Thema: 
Intelligente Energieversorgungsnetze 
Datum: 
08.11.21 
Uhrzeit: 
16:15 
Ort: 
H4 
Vortragender: 

FH Bielefeld 

Inhalt: 

Ansprechpartner: 
Thema: 
Random matrices, spin glasses, and machine learning 
Datum: 
23.07.21 
Uhrzeit: 
16:15 
Ort: 
ZOOM/Konferenzschaltung 
Vortragender: 

Oxford University 

Inhalt: 
I will describe some problems relating to machine learning and their connections to random matrix theory and spin glasses. These connections give a mathematical framework for understanding in qualitative terms the effectiveness of certain algorithms that are important in machine learning, but developing them into precise models remains a major challenge. I will reflect on the different roles played by models in computer science and physics, focussing on those involving random matrices. 
Ansprechpartner: 
Thema: 
Phenomenological Aspects of AxionLike Particles in Cosmology and Astrophysics 
Datum: 
09.11.21 
Uhrzeit: 
14:15 
Ort: 
D6135 
Vortragender: 
Ahmed Ayad 
Bielefeld University 

Inhalt: 
Cosmology and particle physics are closer today than ever before, with several searches underway at the interface between cosmology, particle physics, and eld theory. The mystery of dark matter (DM) is one of the greatest common unsolved problems between these elds. It is established now based on many astrophysical and cosmological observations that only a small fraction of the total matter content of the universe is made of baryonic matter, while the vast majority is constituted by dark matter. However, the nature of such a component is still unknown. One theoretically wellmotivated approach to understanding the nature of dark matter would be through looking for light pseudoscalar candidates for dark matter such as axions and axionlike particles (ALPs). Axions are hypothetical elementary particles resulting from the PecceiQuinn (PQ) solution to the strong CP problem in quantum chromodynamics (QCD). Furthermore, many theoretically wellmotivated extensions to the standard model of particle physics (SMPP) predicted the existence of more pseudoscalar particles similar to the QCD axion and called ALPs. Axions and ALPs are characterized by their coupling with two photons. While the coupling parameter for axions is related to the axion mass, there is no direct relation between the coupling parameter and the mass of ALPs. Nevertheless, it is expected that ALPs share the same phenomenology of axions. In the past years, axions and ALPs regained popularity and slowly became one of the most appealing candidates that possibly contribute to the dark matter density of the universe. In my talk, I will show that the phenomenology of axions and ALPs interactions with photons can be used to constrain some of their properties and explain several astrophysical phenomena. 
Ansprechpartner: 
Thema: 
Numerical Studies of Kitaev Materials at finite Temperature and Field 
Datum: 
19.11.21 
Uhrzeit: 
14:15 
Ort: 
D5153 
Vortragender: 

GoetheUniversität Frankfurt am Main 

Inhalt: 
In this talk I present various theoretical efforts that have gone into understanding the physics of the Kitaev candidate material $\alpha$RuCl$_3$. In such materials, both conventional linear spinwave theory as well as Kitaev's exact solution break down. Therefore, the more reliable theoretical methods have been exact diagonalization techniques like the finitetemperature Lanczos method. By applying these methods to abinitio guided spin models, we have found good agreement with many experiments and gained insight into the relevant phases. 
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: 
Planar symplectic ensembles: from scaling limits to Wronskian structures 
Datum: 
27.10.21 
Uhrzeit: 
09:00 
Ort: 
ZOOM / Konferenzschaltung 
Vortragender: 

Korea Institute for Advanced Study 

Inhalt: 
In this talk, I will discuss complex eigenvalues of nonHermitian random matrices with symplectic symmetry, which are known to form Pfaffian point processes. In particular, I will present various scaling limits of symplectic ensembles and explain their unified integrable structure of Wronskian form. Examples include edge scaling limits of the Ginibre ensemble (with boundary confinements) and bulk/edge scaling limits of the elliptic Ginibre ensemble in the almostHermitian regime. Beyond standard universality classes, I will also introduce scaling limits of the MittagLeffler ensemble at the singularity. Furthermore, for symplectic ensembles with general external potentials, I will present the characterization of translation invariant scaling limits by virtue of rescaled massone and Ward’s equations. This talk is based on two joint works: one with Gernot Akemann and NamGyu Kang and the other with Markus Ebke and SeongMi Seo. 
Ansprechpartner: 