timo – Holography, strings and transport in Ljubljana

Thursday 27th May 2021

Mihailo Čubrović (SCL – Institute of physics Belgrade)

Title: “Holography of traversable wormholes: non-maximal chaos and teleportation”

Abstract:
I will discuss the time-ordered and time-disordered correlation functions in the background of the Gao-Jafferis-Wall (GJW) traversable wormhole. The time-disordered correlators exhibit a spectrum of Lyapunov exponents with some or all exponents below the maximal chaos bound. This is rooted in the absence of the black hole horizon and the non-local coupling necessary to produce the wormhole in the first place. The question is now: what is the field theory dual of the GJW wormhole? In principle, we may interpret the wormhole as an EPR pair of entangled systems allowing teleportation, or as a single system in contact with a heat bath. In the former case the Lyapunov exponents are related to the fidelity of the teleportation and in the latter to the quantum chaos in the system. To understand this dichotomy I consider the scalar field on the wormhole background and find a large freedom in defining the boundary action on the two-sided boundary, corresponding to the symmetry of thermofield dynamics (TFD) Hamiltonians. The details of the field theory dual thus depend on the choice of the boundary terms in the action.

Thursday 3rd December 2020

Marko Medenjak (ENS Paris)

Title:
“TTbar-deformed conformal field theories out of equilibrium”

Abstract:
In the seminar I will discuss out-of-equilibrium properties of conformal field theories that are deformed by the TTbar-deformation from two perspectives: integrability and holography. I will focus on the energy and momentum Drude weights and diffusion constants, as well as the nonequilibrium steady states, which emerge after the inhomogeneous quench. Surprisingly, the transport coefficients and nonequilibrium steady states admit a universal closed form expressions, which do not depend on the field content of the conformal field theory. The matching of the results between the two methods serves as the first check of the TTbar-deformed holographic correspondence from the dynamical standpoint, and establishes the connection between the generalized hydrodynamics and holography.

Medenjak Slides

Slides:

Thursday 22nd October 2020

Napat Poovuttikul (Durham University)

Title: “Hydrodynamics of 2-group global symmetry”

Abstract:
Can one always construct hydrodynamics descriptions out of global symmetry? Even if that symmetry is not a group?

2-group is a genuine symmetry structure resulting from extending the ordinary symmetry by one-form symmetry. A QFT with 2-group shares similar features with anomalous QFT, despite being anomaly free. I will give a few example of QFTs with 2-group global symmetry, particularly those obtained by gauging non-anomalous subgroup of a QFT with anomaly. I will outline how to construct hydrodynamic description of an interacting QFT with 2-group global symmetry in the IR.

If time allows, I will also briefly discussed the holographic dual of 2-group global symmetry.

Poovuttikul Slides

Slides:

Thursday 14th January 2021

Matteo Baggioli (IFT Madrid and Shanghai)

Title: “Five little stories about liquids”

Abstract:
There are two famous italian sayings about water: ‘perdersi in un bicchiere d’acqua’ (get lost in a glass of water) and ‘facile come bere un bicchiere d’acqua’ (simple as drinking a glass of water). Both of them suggest the extreme simplicity of water and liquids in general. And both of them are totally wrong! Contrary to solids and gases, fluids are very poorly understood. In this talk, I will present five little stories to prove the above statement and I will discuss with you the reasons behind, and possible recent scenarios to overcome them.