Probing Physics in the Standard Model and Beyond with Electroweak Baryogenesis and Effective Theories of the Strong Interactions
This thesis explores two different avenues aimed at improving our ability to calculate reliably in the Standard Model of particle physics and probing possible new particles which may exist beyond it. In the first part, we explore whether baryogenesis at the electroweak phase transition could successfully account for the observed density of baryons in the Universe, using the closed-time-path (CTP) formalism of quantum field theory to calculate the buildup and relaxation of particle densities during the phase transition. Adopting the MSSM for its new sources of CP violation, we look for regions of parameter space which could give rise to sufficiently large baryon asymmetry without violating constraints on these parameters from existing experiments, especially searches for electric dipole moments of elementary particles. In the second part, we explore how to get around our ignorance of the dynamics of strongly interacting particles in the nonperturbative regime of Quantum Chromodynamics (QCD) by the use of effective field theories. Two applications are explored: the production of hadronic jets in Z decay or e+e- annihilation using soft-collinear effective theory (SCET), and the radiative decays of quarkonia to light hadrons using SCET and non-relativistic QCD (NRQCD). These tools facilitate the proof of factorization of decay rates into perturbatively-calculable and nonperturbative parts. Universality of the latter among different observables provides predictive power even in our ignorance of the details of the nonperturbative physics.