Search for exotic contributions to atmospheric neutrino oscillations
The energy spectrum of neutrino-induced upward-going muons in MACRO has been analyzed in terms of effects of violating relativity principles, keeping standard mass-induced atmospheric neutrino oscillations as the dominant source of νμ → ντ transitions. The data disfavor these exotic possibilities even at a subdominant level, and stringent 90% C.L. limits are placed on the Lorentz invariance violation parameter |Δυ| < 6 × 10−24 at sin(2ϑυ) = 0 and |Δυ| < (2.5–5) × 10−26 at sin(2ϑυ) = ±1. These limits can also be reinterpreted as upper bounds on the parameters describing violation of the equivalence principle.