ELFT HÍRADÓ

[Andras LASZLO <laszlo.andras AT wigner.hu>]

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Date: Thu, 6 Apr 2023 13:34:43 +0200 (CEST)
From: Daniel Nogradi <nogradi AT bodri.elte.hu>
To: Daniel Nogradi <nogradi AT bodri.elte.hu>
Subject: ELTE particle physics seminar - 11 April


Date/Time: 11 April, Tuesday, 14:15

Location: ELTE TTK, second floor, 2.54 Novobatzky room

Speaker: David Pesznyak (ELTE)

Title: Fighting the sign problem in a chiral random matrix model with contour 
deformations

Abstract:

First principle studies of Euclidean quantum field theories at finite chemical 
potential are hindered by the so-called complex action problem, i.e. the 
Boltzmann weights of the path integral cannot be regarded as a probability 
density function. Upon reweighting from an appropriately modified theory the 
complex action problem reduces to the sign problem: cancellations in the 
sampled data lead to small signal-to-noise ratios in the expectation values of 
observables. The sign problem is present in a number of theories, e.g. QCD at 
finite baryon density or the Hubbard model away from half-filling. Our goal is 
to ameliorate the severity of the sign problem through complex integration 
contour deformations in the path integrals. In the presented work we study the 
chiral random matrix theory of Stephanov - a toy model of QCD at finite 
baryochemical potential - which also has a sign problem. We studied integration 
contour deformations with simple ansatze and optimized their parameters with 
machine learning techniques. Furthermore, we also investigated contour 
deformations via the holomorphic flow equations, which is an alternative way to 
obtain integration manifolds with a less severe sign problem. Our findings show 
that the optimization of a single parameter leads to a considerable improvement 
in the severity of the sign problem, and that it is also exponential in the 
degrees of freedom of the system.



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