New ambiguity in probing CP violation in neutrino oscillations

Understand

If neutrinos get mass via the seesaw mechanism the mixing matrix describing neutrino oscillations can be effectively non-unitary.

• We show that in this case the neutrino appearance probabilities involve a new CP phase, phi, associated to non-unitarity.
• This leads to an ambiguity in extracting the "standard" three--neutrino phase delta_CP, which can survive even after neutrino and antineutrino channels are combined.
• Its existence should be taken into account in the planning of any oscillation experiment aiming at a robust measurement of delta_CP.