Neutrino mass constraints on μ -decay and π 0 →ν ν ¯
Abstract
In this letter, we show that upper-limits on neutrino mass translate into upper-limits on the class of neutrino-matter interactions that can generate loop corrections to the neutrino mass matrix. We apply our results to
μ
- and
π
-decays and derive model-independent limits on six of the ten parameters used to parametrize contributions to
μ
-decay that do not belong to the standard model.
These upper-limits provide improved constraints on the five Michel parameters,
ρ,
ξ
′
,
ξ
′′
,α,
α
′
, that exceed PDG constraints by at least one order of magnitude. For
π
0
→ν
ν
¯
we find for the branching ratio:
B(
π
0
→ν
ν
¯
)<
10
−10
.