Category: Uncategorized

Title:
“Entanglement entropy at strong coupling – thermalisation and expanding spacetimes”

Abstract:
In this seminar I will present two recent results on entanglement in strongly coupled QFTs. First I will introduce the thermalisation of entanglement of generic entangling regions after a quench [1]. Depending on the ratio of the axes of ellipsoids the entanglement entropy thermalises with either the entanglement velocity or with the butterfly velocity. The butterfly velocity is an upper bound for thermalisation and we show that this upper bound is saturated for a large class of entangling regions. The second part of the talk will be about entanglement entropy in empty 4-dimensional de Sitter spacetime of a non-conformal QFT [2]. Interestingly, we show that extremal surfaces in the holographic dual of spherical entangling regions on the boundary QFT probe beyond the dual event horizon if and only if the entangling region is larger than the cosmological horizon.

[1] Márk Mezei and WS, Black holes often saturate entanglement entropy the fastest, 2001.03172 (PRL)
[2] Jorge Casalderrey-Solana, Christian Ecker, David Mateos and WS, Strong-coupling dynamics and entanglement in de Sitter space, 2011.08194

Slides:

Time: 15:00 instead of the usual 13:00

Title: “Pole skipping and related probes away from maximal chaos”

Abstract:
Quantum chaotic dynamics is associated to diverse physical phenomena and signatures. In this talk, we focus on the pole skipping phenomenon in non-maximally chaotic theories. Our discussion is informed by results from AdS/CFT and from models of SYK type. We study the interplay of the pole skipping phenomenon with the quantum butterfly effect and thermalization through the lens of entanglement entropy.

Slides:

Title:
“The phase of UV complete theories at high temperature”

Abstract:
Although in most cases symmetries are restored at high temperature, this is not always the case. This counter-intuitive phenomenon of symmetry non-restoration has been observed in some systems and can solve some well known cosmological problems. The models used in these cases have been so far effective theories believed to be valid below the physical cutoff of the Planck scale and so their extreme UV behaviour was not important. In this seminar I will try to see how difficult it is, if possible at all, to construct UV complete theories with symmetry non-restoration at high temperature.

Slides

Title:
“False vacuum decay: polygonal bounces and quartic prefactors”

Abstract:
We will discuss the physics of metastable transitions in quantum and thermal field theories. The presence of false vacua may trigger first order phase transitions that manifest themselves in cosmological observables, such as stochastic gravitational waves. I will discuss how the dominant semiclassical bounce contribution may be calculated exactly and how a universal semi-analytic method of polygonal bounces was developed and successfully implemented. Finally, I will focus on one loop corrections that involve summing up quantum fluctuations. I will show an exact one loop result for quartic potentials, which provides an analytic understanding of all the relevant features, including the bounce, removal of zeroes and renormalization.

Slides: