times in holography
| Speaker: | Hong Liu |
| Institution: | MIT |
| Time: | Tuesday 12 April 2022, 18:00 |
| Venue: | Webinar |
| Abstract: | In holographic duality an eternal AdS black hole is described by two copies of the boundary CFT in the thermal field double state. We provide explicit constructions in the boundary theory of infalling time evolutions which can take bulk observers behind the horizon. The constructions also help to illuminate the boundary emergence of the black hole horizons, the interiors, and the associated causal structure. A key element is the emergence, in the large N limit of the boundary theory, of a type III1 von Neumann algebraic structure and the half-sided modular translation structure associated with it. |
| Recording: | The recorded talk can be found here. |
Fractons and D-branes
| Speaker: | Shamit Kachru |
| Institution: | Stanford |
| Time: | Tuesday 03 May 2022, 19:00 |
| Venue: | Webinar |
| Abstract: | I discuss theories of fractons, with a focus on the role of foliated field theories and field theories with exotic symmetry in their construction. I then turn to the realization — on systems of branes in string theory — of several novel theories of this sort. |
| Recording: | The recorded talk can be found here. |
On Stability in String and M-Theory
| Speaker: | Luca Martucci |
| Institution: | Padua Uinversity |
| Time: | Thursday 05 May 2022, 15:00 |
| Venue: | Webinar |
| Abstract: | String/M-theory compactifications may suffer from instabilities, which are generically difficult to analyze. I will consider this issue from a higher dimensional perspective. I will first focus on supersymmetric vacua, showing how to adapt familiar positive-energy theorems directly to M-theory and type II supergravity, rather than to their effective lower-dimensional reductions, and showing how to consistently include localized sources. I will then discuss how one might extend these results to non-supersymmetric vacua. |
| Recording: | The recorded talk can be found here. |
Decoding the Path Integral: Resurgence and Non-Perturbative Physics
| Speaker: | Gerald Dunne |
| Institution: | University of Connecticut |
| Time: | Tuesday 10 May 2022, 16:00 |
| Venue: | Webinar |
| Abstract: | There are several important conceptual and computational questions concerning path integrals which have recently been approached from new perspectives motivated by "resurgent asymptotics", a novel mathematical formalism that seeks to unify perturbative and non-perturbative physics. This talk will review the basic ideas behind the connections between resurgent asymptotics and physics, starting from the work of Airy and Stokes, and the development of trans-series by Ecalle, and then turn to several recent applications in quantum mechanics and quantum field theory. The main motivation is to develop a deeper understanding of field theoretic path integrals directly from a saddle point Lefschetz thimble decomposition, and also by reconstruction from perturbative information. |
| Recording: | The recorded talk can be found here. |
Soft photon radiation and entanglement
| Speaker: | Nick Toumbas |
| Institution: | University of Cyprus |
| Time: | Thursday 12 May 2022, 15:00 |
| Venue: | Webinar |
| Abstract: | In this talk, I will discuss patterns of entanglement and information flow between the hard and soft particles produced in QED scattering procesees. Specifically, I will discuss the scaling of the Renyi and the entanglement entropies with the IR cutoff, at fixed order in perturbation theory, as well as to all orders, in the large volume limit. The leading perturbatve entanglement entropy is logarithmically divergent, with the coefficient exhibiting universality properties. In a particular kinematical limit, it is proportional to the cusp anomalous dimension of QED. The all orders Renyi entropies are free of IR divergences. On the other hand, the entanglement entropy retains non-analytic behavior with respect to the IR cutoff even to all orders in perturbation theory. |
| Recording: | The recorded talk can be found here. |
Field theories with dipole symmetries: gauging and coupling to curved spacetime
| Speaker: | Jelle Hartong |
| Institution: | University of Edinburgh |
| Time: | Thursday 19 May 2022, 15:00 |
| Venue: | Webinar |
| Abstract: | In the context of fracton physics, an interesting class of field theories has emerged that enjoys dipole symmetry. In this talk I will discuss complex scalar theories with dipole symmetry and present a nogo-theorem that states that such a theory cannot simultaneously be Gaussian, have linearly realised dipole symmetry and contain gradient terms. Another way of putting this is that a Gaussian theory with linear dipole symmetry must be Carrollian. I will then discuss the Noether procedure that leads to the gauging of dipole symmetry and discuss the resulting gauge theory from a Hamiltonian perspective. The resulting gauge theory is a gauge theory for a scalar and a symmetric tensor gauge field. It has a rich spectrum of propagating modes, and I will discuss its coupling to worldline actions. Finally, I will turn to the topic of how to couple these scalar and gauge theories to curved spacetime. It turns out that the relevant geometry is known as Aristotelian geometry, a geometric structure that has also appeared elsewhere in the literature, whenever the theory has no boost symmetry. |
| Recording: | The recorded talk can be found here. |