# Aktuelle Veranstaltungen

## Kolloquium

Thema:

### Soft Pions and the Dynamics of the Chiral Phase Transition

Datum:

11.07.22

Uhrzeit:

16:15

Ort:

Y0-111

Vortragender:

Derek Teaney

Stony Brook University

Inhalt:

I will first review lattice simulations of the QCD phase diagram, focusing on chiral symmetry and chiral symmetry breaking. In the limit of two massless quark flavors (up and down) the chiral phase transition is second order and is in the O(4) universality class. The fingerprints of this critical point are seen in lattice simulations of real world QCD. Next I will review heavy ion experiments, presenting an overview of some of the most important measurements from heavy ion collisions. These measurements provide compelling evidence that classical hydrodynamics is an appropriate effective theory for understanding these collisions. In current hydrodynamic simulations of these events, chiral symmetry breaking and its consequences are largely ignored. However, if the quark mass is small enough, one would expect that the pattern of chiral symmetry breaking seen on the lattice could provide a useful organizing principle for hydrodynamics, increasing its predictive power. I describe our efforts to simulate the real time dynamics of the O(4) critical point using hydrodynamics. Then I point out some discrepancies between the measured yields of soft pions and current hydrodynamic simulations. I suggest that incorporating the chiral phase transition into the hydrodynamic description could fix the discrepancies.

Ansprechpartner:

S. Schlichting / TR211

## Kolloquium Mathematische Physik

Thema:

### Vertex Algebras for 2- and 4-Dimensional Conformal Field Theories

Datum:

01.07.22

Uhrzeit:

16:15

Ort:

D5-153

Vortragender:

Sven Möller

Universität Hamburg

Inhalt:

Vertex (operator) algebras axiomatise 2-dimensional conformal field theories in physics. They were introduced in the 1980s to explain mysterious connections between number and representation theory (monstrous moonshine). Not long ago, they were also shown to capture certain aspects of 4-dimensional superconformal field theories. In this talk I will describe recent classification results for holomorphic vertex algebras of central charge 24 by means of certain modular forms (vector-valued Eisenstein series). Moreover, I will sketch classification problems arising in the context of 4-dimensional field theories.

Ansprechpartner:

G. Akemann

## Seminar Hochenergiephysik

Thema:

### Schwinger Model at Finite Temperature and Density with Beta VQE

Datum:

16.08.22

Uhrzeit:

14:15

Ort:

D6-135

Vortragender:

Akio Tomiya

International Professional University of Technology in Osaka

Inhalt:

We investigate a quantum gauge theory at finite temperature and density using a variational algorithm for near-term quantum devices. We adapt ?-VQE to evaluate thermal and quantum expectation values and study the phase diagram for massless Schwinger model along with the temperature and density. By compering the exact variational free energy, we find the variational algorithm work for T>0 and ?>0 for the Schwinger model. No significant volume dependence of the variational free energy is observed in ?/g?[0,1.4]. We calculate the chiral condensate and take the continuum extrapolation. As a result, we obtain qualitative picture of the phase diagram for massless Schwinger model.

Ansprechpartner:

O. Kaczmarek

## Seminar Kondensierte Materie

Thema:

### Das Perzeptron: Grundbaustein neuronaler Netze und kuenstlicher Intelligenz

Datum:

07.07.22

Uhrzeit:

14:15

Ort:

D5-153

Vortragender:

Paul Angelike

Universität Bielefeld

Inhalt:

Ansprechpartner:

Peter Reimann

## Seminar Mathematische Physik

Thema:

### Many-particles diffusing with resetting: study of the large-deviation properties of the flux distribution

Datum:

05.05.22

Uhrzeit:

16:00

Ort:

D5-153

Vortragender:

Costantino Di Bello

Inhalt:

In this paper we studied a model of noninteracting particles moving on a line following a common dynamics. In particular we considered either a diffusive motion with Poissonian resetting, and a run-and-tumble motion with Poissonian resetting. We were interested in studying the distribution of the random variable $Q_t$ defined as the flux of particles through origin up to time $t$. We used the notation $P(Q,t)$ to identify the probability $\mathbb{P}\{Q_t=Q\}$. We considered particles initially located on the negative half line with a fixed density $\rho$. In fully analogy with disordered systems, we studied both the annealed and the quenched case for initial conditions. In the former case we found that, independently from the specific dynamics, $P_\mathrm{an}(Q,t)$ has a Poissonian shape; while in the latter case, for what concerns the diffusive dynamics with resetting, the large deviation form of the quenched distribution reads $P_\mathrm{qu}(Q,t)\sim \exp\left[-r^2t^2 \Psi_\mathrm{diff}\left(\dfrac{Q}{\rho t}\right)\right]$ with the large deviation function $\Psi_\mathrm{diff}(x)$ exhibiting a discontinuity in the third derivative, hence aiming, despite the simplicity of the model, at the exhistence of a dynamical phase transition. The quenched distribution for the run-and-tumble dynamics, instead, does not exhibit any kind of phase transition. Importance sampling Monte Carlo simulations were performed to prove the analytical results. References: Current fluctuations in noninteracting run-and-tumble particles in one dimension Tirthankar Banerjee, Satya N. Majumdar, Alberto Rosso, and Grégory Schehr, Phys. Rev. E 101, 052101 https://doi.org/10.1103/PhysRevE.101.052101 Current Fluctuations in One Dimensional Diffusive Systems with a Step Initial Density Profile B. Derrida and A. Gerschenfeld, J. Stat. Phys. 137, 978 (2009) https://doi.org/10.1007/s10955-009-9830-1

Ansprechpartner:

Gernot Akemann

## Seminar Bielefeld-Melbourne Zufallsmatrizen

Thema:

### Stochastic Geometry Beyond Independence and its Applications

Datum:

13.07.22

Uhrzeit:

09:00

Ort:

ZOOM / Konferenzschaltung

Vortragender:

Subhro Ghosh

National University of Singapore

Inhalt:

The classical paradigm of randomness is the model of independent and identically distributed (i.i.d.) random variables, and venturing beyond i.i.d. is often considered a challenge to be overcome. In this talk, we will explore a different perspective, wherein stochastic systems with constraints in fact aid in understanding fundamental problems. Our constrained systems are well-motivated from statistical physics, including models like the random critical points and determinantal probability measures. These will be used to shed important light on natural questions of relevance in understanding data, including problems of likelihood maximization and dimensionality reduction. En route, we will explore connections to spiked random matrix models and novel asymptotics for the fluctuations of spectrally constrained random systems. Based on the joint works below. [1] Gaussian determinantal processes: A new model for directionality in data, with P. Rigollet, Proceedings of the National Academy of Sciences, vol. 117, no. 24 (2020), pp. 13207--13213 [2] Fluctuation and Entropy in Spectrally Constrained random fields, with K. Adhikari, J.L. Lebowitz, Communications in Math. Physics, 386, 749–780 (2021). [3] Maximum Likelihood under constraints: Degeneracies and Random Critical Points, with S. Chaudhuri, U. Gangopadhyay, submitted.

Ansprechpartner:

Anas Rahman

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