Neutrino mass constraints on mu decay and pi0--> nunu.

In this Letter, we show that upper limits on the 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 mu and pi decays and derive model-independent limits on six of the ten parameters used to parametrize contributions to mu decay that do not belong to the standard model. These upper limits provide improved constraints on the five Michel parameters, rho, xi', xi", alpha, alpha', that exceed Particle Data Group constraints by at least one order of magnitude.

New contribution to scattering of weakly interacting massive particles on nuclei.

A weakly interacting massive particle (WIMP) is perhaps the most promising candidate for the dark matter in the Galactic halo. The WIMP detection rate in laboratory searches is fixed by the cross section for elastic WIMP-nucleus scattering. Here we calculate the contribution to this cross section from two-nucleon currents from pion exchange in the nucleus and show that it may, in some cases, be comparable to the one-nucleon current that has been considered in prior work and perhaps help resolve the discrepancies between the various direct dark-matter search experiments.