Over the past decade, an outstanding open problem in solar physics has emerged, as solar photospheric abundances of metallic elements have been significantly revised downward. Standard solar models cannot reproduce helioseismic measurements, such as the convection zone radius, the surface helium abundance and the sound speed profile, when using these revised abundances. This gave rise to the solar composition problem, motivating a rapid growth of research efforts in the field. With this problem of in mind, I study two main microscopic phenomena occurring in the Solar interior, and discuss their theoretical uncertainties and ways to reduce them. Firstly, the fusion rate of two protons into a deuteron, which is too rare to measure terrestrially in the solar conditions, is studied using a novel application of pion-less effective field theory.
Secondly, I use a new atomic code “STAR" to study two major plasma effects on the solar profile, namely ionic correlations and line broadening. These effects are untested in the relevant thermodynamic conditions, and use crude approximations, whose applicability at this regime is unclear. Both microscopic phenomena have a significant effect on the solar problem. Moreover, we argue that the solar opacity problem is hindered due to the large uncertainties. In the case of the atomic effects, we propose a method to measure opacities at solar temperatures and densities that were never reached in the past via laboratory radiation flow experiments.