Extreme States of Matter in Strong Interaction Physics by Helmut Satz

Author:Helmut Satz
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

7.5 QCD at Finite Baryon Density

Given the various model proposals for the phase diagram of QCD as function of temperature and baryon density, the interest in ab initio QCD calculations became more and more intensive, in spite of the known difficulties. Could one find evidence for a critical point at some μ and T, at which the “rapid cross-over” would terminate in a critical point and then turn into a discontinuous transition?

The basic problem for lattice evaluations of finite baryon density QCD is that the weight in the integral (5.39)/(5.40) is no longer positive-definite, since the Fermion determinant Q becomes complex when μ ≠ 0. The standard Metropolis procedure for reaching equilibrium configurations is thus no longer applicable, so that some new approach is required.

First such attempts have appeared in the past few years. In the reweighting method [62], the lattice configurations are calculated at μ = 0 and extended to finite μ with the help of the ratios of the fermion determinants at μ = 0 and μ > 0, which are then used to establish the weight of a given configuration.

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