Nonperturbative effects in inclusive B-meson decays

Despite its tremendous success, the Standard Model of particle physics is incomplete, and a major effort in particle physics is the search for new physics beyond the Standard Model. The sensitivity to new physics can be maximized by overconstraining the Standard Model parameters by performing many redundant precision measurements and thereby looking for inconsistencies between measurements and Standard Model predictions. Measurements probing the gauge and flavor sectors of the Standard Model already place stringent limits on possible new physics scenarios.;The study of B-meson decays offers many ways to explore whether the Standard Model correctly describes flavor physics. Some of the best sensitivity to new physics is achieved by precise, overconstraining measurements of the sides and angles of the so-called Unitarity Triangle, as well as by probing flavor-changing neutral-current processes, which are loop-suppressed in the Standard Model and thus very sensitive to new physics.;The sensitivity to new physics is limited by the experimental and theoretical precision, and the theoretical uncertainties are often dominated by nonperturbative QCD effects that are incalculable from first principles. These nonperturbative QCD effects can be related between different processes. This can be exploited by using experimental information on one process to extract the nonperturbative parameters and then use them to obtain predictions for a different process in a model-independent way.;In this work, I show how nonperturbative QCD effects can be taken into account systematically for inclusive semileptonic B → Xuℓν decays, which are important to overconstrain the Unitarity Triangle. I also develop a strategy to maximize the sensitivity to new physics in flavor-changing neutral current B → Xsℓ+ℓ- decays. Compared to B → Xuℓν, nonperturbative corrections in B → Xsℓ +ℓ- have received little attention previously, but could spoil the sensitivity to new physics. The same theoretical tools can be applied to understand the nonperturbative contributions in both of these seemingly unrelated processes. I demonstrate how to account for nonperturbative contributions model-independently to obtain accurate predictions in B → Xsℓ+ℓ -, such that the sensitivity to new physics is retained.