Second Order Electroweak Matrix Elements in Light Nuclei
A method to probe second order electroweak interactions in light nuclei is proposed and explored with a focus on double-β decay. The potential importance of short-distance nuclear effects in double-β decay is assessed using a lattice QCD calculation of the nn→pp transition and effective field theory methods. These effects, encoded in the isotensor axial polarisability, are found at the unphysical quark masses used in the calculation to be of similar magnitude to the nuclear modification of the single axial current. While the latter effects are included in phenomenological nuclear many-body calculations, the short distance contributions are neglected. The prospects of constraining the isotensor axial polarisabilities of nuclei using lattice QCD input into nuclear many-body calculations are discussed.