  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.
