The QCD phase diagram for small densities from imaginary chemical potential

TL;DR

This paper maps the QCD phase diagram at small baryon densities using simulations with imaginary chemical potential, enabling controlled analytic continuation to real chemical potential and avoiding reweighting issues.

Contribution

It introduces a method to determine the QCD phase diagram at small densities through simulations at imaginary chemical potential, ensuring systematic control and rapid convergence.

Findings

The pseudo-critical temperature T_c(mu_I) is an analytic function for mu_I/T <= pi/3.

The Taylor expansion of T_c(mu_I) converges rapidly with small truncation errors.

The method allows reliable continuation to real mu_B up to approximately 500 MeV.

Abstract

We present results on the QCD phase diagram for mu_B <= pi T. Our simulations are performed with an imaginary chemical potential mu_I for which the fermion determinant is positive. On an 8^3 x 4 lattice with 2 flavors of staggered quarks, we map out the phase diagram and identify the pseudo-critical temperature T_c(mu_I). For mu_I/T <= pi/3, this is an analytic function, whose Taylor expansion is found to converge rapidly, with truncation errors far smaller than statistical ones. The truncated series may then be continued to real mu, yielding the corresponding phase diagram for mu_B <~ 500 MeV. This approach provides control over systematics and avoids reweighting. We compare it with other recent work.