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We study QCD at finite density and low temperature by using the complex Langevin method. We employ the gauge cooling to control the unitarity norm and introduce a deformation parameter in the Dirac operator to avoid the singular-drift…

High Energy Physics - Lattice · Physics 2018-04-18 Keitro Nagata , Jun Nishimura , Shinji Shimasaki

In many interesting physical systems, the determinant which appears from integrating out fermions becomes complex, and its phase plays a crucial role in the determination of the vacuum. An example of this is QCD at low temperature and high…

High Energy Physics - Lattice · Physics 2017-01-04 Yuta Ito , Jun Nishimura

It is well known that investigating QCD at finite density by standard Monte Carlo methods is extremely difficult due to the sign problem. Some years ago, the complex Langevin method with gauge cooling was shown to work at high temperature,…

High Energy Physics - Lattice · Physics 2019-01-15 Keitaro Nagata , Jun Nishimura , Shinji Shimasaki

We study full QCD at finite density and low temperature with light quark mass using the complex Langevin method. Since the singular drift problem turns out to be mild on a $4^3 \times 8$ lattice we use, the gauge cooling is performed only…

High Energy Physics - Lattice · Physics 2016-11-28 Keitaro Nagata , Hideo Matsufuru , Jun Nishimura , Shinji Shimasaki

We present new results of full QCD at nonzero chemical potential. In PRD 92, 094516 (2015) the complex Langevin method was shown to break down when the inverse coupling decreases and enters the transition region from the deconfined to the…

High Energy Physics - Lattice · Physics 2018-04-18 Jacques Bloch , Olaf Schenk

QCD at nonzero baryon chemical potential suffers from the sign problem, due to the complex quark determinant. Complex Langevin dynamics can provide a solution, provided certain conditions are met. One of these conditions, holomorphicity of…

High Energy Physics - Lattice · Physics 2017-06-07 Gert Aarts , Erhard Seiler , Denes Sexty , Ion-Olimpiu Stamatescu

In many interesting systems, the fermion determinant becomes complex and its phase plays a crucial role in the determination of the vacuum. For instance, in finite density QCD at low temperature and high density, exotic fermion condensates…

High Energy Physics - Lattice · Physics 2016-12-05 Yuta Ito , Jun Nishimura

We study a random matrix model for QCD at finite density via complex Langevin dynamics. This model has a phase transition to a phase with nonzero baryon density. We study the convergence of the algorithm as a function of the quark mass and…

High Energy Physics - Lattice · Physics 2017-04-05 Jacques Bloch , Jonas Glesaaen , Owe Philipsen , Jacobus Verbaarschot , Savvas Zafeiropoulos

In the complex Langevin approach to lattice simulations at nonzero density, zeroes of the fermion determinant lead to a meromorphic drift and hence a need to revisit the theoretical derivation. We discuss how poles in the drift affect the…

High Energy Physics - Lattice · Physics 2016-11-10 Gert Aarts , Erhard Seiler , Denes Sexty , Ion-Olimpiu Stamatescu

Statistical sampling with the complex Langevin (CL) equation is applied to (0+1)-dimensional Thirring model, and its uniform-field variant, at finite fermion chemical potential $\mu$. The CL simulation reproduces a crossover behavior which…

High Energy Physics - Lattice · Physics 2017-10-25 Hirotsugu Fujii , Syo Kamata , Yoshio Kikukawa

In this paper we test the complex Langevin algorithm for numerical simulations of a random matrix model of QCD with a first order phase transition to a phase of finite baryon density. We observe that a naive implementation of the algorithm…

High Energy Physics - Lattice · Physics 2018-04-04 J. Bloch , J. Glesaaen , J. J. M. Verbaarschot , S. Zafeiropoulos

In our previous paper [JHEP 10 (2020) 144], we found that the complex Langevin (CL) method works for QCD at finite density on the $16^3 \times 32$ lattice in the low-temperature high-density regime within the range $\mu / T = 1.6 - 9.6$…

High Energy Physics - Lattice · Physics 2025-10-28 Shoichiro Tsutsui , Yuhma Asano , Yuta Ito , Hideo Matsufuru , Yusuke Namekawa , Jun Nishimura , Shinji Shimasaki , Asato Tsuchiya

Computing the trace of the inverse of large matrices is typically addressed through statistical methods. Deflating out the lowest eigenvectors or singular vectors of the matrix reduces the variance of the trace estimator. This work…

Numerical Analysis · Mathematics 2020-03-18 Eloy Romero , Andreas Stathopoulos , Kostas Orginos

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…

High Energy Physics - Lattice · Physics 2018-10-30 Manuel Scherzer , Erhard Seiler , Dénes Sexty , Ion-Olimpiu Stamatescu

We show that the spectrum of the Dirac operator in complex Langevin simulations of QCD at non-zero chemical potential must behave in a way which is radically different from the one in simulations with ordinary non-complexified gauge fields:…

High Energy Physics - Lattice · Physics 2015-03-05 K. Splittorff

We demonstrate analytically that complex Langevin dynamics can solve the sign problem in one-dimensional QCD in the thermodynamic limit. In particular, it is shown that the contributions from the complex and highly oscillating spectral…

High Energy Physics - Lattice · Physics 2014-11-21 Gert Aarts , K. Splittorff

The ability to describe strongly interacting matter at finite temperature and baryon density provides the means to determine, for instance, the equation of state of QCD at non-zero baryon chemical potential. From a theoretical point of…

High Energy Physics - Lattice · Physics 2019-01-30 Felipe Attanasio , Benjamin Jäger

QCD at non-zero chemical potential ($\mu$) for quark number has a complex fermion determinant and thus standard simulation methods for lattice QCD cannot be applied. We therefore simulate this theory using the Complex-Langevin algorithm…

High Energy Physics - Lattice · Physics 2015-10-22 D. K. Sinclair , J. B. Kogut

We study the Stephanov model, which is an RMT model for QCD at finite density, using the Complex Langevin algorithm. Naive implementation of the algorithm shows convergence towards the phase quenched or quenched theory rather than to…

High Energy Physics - Lattice · Physics 2018-04-18 Jacques Bloch , Jonas Glesaaen , Jacobus Verbaarschot , Savvas Zafeiropoulos

Monte Carlo studies of QCD at finite density suffer from the sign problem, which becomes easily uncontrollable as the chemical potential $\mu$ is increased even for a moderate lattice size. In this work we make an attempt to approach the…

High Energy Physics - Lattice · Physics 2018-12-06 Yuta Ito , Hideo Matsufuru , Jun Nishimura , Shinji Shimasaki , Asato Tsuchiya , Shoichiro Tsutsui
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