Exploring new Physics with neutrino oscillation experiments

Abstract

Neutrino oscillation experiments set out to measure the differences in mass between the three neutrino flavors of the Standard Model of particle physics, and probe the elements of the lepton mixing (PMNS) matrix encoding the relationship between neutrino mass and interaction eigenstates. In this work, we use the results of these experiments for a different purpose: to place constraints on parameters which, if found to be nonzero, would indicate the existence of new physics (NP) beyond the Standard Model. Neutrino flavor oscillations arise from differences in mass between the three neutrino mass eigenstates, which enter the Hamiltonian in a term inversely proportional to the energy of the propagating neutrino. In the high-energy limit, all three flavors are effectively massless, the mass splittings vanish, and the oscillation wavelength grows too large for oscillations to be detectable. The NP effects we consider here result from introducing new terms into the Hamiltonian with a different energy dependence, either: • independent of energy, for the case of “vector-like” interactions, or • directly proportional to energy, for the case of “tensor-like” interactions. Thus, the new physics would manifest as a deviation from the expected suppression of neutrino flavor oscillations at high energy. If such new physics exists, and is detectable in current experiments, we would expect to observe a contribution to the oscillation wavelength which remains constant or grows with energy. The effects which may be represented within this generic framework include nonstandard interactions between neutrinos and matter, couplings with spacetime torsion fields, violations of Lorentz invariance or of the equivalence principle, and violations of CPT symmetry. The 2004 work of Gonzalez Garcia & Maltoni inferred limits on parameters encoding NP effects on two-flavor neutrino oscillations, using atmospheric neutrino data from Super-Kamiokande, along with data from the long baseline KEK to Kamioka (K2K) experiment. Here, we continue to use data from atmospheric and accelerator neutrino experiments to compute upper bounds on NP parameters. We begin by reproducing the results of [1] using updated data on atmospheric neutrino oscillations, incorporating the latest data from Super-Kamiokande, together with new data from DeepCore. We then consider the NP parameters of a model with three neutrino flavors, and calculate constraints using data from particle accelerators: Tokai to Kamioka (T2K), MINOS, and NOvA.