Axial-Current Matrix Elements in Light Nuclei from Lattice QCD

I present results from the first lattice QCD calculations of axial-current matrix elements in light nuclei, performed by the NPLQCD collaboration. Precision calculations of these matrix elements, and the subsequent extraction of multi-nucleon axial-current operators, are essential in refining theoretical predictions of the proton-proton fusion cross section, neutrino-nucleus cross sections and $\beta \beta$-decay rates of nuclei. In addition, they are expected to shed light on the phenomenological quenching of $g_A$ that is required in nuclear many-body calculations.