Search for pi(0)-->nu(mu)nu(mu) decays in the LSND detector

Light Particle Solution to the Cosmic Lithium Problem

We point out that the cosmological abundance of ^{7}Li can be reduced down to observed values if during its formation, big bang nucleosynthesis is modified by the presence of light electrically neutral particles X that have substantial interactions with nucleons. We find that the lithium problem can be solved without affecting the precisely measured abundances of deuterium and helium if the following conditions are satisfied: the mass (energy) and lifetimes of such particles are bounded by 1.6  MeV≤m_{X}(E_{X})≤20  MeV and few100s≲τ_{X}≲10^{4}  s, and the abundance times the absorption cross section by either deuterium or ^{7}Be are comparable to the Hubble rate, n_{X}σ_{abs}v∼H, at the time of ^{7}Be formation. We include X-initiated reactions into the primordial nucleosynthesis framework, observe that it leads to a substantial reduction of the freeze-out abundances of ^{7}Li+^{7}Be, and find specific model realizations of this scenario. Concentrating on the axionlike-particle case, X=a, we show that all these conditions can be satisfied if the coupling to d quarks is in the range of f_{d}^{-1}∼TeV^{-1}, which can be probed at intensity frontier experiments.

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. For pi(0) --> nunu we find, for the branching ratio, B(pi(0) --> nunu) < 10(-10).