Extreme scenarios of new physics in the UHE astrophysical neutrino flavour ratios

We add an energy-independent Hamiltonian to the standard flavour oscillation one. This kind of physics might appear in theories where neutrinos couple differently to a plausible nonzero torsion of the gravitational field or more dramatically in the presence of CPT-violating physics in the flavour oscillations. If this contribution exists, experiments at higher energies are more sensitive to their free parameters, and flavour conversion could be severely modified. We show that this new physics modifies the neutrino mixing angles and find expressions that relate the new, effective, angles to the standard oscillation parameters ∆m2ij , θij and δCP and to the parameters in the new-physics Hamiltonian, within a three-neutrino formalism. We consider scenarios where the new parameters allow for extreme deviations of the expected neutrino flavour ratios at Earth from their standard values. We show that large departures of the standard flavour scenario are plausible, which would be a strong hint of the violation of a conserved symmetry. 1. Motivation and problem By now it has been demonstrated that neutrinos can change flavour. Experiments with solar, atmospheric, reactor and accelerator neutrinos have established that there is a nonzero probability that a neutrino created with a certain flavour is detected with a different one after having propagated for some distance, and that this probability is dependent on the propagated distance, L, and the neutrino energy E. The standard mechanism that explains neutrino flavour transitions makes use of two different bases: the basis of neutrino mass eigenstates, which have well-defined masses, and the basis of neutrino interaction states -the flavour basiswhich are the ones that take part in weak processes such as W decay. The two bases are connected by means of a unitary transformation U , so that we can write each of the flavour states |να〉 as a linear combination of the mass eigenstates |νi〉, i.e. |να〉 = ∑