T-2, Nuclear and Particle Physics, Astrophysics and Cosmology

Progresses in quantum Monte Carlo calculations for nuclear physics and nuclear astrophysics

Diego Lonardoni

Strange nuclear physics has acquired increasing interest over the years for the challenges and implications it involves, from both the experimental and theoretical side. By extending the auxiliary field diffusion Monte Carlo (AFDMC) algorithm to the strange sector, we performed calculations for hypernuclei, bound systems of nucleons and hyperons. We found that, within a phenomenological approach, a three-body hyperon-nucleon interaction is fundamental in order to reproduce the ground state properties of medium-light Λ hypernuclei (3 < A < 91). Within the same framework we also performed the first quantum Monte Carlo study of neutron matter including Λ particles. By employing two different models of the ΛNN force we obtained dramatically different results for the predicted maximum mass of a neutron star, not necessarily incompatible with the recent astronomical observations. Our findings greatly impact the astrophysics community as they clearly indicate that stronger constraints on the hyperon-neutron force are necessary in order to properly assess the role of hyperons in neutron stars. In addition, they will possibly drive the next generation of terrestrial hypernuclear experiments. In the non-strange nuclear sector, the spectral function formalism has proved very successful in explaining the available electron-nucleus scattering data. The measurement of the spectral function of 40Ar through the (e,e'p) reaction is the goal of the recently approved experiment on argon targets at Jefferson Lab. We are currently working on the extension of the cluster variational Monte Carlo (CVMC) algorithm in order to compute the momentum distribution of 40Ar. Our results will provide theoretical constraints for the derivation of the spectral function of argon, that is among the nuclear targets employed in neutrino detectors.


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