Title: Nuclear physics insights for new-physics searches using nuclei: Neutrinoless $ββ$ decay and dark matter direct detection,
Abstract: Experiments using nuclei to probe new physics beyond the Standard Model, such
as neutrinoless $\beta\beta$ decay searches testing whether neutrinos are their
own antiparticle, and direct detection experiments aiming to identify the
nature of dark matter, require accurate nuclear physics input for optimizing
their discovery potential and for a correct interpretation of their results.
This demands a detailed knowledge of the nuclear structure relevant for these
processes. For instance, neutrinoless $\beta\beta$ decay nuclear matrix
elements are very sensitive to the nuclear correlations in the initial and
final nuclei, and the spin-dependent nuclear structure factors of dark matter
scattering depend on the subtle distribution of the nuclear spin among all
nucleons. In addition, nucleons are composite and strongly interacting, which
implies that many-nucleon processes are necessary for a correct description of
nuclei and their interactions. It is thus crucial that theoretical studies and
experimental analyses consider $\beta$ decays and dark matter interactions with
a coupling to two nucleons, called two-nucleon currents.