Pion, muon decays and weak interaction symmetries

We review the recent measurements of the rare pion decays: Pi+ -> Pi0 e+ Nu [pion beta, Pi_(e3), or Pi_beta decay], radiative decay Pi+ -> e+ Nu Gamma [Pi_(e2Gamma) or RPD], and Pi+ -> e+ Nu [Pi_(e2)] decay, as well as the radiative muon decay, Mu -> e Nu Nu-bar Gamma, their theoretical implications, and prospects for further improvement.Comment: 4 pages, 2 figures; talk presented at the Fourth International Symposium on Symmetries in Subatomic Physics (SSP 2009), held at the National Taiwan University, Taipei, Taiwan, 2-5 June 2009; to appear in "Symmetries in Subatomic Physics", P. Hwang, ed., North Holland

Charged Current Universality and the MSSM

We analyze the prospective impact of supersymmetric radiative corrections on tests of charged current universality involving light quarks and leptons. Working within the R-parity conserving Minimal Supersymmetric Standard Model, we compute the corresponding one-loop corrections that enter the extraction of the Cabibbo-Kobayashi-Maskawa matrix element $V_{ud}$ from a comparison of the muon-decay Fermi constant with the vector coupling constant determined from nuclear and neutron $\beta$-decay. We also revisit earlier studies of the corrections to the ratio $R_{e/\mu}$ of pion leptonic decay rates $\Gamma[\pi^+ \to e^+ \nu (\gamma)]$ and $\Gamma[\pi^+ \to \mu^+ \nu (\gamma)]$. In both cases, we observe that the magnitude of the corrections can be on the order of $10^{-3}$. We show that a comparison of the first row CKM unitarity tests with measurements of $R_{e/\mu}$ can provide unique probes of the spectrum of first generation squarks and first and second generation sleptons.Comment: 38 pages, 17 figure

Sterile neutrinos and RKR_K

Peer reviewe

Discovering the New Standard Model: Fundamental Symmetries and Neutrinos

This White Paper describes recent progress and future opportunities in the area of fundamental symmetries and neutrinos.Comment: Report of the Fundamental Symmetries and Neutrinos Workshop, August 10-11, 2012, Chicago, I

PEN experiment: a precise measurement of the pi+ -> e+ nu decay branching fraction

A new measurement of $B_{\pi e2}$, the $\pi^+ \to e^+\nu(\gamma)$ decay branching ratio, is currently under way at the Paul Scherrer Institute. The present experimental result on $B_{\pi e2}$ constitutes the most accurate test of lepton universality available. The accuracy, however, still lags behind the theoretical precision by over an order of magnitude. Because of the large helicity suppression of the $\pi_{e2}$ decay, its branching ratio is susceptible to significant contributions from new physics, making this decay a particularly suitable subject of study.Comment: 4 pages, 3 figures, talk given at the Tenth Conference on the Intersections of Particle and Nuclear Physics (CIPANP 2009), La Jolla/San Diego, CA, 26-31 May 2009; to appear in Proceedings to be published by the American Institute of Physic