A QCD chiral critical point at small chemical potential: is it there or not?

Abstract

For a QCD chiral critical point to exist, the parameter region of small quark masses for which the finite temperature transition is first-order must expand when the chemical potential is turned on. This can be tested by a Taylor expansion of the critical surface (m_{u,d},m_s)_c(mu). We present a new method to perform this Taylor expansion numerically, which we first test on an effective model of QCD with static, dense quarks. We then present the results for QCD with 3 degenerate flavors. For a lattice with N_t=4 time-slices, the first-order region shrinks as the chemical potential is turned on. This implies that, for physical quark masses, the analytic crossover which occurs at mu=0 between the hadronic and the plasma regimes remains crossover in the mu-region where a Taylor expansion is reliable, i.e. mu less than or similar to T. We present preliminary results from finer lattices indicating that this situation persists, as does the discrepancy between the curvature of T_c(m_c(mu=0),mu) and the experimentally observed freeze-out curve.

arXiv comment14 pages, contribution to Lattice 2007 proceedings; more typos corrected

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• Chiral Symmetry Breaking on the Lattice
• Lattice QCD Thermodynamics on the Grid
• Lattice QCD at nonzero temperature and density
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• QCD at non-zero temperature and magnetic field
• Analytic continuation in two-color QCD: new results on the critical line
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• Phase structure of $N_{\mathrm{f}}=3$ QCD at finite temperature and density by Wilson-Clover fermions
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• Towards a determination of the chiral critical surface of QCD
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• Critical endpoint in the continuum limit and critical endline at $N_{\mathrm{T}}=6$ of the finite temperature phase transition of QCD with clover fermions
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