Abstract
We consider the thermodynamics of chiral models in the mean-field approximation and discuss the relevance of the (frequently omitted) fermion vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended version, we show that the fermion vacuum fluctuations can change the order of the phase transition in the chiral limit and strongly influence physical observables. We compute the temperature-dependent effective potential and baryon number susceptibilities in these models, with and without the vacuum term, and explore the cutoff and the pion mass dependence of the susceptibilities. Finally, in the renormalized model the divergent vacuum contribution is removed using the dimensional regularization.
Highlights
The critical properties of strongly interacting matter near the chiral transition at finite temperature and density are studied in first principle calculations using lattice simulations of QCD [1]
A complementary approach is offered by effective chiral models [2,3,4,5,6,7,8,9,10,11], like the Nambu-Jona-Lasinio (NJL) [3] and the chiral quark-meson (QM) [11] models as well as the corresponding extended versions, which include the interaction of quarks with a uniform temporal gluon field
In this paper we demonstrate the importance of the fermion vacuum fluctuations for a consistent formulation of the thermodynamics of the QM and Polyakov loop extended quark-meson (PQM) models in the mean-field approximation [22]
Summary
The critical properties of strongly interacting matter near the chiral transition at finite temperature and density are studied in first principle calculations using lattice simulations of QCD [1]. A complementary approach is offered by effective chiral models [2,3,4,5,6,7,8,9,10,11], like the Nambu-Jona-Lasinio (NJL) [3] and the chiral quark-meson (QM) [11] models as well as the corresponding extended versions, which include the interaction of quarks with a uniform temporal gluon field The latter, the Polyakov loop extended Nambu-Jona-Lasinio (PNJL) [5,6] and quarkmeson (PQM) [7,8] models reproduce prominent features of QCD thermodynamics, obtained in lattice simulations. We study the kurtosis of these fluctuations in the renormalized mean-field approximation to the PQM model
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