QUANTUM-MECHANICS OF NEUTRINO OSCILLATIONS

We present a space-time approach to neutrino oscillations where neutrino emission, propagation, and absorption are treated as a single coherent quantum-mechanical process. The neutrino enters the calculation only as an unobserved intermediate state connecting initial and final states of the neutrino source and target. Equivalently, the neutrino can be considered to be an exchanged particle when the neutrino source ''scatters'' from the target at a macroscopic impact parameter. This approach avoids ambiguities inherent in both the standard ''two-state'' treatment and the ''neutrino wave packet'' treatment of neutrino oscillations and makes clear why and under what conditions oscillations can be observed. In simple situations, transition rates can be calculated showing how oscillations are suppressed for large neutrino mass differences.