Daniel Wyler

Leptoquarks in lepton-quark collisions

Abstract Low-energy experiments permit the existence of leptoquarks with masses of order 100 GeV and couplings to quark-lepton pairs as large as gauge couplings. We study systematically the signatures of all possible scalar and vector leptoquarks in electron (positron)-proton collisions. Clear evidence for leptoquarks would be narrow peaks in the x -distributions of inclusive neutral and charged current processes. At HERA one will be able to explore the mass range up to 300 GeV through direct production, and even somewhat beyond the CM energy of 314 GeV through virtual effects. Conversely, leptoquarks with masses of 200 GeV can be discovered for couplings as small as 10 −3 α em .

On determining a weak phase from charged B decay asymmetries

Abstract We demonstrate a possible determination of the weak phase γ from the CP asymmetry in B±→D01(2)X±, where D01(2) is a CP-even (odd) state and X± is any hadronic state with the flavor of a K±. To obtain the phase one needs separate measurements of the rates Γ(B±→D01(2)X±) and of the equal rates Γ( B ± → D 0 X ± ) = Γ( B ± → D 0 D 0 X ± ) . Certain ambiguities are discussed and resolutions are proposed.

The chiral loop expansion of the nonleptonic weak interactions of mesons

Abstract In the framework of the effective low-energy chiral lagrangian, we determine the one-loop effective action describing the strangeness-changing nonleptonic weak interactions of the pseudoscalar mesons. The effective action includes the counterterms necessary to accomodate the ultraviolet divergences arising from the loops, which we calculate. We obtain a closed expression for the regularized one-loop effective action sufficient to describe amplitudes involving up to four mesons. Finally, we discuss the observability of the tadpole caused by weak interactions.

Gluino Contribution to Radiative B Decays: Organization of QCD Corrections and Leading Order Results

The gluino-induced contributions to the decay b → s are investigated in supersymmetric frameworks with generic sources of flavour violation. It is shown that, when QCD corrections are taken into account, the relevant operator basis of the Standard Model effective Hamiltonian gets enlarged to

Electromagnetic logarithms in B¯→Xsℓ+ℓ−

Abstract The B ¯ → X s l + l − decay rate is known at the next-to-next-to-leading order in QCD. It is proportional to α em ( μ ) 2 and has a ± 4 % scale uncertainty before including the O ( α em ln ( M W 2 / m b 2 ) ) electromagnetic corrections. We evaluate these corrections and confirm the earlier findings of Bobeth et al. Furthermore, we complete the calculation of logarithmically enhanced electromagnetic effects by including also QED corrections to the matrix elements of four-fermion operators. Such corrections contain a collinear logarithm ln ( m b 2 / m l 2 ) that survives integration over the low dilepton invariant mass region 1 GeV 2 m l l 2 6 GeV 2 and enhances the integrated decay rate in this domain. For the low- m l l 2 integrated branching ratio in the muonic case, we find B ( B → X s μ + μ − ) = ( 1.59 ± 0.11 ) × 10 −6 , where the error includes the parametric and perturbative uncertainties only. For B ( B → X s e + e − ) , in the current BaBar and Belle setups, the logarithm of the lepton mass gets replaced by angular cut parameters and the integrated branching ratio for the electrons is expected to be close to that for the muons.

Virtual O (alpha-s) corrections to the inclusive decay b ---> s gamma

We present in detail the calculation of the

Constraints on SU(5)-type leptoquarks

O(\a_s)

K→2π and K→3π decays in next-to-leading order chiral perturbation theory

virtual corrections to the matrix element for

Electromagnetic logarithms in

b \to s \g

\bar B \to X_s l^+ l^-

. Besides the one-loop virtual corrections of the electromagnetic and color dipole operators