Triangle Seminars
Tuesday, 24 Jan 2017
Matrix models for the gauge-gravity correspondence
Nadav Drukker
(King's)
Abstract:
The gauge-gravity correspondence identifies a field theory with a gravitational theory. The gravitational theory is weakly coupled when the field theory has large coupling and vice versa, which mostly prevents matching nontrivial results between the two descriptions. I will discuss cases when the field theory calculation can be reduced to a finite dimensional matrix integral, representing some counting problems. I will then evaluate the integral exactly and reexpand the exact result, which is valid for all coupling, at strong coupling. The resulting expression should match a weak coupling gravitational (or string theoretic) calculation and I’ll comment on what is known from that direction.
The gauge-gravity correspondence identifies a field theory with a gravitational theory. The gravitational theory is weakly coupled when the field theory has large coupling and vice versa, which mostly prevents matching nontrivial results between the two descriptions. I will discuss cases when the field theory calculation can be reduced to a finite dimensional matrix integral, representing some counting problems. I will then evaluate the integral exactly and reexpand the exact result, which is valid for all coupling, at strong coupling. The resulting expression should match a weak coupling gravitational (or string theoretic) calculation and I’ll comment on what is known from that direction.
Posted by: KCL
Wednesday, 25 Jan 2017
AdS crunches from relevant deformations of CFTs
📍 London
Prem Kumar
(Swansea)
Abstract:
We discuss examples of relevant deformations of known CFTs placed in de Sitter spacetime, possessing AdS gravity duals with Big Crunch singularities. We point out generic aspects of such dual backgrounds, including the behaviour in the vicinity of the singularity, holographic correlators in the geodesic approximation, and retarded correlators in an analytically tractable example within the AdS_4/CFT_3 context. We briefly describe an attempt to characterise the bulk crunch and its putative resolution within the O(N) vector model in 3D.
We discuss examples of relevant deformations of known CFTs placed in de Sitter spacetime, possessing AdS gravity duals with Big Crunch singularities. We point out generic aspects of such dual backgrounds, including the behaviour in the vicinity of the singularity, holographic correlators in the geodesic approximation, and retarded correlators in an analytically tractable example within the AdS_4/CFT_3 context. We briefly describe an attempt to characterise the bulk crunch and its putative resolution within the O(N) vector model in 3D.
Posted by: KCL
Universal Formula for the Holographic Speed of Sound
Andres Anabalon
(Adolfo Ibanez U.)
Abstract:
We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner-Freedman window. We show that is possible to derive a universal formula for the speed of sound for any theory. As an example we find all the planar black holes of the single scalar field consistent truncation of type IIB that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. We find the speed of sound for different values of the induced vacuum expectation value when a double trace deformation is induced in the gauge theory. For any theory, we show that the speed of sound is not bounded by any special value.
We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner-Freedman window. We show that is possible to derive a universal formula for the speed of sound for any theory. As an example we find all the planar black holes of the single scalar field consistent truncation of type IIB that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. We find the speed of sound for different values of the induced vacuum expectation value when a double trace deformation is induced in the gauge theory. For any theory, we show that the speed of sound is not bounded by any special value.
Posted by: IC
Thursday, 26 Jan 2017
Cosmic Inflation from String Axions
Susha Parameswaran
(University of Liverpool)
Abstract:
An early epoch of cosmic inflation, driven by a scalar field slowly rolling down a flat potential, provides an elegant solution to several cosmological puzzles. The notorious sensitivity of the slow roll potential to quantum gravity effects, presents both a challenge and opportunity for string theory to connect to observations.
A very promising way to explain slow roll inflation is with an axionic inflaton field, whose flat potential is protected by a perturbative shift symmetry. However, the canonical models of axion inflation - "Natural Inflation" and "Axion Monodromy" - are now both in tension with observations and difficult to embed in a UV complete theory like string theory. I will discuss these challenges, and also a way to overcome them, with an inflationary mechanism - beyond slow roll - that is well-motivated from string theory and consistent with observations, including distinctive signatures to be searched for in future observations.
An early epoch of cosmic inflation, driven by a scalar field slowly rolling down a flat potential, provides an elegant solution to several cosmological puzzles. The notorious sensitivity of the slow roll potential to quantum gravity effects, presents both a challenge and opportunity for string theory to connect to observations.
A very promising way to explain slow roll inflation is with an axionic inflaton field, whose flat potential is protected by a perturbative shift symmetry. However, the canonical models of axion inflation - "Natural Inflation" and "Axion Monodromy" - are now both in tension with observations and difficult to embed in a UV complete theory like string theory. I will discuss these challenges, and also a way to overcome them, with an inflationary mechanism - beyond slow roll - that is well-motivated from string theory and consistent with observations, including distinctive signatures to be searched for in future observations.
Posted by: QMW