Neutron rich nuclei and neutron stars

The PREX experiment at Jefferson Laboratory measures the neutron radius of 208Pb with parity violating electron scattering in a way that is free from most strong interaction uncertainties. The 208Pb radius has important implications for neutron rich matter and the structure of neutron stars. We present first PREX results, describe future plans, and discuss a follow on measurement of the neutron radius of 48Ca. We review radio and X-ray observations of neutron star masses and radii. These constrain the equation of state (pressure versus density) of neutron rich matter. We present a new energy functional that is simultaneously fit to both nuclear and neutron star properties. In this approach, neutron star masses and radii constrain the energy of neutron matter. This avoids having to rely on model dependent microscopic calculations of neutron matter. The functional is then used to predict the location of the drip lines and the properties of very neutron rich heavy nuclei.Comment: 8 pages, 4 figures, proceedings of International Conference on Fission and Neutron Rich Nuclei 5, Sanibel, F

Multi-messenger observations of neutron rich matter

Neutron rich matter is central to many fundamental questions in nuclear physics and astrophysics. Moreover, this material is being studied with an extraordinary variety of new tools such as the Facility for Rare Isotope Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory (LIGO). We describe the Lead Radius Experiment (PREX) that uses parity violating electron scattering to measure the neutron radius in $^{208}$Pb. This has important implications for neutron stars and their crusts. We discuss X-ray observations of neutron star radii. These also have important implications for neutron rich matter. Gravitational waves (GW) open a new window on neutron rich matter. They come from sources such as neutron star mergers, rotating neutron star mountains, and collective r-mode oscillations. Using large scale molecular dynamics simulations, we find neutron star crust to be very strong. It can support mountains on rotating neutron stars large enough to generate detectable gravitational waves. Finally, neutrinos from core collapse supernovae (SN) provide another, qualitatively different probe of neutron rich matter. Neutrinos escape from the surface of last scattering known as the neutrino-sphere. This is a low density warm gas of neutron rich matter. Observations of neutrinos can probe nucleosyntheses in SN. Simulations of SN depend on the equation of state (EOS) of neutron rich matter. We discuss a new EOS based on virial and relativistic mean field calculations. We believe that combing astronomical observations using photos, GW, and neutrinos, with laboratory experiments on nuclei, heavy ion collisions, and radioactive beams will fundamentally advance our knowledge of compact objects in the heavens, the dense phases of QCD, the origin of the elements, and of neutron rich matter.Comment: 13 pages, 4 figures, Added discussion of dipole polarizability, pygmy resonances, and neutron skin

Neutrino scattering in supernovae and spin correlations of a unitary gas

Core collapse supernova simulations can be sensitive to neutrino interactions near the neutrinosphere. This is the surface of last scattering. We model the neutrinosphere region as a warm unitary gas of neutrons. A unitary gas is a low density system of particles with large scattering lengths. We calculate modifications to neutrino scattering cross sections because of the universal spin and density correlations of a unitary gas. These correlations can be studied in laboratory cold atom experiments. We find significant reductions in cross sections, compared to free space interactions, even at relatively low densities. These reductions could reduce the delay time from core bounce to successful explosion in multidimensional supernova simulations.Comment: 5 pages, 2 figures, minor corrections in response to referee, Phys. Rev. C in pres