Radiative corrections to K_{l3} decays

We present a complete calculation of the K_{l3} decays K^+ --> pi^0 l^+ nu_l and K^0 --> pi^- l^+ nu_l to O(p^4, (m_d-m_u) p^2, e^2 p^2) in chiral perturbation theory with virtual photons and leptons. We introduce the concept of generalized form factors and kinematical densities in the presence of electromagnetism, and propose a possible treatment of the real photon emission in K^+_{l3} decays. We illustrate our results by applying them to the extraction of the Kobayashi--Maskawa matrix element |V_{us}| from the experimental K^+_{e3} decay parameters.Comment: 13 page

Remarks on the consistency of minimal deviations from General Relativity

We study the consequences of the modification of the phase space structure of General Relativity imposed by breaking the full diffeomorphism invariance but retaining the time foliation preserving diffeomorphisms. We examine the different sectors in phase space that satisfy the new structure of constraints. For some sectors we find an infinite tower of constraints. In spite of that, we also show that these sectors allow for solutions, among them some well known families of black hole and cosmologies which fulfill all the constraints. We raise some physical concerns on the consequences of an absolute Galilean time, on the thermodynamical pathologies of such models and on their unusual vacuum structure.Comment: latex 28 pages, 1 figure. Added comments and a reference. Text improved

Chiral Perturbation Theory with Virtual Photons and Leptons

We construct a low-energy effective field theory which allows the full treatment of isospin-breaking effects in semileptonic weak interactions. To this end, we enlarge the particle spectrum of chiral perturbation theory with virtual photons by including also the light leptons as dynamical degrees of freedom. Using super-heat-kernel techniques, we determine the additional one-loop divergences generated by the presence of virtual leptons and give the full list of associated local counterterms. We illustrate the use of our effective theory by applying it to the decays pi -> l nu_{l} and K -> l nu_{l}.Comment: 22 pages, no figure

Kinetics of recovery from anhydrobiosis in Pratylenchus thornei, Merlinius brevidens and Heterodera avenae from dry field soils and dry roots of the host plant

Le comportement de #Pratylenchus thornei, Merlinius brevidens et #Heterodera avenae dans un sol particulièrement sec du sud de l'Espagne a été étudié, après la saison d'été. Six périodes de récupération, allant jusqu'à 135 h de réhydratation suivie de migration, permettent de récupérer plus de 95 % de la population de #Merlinius$. Mais, pour "P. thornei$ - qui semble l'espèce dominante et la plus importante dans la zone considérée - la récupération au taux de 95 %, après culture de blé var, yecora, n'est atteinte qu'après douze périodes, et 279 h, pour autant que toutes les racines présentes dans le sol soient elles aussi traitées. Les #Pratylenchus survivant dans les racines desséchées du blé semblent être la cause de pertes de récolte encore inexpliquées atteignant cette culture. #Heterodera avenae ne paraît jouer qu'un rôle secondaire dans ces sols secs. (Résumé d'auteur

Aspects of the Screening Length and Drag Force in Two Alternative Gravity Duals of the Quark-gluon Plasma

We compute the screening length of mesons with different angular momentum $J$ from two gravity dual theories. Both the asymptotically $AdS_{5}$ and Sakai-Sugimoto metrics are considered in the calculations. Using the dual description of the quark as a classical string ending on the probe brane, we obtain the interacting potential between the heavy quark and antiquark after rotating the background metric. The result shows that the screening length of mesons with different $J$ is well fit to $a_{J}/T$. The constant $a_{J}$ is determined for $J=0,1,2$ by taking advantage of numerical techniques. Finally, we calculate the drag force and relaxation times from the Sakai-Sugimoto metric and compare with the ones obtained in the $AdS_{5}$. The application of our result to charmonium and bottomonium at RHIC and LHC is briefly discussed.Comment: 18 pages, 6 figures, 2 tables, version to appear in JHEP, acknowledgment adde

Conformal and Nonconformal Symmetries in 2d Dilaton gravity

We study finite-dimensional extra symmetries of generic 2D dilaton gravity models. Using a non-linear sigma model formulation we show that the unique theories admitting an extra (conformal) symmetry are the models with an exponential potential $V \propto e^{\beta\phi}$ ($S ={1\over2\pi} \int d^2 x \sqrt{-g} [ R \phi + 4 \lambda^2 e^{\beta\phi} ]$), which include the CGHS model as a particular though limiting ($\beta=0$) case. These models give rise to black hole solutions with a mass-dependent temperature. The underlying extra symmetry can be maintained in a natural way in the one-loop effective action, thus implying the exact solubility of the semiclassical theory including back-reaction. Moreover, we also introduce three different classes of (non-conformal) transformations which are extra symmetries for generic 2D dilaton gravity models. Special linear combinations of these transformations turn out to be the (conformal) symmetries of the CGHS and $V \propto e^{\beta\phi}$ models. We show that one of the non-conformal extra symmetries can be converted into a conformal one by means of adequate field redefinitions involving the metric and the derivatives of the dilaton. Finally, by expressing the Polyakov-Liouville effective action in terms of an invariant metric, we are able to provide semiclassical models which are also invariant. This generalizes the solvable semiclassical model of Bose, Parker and Peleg (BPP) for a generic 2D dilaton gravity model.Comment: Latex, no figures. Revised version published i