Abstract
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 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.
Highlights
With the near start of the LHC, particle physics will enter a new era
We have investigated how non-standard neutrino interactions (NSIs) with matter can be induced by new physics beyond the Standard Model (SM) and derived the corresponding constraints
One motivation for this study was that while NSIs at the source and detector are typically assumed to be strongly constrained, in many phenomenological studies very large NSIs with matter (εmαβ,f parameters O(1)) are considered, saturating their weak direct bounds. To justify such large NSIs with matter (while escaping the stronger constraints that would stem from their charged fermion SU(2)L doublet counterparts) it is often referred to specific classes of higher-dimensional operators
Summary
With the near start of the LHC, particle physics will enter a new era. With unprecedented energy reach and luminosity, the LHC will allow to clarify the origin of electroweak symmetry breaking and look for new physics at TeV energies. New physics may lead to confusions of effects from new (CP violating) interactions with the leptonic Dirac CP phase, in the standard parameterisation of the leptonic mixing matrix, or with the small mixing parameter θ13 To avoid such confusion when measuring the remaining unknown parameters in the lepton sector, a better knowledge of the constraints on the new physics relevant to these experiments is highly desirable. With respect to their effects on neutrino oscillations, one convenient way to describe new interactions with neutrinos in the electroweak (EW) broken phase are the so-called NSI parameters for non-standard neutrino interactions at the source (εsαβ ), detector (εdαβ) [2] and with matter (εmαβ) [3,4,5].
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