IFIC Seminar: Limits on Heavy Neutral Leptons and Their Connection with Effective Operators

by Josu Hernandez (IFIC, Valencia)

Tuesday 5 Mar 2024, 12:00 → 13:30 Europe/Madrid

1001-Primera-1-1-1 - Paterna. Seminario (Universe)

One of the most promising open windows to look for Physics beyond the Standard Model (SM) of particle physics, is the evidence for neutrino masses and mixings; observed in neutrino oscillation experiments, and which cannot be accommodated with the SM particle content. One possibility is to extend the SM with heavy right-handed neutrinos; also known as heavy neutral leptons (HNLs), within the type-I seesaw model. The gauge-singlet nature of these HNLs allows a Majorana mass term for them. This mass represents a New Physics scale, not related to the electroweak (EW) scale, and for which experimental verification is needed. These HNLs would mix with the SM neutrinos; and hence, depending on their mass scale, different kind of experiments can search for their production and decay. In this seminar, the present status of the laboratory constraints on the HNL mixing, as a function of its mass, will be reviewed. Then, the effective interactions between light mesons, and HNLs will be introduced in order to compute the expected sensitivity of future beam-dump experiments to HNLs. The proposed near detector of the Deep Underground Neutrino Experiment (DUNE) will be taken as a benchmark for the discussion. In the last part of the seminar, I will assume that HNLs are fundamental building blocks, with masses below the EW scale. Thus, the effective operators of the neutrino SM Effective Field Theory (nu-SMEFT) would parametrized additional New Physics mediating new interactions between SM particles and the HNLs at higher energies. In particular, the set of dimension-6 operators involving one HNL will be considered. And the present bounds on the HNL mixing; reviewed during the introduction of this seminar, will be recasted to constrain the Wilson coefficients of each dimension-6 operator as a function of the HNL mass.

During this seminar, I will try to cover the most relevant results from https://arxiv.org/pdf/2007.03701.pdf and https://arxiv.org/pdf/2304.06772.pdf. 

Josu.pdf