### PhD project: Beta Decays as Probes of New Physics

#### Supervisor: Prof. Frank Deppisch

Nuclear beta decays have been playing a crucial role in our understanding of neutrinos. In fact, single beta decay, more specifically, its electron energy spectrum, was the reason for Wolfgang Pauli to "invent" neutrinos in the first place. Beta decays continue to be an important probe in modern particle physics, especially to measure the absolute mass of neutrinos using the beta-decaying hydrogen isotope tritium. Beta decays can also occur twice, simultaneously in a given nucleus, giving rise to so-called two-neutrino double beta decay and neutrinoless double beta decay. The latter is only possible if neutrinos are Majorana fermions (i.e., they are identical to their own anti-particle). Neutrinoless double beta decay is our most important tool to understand the nature of neutrinos and how they acquire their small but finite masses. Observing it would have profound consequences for our understanding, not only of neutrinos but of particle physics in general.

Current and future experiments are becoming so sensitive and precise that theoretical calculations need to keep pace. In order to interpret experimental outcomes, theoretical corrections such as the emission of soft photons and final state interactions must be included. In turn, this allows probing New Physics effects that will help uncover the nature of neutrinos. In this project, you will make theoretical predictions of single and double beta decay, including precision calculations of corrections to the decay spectra from higher order Standard Model effects. You will explore the sensitivity of beta decay and related experiments to New Physics interactions of neutrinos, including sterile states. Together with members of the research group, you will help build new models that can be probed in future experiments. Your research will be primarily in the field of theoretical particle physics using perturbative Quantum Field Theory techniques. Given the connection to experimental results, you will also conduct phenomenological analyses, requiring the use of standard software tools such as Python and Mathematica.

More details on HEP theory at UCL can be found here.

For more details please contact f.deppisch at ucl.ac.uk