Thema: 
Continuing to finite density  the QCD phase diagram with Lattice QCD 
Datum: 
31.01.22 
Uhrzeit: 
16:15 
Ort: 
cyberspace 
Vortragender: 
Jana Günther 
Wuppertal University 

Inhalt: 
The QCD phase diagram is an important ingredient to understand both the development of the early universe and the results of resent heavy ion collision experiments. At zero baryon density lattice QCD is the established tool, that provides precise theoretical results. However, to explore the phase diagram at nonzero density new techniques are required to deal with the infamous sign problem. In this talk, I will take you along on our journey investigating the area around the QCD transition away from the zero density axis. 
Ansprechpartner: 
Thema: 
Quasicompact Operators and Uniquely Ergodic Dynamical Systems 
Datum: 
04.02.22 
Uhrzeit: 
16:15 
Ort: 
ZOOM/Konferenzschaltung 
Vortragender: 

Open University, Milton Keynes 

Inhalt: 
Primitive substitutions on finite alphabets are well studied objects in symbolic dynamics and are known to generate uniquely ergodic dynamical systems via the classical PerronFrobenius theory. There is a similar notion of primitivity for substitutions on compact alphabets, but this no longer guarantees unique ergodicity. In this talk, we define the associated substitution operator, discuss its spectral properties, and give several criteria which guarantees unique ergodicity. We conclude by illustrating how it is satisfied for several classes of examples. This is based on joint work with Dan Rust and Jamie Walton. 
Ansprechpartner: 
Thema: 
Gravitational Waves from Strong FirstOrder Phase Transitions 
Datum: 
15.02.22 
Uhrzeit: 
14:15 
Ort: 
Online, via ZOOM 
Vortragender: 

University of Helsinki 

Inhalt: 
In many extensions of the Standard Model, the electroweak transition is first order  in some cases, strongly so. The ensuing phase transition would result in collisions of bubbles of the new Higgs phase. These collisions, and the associated interactions of sound waves in the plasma, are substantial sources of gravitational waves. For a phase transition at or around the electroweak scale, these gravitational waves may be detectable by future missions such as LISA. They can indirectly provide a probe of particle physics beyond the Standard Model, complementary to future colliders. However, concrete predictions of the resulting gravitational waves will require good understanding both of the particle physics models themselves, as well as the nonequilibrium physics of the transition. In other words, we need accurate studies of the phase diagrams in the underlying particle physics theories, as well as good predictions of the expected gravitational wave signal from simulations. These feed into one another, forming a socalled 'pipeline'. The stronger the phase transition, the better the chance of being detected (or constrained) by future missions like LISA. However, strong transitions are also the most poorly understood. In this talk I will discuss some recent results from different points along the 'pipeline', with a focus on the consequences for strong firstorder phase transitions. 
Ansprechpartner: 
Thema: 
Toroidale Momente in anisotropen Spinsystemen 
Datum: 
21.01.22 
Uhrzeit: 
14:15 
Ort: 
Hybrid  Zoom/D5153 
Vortragender: 
Daniel Pister 
Universität Bielefeld 

Inhalt: 

Ansprechpartner: 
Thema: 
On NonHermitian BetaEnsembles 
Datum: 
14.10.21 
Uhrzeit: 
16:00 
Ort: 
D5153 
Vortragender: 

Universität Bielefeld 

Inhalt: 
Loggases with inverse temperature beta are systems with many applications in physics, for example in the theory of superconductors or the fractional quantum Hall effect. For some specific values of beta a correspondence to random matrix theory (RMT) is well established. The advantage of this connection is the usage of the RMT methods in the study of those systems. The goal of this talk is the discussion of Loggases in two dimensions, i.e. in the nonHermitian case, for more general values of the inverse temperature. Therefore, we study in the first part a model of normal 2 × 2 matrices with beta in [0,2] and discuss whether we find a surmise for the nearestneighbour spacing distribution of large matrices. In the second part of the talk we introduce the study of symmetry classes in nonHermitian RMT. We conjecture that the classes of complex symmetric and complex quaternion matrices can be effectively described by Loggases in two dimensions with noninteger inverse temperatures. 
Ansprechpartner: 
Thema: 
Symmetries and universality in the nonHermitian SachdevYeKitaev model 
Datum: 
09.02.22 
Uhrzeit: 
09:00 
Ort: 
ZOOM / Konferenzschaltung 
Vortragender: 
Lucas de Barros Pacheco Seara de Sá 
Tecnico Lisboa 

Inhalt: 
The nonHermitian SachdevYeKitaev model (nHSYK), a model of N stronglycoupled Majorana fermions with random alltoall qbody nonunitary interactions, is receiving increasing attention because of its possible role as a paradigmatic solvable example of nonHermitian quantum chaos. In this talk, I will discuss how its local level statistics are well described by (nonHermitian) random matrix theory (RMT) for q>2, while for q=2 it is given by the equivalent of Poisson statistics. For that comparison, we combine exact diagonalization numerical techniques with tools from RMT, in particular complex spacing ratios. Depending on q and N, we identify 19 out of the 38 nonHermitian universality classes in the nHSYK model, some of which involve universal bulk correlations of classes AI† and AII†, beyond the Ginibre ensembles. At the end, I will also address the probability distribution of the singular values of the nHSYK model, which, in the limit of a large number N of Majoranas, can be related to the weight function of the AlSalamChihara QLaguerre polynomials. 
Ansprechpartner: 