Distinguishing between Dirac and Majorana neutrinos in the presence of general interactions

Abstract

Abstract:We revisit the possibility of distinguishing between Dirac and Majorana neutrinos via neutrino-electron elastic scattering in the presence of all possible Lorentz-invariant interactions. Defining proper observables, certain regions of the parameter space can only be reached for Dirac neutrinos, but never for Majorana neutrinos, thus providing an alternative method to differentiate these two possibilities. We first derive analytically and numerically the most general conditions that would allow to distinguish Dirac from Majorana neutrinos, both in the relativistic and non-relativistic cases. Then, we apply these conditions to data on ν µ -e andν e -e scatterings, from the CHARM-II and TEXONO experiments, and find that they are consistent with both types of neutrinos. Finally, we comment on future prospects of this kind of tests.

General neutrino interactions from an effective field theory perspective

“…There are no bounds implied by µ → eee on the scalar and tensor interactions ǫ eµee S/P/T,e (cf. Table 6), but the direct bounds from CHARM-II calculated in [8] can be applied, namely |ǫ αµee T,e | ≤ 0.04, |ǫ αµee S/P,e | ≤ 0.4 for any single α, which is also expected to improve with DUNE near detector data by a factor of 2-4 [30].…”

“…Since the flavour of the outgoing neutrino is not measured in both cases, one may as well take β = e here, assuming Dirac neutrinos. 8 We consider three scenarios, first the minimal scenario of one non-vanishing scalar operator, second the scenario of both scalar operators non-vanishing and correlated, and third the scenario of only the tensor operator O ′ lN qd .…”

Searching for BSM neutrino interactions in dark matter detectors

“…(26). For Majorana neutrinos, there are further constraints on the SPVAT interactions such that the allowed parameter space is actually smaller, containing only 6 free parameters [33]. Such a difference could be used to distinguish between Dirac and Majorana neutrinos [89].…”

Tensor and scalar interactions of neutrinos may lead to observable neutrino magnetic moments

“…Currently the effective coupling G X can be constrained by various elastic neutrino scattering data from CHARM II, LSND, TEXONO, Borexino, COHERENT, etc. In general, these experiments have G X sensitivity ranging from 0.1 to 1 G F [22,25,30,52], depending on the neutrino flavors, the charged fermion ψ, the specific forms of new interactions, etc. With these details involved and the uncertainties of theoretical predictions due to the UV incompleteness, here we refrain from more specific discussions and show merely two bands (red) of G X = 0.1 ∼ 1G F in Fig.…”

“…Here the GEMMA, TEXONO and LZ-51 Cr bounds are only for the effective magnetic moment µ νe defined in Eq. (24); the Borexino bound is based on solar neutrinos which should be applied to µ S given in Eq (25)(26)…”