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

Form factors of radiative pion decays in nonlocal chiral quark models

We study the radiative pion decay pi+ -> e+ nu_e gamma within nonlocal chiral quark models that include wave function renormalization. In this framework we analyze the momentum dependence of the vector form factor F_V(q^2), and the slope of the axial-vector form factor F_A(q^2) at threshold. Our results are compared with available experimental information and with the predictions given by the NJL model. In addition we calculate the low energy constants l_5 and l_6, comparing our results with the values obtained in chiral perturbation theory.Comment: 22 pages, 1 figure. arXiv admin note: substantial text overlap with arXiv:1011.640

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

Magnetic field driven enhancement of the weak decay width of charged pions

We study the effect of a uniform magnetic field $\vec B$ on the decays $\pi^-\to l^-\,\bar{\nu}_l$, where $l^-\,=e^-,\,\mu^-$, carrying out a general analysis that includes four $\pi^-$ decay constants. Taking the values of these constants from a chiral effective Nambu-Jona--Lasinio (NJL) model, it is seen that the total decay rate gets strongly increased with respect to the $B=0$ case, with an enhancement factor ranging from $\sim 10$ for $eB=0.1\,\mathrm{GeV}^2$ up to $\sim 10^3$ for $eB=1\,\mathrm{GeV}^2$. The ratio between electronic and muonic decays gets also enhanced, reaching a value of about $1:2$ for $eB=1\,\mathrm{GeV}^2$. In addition, we find that for large $B$ the angular distribution of outgoing antineutrinos shows a significant suppression in the direction of the magnetic field.Comment: 23 pages, 2 figure

Weak decays of magnetized charged pions in the symmetric gauge

We consider the decay $\pi^- \to l \, \bar{\nu}_l$ ($l=e^-,\,\mu^-$) in the presence of an arbitrary large uniform magnetic field, using the symmetric gauge. The consequences of the axial symmetry of the problem and the issue of angular momentum conservation are discussed in detail. In particular, we analyze the projection of both the canonical and the mechanical total angular momenta along the direction of the magnetic field. It is found that while the former is conserved in the symmetric gauge, the latter is not conserved in both the symmetric and Landau gauges. We derive an expression for the integrated $\pi^- \to l \, \bar{\nu}_l$ width that coincides exactly with the one we previously found using the Landau gauge, providing an explicit test of the gauge independence of that result. Such an expression implies that for nonzero magnetic fields the decay width does not vanish in the limit in which the outgoing charged leptons can be considered as massless, i.e. it does not exhibit the helicity suppression found in the case of no external field.Comment: 24 pages, no figure

Strongly interacting matter under external magnetic fields within nonlocal NJL-type models

We study the behavior of strongly interacting matter under an external magnetic field in the context of nonlocal Nambu-Jona-Lasinio (NJL) -like models. We find that at zero temperature the condensates display the well-known Magnetic Catalysis effect, showing a good quantitative agreement with lattice QCD (LQCD) results. Moreover, when extended to finite temperature we find that (contrary to what happens in the local NJL model) the Inverse Magnetic Catalysis (IMC) effect is naturally incorporated. We also analyze the magnetic susceptibility of the QCD vacuum in the limit of small magnetic field, considering two different model parametrizations, and compare our numerical results to those obtained in other theoretical approaches and in LQCD calculations.Facultad de Ciencias Exacta

Effect of inbreeding on the longevity of Landrace sows

Ponencia publicada en ITEA, vol.104La consanguinidad es un fenómeno biológico de especial relevancia en las especies domésticas, pudiéndose caracterizar tanto en términos de coeficiente de consanguinidad como fraccionando la contribución de cada individuo fundador en coeficientes de consanguinidad parcial (CP). A partir de los registros de longevidad de 4.226 cerdas de raza Landrace, este trabajo se ha centrado en la modelización de los CP bajo modelos Weibull de riesgos proporcionales y su posterior comparación mediante el DIC (deviance information criterion). Se asumieron tres distribuciones a priori distintas para los efectos de CP, resultando la normal asimétrica (DIC = 55.064,6) claramente preferible a la normal simétrica (DIC = 55.069,2) y a la distribución uniforme (DIC = 55.077,9). Se descartó, también, el modelo estándar con la consanguinidad global de cada individuo (DIC = 55.078,4). En el caso del modelo con DIC mínimo, la distribución posterior de los efectos de CP fue claramente asimétrica, con el 85,15% de las estimas afectando negativamente a la longevidad de las cerdas y el 14,85% restante con efecto neutro o incluso positivo. Señalar por último, que la heredabilidad para el carácter longevidad fue de 0,159.Inbreeding is a biological phenomenon of special relevance in domestic species, where the overall inbreeding coefficient can be partitioned in founder-specific partial inbreeding (PI) coefficients. Taking longevity data of 4,226 Landrace sows as starting point, this research proposed alternative parameterization for PI effects under Weibull proportional hazard models, and compared their performance through the deviance information criterion (DIC). Three different a priori distributions were assumed for PI effects, asymmetric normal (DIC = 55,064.6), symmetric normal (DIC = 55,069.2) and flat (DIC = 55,077.9). Additionally, the standard model accounting for the overall inbreeding coefficient was clearly discarded (DIC = 55,078.4). For the model with asymmetric Gaussian prior, the posterior distribution of PI effects was clearly skewed. An 85.15% of the estimates showed negative effect on sow longevity whereas the remaining 14.85% ones had null or even positive effect on sow survival. Estimated heritability was 0.159

Strongly interacting matter under external magnetic fields within nonlocal NJL-type models

We study the behavior of strongly interacting matter under an external magnetic field in the context of nonlocal Nambu-Jona-Lasinio (NJL) -like models. We find that at zero temperature the condensates display the well-known Magnetic Catalysis effect, showing a good quantitative agreement with lattice QCD (LQCD) results. Moreover, when extended to finite temperature we find that (contrary to what happens in the local NJL model) the Inverse Magnetic Catalysis (IMC) effect is naturally incorporated. We also analyze the magnetic susceptibility of the QCD vacuum in the limit of small magnetic field, considering two different model parametrizations, and compare our numerical results to those obtained in other theoretical approaches and in LQCD calculations.Facultad de Ciencias Exacta

Programa Futuros Egresados. Seguimiento pedagógico de estudiantes demorados en el egreso en la Facultad de Ciencias Políticas y Sociales de la UNCuyo. Análisis de los primeros resultados.

El Programa “Futuros Egresados” es una experiencia que se realiza en la Facultad de Ciencias Políticas y Sociales de la Universidad Nacional de Cuyo desde el año 2007 y está destinado a estudiantes con demora en su egreso. La iniciativa se implementa desde el Servicio de Apoyo Psicopedagógico y Orientación al Estudiante (SAPOE). En primer lugar definimos a la población “futuro egresado”: es aquel/la estudiante que ingresó a la Facultad antes del año 2000 y aún adeuda 5 o menos materias además del trabajo de Tesina. El rastreo inicial ha dado como resultado que alrededor de 700 estudiantes están en esta situación en las cuatro carreras: Trabajo Social, Sociología, Ciencias Políticas y Administración Pública y Comunicación Social. 450 de ellos participan del Programa, 30 ya han egresado y el resto ha comenzado a rendir y aprobar exámenes finales. Los objetivos que se plantea el Programa son: Detectar causas por las que los estudiantes demoran en recibirse. Ofrecer acciones concretas para orientar y ayudar a los estudiantes a graduarse. Los estudiantes que responden a la convocatoria realizan una entrevista en el SAPOE donde se registran sus datos personales, situación académica y los motivos de la demora en el egreso. Las acciones que se han implementado siguen dos vertientes: por un lado, administrativa: se tomaron una serie de decisiones con la finalidad de disminuir la presión que experimentan los estudiantes. Y por el otro psicológica y pedagógica: que tienen el propósito de facilitar que las acciones se focalicen en estrategias más vinculadas a la resolución de su situación de demora. Estas últimas están orientadas a establecer lazos de comunicación entre los estudiantes y la Facultad y generar condiciones de intercambio entre estudiantes en las mismas condiciones

Pion distribution amplitude and the pion-photon transition form factor in a nonlocal chiral quark model

We study the pion distribution amplitude (pi DA) in the context of a nonlocal chiral quark model. The corresponding Lagrangian reproduces the phenomenological values of the pion mass and decay constant, as well as the momentum dependence of the quark propagator obtained in lattice calculations. It is found that the obtained pi DA has two symmetric maxima, which arise from the new contributions generated by the nonlocal character of the interactions. This pi DA is applied to leading order and next-to-leading order calculations of the pion-photon transition form factor. Implications of the results are discussed