University of Crete HEP Seminars: Spring 2016


Holographic universal bounds: To be, or not to be?

Speaker: Matteo Baggioli
Institution: IFAE and Universitat Autònoma Barcelona
Time: Tuesday 8 March 2016, 15:00
Venue: 2nd floor seminar room
Abstract: I will analyze the role and the features of massive gravity models in the context of holographic effective theories for condensed matter. I will present a systematic treatment of this framework along with its recent developments. I will discuss the (bad) fate of the conjectured universal viscosity and conductivity bounds and the remaining open questions within these scenarios.

Conformal invariance in momentum space

Speaker: Paul McFadden
Institution: Imperial College London
Time: Tuesday 15 March 2016, 15:00
Venue: 2nd floor seminar room
Abstract: Conformal invariance places powerful constraints on the properties of a quantum field theory. In position space, the form of 2- and 3-point correlation functions is completely fixed by this symmetry up to just a few constants. In this talk, we examine the corresponding story in momentum space. Starting from first principles, we show how to construct the momentum-space 2- and 3-point functions of a general conformal field theory. For certain space-time and operator dimensions a non-trivial renormalisation is required due to the presence of contact terms. We show how to perform this renormalisation directly in momentum space, leading to novel conformal anomalies and beta functions. The results have potential applications to many fields, including holographic cosmology and condensed matter physics.

Power spectra for scalar potential models of inflation

Speaker: Daniel Brooker
Institution: University of Florida
Time: Tuesday 22 March 2016, 15:00
Venue: 2nd floor seminar room
Abstract: We exploit a new numerical technique for evaluating the tree order contributions to the primordial scalar and tensor power spectra for scalar potential models of inflation. Among other things, we develop a good analytic approximation for the nonlocal corrections from evolution before and after horizon crossing.

Bootstrapping N=2 SCFTs

Speaker: Madalena Lemos
Institution: DESY Hamburg
Time: Tuesday 12 April 2016, 15:00
Venue: 2nd floor seminar room
Abstract: In this talk we will discuss the bootstrap program applied to four-dimensional N=2 superconformal field theories, with focus on analytical results. After a brief review of the protected subsector captured by a two-dimensional chiral algebra, we will show how analytic bounds on anomaly coefficients are obtained and constrain the space of allowed SCFTs. Finally, we will comment the implications for the numerical bootstrap program.

Anti-branes, fluxes and black holes

Speaker: Bert Vercnocke
Institution: University of Amsterdam
Time: Thursday 14 April 2016, 15:00
Venue: 2nd floor seminar room
Abstract: This talk will be about non-supersymmetric solutions of string theory. I will start with reviewing the recent debate on anti-branes in flux backgrounds and their relation to string vacua. Then I will exploit the strong analogy with microstates of non-supersymmetric black holes and expand on the fruit we can get from this cross-pollination.

Coupled dark energy and dark matter from axions

Speaker: Robert Brandenberger
Institution: McGill University
Time: Friday 22 April 2016, 12:15
Venue: 2nd floor seminar room
Abstract: The QCD axion is a candidate for dark matter. I will explore the possibility that an axion associated with a hidden sector could provide both dark matter and dark energy.

From hydrodynamic transport towards its destruction

Speaker: Sašo Grozdanov
Institution: Leiden University
Time: Tuesday 24 May 2016, 15:00
Venue: 2nd floor seminar room
Abstract: Holography is a tool that can be most readily applied to studies of transport properties in gauge theories with infinitely strong interactions. Coupling constant corrections can then be incorporated through higher-derivative (α′) corrections to the supergravity action in the bulk. In the first part of this talk, I will discuss the dependence of hydrodynamic transport, the relaxation time and the full quasi-normal spectrum on the coupling constant in duals of Type IIB supergravity and curvature-squared theories. In relation to the membrane paradigm, I will then present higher-order generalisations of the universal "η/s" relation and anomalous conductivities at finite coupling. Recently, studies of holographic transport in the presence of broken translational symmetry and disorder have received much attention. In particular, it has been shown how thermo-electric conductivities can be computed by using the membrane paradigm. Through the power of the membrane paradigm and with a view towards future models of many-body localisation without hydrodynamic transport, in the second part of this talk, I will discuss the proofs of bounds on thermal and electrical conductivities in a large family of holographic theories with arbitrarily strong disorder.

Entanglement, geometry, and black holes in Matrix theory

Speaker: Vatche Sahakian
Institution: Harvey Mudd College
Time: Thursday 26 May 2016, 15:00
Venue: 2nd floor seminar room
Abstract: In the context of the Banks–Fischler–Shenker–Susskind Matrix model of M-theory, black holes and geometry are encoded in matrix degrees of freedom. I elaborate on this map by demonstrating that the relevant dynamics is realized through a system of qubits with a dense network of interactions. Using methods from quantum information theory, I compute the information scrambling time in Matrix black holes; and I present evidence that geometry is encoded in qubit entanglement entropy.

Weyl semimetals and holography

Speaker: Francisco Peña-Benitez
Institution: INFN Perugia
Time: Tuesday 31 May 2016, 15:00
Venue: 2nd floor seminar room
Abstract: In this talk I will review the main properties of Weyl semimetals. Then I’ll discuss a holographic model that realizes some of the features of these materials. In particular, I will analyze the electrical conductivity and its frequency dependence.

AdS4 solutions of massive IIA from dyonic supergravity and their simple Chern–Simons duals

Speaker: Oscar Varela
Institution: Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Potsdam and Utah State University
Time: Tuesday 23 August 2016, 15:00
Venue: 2nd floor seminar room
Abstract: It has been recently pointed out that maximal gauged supergravities in four dimensions often come in one-parameter families. The parameter measures the combination of electric and magnetic vectors in D=4 that participate in the gauging. I will explain the higher-dimensional origin of these dyonic gaugings, when the gauge group is chosen to be ISO(7). This supergravity arises from consistent truncation of massive IIA on the six-sphere, with the dyonically-gauging parameter identified with the Romans mass. The (AdS) vacua of the 4D supergravity uplift to new, explicit AdS4 backgrounds of massive type IIA. I will also show that the 3D field theories dual to these AdS4 solutions are Chern–Simons–matter theories with a simple gauge group and level k also identified with the Romans mass.

Black hole jets and force-free electrodynamics

Speaker: Maria Rodriguez
Institution: Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Potsdam and Utah State University
Time: Thursday 25 August 2016, 14:00
Venue: 2nd floor seminar room
Abstract: Plasma-filled magnetospheres can extract energy from spinning black holes and power a variety of observed astrophysical phenomena, such as jets. These magnetospheres are described by the highly nonlinear equations of force-free electrodynamics, or FFE. Typically these equations can only be solved numerically. In this talk I will explain how to analytically obtain several infinite families of exact solutions of the full nonlinear FFE equations very near the horizon of a maximally spinning black hole, where the energy extraction takes place.