  The $pp$-chain of nuclear reactions is the primary route for energy
production in the Sun. The first step in that reaction sequence converts two
protons to a deuterium nucleus with the emission of a positron and electron
neutrino. This reaction is extremely slow because it is a weak interaction, and
significantly, it involves quantum tunneling through the Coulomb barrier.
Though the reaction rate can be calculated with high confidence in the Standard
Model, it has not been measured at solar energies. If there exist interactions
that are engendered by non-standard mediators then the rate of this reaction in
the Sun could be altered. We probe such non-standard interactions by comparing
calculations of solar evolution to the current solar system age in the presence
and absence of the non-standard mediators. These reveal ranges of non-standard
mediator mass and couplings that are inconsistent with measured properties of
the Sun, including solar neutrino results. Our constraints on these
non-standard parameters, in many cases overlapping those derived via other
considerations, could be extended further with better confidence in the value
of the metalicity of the Sun and the solar neutrino CNO flux. Intriguingly, our
work reveals a degeneracy between the solar metalicity and the presence of the
invoked non-standard mediators.
