Non-Standard Neutrino Interactions with Matter from Physics Beyond the Standard Model

We investigate how non-standard neutrino interactions (NSIs) with matter can be generated by new physics beyond the Standard Model (SM) and analyse the constraints on the NSIs in these SM extensions. We focus on tree-level realisations of lepton number conserving dimension 6 and 8 operators which do not induce new interactions of four charged fermions (since these are already quite constrained) and discard the possibility of cancellations between diagrams with different messenger particles to circumvent experimental constraints. The cases studied include classes of dimension 8 operators which are often referred to as examples for ways to generate large NSIs with matter. We find that, in the considered scenarios, the NSIs with matter are considerably more constrained than often assumed in phenomenological studies, at least ${\cal O}(10^{-2})$. The constraints on the flavour-conserving NSIs turn out to be even stronger than the ones for operators which also produce interactions of four charged fermions at the same level. Furthermore, we find that in all studied cases the generation of NSIs with matter also gives rise to NSIs at the source and/or detector of a possible future Neutrino Factory.