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Dense matter equation of state for neutron star mergers
In simulations of binary neutron star mergers, the dense matter equation of
state (EOS) is required over wide ranges of density and temperature as well as
under conditions in which neutrinos are trapped, and the effects of magnetic
fields and rotation prevail. Here we assess the status of dense matter theory
and point out the successes and limitations of approaches currently in use. A
comparative study of the excluded volume (EV) and virial approaches for the
system using the equation of state of Akmal, Pandharipande and
Ravenhall for interacting nucleons is presented in the sub-nuclear density
regime. Owing to the excluded volume of the -particles, their mass
fraction vanishes in the EV approach below the baryon density 0.1 fm,
whereas it continues to rise due to the predominantly attractive interactions
in the virial approach. The EV approach of Lattimer et al. is extended here to
include clusters of light nuclei such as d, H and He in addition to
-particles. Results of the relevant state variables from this
development are presented and enable comparisons with related but slightly
different approaches in the literature. We also comment on some of the sweet
and sour aspects of the supra-nuclear EOS. The extent to which the neutron star
gravitational and baryon masses vary due to thermal effects, neutrino trapping,
magnetic fields and rotation are summarized from earlier studies in which the
effects from each of these sources were considered separately. Increases of
about occur for rigid (differential) rotation with
comparable increases occurring in the presence of magnetic fields only for
fields in excess of Gauss. Comparatively smaller changes occur due to
thermal effects and neutrino trapping. Some future studies to gain further
insight into the outcome of dynamical simulations are suggested.Comment: Revised manuscript with one additional figure and previous Fig. 4
replaced, 19 additional references and new tex
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