Thema: 
The Genteel Xtremist : How the QCD phase diagram was unravelled by a Bielefelder 
Datum: 
28.10.19 
Uhrzeit: 
16:15 
Ort: 
H6 
Vortragender: 
Prof. Urs Heller and Prof. Rajiv Gavai 
American Physical Society and TIFR Mumbai / Bielefeld University 

Inhalt: 
Matter undergoes phase changes as its temperature or pressure is raised. Its fate under very high temperatures, as may have been witnessed few microseconds after the Big Bang and is now being explored in heavy ion collisions, or at very high densities feasible in dense neutron stars has fascinated physicists since long. With the advent of Quantum Chromo Dynamics (QCD) as the theory of strongly interacting matter, and discrete spacetime lattice as the reliable tool to extract predictions of QCD, the field has witnessed enormous progress. Pioneering contributions have come from the Bielefeld group. Major results and their impact will be discussed. 
Ansprechpartner: 
Thema: 
Relativistic hydrodynamics, heavyion collisions, dynamical black holes and resurgent series 
Datum: 
18.10.19 
Uhrzeit: 
16:15 
Ort: 
V3201 
Vortragender: 

MaxPlanckInstitute for Gravitational Physics, Potsdam 

Inhalt: 
The past 12 years has constituted the golden age for theoretical studies of relatativistic hydrodynamics. The experimental motivation for these developments came from ultrarelativistic heavyion collision at RHIC and LHC accelerators in which the paradigm of stronglyinteracting medium modelled hydrodynamically became the working horse for explaining the data. These experimental and phenomenological developments have come handinhand with theoretical progress in understanding relativistic hydrodynamics as an effective description embedded in quantum field theory. In my colloquium I will review the line of thought based on AdS/CFT (holography), an approach to study stronglycoupled quantum field theories using gravitational techniques, focusing on understanding the limits of applicability of relativistic hydrodynamics in farfromequilibrium quantum field theory. A beautiful spinoff of this analysis is understanding hydrodynamic gradient expansion as a part of a transseries, which encodes, through resurgence, information about genuinely nonequilibrium excitations of a collective state of matter. Based on a series of works reviewed in arXiv:1610.02023 and arXiv:1707.02282, as well as some later / ongoing work. 
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Thema: 
Quark Mass Definition and Extraction from (2+1+1)Flavor Lattice QCD 
Datum: 
24.10.19 
Uhrzeit: 
14:15 
Ort: 
D6135 
Vortragender: 

American Physical Society 

Inhalt: 
I summarize a new heavy quark mass definition, the minimal renormalon subtracted (MRS) mass by the TUM QCD collaboration. It is based on the relation between the heavy quark mass and heavylight meson masses in heavy quark effective theory. The Fermilab Lattice, MILC, and TUM QCD collaborations then used this new method to extract heavy quark masses using (2+1+1)flavor HISQ ensembles of the MILC collaboration including ensembles with physical light quarks. I end with showing results on heavylight pseudoscalar meson decay constants obtained in a similar analysis. 
Ansprechpartner: 
Thema: 
Dirac Spin Liquid on the Spin1/2 Triangular Heisenberg Antiferromagnet 
Datum: 
31.10.19 
Uhrzeit: 
14:15 
Ort: 
D5153 
Vortragender: 
Shijie Hu 
Kaiserlautern University 

Inhalt: 
We study the spin liquid candidate of the spin1/2 J1J2 Heisenberg antiferromagnet on the triangular lattice by means of density matrix renormalization group (DMRG) simulations [1]. By applying an external AharonovBohm flux insertion in an infinitely long cylinder, we find unambiguous evidence for gapless U(1) Dirac spin liquid behavior [2]. The flux insertion overcomes the finite size restriction for energy gaps and clearly shows gapless behavior at the expected wavevectors. Using the DMRG transfer matrix, the lowlying excitation spectrum can be extracted, which shows characteristic Dirac cone structures of both spinonbilinear and monopole excitations. Finally, we confirm that the entanglement entropy follows the predicted universal response under the flux insertion [2,3]. [1] Phys. Rev. X 7, 031020 (2017). [2] arXiv:1905.09837 (PRL accepted). [3] Science Advances 4, eaat5535 (2018). 
Ansprechpartner: 
Thema: 
Critical behaviour and characteristic polynomials of nonHermitian random matrices 
Datum: 
23.05.19 
Uhrzeit: 
16:15 
Ort: 
D5153 
Vortragender: 

University of Sussex 

Inhalt: 
I will discuss some recent developments regarding the normal matrix model. In particular my interest will be in certain critical models where the limiting support of the eigenvalues can radically change its topology by slightly adjusting an external parameter. I will discuss how aspects of the model can be explicitly mapped to the study of expectations of characteristic polynomials of nonHermitian random matrices (e.g. Ginibre or truncated unitary). Many of these averages are related to Painlevé transcendents, and by exploiting this, a precise and nontrivial asymptotic expansion of partition functions can be calculated in the critical models. This is joint work with Alfredo Deaño (University of Kent). 
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Thema: 
Spectral radius of random matrices with independent entries 
Datum: 
23.10.19 
Uhrzeit: 
16:15 
Ort: 
V3201 
Vortragender: 
Johannes Alt 
University of Geneva 

Inhalt: 
We consider random n x n matrices X with independent and centered entries and a general variance profile. We show that the spectral radius of X converges with very high probability to the square root of the spectral radius of the variance matrix of X when n tends to infinity. We also establish the optimal rate of convergence, that is a new result even for general i.i.d. matrices beyond the explicitly solvable Gaussian cases. The main ingredient is the proof of the local inhomogeneous circular law [arXiv:1612.07776] at the spectral edge. This is joint work with L\'{a}szl'{o} Erd\'"os and Torben Kr\"uger. 
Ansprechpartner: 