Found 8 result(s)

### 24.02.2021 (Wednesday)

#### Causalsymmetrybreaking:fromquantumchaostowormholes

Regular Seminar Julian au:Sonner'><span class='hl'>Julian</span> Sonner (University of Geneva)

 at: 13:15 KCLroom Zoom, See abstract abstract: Quantum chaotic systems are often defined via the assertion that their spectral statistics coincides with, or is well approximated by, random matrix theory. In this talk I will explain how the universal content of random matrix theory emerges as the consequence of a simple symmetry-breaking principle and its associated Goldstone modes. This approach gives a natural way to identify wormhole-like correlations, even for individual theories, in particular in theories with gravity duals. I will also discuss how to extend the Goldstone effective-field-theory approach to study operator correlation functions, and explain the relation of the EFT of quantum chaos to the bulk physics of wormhole-like geometries. [Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]

### 12.11.2015 (Thursday)

#### ExactResultsforEntanglementandRenyiEntropies,andtheirGravityDuals

Regular Seminar Julian au:Sonner'><span class='hl'>Julian</span> Sonner (University of Geneva)

 at: 14:00 QMWroom G.O. Jones 610 abstract: The recent focus on entanglement entropy in holography has many motivations, ranging from the applied (e.g. AdS/CMT) to the foundational (emergence of gravity). For all of these programs It is important to find examples, where the quantities of interest can be directly calculated in strongly-coupled field theories and, moreover, the dual geometry constructed at strong coupling. In this talk I will describe joint work with Crossley and Dyer on using localization methods to obtain entanglement and (super-) Renyi entropies of the N=4 SYM theory with gauge group SU(N) in 4D at all values of the â€™t Hooft coupling \lambda and number of colors N. Since obtaining quantities like entanglement and Renyi entropies involves working on singular spaces, which typically break the supersymmetry, we focus on a supersymmetric generalization, the so-called super-Renyi entropy where the supersymmetry breaking effects of the singularities are suitably compensated. I will also discuss dual gravity solutions as five-dimensional BPS black holes with hyperbolic horizon. I will conclude with a description of Wilson loops, that is the contribution to the entanglement and Renyi entropies due to adding fundamental matter to the theory.

### 11.11.2015 (Wednesday)

#### ExactResultsforEntanglementandRenyiEntropies,andtheirGravityDuals

Regular Seminar Julian au:Sonner'><span class='hl'>Julian</span> Sonner (University of Geneva)

 at: 14:30 ICroom H503 abstract: The recent focus on entanglement entropy in holography has many motivations, ranging from the applied (e.g. AdS/CMT) to the foundational (emergence of gravity). For all of these programs It is important to find examples, where the quantities of interest can be directly calculated in strongly-coupled field theories and, moreover, the dual geometry constructed at strong coupling. In this talk I will describe joint work with Crossley and Dyer on using localization methods to obtain entanglement and (super-) Renyi entropies of the N=4 SYM theory with gauge group SU(N) in 4D at all values of the â€™t Hooft coupling \lambda and number of colors N. Since obtaining quantities like entanglement and Renyi entropies involves working on singular spaces, which typically break the supersymmetry, we focus on a supersymmetric generalization, the so-called super-Renyi entropy where the supersymmetry breaking effects of the singularities are suitably compensated. I will also discuss dual gravity solutions as five-dimensional BPS black holes with hyperbolic horizon. I will conclude with a description of Wilson loops, that is the contribution to the entanglement and Renyi entropies due to adding fundamental matter to the theory.

### 31.03.2011 (Thursday)

#### HolographyandSuperconductors

Regular Seminar Julian au:Sonner'><span class='hl'>Julian</span> Sonner (IC)

 at: 14:00 QMWroom 602 abstract: Holographic superconductors are gravitational backgrounds, in the sense of gauge-gravity duality, that produce the symmetry breaking pattern and associated phenomenology of superconductors in the boundary theory dual to the gravity solution. In this talk I will describe how such systems are constructed, how they can be embedded into M-theory (and string theory) and how their hydrodynamic description at strong coupling can be derived from the gravity picture.

### 23.03.2011 (Wednesday)

#### Derivingthehydrodynamicaldescriptionofholographicsuperfluids

Regular Seminar Julian au:Sonner'><span class='hl'>Julian</span> Sonner (Imperial and Cambridge)

 at: 13:15 KCLroom 423 abstract: In my talk I will describe a class of gravitational solutions which, in the context of AdS/CFT, are dual to boundary field theories with spontaneous symmetry breaking and thus give rise to a superfluid phase. I will give a general introduction to the ideas of quantum criticality and how AdS/CFT techniques may be applied to such systems. I will then use the tools of gauge/gravity duality to demonstrate that the boundary description of such systems, in the hydrodynamical limit, is governed by a relativistic generalisation of the Tisza-Landau two-fluid model.

### 09.03.2010 (Tuesday)

#### SuperconductorsandQuantum-CriticalM-Theory

Regular Seminar Julian au:Sonner'><span class='hl'>Julian</span> Sonner (Imperial College)

 at: 13:30 City U.room C335 abstract: The Renormalisation Group tells us that, quite generically, quantum and classical many-body systems exhibit interesting scaling behaviour near critical points. Quantum critical points form a subset of these, corresponding to zero-temperature phase transitions. In the last decade, the AdS/CFT correspondence between conformal field theories on one side and string or M-Theory on the other side has developed into a rich and exciting subject. Until recently the applications of this 'duality' were mostly focused on theories relevant to model quantum field theories that are considered interesting from the point of view of high-energy particle physics - the prime example being N=4 SYM in d=4. In this talk I will describe how similar methods can be fruitfully applied to the theory of quantum critical phenomena in 2+1 dimensions. These systems are of practical interest, as it has been proposed that a quantum critical point underlies the strange behaviour of high-TC superconductors falling into the copper-oxide group.

### 11.11.2009 (Wednesday)

#### SuperconductorsandquantumcriticalityinM-theory

Regular Seminar Julian au:Sonner'><span class='hl'>Julian</span> Sonner (Imperial)

 at: 13:15 KCLroom 423 abstract: Quantum phase transitions imply certain scaling relations among space and time. A subclass of quantum critical systems is in fact invariant under relativstic conformal symmetries. Such theories have recently been studied as a new class of duals in AdS/CFT. I will describe how one can exactly embed so-called holographic superconductors in M-theory and how this embedding has already lead to new insights about the low-temperature behaviour of holgraphic superconductors with an underlying quantum critical point.