Pion-to-vacuum vector and axial vector amplitudes and weak decays of pions in a magnetic field

We propose a model-independent parametrization for the one-pion-to-vacuum matrix elements of the vector and axial vector hadronic currents in the presence of an external uniform magnetic field. It is shown that, in general, these hadronic matrix elements can be written in terms of several gauge covariant Lorentz structures and form factors. Within this framework we obtain a general expression for the weak decay $\pi^- \to l\,\bar\nu_l$ and discuss the corresponding limits of strong and weak external magnetic fields.Comment: 33 page

Orquestres cerverines durant la postguerra

S'acostuma a creure que els anys de la postguerra van ser foscos i depressius pel que fa a les festes i als balls i quela música era pràcticament inexistent, però Cervera, que havia tingut una vida musical molt intensa, tan aviat com es va acabar la guerra vam comptar amb bandes de música professionals

La relación del hombre con su entorno en los cuentos de Miguel Torga

En torno a la década de los cuarenta del siglo XX, el escritor portugués Miguel Torga (1907-1995) publicó cinco libros de cuentos: Bichos (1940), Cuentos de la montaña (1941), Rúa (1942), Nuevos cuentos de la montaña (1944) y Piedras labradas (1951). Estos relatos que fueron escritos en una misma época se caracterizan por su unidad temática. El objetivo de este artículo es describir cómo se plasma en ellos el asunto de la relación del hombre con su entorno atendiendo a cuatro cuestiones: a) la relación con el reino animal y vegetal; b) la relación con el espacio físico; c) la relación con la norma; y d) la relación con el misterio

Model analysis of the world data on the pion transition form factor

We discuss the impact of recent Belle data on our description of the pion transition form factor based on the assumption that a perturbative formalism and a nonperturbative one can be matched in a physically acceptable manner at a certain hadronic scale $Q_{0}$. We discuss the implications of the different parameters of the model in comparing with world data and conclude that within experimental errors our description remains valid. Thus we can assert that the low $Q^2$ nonperturbative description together with an additional $1/Q^2$ term at the matching scale have a strong influence on the $Q^2$ behavior up to very high values of $Q^2$ .Comment: 6 pages and 3 figures. Contains a comparison with other models and additional reference

The eta-photon transition form factor

The eta-photon transition form factor is evaluated in a formalism based on a phenomenological description at low values of the photon virtuality, and a QCD-based description at high photon virtualities, matching at a scale $Q_{0}^{2}$. The high photon virtuality description makes use of a Distribution Amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars regularization at the matching scale $Q_{0}^{2}$, and QCD evolution from $Q_{0}^{2}$ to higher values of $Q^{2}$. A good description of the available data is obtained. The analysis indicates that the recent data from the BaBar collaboration on pion and eta transition form factor can be well reproduced, if a small contribution of twist three at the matching scale $Q_{0}^{2}$ is included.Comment: 14 pages, 3 figures, revised version, minor corrections, references added, conclusions unchanged. Accepted for publication in Phys. Rev.

Magnetism and half-metallicity at the O surfaces of ceramic oxides

The occurence of spin-polarization at ZrO$_{2}$, Al$_{2}$O$_{3}$ and MgO surfaces is proved by means of \textit{ab-initio} calculations within the density functional theory. Large spin moments, as high as 1.56 $\mu_B$, develop at O-ended polar terminations, transforming the non-magnetic insulator into a half-metal. The magnetic moments mainly reside in the surface oxygen atoms and their origin is related to the existence of $2p$ holes of well-defined spin polarization at the valence band of the ionic oxide. The direct relation between magnetization and local loss of donor charge makes possible to extend the magnetization mechanism beyond surface properties