How neutron stars constrain the nuclear equation of state

Recently, the mass of the pulsar PSR J1614-2230 has been measured with high accuracy to be 1.97±0.04 solar masses. This, in addition to statistical analyses of neutron-star radii, leads to tight constraints for the equation of state of dense baryonic matter inside neutron stars. We combine a realistic phenomenological equation of state at low densities with equations of state around nuclear density derived from chiral effective field theory, on one hand, and from the Polyakov-loop-extended Nambu-Jona-Lasinio model, on the other. In the latter case, we investigate also the particular role of a vector interaction for the chiral phase transition. Our analysis strongly supports a very stiff equation of state of ordinary nuclear matter, without the need of exotic-matter admixtures, in order to reproduce the empirical observations for neutron stars.