W-propagator corrections to muon and tau leptonic decays

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.Comment: 5 pages, no figures, accepted for publicatio

Radiative μ\mu and τ\tau leptonic decays at NLO

We present the differential rates and branching ratios of the radiative decays $\tau \to l \bar{\nu} \nu \gamma$, with $l=e$ or $\mu$, and $\mu \to e \bar{\nu} \nu \gamma$ in the Standard Model at next-to-leading order. Radiative corrections are computed taking into account the full depencence on the mass $m_l$ of the final charged leptons, which is necessary for the correct determination of the branching ratios. Only partial agreement is found with previous calculations performed in the $m_l \to 0$ limit. Our results agree with the measurements of the branching ratios $\mathcal{B} (\mu \to e \bar{\nu} \nu \gamma)$ and $\mathcal{B} (\tau \to \mu \bar{\nu} \nu \gamma)$ for a minimum photon energy of 10 MeV in the $\mu$ and $\tau$ rest frames, respectively. Babar's recent precise measurement of the branching ratio $\mathcal{B} (\tau \to e \bar{\nu} \nu \gamma)$, for the same photon energy threshold, differs from our prediction by 3.5 standard deviations.Comment: 13 pages, 1 figure, results included as ancillary file

Higher QCD corrections for inclusive semileptonic B decays

In these proceedings we review the calculation of the total decay rate for inclusive $B→X_{c}ℓ \overline{ν}_{ℓ}$ decays to higher orders in perturbative QCD. The partonic rate is obtained via an asymptotic expansion around the limit $1−m_{c}/m_{b}≪1$. The same method can be used to compute kinematic moments in case no experimental cuts are applied, i.e.\ moments of the differential rate integrated over the whole phase space. We discuss the impact of the $O(α^3_{s})$ corrections on the total semileptonic decay rate and the moments of the dilepton invariant mass $q^{2}$

τ→ μμμ at a rate of one out of 10¹⁴ tau decays?

We present in a full analytic form the partial widths for the lepton flavour violating decays μ±→e±e+e− and τ±→ℓ±ℓ′+ℓ′−, with ℓ,ℓ′=μ,e, mediated by neutrino oscillations in the one-loop diagrams. Compared to the first result by Petcov (Sov J Nucl Phys 25:340, 1977), obtained in the zero momentum limit P≪mν≪MW, we retain full dependence on P, the momenta and masses of external particles, and we determine the branching ratios in the physical limit mν≪P≪MW. We show that the claim presented in Pham (Eur Phys J C8:513, 1999) that the τ→ℓℓ′ℓ′ branching ratios could be as large as 10−14, as a consequence of keeping the P dependence, is flawed. We find rates of order 10−55, even smaller than those obtained in the zero momentum limit, as the latter prediction contains an unphysical logarithmic enhancement

Clear-water scour at comparatively large cylindrical piers

New long-duration clear-water scour data were collected at single cylindrical piers with the objective of investigating the effect of sediment coarseness, Dp=D50 (Dp = pier diameter; D50 = median grain size) on the equilibrium scour depth and improving the scour depth time evolution modeling by making use of the exponential function suggested in the literature. Experiments were carried out for the flow intensity close to the threshold condition of initiation of sediment motion, imposing wide changes of sediment coarseness and flow shallowness, d=Dp (d = approach flow depth). The effect of sediment coarseness on the equilibrium scour depth was identified; existing predictors were modified to incorporate this effect for U=Uc ≈ 1.0; Dp=D50 > ≈60 and d=Dp ≥ 0.5; the complete characterization of a known scour depth time evolution model was achieved for U=Uc ≈ 1.0, 60 < Dp=D50 < 500 and 0.5 ≤ d=Dp ≤ 5.0

The daring Bridge Pavillion (Pabellón Puente) over the river Ebro (Expo 2008): affect on river erosion and protection and auscultation requirements

El artículo trata del riesgo de erosión fluvial en una pila compleja de gran anchura, construida en el cauce del río Ebro en Zaragoza. Se describe el problema de erosión local en la pila, las características del modelo físico ensayado y los mantos de escollera que consiguen detener la erosión, así como la ejecución y auscultación de esta protección.The paper deals with the risk of scouring at a very wide complex pier built within the channel of Ebro river at Zaragoza (Spain). The main points described in the paper are: the local scour problem, the characteristics of the physical model used and the riprap apron able to stop scouring, as well as the execution and monitoring of this protection.Peer ReviewedPostprint (published version