Symmetry Parameter Constraints from a Lower Bound on Neutronmatter Energy
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Abstract
We propose the existence of a lower bound on the energy of pure neutron matter (PNM) on the basis of unitarygas considerations. We discuss its justification from experimental studies of cold atoms as well as from theoretical studies of neutron matter. We demonstrate that this bound results in limits to the densitydependent symmetry energy, which is the difference between the energies of symmetric nuclear matter and PNM. In particular, this bound leads to a lower limit to the volume symmetry energy parameter S 0. In addition, for assumed values of S 0 above this minimum, this bound implies both upper and lower limits to the symmetry energy slope parameter L , which describes the lowestorder density dependence of the symmetry energy. A lower bound on neutronmatter incompressibility is also obtained. These bounds are found to be consistent with both recent calculations of the energies of PNM and constraints from nuclear experiments. Our results are significant because several equations of state that are currently used in astrophysical simulations of supernovae and neutron star mergers, as well as in nuclear physics simulations of heavyion collisions, have symmetry energy parameters that violate these bounds. Furthermore, below the nuclear saturation density, the bound on neutronmatter energies leads to a lower limit to the densitydependent symmetry energy, which leads to upper limits to the nuclear surface symmetry parameter and the neutronstar crust–core boundary. We also obtain a lower limit to the neutronskin thicknesses of neutronrich nuclei. Above the nuclear saturation density, the bound on neutronmatter energies also leads to an upper limit to the symmetry energy, with implications for neutronstar cooling via the direct Urca process.
Journal

 The Astrophysical Journal

The Astrophysical Journal 848(2), 20171020
American Astronomical Society