A bstract The non-unitarity of the effective leptonic mixing matrix at low energies is a generic
signal of extensions of the Standard Model (SM) with extra fermionic singlet particles, ie …

We review the current status and future prospects of rare kaon and pion decay research
programs. Our emphasis is on experimental probes of New Physics beyond the Standard …

A search for massive neutrinos has been made in the decay π+→ e+ ν. No evidence was
found for extra peaks in the positron energy spectrum indicative of pion decays involving …

A new measurement of the branching ratio R e/μ= Γ (π+→ e+ ν+ π+→ e+ ν γ)/Γ (π+→ μ+ ν+
π+→ μ+ ν γ) resulted in R e/μ exp=[1.2344±0.0023 (stat)±0.0019 (syst)]× 10-4. This is in …

The combination of simple dynamics, small number of available decay channels, and
extremely well controlled radiative and loop corrections, make charged pion decays a …

In the present work of the PIENU experiment, heavy neutrinos were sought in pion decays
π+→ μ+ ν at rest by examining the observed muon energy spectrum for extra peaks in …

Evidence of massive neutrinos in the π+→ e+ ν decay spectrum was sought with the
background π+→ μ+→ e+ decay chain highly suppressed. Upper limits (90% CL) on the …

The three body pion decays π+→ l+ ν X (l= e, μ), where X is a weakly interacting neutral
boson, were searched for using the full data set from the PIENU experiment. An improved …

Charged lepton flavor violating muon decay μ+→ e+ XH, where XH is a massive neutral
boson, was sought by searching for extra peaks in the muon decay μ+→ e+ ν ν¯ energy …

The nonunitarity of the leptonic mixing matrix is a generic signal of new physics aiming at the
generation of the observed neutrino masses. We discuss the Minimal Unitarity Violation …