No abstract

The hitherto unobserved purely leptonic decays B ± → τ ± ν τ and B ± → µ ± ν µ are of much interest in current and future runs of the e + e − B factories. Such decays are sensitive to charged Higgs bosons (H ± ) at the tree-level and provide important constraints on tan β/m H ± . We include the large corrections to the H ± ub coupling induced by virtual SUSY effects and show that the bounds on tan β/m H ± can be significantly weakened or strengthened.

The recent observation of B d → π 0 π 0 at the B factories with a surprisingly large branching ratio represents a challenge for theory, and complements the amazingly small B d → π + π − rate. We point out that all puzzling B → ππ features can be accommodated in the Standard Model (SM) through non-factorizable hadronic interference effects, extract the relevant parameters, and predict the CP asymmetries of B d → π 0 π 0 . Using then SU (3) flavour-symmetry and plausible dynamical assumptions, we fix the hadronic B → πK parameters through their B → ππ counterparts, and determine the CKM angle γ, with a result in remarkable accordance with the usual fits for the unitarity triangle. We may then analyse the B → πK system in the SM, where we find agreement with the experimental picture, with the exception of those observables that are significantly affected by electroweak (EW) penguins, thereby suggesting new physics (NP) in this sector. Indeed, a moderate enhancement of these topologies and a large CP-violating NP phase allow us to describe any currently observed feature of the B → πK modes, and to predict the CP-violating B d → π 0 K S observables. If we then restrict ourselves to a specific scenario where NP enters only through Z 0 penguins, we obtain a link to rare K and B decays, where the most spectacular NP effects are an enhancement of the K L → π 0 νν rate by one order of magnitude with BR(K L → π 0 νν) ≈ 4BR(K + → π + νν), BR(K L → π 0 e + e − ) = O(10 −10 ), (sin 2β) πνν < 0, and a large forward-backward CP asymmetry in B d → K * µ + µ − . We address also ε ′ /ε and other prominent decays, including B → φK and B → J/ψK modes. February 20042.12 ± 0.37 (1.1) R ππ 00 ≡ 2 BR(B 0 d → π 0 π 0 ) + BR(B 0 d → π 0 π 0 ) BR(B 0 d → π + π − ) + BR(B 0 d → π + π − ) = 0.83 ± 0.23.( 1.2)

We investigate the rare decay Λ b → Λγ which receives both short and long distance contributions. We estimate the long distance contributions and find them very small. The form factors are obtained from Λ c → Λℓν ℓ using heavy quark symmetry and a pole model. The short distance piece opens a window to new physics and we discuss the sensitivity of Λ b → Λγ to such effects.