Electroweak phenomenology beyond the standard model

This thesis examines low energy consequences of extensions of the Standard Model that call for new particle content and symmetries. In particular, we examine the ramifications of new scalar interactions on pion physics, of induced lepton flavour violation (LFV) in the constrained minimal supersymmetric standard model (CMSSM) with seesaw generated neutrino masses, and of induced LFV in lopsided SO(10) models.; New interactions with Lorentz scalar structure, arising from physics beyond the standard model of electroweak interactions, will induce effective pseudoscalar interactions after renormalization by weak interaction loop corrections. Such induced pseudoscalar interactions are strongly constrained by data on pi +/- → +/- lnul decay. These limits on induced pseudoscalar interactions imply limits on the underlying fundamental scalar interactions that in many cases are substantially stronger than limits on scalar interactions from direct, beta-decay searches.; The see-saw mechanism of neutrino mass generation; when incorporated in supersymmetric theories with supergravity mediated supersymmetry breaking, results in low-energy lepton-flavour violation arising from the soft supersymmetry breaking slepton masses. The parameter space of supergravity theories with conserved R-parity is severely constrained by the requirement that the LSP provide cold dark matter with a relic density in the range indicated by the recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements, as well as by laboratory constraints. We calculate the mu → e gamma branching ratio for the CMSSM, over the range of parameters consistent with WMAP and laboratory constraints, in families of see-saw model parameterizations which fit the low energy neutrino measurements.; A class of predictive SO(10) grand unified theories with highly asymmetric mass matrices, known as lopsided textures, which was developed to accommodate the observed mixing in the neutrino sector, can effectively determine the rate for charged lepton flavour violation, and in particular the branching ratio for mu → egamma. Assuming that the supersymmetric GUT breaks directly to the CMSSM, we find that in light of the combined constraints on the CMSSM parameters from direct searches and from the WMAP satellite observations, the resulting predicted rate for mu → egamma in this model class can be within the current experimental bounds for low tan beta but that the next generation of mu → egamma experiments would effectively rule out this model class if LFV is not detected.