No abstract

Using methods of effective field theory, factorized expressions for arbitraryB → X u l −ν decay distributions in the shape-function region of large hadronic energy and moderate hadronic invariant mass are derived. Large logarithms are resummed at next-to-leading order in renormalization-group improved perturbation theory. The operator product expansion is employed to relate moments of the renormalized shape function with HQET parameters such as m b ,Λ and λ 1 defined in a new physical subtraction scheme. An analytic expression for the asymptotic behavior of the shape function is obtained, which reveals that it is not positive definite. Explicit expressions are presented for the chargedlepton energy spectrum, the hadronic invariant mass distribution, and the spectrum in the hadronic light-cone momentum P + = E H − | P H |. A new method for a precision measurement of |V ub | is proposed, which combines good theoretical control with high efficiency and a powerful discrimination against charm background.

We present "state-of-the-art" theoretical expressions for the triple differentialB → X u l −ν decay rate and for theB → X s γ photon spectrum, which incorporate all known contributions and smoothly interpolate between the "shape-function region" of large hadronic energy and small invariant mass, and the "OPE region" in which all hadronic kinematical variables scale with M B . The differential rates are given in a form which has no explicit reference to the mass of the b quark, avoiding the associated uncertainties. Dependence on m b enters indirectly through the properties of the leading shape function, which can be determined by fitting theB → X s γ photon spectrum. This eliminates the dominant theoretical uncertainties from predictions forB → X u l −ν decay distributions, allowing for a precise determination of |V ub |. In the shape-function region, short-distance and long-distance contributions are factorized at next-to-leading order in renormalization-group improved perturbation theory. Higher-order power corrections include effects from subleading shape functions where they are known. When integrated over sufficiently large portions in phase space, our results reduce to standard OPE expressions up to yet unknown O(α 2 s ) terms. Predictions are presented for partial B → X u l −ν decay rates with various experimental cuts. An elaborate error analysis is performed that contains all significant theoretical uncertainties, including weak annihilation effects. We suggest that the latter can be eliminated by imposing a cut on high lepton invariant mass.

We analyze flavor constraints in the littlest Higgs model with T-parity. In particular, we focus on neutral meson mixing in the K, B, and D systems due to one loop contributions from T-parity odd fermions and gauge bosons. We calculate the short distance contributions to mixing for a general choice of T-odd fermion Yukawa couplings. We find that for a generic choice of textures, a TeV scale GIM suppression is necessary to avoid large contributions. If order one mixing angles are allowed in the extended flavor structure, the mass spectrum is severely constrained, and must be degenerate at the 1-5% level. However, there are still regions of parameter space where only a loose degeneracy is necessary to avoid constraints. We also consider the B s system, and identify a scenario in which the mixing can be significantly enhanced beyond the standard model prediction while still satisfying bounds on the other mixing observables. We present both analytical and numerical results as functions of the T-odd fermion mass eigenvalues.

Constraints from analyticity are combined with experimental electron-proton scattering data to determine the proton charge radius. In contrast to previous determinations, we provide a systematic procedure for analyzing arbitrary data without model-dependent assumptions on the form factor shape. We also investigate the impact of including electron-neutron scattering data, and ππ → NN data. Using representative datasets we find r p E = 0.870 ± 0.023 ± 0.012 fm using just proton scattering data; r p E = 0.880 +0.017 −0.020 ± 0.007 fm adding neutron data; and r p E = 0.871 ± 0.009 ± 0.002 ± 0.002 fm adding ππ data. The analysis can be readily extended to other nucleon form factors and derived observables.

The contributions of subleading shape functions to inclusive decay distributions of B mesons are derived from a systematic two-step matching of QCD current correlators onto soft-collinear and heavy-quark effective theory. At tree-level, the results can be expressed in terms of forward matrix elements of bi-local light-cone operators. Fourquark operators, which arise at O(α s ), are included. Our results are in disagreement with some previous studies of subleading shape-function effects. A numerical analysis ofB → X u l −ν decay distributions suggests that power corrections are small, with the possible exception of the endpoint region of the charged-lepton energy spectrum.

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Using methods from soft-collinear and heavy-quark effective theory, a systematic factorization analysis is performed for theB → X s γ photon spectrum in the endpoint region m b − 2E γ = O(Λ QCD ). It is proposed that, to all orders in 1/m b , the spectrum obeys a novel factorization formula, which besides terms with the structure H J ⊗ S familiar from inclusiveB → X u lν decay distributions contains "resolved photon" contributions of the form H J ⊗ S ⊗J and H J ⊗ S ⊗J ⊗J. Here S andJ are new soft and jet functions, whose form is derived. These contributions arise whenever the photon couples to light partons instead of coupling directly to the effective weak interaction. The new contributions appear first at order 1/m b and are related to operators other than Q 7γ in the effective weak Hamiltonian. They give rise to non-vanishing 1/m b corrections to the total decay rate, which cannot be described using a local operator product expansion. A systematic analysis of these effects is performed at tree level in hard and hard-collinear interactions. The resulting uncertainty on the decay rate defined with a cut E γ > 1.6 GeV is estimated to be approximately ±5%. It could be reduced by an improved measurement of the isospin asymmetry ∆ 0− to the level of ±4%. We see no possibility to reduce this uncertainty further using reliable theoretical methods.