Tachyonic Quintessential Inflation

We study the possibility to construct an observationally viable scenario where both early Inflation and the recently detected accelerated expansion of the universe can be explained by using a single scalar field associated with the Tachyon. The Reheating phase becomes crucial to enable us to have a consistent cosmology and also to get a second accelerated expansion period. A discussion using an exponential potential is presented.Comment: 5 pages, Revtex4. Added some references. To be published in Physical Review

Percolation study for the capillary ascent of a liquid through a granular soil

Capillary rise plays a crucial role in the construction of road embankments in flood zones, where hydrophobic compounds are added to the soil to suppress the rising of water and avoid possible damage of the pavement. Water rises through liquid bridges, menisci and trimers, whose width and connectivity depends on the maximal half-length {\lambda} of the capillary bridges among grains. Low {\lambda} generate a disconnect structure, with small clusters everywhere. On the contrary, for high {\lambda}, create a percolating cluster of trimers and enclosed volumes that form a natural path for capillary rise. Hereby, we study the percolation transition of this geometric structure as a function of {\lambda} on a granular media of monodisperse spheres in a random close packing. We determine both the percolating threshold {\lambda}_{c} = (0.049 \pm 0.004)R (with R the radius of the granular spheres), and the critical exponent of the correlation length {\nu} = (0.830 \pm 0.051), suggesting that the percolation transition falls into the universality class of ordinary percolation

Effect of support redox character on catalytic performance in the gas phase hydrogenation of benzaldehyde and nitrobenzene over supported gold

The authors are grateful to Dr. N. Perret for her involvement in this work. EPSRC support for free access to the TEM facility at the University of St. Andrews and financial support to Dr. M. Li and Dr. X. Wang through the Overseas Research Students Award Scheme (ORSAS) are also acknowledged.Peer reviewedPostprin

R^2-corrections to Chaotic Inflation

Scalar density cosmological perturbations, spectral indices and reheating in a chaotic inflationary universe model, in which a higher derivative term is added, are investigated. This term is supposed to play an important role in the early evolution of the Universe, specifically at times closer to the Planck era.Comment: 14 pages, accepted for publication in MPL

Contact forces distribution for a granular material from a Monte Carlo study on a single grain

The force network ensemble is one of the most promising statistical descriptions of granular media, with an entropy accounting for all force configurations at mechanical equilibrium consistent with some external stress. It is possible to define a temperature-like parameter, the angoricity {\alpha}^{-1}, which under isotropic compression is a scalar variable. This ensemble is frequently studied on whole packings of grains; however, previous works have shown that spatial correlations can be neglected in many cases, opening the door to studies on a single grain. Our work develops a Monte Carlo method to sample the force ensemble on a single grain at constant angoricity on two and three-dimensional mono-disperse granular systems, both with or without static friction. The results show that, despite the steric exclusions and the constrictions of Coulomb's limit and repulsive normal forces, the pressure per grain always show a gamma distribution with scale parameter {\nu} = {\alpha}^{-1} and shape parameter k close to k', the number of degrees of freedom in the system. Moreover, the average pressure per grain fulfills an equipartition theorem =k'{\alpha}^{-1} in all cases (in close parallelism with the one for an ideal gas). These results suggest the existence of k' independent random variables (i.e. elementary forces) with identical exponential distributions as the basic elements for describing the force network ensemble at low angoricities under isotropic compression, in analogy with the volume ensemble of granular materials

The Higgs decay rate to two photons in a model with two fermiophobic-Higgs doublets

We consider a three Higgs doublet model with an $S_3$ symmetry in which beside the SM-like doublet there are two fermiophobic doublets. Due to the new charged scalars there is an enhancement in the two-photon decay while the other channels have the same decay widths that the SM neutral Higgs. The fermiophobic scalars are mass degenerated unless soft terms breaking the $S_3$ symmetry are added.Comment: typos were corrected, the figures have been modified and the conclusions were increased. Still contains 15 pages, 2 figure

Aprendizaje basado en problemas y en comparación de soluciones en un contexto semipresencial

Este trabajo propone un método de evaluación continua, no presencial e implementable a través de entornos de aprendizaje en línea. En una primera fase, el profesor propone un problema y define una fecha de entrega, antes de la cual los alumnos deberán enviar sus soluciones (resultado A). Cumplido este plazo, el profesor publica una solución correcta. En una segunda fase, los alumnos comparan sus soluciones con la del profesor, y elaboran un informe de autoevaluación (resultado B). De la entrega A se evalúa corrección y optimalidad, mientras que de B se valora la capacidad del alumno para realizar un análisis crítico de los errores y singularidades de su solución. Como evaluación global del ejercicio se propone una media ponderada de las notas de ambos resultados, A y B.SUMMARY -- This paper proposes a method of continuous assessment that can be implemented through online learning environments. In a first phase, the teacher poses a problem and sets a deadline for students to submit their individual solutions (outcome A), after which a correct solution is published. In a second phase, students will compare their solutions with that of the teacher, and write a self-assessment report (outcome B). The outcome A is evaluated based on its correctness and optimality, while B is assessed considering students' ability to detect their errors and to make a reasoned defense of their solutions. The overall evaluation is intended as a weighted average of the notes of both deliverables, A and B.Peer Reviewe