  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 non-zero 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 \Delta_m_{ij}^2, \theta_{ij} and \delta_{CP},
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.
