The violation of equivalence principle and four neutrino oscillations for long baseline neutrinos

Violation of equivalence principle predicts that neutrinos of different flavor couple differently with gravity. Such a scenario can give rise to gravity induced flavor oscillations in addition to the usual mass flavor neutrino oscillations during the neutrino propagation. Even if the equivalence principle is indeed violated, their measure will be extremely small. We explore the possibility to probe the violation of equivalence principle (VEP) for the case of long baseline (LBL) neutrinos in a 4-flavor neutrino framework (3 active + 1 sterile) where both mass and gravity induced oscillations are considered. To this end, we have explicitly calculated the oscillation probability in 4-flavor framework that includes in addition to the mass-flavor mixing in matter, the gravity-flavor mixing also. The energy eigenvalues are then obtained by diagonalizing such a 4-flavor mixing matrix. The formalism is then employed to estimate the wrong and right sign muon yields at a far detector for neutrinos produced in a neutrino factory and travel through the Earth matter. These results are compared with the similar estimations when the usual three active neutrinos are considered.

Neutrino oscillations in matter: from microscopic to macroscopic description

Neutrino flavour transmutations in nonuniform matter are described by a Schrödinger-like evolution equation with coordinate-dependent potential. In all the derivations of this equation it is assumed that the potential, which is due to coherent forward scattering of neutrinos on matter constituents, is a continuous function of coordinate that changes slowly over the distances of the order of the neutrino de Broglie wavelength. This tacitly assumes that some averaging of the microscopic potential (which takes into account the discrete nature of the scatterers) has been performed. The averaging, however, must be applied to the microscopic evolution equation as a whole and not just to the potential. Such an averaging has never been explicitly carried out. We fill this gap by considering the transition from the microscopic to macroscopic neutrino evolution equation through a proper averaging procedure. We discuss some subtleties related to this procedure and establish the applicability domain of the standard macroscopic evolution equation. This, in particular, allows us to answer the question of when neutrino propagation in rarefied media (such as e.g. low-density gases or interstellar or intergalactic media) can be considered within the standard theory of neutrino flavour evolution in matter.

Rephasing Invariant for Three-Neutrino Oscillations Governed by a Non-Hermitian Hamiltonian

Time-reversal symmetry is broken for mixed and possibly unstable Dirac neutrino propagation through absorbing media. This implies that interplay between the neutrino mixing, refraction, absorption and/or decay can be described by non-Hermitian quantum dynamics. We derive an identity which sets up direct connection between the fundamental neutrino parameters (mixing angles, CP-violating phase, mass-squared splittings) in vacuum and their effective counterparts in matter.

Testing NSI suggested by solar neutrino tension in T2HKK and DUNE

It was shown that the tension between the mass-squared differences obtained from solar neutrinos and those acquired through KamLAND experiments may be solved by the introduction of a non-standard flavor-dependent interaction (NSI) in neutrino propagation. In this study, we discuss the possibility of testing such a hypothesis using the future long-baseline neutrino experiments T2HKK and DUNE. Assuming that the NSI does not exist, we provide the excluded region within the ([Formula: see text], [Formula: see text]) plane, where [Formula: see text] and [Formula: see text] are the parameters appearing in the solar neutrino analysis conducted with the NSI. We find that the best fit value from the solar neutrino and KamLAND data (global analysis of a particular coupling to quarks) can be tested at more than [Formula: see text] by these two experiments for most of the parameter space.

A multidimensional implementation of the Advanced Spectral neutrino Leakage scheme

ABSTRACT We present a new, multidimensional implementation of the Advanced Spectral Leakage (ASL) scheme with the purpose of modelling neutrino–matter interactions in neutron star mergers. A major challenge is the neutrino absorption in the semitransparent regime, which is responsible for driving winds from the merger remnant. The composition of such winds is crucial in the understanding of the electromagnetic emission in the recently observed macronova following GW170817. Compared to the original version, we introduce an optical-depth-dependent flux factor to model the average angle of neutrino propagation, and a modulation that accounts for flux anisotropies in non-spherical geometries. We scrutinize our approach by first comparing the new scheme against the original one for a spherically symmetric core-collapse supernova snapshot, both in 1D and in 3D, and additionally against a two-moment (M1) scheme as implemented in 1D into the code GR1D. The luminosities and mean energies agree to a few per cents in most tests. Finally, for the case of a binary merger remnant snapshot we compare the new ASL scheme with the M1 scheme that is implemented in the Eulerian adaptive mesh refinement code flash. We find that the neutrino absorption distribution in the semitransparent regime is overall well reproduced. Both approaches agree to within $\lesssim 15{{\ \rm per\ cent}}$ for the average energies and to better than $\sim 35 {{\ \rm per\ cent}}$ in the total luminosities.

Electron capture beta decay of partially polarized nuclei

In this paper, we compute the spin excess for the neutrinos radiated in the process of electron capture beta decay of partially polarized nuclei. The results of computation are presented for the [Formula: see text] nuclei polarized by the strong hyperfine field in a ferromagnetic substance. This system was suggested as a possible source of monoenergetic neutrino radiation with a preferable direction of neutrino propagation. We directly compute the spin excess of radiated neutrinos and show that it is slightly greater than that estimated previously under simplifying assumptions.