The QCD phase diagram for three degenerate flavors and small baryon density

Abstract

We present results for the phase diagram of three flavor QCD for µ B < ∼ 500 MeV. Our simulations are performed with imaginary chemical potential µ I for which the fermion determinant is positive. Physical observables are then fitted by truncated Taylor series and continued to real chemical potential. We map out the location of the critical line T c (µ B ) with an accuracy up to terms of order (µ B /T ) 6 . We also give first results on a determination of the critical endpoint of the transition and its quark mass dependence. Our results for the endpoint differ significantly from those obtained by other methods, and we discuss possible reasons for this.

Continuum limit and universality of the Columbia plot

“…To reduce the computing effort, we chose N 0 s ≥ 2N t and N 0 t ≥ 4N t , i.e. we used a 20 3 × 40 "zero-temperature" lattice in combination with a 20 3 × 10 finite-temperature lattice. We are aware that our choice is only marginally satisfactory, and causes systematic errors in the extracted pion mass.…”

Deconfinement, chiral transition and localisation in a QCD-like model

“…While the low and high temperature phases of QCD are connected by an analytic crossover, such a model displays a genuine deconfining and (approximately) chirally-restoring first-order phase transition at some critical value of the gauge coupling β [30][31][32]. This allows us to study the relation between deconfinement, chiral restoration and localisation in a more clear-cut setting.…”

“…The relevant symmetries of this model are an SU(3) chiral symmetry, softly broken by the fermion mass term, and a Z 3 center symmetry, broken by the presence of fermions. It is known [30][31][32] that this model displays a first-order deconfining and chirally-restoring phase transition, for bare quark masses below the critical value m < 0.0259 [32]. More precisely, what one observes is a finite jump in the relevant order parameters, namely the Polyakov loop and the chiral condensate, as the gauge coupling is increased beyond a critical value.…”

“…Another useful model for the study of these issues is provided by unimproved staggered fermions on lattices with temporal extension N T = 4 (in lattice units) [30][31][32]. Differently from pure-gauge SU(3), this model possesses a true (albeit softly broken) chiral symmetry.…”

Nambu–Jona-Lasinio-based study of the QCD critical line

“…The most commonly used between them are the study of QCD at imaginary chemical potential [6,7,8], the reweighting procedure [4] and Taylor expansion in µ/T [9,10]. A possible way of avoiding the sign problem is to consider QCD at finite isospin chemical potential µ I : in this case, the fermion determinant is real and positive definite, * Electronic address: barducci@fi.infn.it, casalbuoni@fi.infn.it, pettini@fi.infn.it, ravagli@fi.infn.it and standard Monte Carlo simulations are allowed [11,12].…”