# Nuclear physics insights for new-physics searches using nuclei: Neutrinoless $\beta\beta$ decay and dark matter direct detection

## TL;DR

This paper discusses how detailed nuclear physics knowledge is essential for interpreting experiments searching for new physics like neutrinoless double beta decay and dark matter, emphasizing the importance of nuclear structure and two-nucleon currents.

## Contribution

It highlights the critical role of nuclear structure details and two-nucleon currents in improving the accuracy of new physics searches using nuclei.

## Key findings

- Nuclear correlations significantly affect neutrinoless double beta decay matrix elements.
- Spin-dependent structure factors are sensitive to nuclear spin distribution.
- Two-nucleon currents are crucial for accurate nuclear interaction modeling.

## 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.