Non-perturbative decay of Non-Abelian hair

We construct a solution of Heterotic supergravity which interpolates between two different AdS$_{3}\times S^{3}\times T^{4}$ geometries corresponding to the near-horizon limits of two 5-dimensional black holes, only one of which has non-Abelian hair. This solution can be used to estimate the amplitude of probability of the non-perturbative decay of the gauge 5-brane responsible for the non-Abelian hair into eight solitonic 5-branes by evaluating its Euclidean action. The Wick rotation of this solution poses several problems which we argue can be overcome by using a non-extremal off-shell (NEOS) deformation of the solution. This NEOS field configuration can be Wick rotated straight away and its Euclidean action can be computed for any value of the deformation parameter. The Euclidean result can then be anti-Wick-rotated and its extremal limit gives the Euclidean action of the original solution, which turns out to be one half of the difference between the entropies of the 5-dimensional black holes.Comment: Few typos corrected. Two references and a footnote added. Version to be published in JHE

Regular Stringy Black Holes?

We study the first-order $\alpha'$ corrections to the singular 4-dimensional massless stringy black holes studied in the nineties in the context of the Heterotic Superstring. We show that the $\alpha'$ corrections not only induce a non-vanishing mass and give rise to an event horizon, but also eliminate the singularity giving rise to a regular spacetime whose global structure includes further asymptotically flat regions in which the spacetime's mass is positive or negative. We study the timelike and null geodesics and their effective potential, showing that the spacetime is geodesically complete. We discuss the validity of this solution, arguing that the very interesting and peculiar properties of the solution are associated to the negative energy contributions coming from the terms quadratic in the curvature. As a matter of fact, the 10-dimensional configuration is singular. We extract some general lessons on attempts to eliminate black-hole singularities by introducing terms of higher order in the curvature.Comment: 5 pages, 2 figure

Non-Abelian black holes in string theory

We study a family of 5-dimensional non-Abelian black holes that can be obtained by adding an instanton field to the well-known D1D5W Abelian black holes. Naively, the non-Abelian fields seem to contribute to the black-hole entropy but not to the mass due to their rapid fall-off at spatial infinity. By uplifting the 5-dimensional supergravity solution to 10-dimensional Heterotic Supergravity first and then dualizing it into a Type-I Supergravity solution, we show that the non-Abelian fields are associated to D5-branes dissolved into the D9-branes (dual to the Heterotic "gauge 5-branes") and that their associated RR charge does not, in fact, contribute to the entropy, which only depends on the number16 pages of D-strings and D5 branes and the momentum along the D-strings, as in the Abelian case. These "dissolved" or "gauge" D5-branes do contribute to the mass in the expected form. The correct interpretation of the 5-dimensional charges in terms of the string-theory objects solves the non-Abelian hair puzzle, allowing for the microscopic accounting of the entropy. We discuss the validity of the solution when alpha prime corrections are taken into account.Comment: Latex 2e file, 21 pages. A full appendix on alpha prime corrections and the corresponding discussions have been added. The conclusions have suffered minor changes. Version accepted in JHE

Utilization of morphological and AFLP molecular markers in the identification of native and cultivated germplasm of Elymus scabrifolius (Poaceae)

Elymus scabrifolius es una gramínea perenne nativa de Sudamérica con gran potencial como recurso forrajero para ambientes con limitantes edáficas. En el presente trabajo se analizó la utilización de caracteres morfológicos y marcadores moleculares AFLP para la identificación genotípica de seis accesiones, un cultivar comercial y siete híbridos artificiales de esta especie. Ambos tipos de marcadores permitieron diferenciar a los materiales analizados en los respectivos dendrogramas, aunque las relaciones entre materiales variaron según el tipo de marcador. El Análisis de Componentes Principales permitió identificar las variables más relevantes para la diferenciación morfológica. Los híbridos se diferenciaron morfológicamente de ambos parentales, excepto un híbrido que se agrupó con su material paterno. Aunque en el análisis de los marcadores AFLP los híbridos se agruparon con uno de sus parentales, se pudo corroborar su origen híbrido mediante el registro de bandas paternas y polimórficas entre parentales. Se concluye que las metodologías empleadas para caracterizar los materiales analizados de E. scabrifolius serían de gran utilidad para el manejo eficiente de colecciones de germoplasma como así también para su utilización en programas de mejoramiento genético.Elymus scabrifolius is a South American perennial grass exhibiting great potential as a forage resource, especially for environments with edaphic limitations. In the present work we use morphological traits and AFLP molecular markers to genotypically identify six E. scabrifolius accessions, one commercial cultivar and seven artificial hybrids of this species. Both types of marker systems resulted in an accurate differentiation of the interrogated E. scabrifolius germplasm in the dendrograms. Moreover, relationships between the tested germplasm tend to vary according to the type of marker system used. Principal Component Analysis was used to identify the traits that best described the morphological variation. The morphological study revealed that almost all hybrids were different from their parents, with exception of one hybrid that was clustered with their own male parent. In the AFLP marker analysis, all the hybrids were clustered with one of their own parents. However, hybrid origin of those individuals was verified by the presence of paternal bands and polymorphic bands. In conclusion, the use of different methodologies to characterize and analyze E. scabrifolius materials has the potential to become of great benefit for the efficient management of germplasm collections and also for their utilization in breeding programs.Fil: Tomas, Pablo A.. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias. Cátedra de Mejoramiento Vegetal y Animal.Fil: Gottlieb, Alexandra M.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución.Fil: Schrauf, Gustavo E.. Universidad de Buenos Aires. Facultad de AgronomíaFil: Poggio, Lidia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución

The decay of Batchelor and Saffman rotating turbulence

The decay rate of isotropic and homogeneous turbulence is known to be affected by the large-scale spectrum of the initial perturbations, associated with at least two cannonical self-preserving solutions of the von K\'arm\'an-Howarth equation: the so-called Batchelor and Saffman spectra. The effect of long-range correlations in the decay of anisotropic flows is less clear, and recently it has been proposed that the decay rate of rotating turbulence may be independent of the large-scale spectrum of the initial perturbations. We analyze numerical simulations of freely decaying rotating turbulence with initial energy spectra $\sim k^4$ (Batchelor turbulence) and $\sim k^2$ (Saffman turbulence) and show that, while a self-similar decay cannot be identified for the total energy, the decay is indeed affected by long-range correlations. The decay of two-dimensional and three-dimensional modes follows distinct power laws in each case, which are consistent with predictions derived from the anisotropic von K\'arm\'an-Howarth equation, and with conservation of anisotropic integral quantities by the flow evolution

The decay of turbulence in rotating flows

We present a parametric space study of the decay of turbulence in rotating flows combining direct numerical simulations, large eddy simulations, and phenomenological theory. Several cases are considered: (1) the effect of varying the characteristic scale of the initial conditions when compared with the size of the box, to mimic "bounded" and "unbounded" flows; (2) the effect of helicity (correlation between the velocity and vorticity); (3) the effect of Rossby and Reynolds numbers; and (4) the effect of anisotropy in the initial conditions. Initial conditions include the Taylor-Green vortex, the Arn'old-Beltrami-Childress flow, and random flows with large-scale energy spectrum proportional to $k^4$. The decay laws obtained in the simulations for the energy, helicity, and enstrophy in each case can be explained with phenomenological arguments that separate the decay of two-dimensional from three-dimensional modes, and that take into account the role of helicity and rotation in slowing down the energy decay. The time evolution of the energy spectrum and development of anisotropies in the simulations are also discussed. Finally, the effect of rotation and helicity in the skewness and kurtosis of the flow is considered.Comment: Sections reordered to address comments by referee