Triangle Seminars
Tuesday, 3 Dec 2019
TBA
Andrei Parnachev
Postponed due to strike till Friday
Ignacio Reyes
(AEI)
Wednesday, 4 Dec 2019
The chaos bound in CFT_2 and higher spin holography
Prem Kumar
(Swansea)
Abstract:
I will describe thermodynamics and calculation of real time correlators in CFTs with extended W-symmetries, dual to AdS_3 gravity with a finite number of higher spin fields. I will point out mechanisms, including the appearance of a novel effective temperature, by which the proposed chaos bound due to Maldacena-Shenker-Stanford is violated in these theories.
I will describe thermodynamics and calculation of real time correlators in CFTs with extended W-symmetries, dual to AdS_3 gravity with a finite number of higher spin fields. I will point out mechanisms, including the appearance of a novel effective temperature, by which the proposed chaos bound due to Maldacena-Shenker-Stanford is violated in these theories.
Posted by: IC
Some physics behind supertranslations and superrotations
Geoffrey Compere
(U Brussels)
Abstract:
I will first provide a bird-eye view upon the infrared structure of gravity. I will shortly describe the relationship between BMS symmetry, soft theorems and memory effects at leading and subleading orders in the large radius expansion, while emphasizing the specificities of super-Lorentz symmetries. Secondly, I will present a no-go result on the soft hair conjecture: supertranslations induced by matter creating and falling inside black holes do not affect Hawking radiation, though they do affect scattering amplitudes. I will start by proving that Unruh radiation is unaffected by supertranslations induced by a shockwave and then show that Hawking radiation is mathematically related to this system, as a consequence of the principle of equivalence. Third, I will explain how BMS symmetry is associated to flux-balance laws that provide constraints upon the motion of binary compact mergers. Finally, I will present the extension of the BMS group to asymptotically de Sitter spacetimes.
I will first provide a bird-eye view upon the infrared structure of gravity. I will shortly describe the relationship between BMS symmetry, soft theorems and memory effects at leading and subleading orders in the large radius expansion, while emphasizing the specificities of super-Lorentz symmetries. Secondly, I will present a no-go result on the soft hair conjecture: supertranslations induced by matter creating and falling inside black holes do not affect Hawking radiation, though they do affect scattering amplitudes. I will start by proving that Unruh radiation is unaffected by supertranslations induced by a shockwave and then show that Hawking radiation is mathematically related to this system, as a consequence of the principle of equivalence. Third, I will explain how BMS symmetry is associated to flux-balance laws that provide constraints upon the motion of binary compact mergers. Finally, I will present the extension of the BMS group to asymptotically de Sitter spacetimes.
Posted by: IC
Thursday, 5 Dec 2019
Logarthmic vs rational conformal field theory – Who really wants to be rational anyway?
Simon Wood
(Cardiff University)
Abstract:
Two-dimensional conformally invariant quantum field theories (CFTs for short) form a sprawling network of ideas connecting many areas of physics and mathematics. A particularly celebrated class are the rational CFTs. These are essentially characterised by having a completely reducible representation theory and only a finite number of inequivalent irreducible representations. Rational CFTs exhibit a number of extraordinary features, foremost being the Verlinde formula which determines correlation functions from certain transformation properties of the CFTs characters. Logarithmic CFTs by contrast are almost maximally awful in that their representation theory is necessarily not completely reducible and need not have finitely many inequivalent irreducible representations. I will present recent results on such logarithmic CFTs and argue that suitable generalisations of rational features exist, at least in certain cases. So things are not as bad as one might fear.
Two-dimensional conformally invariant quantum field theories (CFTs for short) form a sprawling network of ideas connecting many areas of physics and mathematics. A particularly celebrated class are the rational CFTs. These are essentially characterised by having a completely reducible representation theory and only a finite number of inequivalent irreducible representations. Rational CFTs exhibit a number of extraordinary features, foremost being the Verlinde formula which determines correlation functions from certain transformation properties of the CFTs characters. Logarithmic CFTs by contrast are almost maximally awful in that their representation theory is necessarily not completely reducible and need not have finitely many inequivalent irreducible representations. I will present recent results on such logarithmic CFTs and argue that suitable generalisations of rational features exist, at least in certain cases. So things are not as bad as one might fear.
Posted by: QMW
Friday, 6 Dec 2019
Fermionic entanglement on the torus
Ignacio Reyes
(AEI)
Abstract:
Concepts from quantum information theory have become increasingly important in our understanding of entanglement in QFTs. One prominent example of this is the modular Hamiltonian, which is closely related to the Unruh effect. Using complex analysis, we determine this operator for the chiral fermion at finite temperature on the circle and show that it exhibits surprising new features. This simple system illustrates how a modular flow can transition from complete locality to complete non-locality, thus bridging the gap between previously known limits. We derive the first exact results for the entropy in the different spin sectors, and comment on the analytic continuation of the Rényi entropies to the complex plane.
Concepts from quantum information theory have become increasingly important in our understanding of entanglement in QFTs. One prominent example of this is the modular Hamiltonian, which is closely related to the Unruh effect. Using complex analysis, we determine this operator for the chiral fermion at finite temperature on the circle and show that it exhibits surprising new features. This simple system illustrates how a modular flow can transition from complete locality to complete non-locality, thus bridging the gap between previously known limits. We derive the first exact results for the entropy in the different spin sectors, and comment on the analytic continuation of the Rényi entropies to the complex plane.
Posted by: CityU2