### Quasi-particle Properties of Neutron Matter

**
Adam Richie-Halford, University of Washington
**

Understanding the ground state properties of neutron matter is crucial in answering central questions in both nuclear physics and astrophysics. For example, the structure of neutron stars, the interpretation of gravitational waves from neutron star mergers and the identification of astrophysical sites for r-process nucleosynthesis depend on the equation of state of neutron matter at high densities. Conversely, low-density neutron matter affects our understanding of neutron-rich nuclei. We have introduced an auxiliary-field quantum Monte Carlo (AFQMC) method to study neutron matter at low to intermediate densities. The key advantage of this approach is in employing the chiral effective field theory framework while avoiding the numerical sign problem by using an attractive, spin-independent effective Hamiltonian. Our current research builds upon the success of this approach to explore the quasiparticle properties of neutron matter. To do this, we calculate slight differences in energy caused by the addition or subtraction of neutrons to the system, necessarily introducing a sign problem. However, this sign problem is small enough to be amenable to reweighting methods. We present our calculation of the quasi-particle effective mass and pairing gap in neutron matter and discuss further work.

**Abstract Author(s): **A. Richie-Halford, A. Bulgac, G. Wlazlowski, J. Holt