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Nuclear Chiral Thermodynamics and the Functional Renormalization Group
Non-perturbative mesonic (in particular: pionic) fluctuations in symmetric and asymmetric nuclear matter as well as in neutron matter are studied starting from a chiral nucleon-meson Lagrangian and using FRG methods. The resulting systematics of the nuclear phase diagram (the nuclear liquid-gas transition and its disappearance with increasing proton-to-neutron ratio) turn out to be remarkably close to results of three-loop in-medium chiral effective field theory calculations. The chiral order parameter in both symmetric nuclear matter and neutron matter is explored. It is generally found that dynamics beyond mean-field approximation shifts the tendency towards chiral symmetry restoration to very high baryon densities, much above three times the density of normal nuclear matter in equilibrium. Extrapolations to neutron star matter and corresponding constraints are also discussed.