arXiv 0711.02622007-11hep-lathep-phnucl-th

小化学势下的QCD手性临界点：存在还是不存在？

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

Philippe de Forcrand, Seyong Kim, Owe Philipsen

备注：: 14 pages, contribution to Lattice 2007 proceedings; more typos corrected
发表信息：: PoSLAT2007:178,2007

摘要：

对于QCD手征临界点的存在，当化学势打开时，有限温度跃迁为一阶的小夸克质量的参数区域必须扩张，这可以通过临界面（m_{u,d}，m_s）_c（mu）的Taylor展开来检验.我们提出了一种新的方法来执行这个泰勒展开数值，我们首先测试一个有效的模型QCD静态，密集的夸克。然后，我们提出的结果与3个退化的口味QCD。对于N_t=4个时间片的格点，当化学势打开时，一级区域收缩，这意味着对于物理夸克质量，强子区和等离子体区在μ =0处的解析交叉，在泰勒展开可靠的μ区域（即μ小于或近似于T）仍然是交叉的。我们提出的初步结果表明，这种情况仍然存在，因为T_c（m_c（mu=0），mu）和实验观察到的冻结曲线的曲率之间的差异。

英文摘要：

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.

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