Stochastic quantization at finite chemical potential

A nonperturbative lattice study of QCD at finite chemical potential is complicated due to the complex fermion determinant and the sign problem. Here we apply the method of stochastic quantization and complex Langevin dynamics to this problem. We present results for U(1) and SU(3) one link models and QCD at finite chemical potential using the hopping expansion. The phase of the determinant is studied in detail. Even in the region where the sign problem is severe, we find excellent agreement between the Langevin results and exact expressions, if available. We give a partial understanding of this in terms of classical flow diagrams and eigenvalues of the Fokker-Planck equation.Comment: 37 pages, many eps figures; references added, to appear in JHE

Simple QED- and QCD-like Models at Finite Density

In this paper we discuss one-dimensional models reproducing some features of quantum electrodynamics and quantum chromodynamics at nonzero density and temperature. Since a severe sign problem makes a numerical treatment of QED and QCD at high density difficult, such models help to explore various effects peculiar to the full theory. Studying them gives insights into the large density behavior of the Polyakov loop by taking both bosonic and fermionic degrees of freedom into account, although in one dimension only the implementation of a global gauge symmetry is possible. For these models we evaluate the respective partition functions and discuss several observables as well as the Silver Blaze phenomenon.Comment: 5 pages, 2 figures. Final published versio

1/M correction to quenched QCD with non-zero baryon density

We study the \kappa^2 corrections to the quenched limit of \mu>0 QCD. We use an improved reweighting procedure.Comment: Lattice2001(hightemp), 3 page

Complex Langevin: Boundary terms and application to QCD

We employ the Complex Langevin method for simulation of complex-valued actions. First, we show how to test for convergence of the method by explicitely computing boundary terms and demonstrate this in a model. Then we investigate the deconfinement phase transition of QCD with $N_f=2$ Wilson-fermions using the Complex Langevin Method and. We give preliminary results for the transition temperatures up to $\mu/T_c(\mu=0)\approx 5$ and compute the curvature coefficient $\kappa_2$.Comment: Proceedings for The 36th Annual International Symposium on Lattice Field Theory - LATTICE2018; update: added some acknowledgement