Probing CP violation with non-unitary mixing in long-baseline neutrino oscillation experiments: DUNE as a case study

Abstract

When neutrino masses arise from the exchange of neutral heavy leptons, as in most seesaw schemes, the effective lepton mixing matrix N describing neutrino propagation is non-unitary, hence neutrinos are not exactly orthonormal. New CP violation phases appear in N that could be confused with the standard phase CP d characterizing the three neutrino paradigm. We study the potential of the longbaseline neutrino experiment DUNE in probing CP violation induced by the standard CP phase in the presence of non-unitarity. In order to accomplish this we develop our previous formalism, so as to take into account the neutrino interactions with the medium, important in long baseline experiments such as DUNE. We find that the expected CP sensitivity of DUNE is somewhat degraded with respect to that characterizing the standard unitary case. However the effect is weaker than might have been expected thanks mainly to the wide neutrino beam. We also investigate the sensitivity of DUNE to the parameters characterizing non-unitarity. In this case we find that there is no improvement expected with respect to the current situation, unless the near detector setup is revamped.

Determination of the θ23 octant in long baseline neutrino experiments within and beyond the standard model

“…This is in contrast with the determination of the CP violation, where the presence of sterile neutrinos could jeopardize the sensitivity [29,34,35].…”

“…Nevertheless, due to the strictness of the existing bounds for the nonunitarity parameters α ij , i, j ¼ 1, 2, 3 derived in Ref. [35] and for α ll 0 , l; l 0 ¼ e, μ, τ derived in Ref. [29] the observed drop in the octant sensitivity was found to be very small.…”

“…This type of simulation corresponds to a new physics scenario, where sterile neutrinos are associated with other new physics effects, not taken into account in Refs. [29,35] when deriving the bounds for the nonunitary and light sterile mixing effects. An example of this could be nonstandard interactions involved in the neutrino propagation.…”

“…These bounds have been evaluated for nonunitary mixing in two independent references; for the α ij basis they are provided in Ref. [35] and for α ll 0 in Ref. [29], and they are both shown in Table II.…”

“…An example of this situation could be a scenario where the sterile neutrinos are accompanied by nonstandard interactions (see e.g. [35]) mediated by new Higgs particles, as is the case in left-right symmetric models. Due to its unknown nature, we consider an arbitrary form of new physics by calculating the χ 2 values with no constraints on the α parameters.…”