Plasma screening of nuclear fusion reactions in liquid layers of compact degenerate stars: a first-principle study

TL;DR

This study uses first-principles quantum-mechanical path integral calculations to accurately determine plasma screening effects on nuclear fusion reactions in dense liquid layers of white dwarfs and neutron stars, revealing deviations from previous models at high coupling.

Contribution

It introduces a novel first-principles method for calculating plasma screening effects on nuclear fusion rates in stellar environments, avoiding common approximations used in prior work.

Findings

Good agreement with previous models at moderate coupling

Discovery of deviations from existing parametrizations at high coupling

Provision of an analytic expression for strongly coupled regimes

Abstract

A reliable description of nuclear fusion reactions in inner layers of white dwarfs and envelopes of neutron stars is important for realistic modelling of a wide range of observable astrophysical phenomena from accreting neutron stars to type Ia supernovae. We study the problem of screening of the Coulomb barrier impeding the reactions, by a plasma surrounding the fusing nuclei. Numerical calculations of the screening factor are performed from the first principles with the aid of quantum-mechanical path integrals in the model of a one-component plasma of atomic nuclei for temperatures and densities typical for dense liquid layers of compact degenerate stars. We do not rely on various quasiclassic approximations widely used in the literature, such as factoring-out the tunneling process, tunneling in an average spherically symmetric mean-force potential, usage of classic free energies and pair correlation functions, linear mixing rule and so on. In general, a good agreement with earlier results from the thermonuclear limit to $\Gamma \sim 100$ is found. For a very strongly coupled liquid $100 \lesssim \Gamma \leq 175$, a deviation from currently used parametrisations of the reaction rates is discovered and approximated by a simple analytic expression. The developed method of nuclear reaction rate calculations with account of plasma screening can be extended to ion mixtures and crystallised phases of stellar matter.