Search results for "Modelo"
showing 10 items of 444 documents
Photoproduction of meson and baryon resonances in a chiral unitary approach
1999
By means of a coupled channel non-perturbative unitary approach, it is possible to extend the strong constrains of Chiral Perturbation Theory to higher energies. In particular, it is possible to reproduce the lowest lying resonances in meson-meson scattering up to 1.2 GeV using the parameters of the O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be tackled along similar lines. We report on an update of these results showing some examples of photon induced reactions where the techniques have been recently applied.
Recent progress on the chiral unitary approach to meson meson and meson baryon interactions
1999
We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and $K^-$ atoms.
Improved unitarized Heavy Baryon Chiral Perturbation Theory for π N scattering
2000
We show how the unitarized description of pion nucleon scattering within Heavy Baryon Chiral Perturbation Theory can be considerably improved, by a suitable reordering of the expansion over the nucleon mass. Within this framework, the $\Delta$ resonance and its associated pole can be recovered from the chiral parameters obtained from low-energy determinations. In addition, we can obtain a good description of the six $S$ and $P$ wave phase shifts in terms of chiral parameters with a natural size and compatible with the Resonance Saturation Hypothesis.
Meson-meson interactions in a nonperturbative chiral approach
1999
A non-perturbative method which combines constraints from chiral symmetry breaking and coupled channel unitarity is used to describe the meson-meson interaction up to about 1.2 GeV. The approach uses the O(p^2) and O(p^4) chiral Lagrangians. The seven free parameters of the O(p^4) Lagrangian are fitted to the data. The results are in good agreement with a vast amount of experimental analyses. The amplitudes develop poles in the complex plane corresponding to the f0, a0, rho, K*, phi, sigma and kappa resonances; the latter two, very broad. The total and partial decay widths of the resonances are also well reproduced. Further extensions and applications of this chiral non-perturbative scheme …
Probing neutrino mass with multilepton production at the Tevatron in the simplest R-parity violation model
2003
We analyze the production of multileptons in the simplest supergravity model with bilinear violation of R parity at the Fermilab Tevatron. Despite the small R-parity violating couplings needed to generate the neutrino masses indicated by current atmospheric neutrino data, the lightest supersymmetric particle is unstable and can decay inside the detector. This leads to a phenomenology quite distinct from that of the R-parity conserving scenario. We quantify by how much the supersymmetric multilepton signals differ from the R-parity conserving expectations, displaying our results in the $m_0 \otimes m_{1/2}$ plane. We show that the presence of bilinear R-parity violating interactions enhances…
Nonperturbative approach to effective chiral Lagrangians and meson interactions
1998
We develop a coupled channel unitary approach describing the behavior at higher energies of systems whose low-energy dynamics is given by effective O(p^2) and O(p^4) chiral Lagrangians. Our free parameters are those of the O(p^4) Lagrangian. When applied to the meson-meson interaction, it yields a remarkable agreement with data up to sqrt{s}=1.2 GeV, dynamically generating the sigma, f_0, a_0,rho and K^* resonances. Further applications are also proposed.
Nature of the axial-vector mesons from their N-c behavior within the chiral unitary approach
2008
By describing within the chiral unitary approach the g-wave interaction of the vector meson nonet with the octet of pseudoscalar Goldstone bosons, we find that the main component of the axial-vector mesons -b(1)(1235), h(1)(1170), h(1)(1380), a(1)(1260), f(1)(1285) and the two states associated to the K-1(1270)- does not follow the QCD dependence on the number of colors for ordinary q (q) over bar mesons.
¿Modelo social europeo de bajo coste?
2008
En este ensayo sostengo que las dificultades de la economía europea para generar suficiente empleo y sostener el bienestar, durante la última década, están dando lugar a políticas orientadas hacia la construcción de un "modelo social de bajo coste", apoyado en la idea de "flexeguridad" y en el desarrollo de los yacimientos de empleo. La política de empleo y la política social aparecen imbricadas a través de la precariedad. Además, sugiero críticamente, que el modelo nórdico de "flexeguridad", propuesto como alternativa por la unión europea, a modo de triangulo mágico que combina la flexibilidad en el empleo, formación continua y la provisión de seguridad pública, no parece muy plausible par…
Análisis de la primera colaboración público-privada en asistencia maternal en atención primaria y especializada en España: una aplicación del análisi…
2021
El Hospital Universitario de La Ribera (Alzira, Valencia) fue la primera experiencia de colaboración público-privada en el Sistema Nacional de Salud español. Además de la necesidad de coordinar dos niveles de atención sanitaria (primaria/especializada) hubo que coordinar dos modelos de gestión de recursos humanos (público/privado). Para ejemplificar esta complejidad, se toma el colectivo de matronas del área de salud, analizando sus pautas relacionales mediante la aproximación metodológica del Análisis de Redes Sociales. En cuanto a resultados, de una población de 31 matronas, las del modelo público ocupan posiciones periféricas y cooperan poco, tanto interna como externamente. Las del mode…
Innovation in Physical Education: Back to the principles of procedure
2018
El sistema educativo español ha sufrido, en los últimos años, numerosas modificaciones que lo han ido transformando. Una parte de ellas se ha centrado en la introducción de nuevos elementos en el currículum, como las competencias clave y los estándares de aprendizaje evaluables, que han cambiado la forma de concebir la educación y que se perciben como posturas innovadoras por parte del profesorado. Desgraciadamente, este modelo por competencias y por estándares ha recuperado un paradigma educativo centrado en el producto, es decir, la pedagogía por objetivos. Este modelo centra la atención del profesorado en ajustar la práctica educativa a criterios preestablecidos por las propias leyes a t…