Nuclear Physics Seminar with Jason Bub and Ziyuan Zhang

"Effective Field Theory Parameter Estimation Using Markov Chain Monte Carlo" presented by Jason Bub from Washington University in St. Louis

Despite our understanding of nuclear interactions improving dramatically over the last century, we still struggle to fully explain the physical phenomena that we observe. In the last few decades, effective field theory (EFT) has become a powerful tool for explaining nuclear interactions while providing a means for accurate calculations of nuclear observables. However, while EFT derived potentials have continued to improve alongside computational methods to yield ever more accurate results, uncertainty quantification for such calculations remains much to be desired. To overcome this, various methods can be introduced. One such method is Markov Chain  Monte Carlo (MCMC) as a means to introduce uncertainty to EFT parameters, and thus the potential itself. To accomplish this, a change to a probabilistic view is required, along with the introduction of new methods into the preexisting computational framework.

"Beta Equilibrium Under Neutron Star Merger Conditions" presented by Ziyuan Zhang from Washington University in St. Louis

We calculate the isospin chemical potential that is required for beta equilibrium in nuclear matter under neutron star merger conditions, in the temperature range 1 MeV < T < 5 MeV. We improve on previous work by using a consistent description of nuclear matter based on the IUF and SFHo relativistic mean field models. This includes using relativistic dispersion relations for the nucleons, which we show is essential in these models. We find that the isospin chemical potential can be of order 10 to 20 MeV, and plays an important role in the correct calculation of Urca rates, which can be wrong by factors of 10 or more if it is neglected.