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

A new approach to evaluate the leading hadronic corrections to the muon g-2

We propose a novel approach to determine the leading hadronic corrections to the muon g-2. It consists in a measurement of the effective electromagnetic coupling in the space-like region extracted from Bhabha scattering data. We argue that this new method may become feasible at flavor factories, resulting in an alternative determination potentially competitive with the accuracy of the present results obtained with the dispersive approach via time-like data.Comment: 7 pages, 3 figures. Version accepted for publication in Phys. Lett.

L'expansion coloniale de la fourmi d'Argentine

La fourmi Linepithema humile fait preuve d'une exceptionnelle aptitude à coloniser de très larges territoires. Cette expansion est favorisée par une organisation sociale bien différente de celle qu'elle adopte dans son pays d'origine. Quelle est la clé de ce changement

Evolution of miniaturisation in inquiline parasitic ants: Timing of male elimination in Plagiolepis pygmaea, the host of Plagiolepis xene

Inquiline ant species are workerless social parasites whose queens rely completely on the host worker force to raise their brood. A remarkable feature of inquiline ants is the small size of sexuals, which are of the same size as or smaller than host workers. It has been suggested that miniaturisation evolved by parasites to prevent host workers from discriminating between their own worker brood and the inquiline sexuals, so that male and female inquilines can develop under conditions where the host species does not produce its own sexuals. In line with the miniaturisation hypothesis, workers of the ant P. pygmaea cull all the male brood of their own species, whereas at the same time males of their inquiline parasite P. xene are reared to adulthood. Here, we tested whether P. pygmaea workers recognize and eliminate males of their own species when they reach the size of the larger workers. Contrary to the assumption that size is indeed the primary cue used by workers to discriminate male from worker brood, we found that males of P. pygmaea are culled between the small and medium larval stages, that is much before reaching the critical size of the largest worker larvae. Based on this finding, we propose an extension of the miniaturisation hypothesis with a first step whereby the parasitic P. xene males escape the caste and sex recognition system of the host during early development. The most likely mechanism is chemical mimicry of host worker larvae. Miniaturisation would have evolved later to prevent the host workers to secondarily use size as a recognition cue to eliminate P. xene males