TOPICS IN HIGH-ENERGY PHYSICS: THE STANDARD MODEL AND BEYOND
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This thesis is compiled from the various projects I completed as a graduate student at the Johns Hopkins University Physics Department. The first project studied threshold effects in excited charmed baryon decays. The strong decays of the Λ+c (2593) are sensitive to finite width effects. This distorts the shape of the invariant mass spectrum in Λ+c1 → Λ+c π+π− from a simple Breit- Wigner resonance, which has implications for the experimental extraction of the Λ+c (2593) mass and couplings. A fit is performed to unpublished CLEO data which gives M(Λ+c (2593)) −M(Λ+c ) = 305.6 ± 0.3 MeV and h22 = 0.24+0.23 −0.11, with h2 the Λc1 → Σcπ strong coupling in the chiral Lagrangian. In the second project, by shining a hypermultiplet from one side of the bulk of a flat five-dimensional orbifold, supersymmetry is broken. The extra dimension is stabilized in a supersymmetric way, and supersymmetry breaking does not damage the radius stabilization mechanism. The low energy theory contains the radion and two complex scalars that are massless in the global supersymmetric limit and are stabilized by tree level supergravity effects. It is shown that radion mediation can play the dominant role in communicating supersymmetry breaking to the visible sector and contact terms are exponentially suppressed at tree level. The third project studied lepton flavor violation in flavor anarchic Randall- Sundrum models. All Yukawa couplings and mixing matrices are generated at the TeV-scale by wavefunction overlaps in the five-dimensional Anti-deSitter geometry present in this theory, without introducing any additional structure. This leads to a TeV-scale solution to both the flavor and electroweak hierarchy problems. A thorough scan of the available parameter space is performed, including the effects ii of allowing the Higgs boson to propagate in the full five-dimensional space-time. These models give constraints at the few TeV level throughout the natural range of parameters. Near-future experiments will definitively test this model.