Four-dimensional gravity on supersymmetric dilatonic domain walls

We investigate the localization of four-dimensional metastable gravity in supersymmetric dilatonic domain walls through massive modes by considering several scenarios in the model. We compute corrections to the Newtonian potential for small and long distances compared with a crossover scale given in terms of the dilatonic coupling. 4D gravity behavior is developed on the brane for distance very much below the crossover scale, while for distance much larger, the 5D gravity is recovered. Whereas in the former regime gravity is always attractive, in the latter regime due to non-normalizable unstable massive graviton modes present on the spectrum, in some special cases, gravity appears to be repulsive and signalizes a gravitational confining phase which is able to produce an inflationary phase of the Universe.Comment: 11 pages, 4 figures, Latex. Version to appear in PL

Spatial patterns and biodiversity in off-lattice simulations of a cyclic three-species Lotka-Volterra model

Stochastic simulations of cyclic three-species spatial predator-prey models are usually performed in square lattices with nearest neighbor interactions starting from random initial conditions. In this Letter we describe the results of off-lattice Lotka-Volterra stochastic simulations, showing that the emergence of spiral patterns does occur for sufficiently high values of the (conserved) total density of individuals. We also investigate the dynamics in our simulations, finding an empirical relation characterizing the dependence of the characteristic peak frequency and amplitude on the total density. Finally, we study the impact of the total density on the extinction probability, showing how a low population density may jeopardize biodiversity.Comment: 5 pages, 7 figures; new version, with new title and figure

Relaxing to a three dimensional brane junction

We suggest a mechanism which leads to 3+1 space-time dimensions. The Universe assumed to have nine spatial dimensions is regarded as a special nonlinear oscillatory system -- a kind of Einstein solid. There are p-brane solutions which manifest as phase oscillations separating different phase states. The presence of interactions allows for bifurcations of higher dimensional spaces to lower dimensional ones in the form of brane junctions. We argue this is a natural way to select lower dimensions.Comment: RevTex, 5 pages; version to appear in Europhys. Let

A statistical study of seasonal winter rainfall prediction in the Comahue region (Argentina)

El objetivo del presente estudio es establecer las posibles causas que determinan la variabilidad de la precipitación en el período mayo-junio-julio (MJJ) en la cuencas de los ríos Limay y Neuquén. Para establecer la existencia de patrones de circulación previos a este trimestre indicativos de la variabilidad interanual de la precipitación acumulada en MJJ, se correlacionó la precipitación media en el área en cada una de las cuencas con diferentes predictores durante el trimestre precedente (febrero-marzo-abril). Los resultados indicaron que la precipitación en MJJ en ambas cuencas está relacionada con la temperatura de la superficie del mar y las alturas geopotenciales en diferentes niveles observadas previamente en áreas específicas del océano Indico y del Pacífico Sur, tal vez debido a los trenes de onda que se inician en esas zonas y que al llegar a proximidades de la Patagonia se manifiestan como sistemas precipitantes. También se observaron buenas correlaciones con la temperatura de la superficie del mar en el Atlántico, en la costa de Brasil y Argentina asociada al ingreso de vapor hacia el continente y con el viento zonal y meridional en las inmediaciones de la cuenca, responsables de la advección de aire húmedo. La aplicación de esquemas de predicción utilizando una regresión lineal múltiple dio como resultado que las variables elegidas explican el 51% de la variabilidad de la lluvia en MJJ en la cuenca del Limay y el 44% en la del Neuquén. El esquema se validó utilizando la metodología de validación cruzada, obteniendo correlaciones significativas entre la precipitación observada y la pronosticada en ambas cuencas. El análisis de la lluvia del invierno 2009 mostró que los indicadores de gran escala fueron útiles para detectar con anticipación la precipitación del invierno.The aim of this study is to detect the possible causes of the May-to-July rainfall (MJJ) over the Limay and Neuquén river basins. In order to establish the existence of previous circulation patterns associated with interannual rainfall variability, the mean areal precipitation in each one of the basins was correlated to some predictors during the previous three month period (February-March-April). The result is that MJJ rainfall in both basins is related to sea surface temperature and geopotential heights at different levels previously observed in some specific areas of Indian and Pacific Oceans, probably due to wave trains which begin in those areas and then displace towards the Argentine Patagonia coast, thus generating precipitation systems. There are also observed significant correlations with sea surface temperature in the Atlantic Ocean over Brazil and the Argentine coast, associated with the water vapor income into the continent and with zonal and meridional wind over the basins, related to humid air advection. The prediction schemes, using multiple linear regressions, showed that the selected variables are the cause of the 51% of the MJJ rainfall variance in the Limay river basin and the 44% in the Neuquén river one. The scheme was validated by using a crossvalidation method and significant correlations were detected between observed and forecast rainfall. The 2009 winter rainfall was analyzed and showed that circulation indicators were useful to predict winter rainfall.Fil: González, Marcela Hebe. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; ArgentinaFil: Skansy, M. M.. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; ArgentinaFil: Losano, F.. Autoridad Interjurisdiccional de las Cuencas de los Ríos Limay, Neuquén y Negro; Argentin

Projected Linear Response Theory for Charge-Exchange Excitations and Double Beta Decay

The projected random phase approximation (PRPA) for charge-exchange excitations is derived from the time-dependent variational principle. Explicit results for the unperturbed energies (including the self-energy corrections), the PRPA matrices, and the transition matrix elements are presented. The effect of the projection procedure on the two-neutrino $\beta\beta$ decay in $^{76}Ge$ is briefly discussed.Comment: 12 pages text (LaTex) and 1 figure upon request, to be published in Phys. Lett.

Junctions and spiral patterns in Rock-Paper-Scissors type models

We investigate the population dynamics in generalized Rock-Paper-Scissors models with an arbitrary number of species $N$. We show, for the first time, that spiral patterns with $N$-arms may develop both for odd and even $N$, in particular in models where a bidirectional predation interaction of equal strength between all species is modified to include one N-cyclic predator-prey rule. While the former case gives rise to an interface network with Y-type junctions obeying the scaling law $L \propto t^{1/2}$, where $L$ is the characteristic length of the network and $t$ is the time, the later can lead to a population network with $N$-armed spiral patterns, having a roughly constant characteristic length scale. We explicitly demonstrate the connection between interface junctions and spiral patterns in these models and compute the corresponding scaling laws. This work significantly extends the results of previous studies of population dynamics and could have profound implications for the understanding of biological complexity in systems with a large number of species.Comment: 6 pages, 8 figures, published versio

Exploring the vicinity of the Bogomol'nyi-Prasad-Sommerfield bound

We investigate systems of real scalar fields in bidimensional spacetime, dealing with potentials that are small modifications of potentials that admit supersymmetric extensions. The modifications are controlled by a real parameter, which allows implementing a perturbation procedure when such parameter is small. The approach allows obtaining the energy and topological charge in closed forms, up to first order in the parameter. We illustrate the procedure with some examples. In particular, we show how to remove the degeneracy in energy for the one-field and the two-field solutions that appear in a model of two real scalar fields.Comment: Revtex, 9 pages, To be published in J. Phys.

Cyclic competition of four species: domains and interfaces

We study numerically domain growth and interface fluctuations in one- and two-dimensional lattice systems composed of four species that interact in a cyclic way. Particle mobility is implemented through exchanges of particles located on neighboring lattice sites. For the chain we find that domain growth strongly depends on the mobility, with a higher mobility yielding a larger domain growth exponent. In two space dimensions, when also exchanges between mutually neutral particles are possible, both domain growth and interface fluctuations display universal regimes that are independent of the predation and exchange rates.Comment: 14 pages, 7 figures, version accepted for publication in J. Stat. Mec