Matthias Neubert

Recent developments in the theory of CP violation in the B-meson system are reviewed, with focus on the determination of sin(2beta) from B-> J/psi K decays, its implications for tests of the Standard Model and searches for New Physics, and the determination of gamma and alpha from charmless hadronic B decays.

These notes provide a pedagogical introduction to the theory of non-leptonic heavy-meson decays recently proposed by Beneke, Buchalla, Sachrajda and myself. We provide a rigorous basis for factorization for a large class of non-leptonic two-body B-meson decays in the heavy-quark limit. The resulting factorization formula incorporates elements of the naive factorization approach and the hard-scattering approach, and allows us to compute systematically radiative (``non-factorizable'') corrections to naive factorization for decays such as B->D+pi and B->pi+pi.

Bauer, Ligeti and Luke have recently proposed a new method for measuring |V_{ub}| in inclusive semileptonic B decays, using a cut on the lepton invariant mass to discriminate against b->c transitions. We investigate the structure of the heavy-quark expansion for this case and show that to all orders the magnitude of the leading perturbative and nonperturbative corrections is controlled by a hadronic scale mu_c=O(m_c) depending on the minimal value of q^2. These corrections can be analyzed using a modified version of the heavy-quark expansion (``hybrid expansion''). We find that the theoretical uncertainty in the extraction of |V_{ub}| is a factor 2.5 larger than previously estimated, which allows for a determination with 10% accuracy.

We study bulk fermion fields in the localized gravity model with non-factorizable metric recently proposed by Randall and Sundrum, and Gogberashvili. In addition to a tower of weak-scale Kaluza-Klein states we find a zero mode for any value of the fundamental fermion mass. If the fermion mass is larger than half the curvature of the compact dimension, the zero mode can be localized on the ``hidden'' 3-brane in the Randall-Sundrum model. Identifying this mode with a right-handed neutrino provides a new way for obtaining small Dirac neutrino masses without invoking a see-saw mechanism. Cancellation of the parity anomaly requires introducing an even number of bulk fermions. This naturally leads to a strong hierarchy of neutrino masses and generically large mixing angles.

Various strategies for extracting or constraining the weak phase gamma with controlled theoretical uncertainties are reviewed. Measurements of the rates for the hadronic decays B^+- -> pi K provide largely model-independent information on gamma. Hadronic uncertainties enter only at the level of nonfactorizable contributions to the decay amplitudes that are power-suppressed in Lambda/m_b and, simultaneously, violate SU(3) flavor symmetry or are doubly Cabibbo suppressed. In addition, these decays have a rich potential for probing physics beyond the Standard Model. Alternative proposals for learning gamma are also discussed briefly.