Global constraints on muon-neutrino non-standard interactions

The search for new interactions of neutrinos beyond those of the Standard Model may help to elucidate the mechanism responsible for neutrino masses. Here we combine existing accelerator neutrino data with restrictions coming from a recent atmospheric neutrino data analysis in order to lift parameter degeneracies and improve limits on new interactions of muon neutrinos with quarks. In particular we re-consider the results of the NuTeV experiment in view of a new evaluation of its systematic uncertainties. We find that, although constraints for muon neutrinos are better than those applicable to tau or electron neutrinos, they lie at the few $\times 10^{-2}$ level, not as strong as previously believed. We briefly discuss prospects for further improvement.Comment: 10 pages, 5 figures, 2 table

On the description of non-unitary neutrino mixing

Neutrino oscillations are well established and the relevant parameters determined with good precision, except for the CP phase, in terms of a unitary lepton mixing matrix. Seesaw extensions of the Standard Model predict unitarity deviations due to the admixture of heavy isosinglet neutrinos. We provide a complete description of the unitarity and universality deviations in the light neutrino sector. Neutrino oscillation experiments involving electron or muon neutrinos and anti-neutrinos are fully described in terms of just three new real parameters and a new CP phase, in addition to the ones describing oscillations with unitary mixing. Using this formalism we describe the implications of non-unitarity for neutrino oscillations and summarize the model-independent constraints on heavy neutrino couplings that arise from current experiments.Comment: 28 pages, 8 figures, typos corrected, modified bounds on non-unitarity parameters, new figs 3 and

Constraining nonstandard neutrino-quark interactions with solar, reactor and accelerator data

We present a reanalysis of nonstandard neutrino-down-quark interactions of electron and tau neutrinos using solar, reactor and accelerator data. In addition updating the analysis by including new solar data from SNO phase III and Borexino, as well as new KamLAND data and solar fluxes, a key role is played in our analysis by the combination of these results with the CHARM data. The latter allows us to better constrain the axial and axial-vector electron and tau-neutrino nonstandard interaction parameters characterizing the deviations from the Standard Model predictions.Comment: 11 pages, 6 figures, 2 tables, typo corrected in Figure 2, version published in Phys. Rev.

Testing the non-unitarity of the leptonic mixing matrix at FASER

The FASER experiment has detected the first neutrino events coming from LHC. Near future high-statistic neutrino samples will allow us to search for new physics within the neutrino sector. Motivated by the forthcoming promising FASER neutrino data, we study its potential for testing the unitarity of the neutrino lepton mixing matrix. Although it would be challenging for FASER to have strong constraints on this kind of new physics, we discuss its role in contributing to a future improved global analysis.Comment: 8 pages, 1 figure, preprin

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

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 δCP characterizing the three neutrino paradigm. We study the potential of the long-baseline 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

Probing non-standard interactions at Daya Bay

In this article we consider the presence of neutrino non-standard interactions (NSI) in the production and detection processes of reactor antineutrinos at the Daya Bay experiment. We report for the first time, the new constraints on the flavor non-universal and flavor universal charged-current NSI parameters, estimated using the currently released 621 days of Daya Bay data. New limits are placed assuming that the new physics effects are just inverse of each other in the production and detection processes. With this special choice of the NSI parameters, we observe a shift in the oscillation amplitude without distorting the L/E pattern of the oscillation probability. This shift in the depth of the oscillation dip can be caused by the NSI parameters as well as by theta(13), making it quite difficult to disentangle the NSI effects from the standard oscillations. We explore the correlations between the NSI parameters and theta(13) that may lead to significant deviations in the reported value of the reactor mixing angle with the help of iso-probability surface plots. Finally, we present the limits on electron, muon/tau, and flavor universal (FU) NSI couplings with and without considering the uncertainty in the normalization of the total event rates. Assuming a perfect knowledge of the event rates normalization, we find strong upper bounds similar to 0.1% for the electron and FU cases improving the present limits by one order of magnitude. However, for a conservative error of 5% in the total normalization, these constraints are relaxed by almost one order of magnitude