Functional renormalization group study of the chiral phase transition including vector and axial-vector mesons

The transition in quantum chromodynamics from hadronic matter to the quark-gluon plasma at high temperatures and/or net-baryon densities is associated with the restoration of chiral symmetry and can be investigated in the laboratory via heavy-ion collisions. We study this chiral transition within the functional renormalization group approach applied to the two-flavor version of the extended linear sigma model (eLSM). The eLSM is an effective model for the strong interaction and features besides scalar and pseudoscalar degrees of freedom also vector and axial-vector mesons. We discuss the impact of the quark masses and the axial anomaly on the order of the chiral transition. We also confirm the degeneracy of the masses of chiral partners above the transition temperature. We find that the mass of the $a_1$ meson ($\rho$ meson) decreases (increases) towards the chiral transition.

Figure 1

Phase transition in the eLSM with $U(2{)}_R\times U(2{)}_L$ symmetry. (a) Order parameter ${\sigma }_0$ as a function of temperature. (b) Screening masses as a function of temperature.

Figure 2

Phase transition in the eLSM with $SU(2{)}_V\times SU(2{)}_A\times U(1{)}_V$ symmetry. (a) Order parameter ${\sigma }_0$ as a function of the temperature $T$. (b) Screening masses as a function of temperature.

Figure 3

Phase transition in the eLSM with ESB and $U(1{)}_A$ anomaly. (a) Order parameter ${\sigma }_0$ as a function of temperature. (b) Screening masses as a function of temperature.