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Register a new userPrecision tests via radiative $mu$ and $tau$ leptonic decays
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The branching fractions of radiative leptonic $tau$ decays $(tau to l u bar{ u} gamma$, $l=e,mu)$ were recently measured by the Babar collaboration with a relative error of about 3%. The measurement of the branching ratio $mathcal{B} (tau to e bar{ u} u gamma)$, for a minimum photon energy of 10 MeV in the $tau$ rest frame, differs from our recent SM prediction by 3.5 standard deviations, whereas our result agrees with Babars value for $mathcal{B} (tau to mu bar{ u} u gamma)$. Our predictions also agree with the measurement of $mathcal{B} (mu to e bar{ u} u gamma)$ by the MEG collaboration. We also report on a recent proposal to test the $tau$ dipole moments via precise measurements of radiative leptonic $tau$ decays at high-luminosity $B$ factories.
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We derive the corrections induced by the W-boson propagator to the differential rates of the leptonic decay of a polarized muon and tau lepton. Results are presented both for decays inclusive of inner bremsstrahlung as well as for radiative ones, when a photon emitted in the decay process is measured. The numerical effect of these corrections is discussed. The definition of the Fermi constant is briefly reviewed.
An exhaustive number of QCD finite energy sum rules for $tau$-decay together with the latest updated ALEPH data is used to test the assumption of global duality. Typical checks are the absence of the dimension $d=2$ condensate, the equality of the gluon condensate extracted from vector or axial vector spectral functions, the Weinberg sum rules, the chiral condensates of dimensions $d=6$ and $d=8$, as well as the extraction of some low-energy parameters of chiral perturbation theory. Suitable pinched linear integration kernels are introduced in the sum rules in order to suppress potential quark-hadron duality violations and experimental errors. We find no compelling indications of duality violations in hadronic $tau$-decay in the kinematic region above $ssimeq2.2$ GeV$^{2}$ for these kernels.
We present a global analysis of leptonic and semileptonic kaon decays data, including all recent results by BNL-E865, KLOE, KTeV, ISTRA+, and NA48. Experimental results are critically reviewed and combined, taking into account theoretical (both analytical and numerical) constraints on the semileptonic kaon form factors. This analysis leads to a very accurate determination of Vus and allows us to perform several stringent tests of the Standard Model.
Adding a hard photon to the final state of a leptonic pseudoscalar-meson decay lifts the helicity suppression and can provide sensitivity to a larger set of operators in the weak effective Hamiltonian. Furthermore, radiative leptonic $B$ decays at high photon energy are well suited to constrain the first inverse moment of the $B$-meson light-cone distribution amplitude, an important parameter in the theory of nonleptonic $B$ decays. We demonstrate that the calculation of radiative leptonic decays is possible using Euclidean lattice QCD, and present preliminary numerical results for $D_s^+ to ell^+ ugamma$ and $K^- to ell^-bar{ u}gamma$.
We study the effects induced by excited leptons on the leptonic tau decay at one loop level. Using a general effective lagrangian approach to describe the couplings of the excited leptons, we compute their contributions to the leptonic decays and use the current experimental values of the branching ratios to put limits on the mass of excited states and the substructure scale.
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