3,053 research outputs found
Leptonic Pion Decay And Physics Beyond The Electroweak Standard Model
The ratio of branching ratios in leptonic pion decay is a powerfully
sensitive probe of new interactions beyond the electroweak standard model. This
is due to the chirality suppression of the standard model amplitude for the
decay, which results in a precise prediction for the ratio, and suppressed
amplitudes for new contributions to interfere with. We calculate, including QCD
corrections, the contributions to arising from a broad selection of
standard model extensions to which it is sensitive, including: R-parity
violating interactions in supersymmetric theories, theories with light
(electroweak scale) leptoquark degrees of freedom, non-minimal models of extra
doublet Higgs bosons, models in which the quarks and leptons are composite both
with and without supersymmetry, and models with strong TeV scale gravitational
interactions. Comparing with existing measurements of we provide
limits on each of these classes of models; our calculations also represent
state of the art theoretical benchmarks against which the results from the
upcoming round of leptonic pion decay experiments may be compared.Comment: 31 pages, 3 figure
Observing The Hidden Sector
We study the effects of renormalization due to hidden-sector dynamics on
observable soft supersymmetry-breaking parameters in the minimal supersymmetric
extension of the Standard Model (MSSM), under various hypotheses about their
universality at a high input scale. We show that hidden-sector renormalization
effects may induce the spurious appearance of unification of the scalar masses
at some lower scale, as in mirage unification scenarios. We demonstrate in
simple two-parameter models of the hidden-sector dynamics that the parameters
may in principle be extracted from experimental measurements, rendering the
hidden sector observable. We also discuss the ingredients that would be
necessary to carry this programme out in practice.Comment: 38 pages, 13 figures, uses UApreprint.cls and subfigure.sty
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