Impact of the equationofstategravity degeneracy on constraining the nuclear symmetry energy from astrophysical observables
Abstract
There is a degeneracy between the equation of state (EOS) of superdense neutronrich nuclear matter and the strongfield gravity in understanding properties of neutron stars. While the EOS is still poorly known, there are also longstanding ambiguities in choosing Einstein's general relativity (GR) or alternative gravity theories in the notsowelltested strongfield regime. Besides the possible appearance of hyperons and new phases, the most uncertain part of the nucleonic EOS is currently the density dependence of nuclear symmetry energy especially at suprasaturation densities. At the same time, the EOS of symmetric nuclear matter (SNM) has been significantly constrained at saturation and suprasaturation densities. To provide information that may help break the EOSgravity degeneracy, we investigate effects of nuclear symmetry energy within its uncertain range determined by recent terrestrial nuclear laboratory experiments on the gravitational binding energy and spacetime curvature of neutron stars within GR and the scalartensor subset of alternative gravity models, constrained by recent measurements of the relativistic binary pulsars J1738 + 0333 and J0348 + 0432. In particular, we focus on effects of the following three parameters characterizing the EOS of superdense neutronrich nucleonic matter: (1) the incompressibility K_{0} of SNM, (2) the slope L of nuclear symmetry energy at saturation density, and (3) the highdensity behavior of nuclear symmetry energy. We find that the variation of either the density slope L or the highdensity behavior of nuclear symmetry energy leads to large changes in both the binding energy and the curvature of neutron stars while effects of varying the more constrained K_{0} are negligibly small. The difference in predictions using the GR and the scalartensor theory appears only for massive neutron stars, and even then it is significantly smaller than the differences resulting from variations in the symmetry energy. We conclude that, within the scalartensor subset of gravity models, the EOSgravity degeneracy has been broken by the recent relativistic pulsar measurements and that measurements of neutronstar properties sensitive to the compactness constrain mainly the density dependence of the symmetry energy at saturation and suprasaturation densities.
 Publication:

Physical Review C
 Pub Date:
 January 2015
 DOI:
 10.1103/PhysRevC.91.015810
 arXiv:
 arXiv:1408.0857
 Bibcode:
 2015PhRvC..91a5810H
 Keywords:

 26.60.Kp;
 21.65.Mn;
 04.40.Dg;
 Equations of state of neutronstar matter;
 Equations of state of nuclear matter;
 Relativistic stars: structure stability and oscillations;
 Nuclear Theory;
 Astrophysics  Solar and Stellar Astrophysics;
 General Relativity and Quantum Cosmology;
 Nuclear Experiment
 EPrint:
 Note a title change in the second version. An additional section has been added. 17 pages, 8 figures (3 additional figures), 1 table