Recent advances in experiments and theory of cold atomic gases, and in neutron star observations, yield important new insights on the equation of state of neutron matter. At low densities, neutron matter is a strongly paired Fermi system, with pairing gaps of up to 1/3 the Fermi energy. The equation of state and the properties of inhomogeneous neutron matter at low to moderate densities are very important to describing the neutron star crust; and microscopic calculations can put severe constraints on density functionals used to describe the crust.
At higher densities the EOS plays a critical role in determining the mass-radius relationship for neutron stars, and is very sensitive to the three- neutron interaction. Microscopic calculations with realistic 2- and 3-nucleon interactions make clear predictions for terrestrial experiments, giving a definite relation between the energy of neutron matter at saturation density and its density dependence, and predictions for astrophysical observations, including the maximum mass and radius for a neutron star given a specified symmetry energy.
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