Is there a monopole problem?

We investigate the high temperature behavior of SU(5) in its minimal version. We show that there exists a range of parameters of the Higgs potential for which the symmetry remains broken at high temperature, thus avoiding the phase transition that gives rise to the overproduction of monopoles . We also show that in such scenario the thermal production of monopoles can be suppressed in a wide range of parameters, keeping their number density below the cosmological limits

Localizing gravity on exotic thick 3-branes

We consider localization of gravity on thick branes with a non trivial structure. Double walls that generalize the thick Randall-Sundrum solution, and asymmetric walls that arise from a Z_2-symmetric scalar potential, are considered. We present a new asymmetric solution: a thick brane interpolating between two AdS_5 spacetimes with different cosmological constants, which can be derived from a ``fake supergravity'' superpotential, and show that it is possible to confine gravity on such branes.Comment: Final version, minor changes, references adde

Ricci Collineations for type B warped space-times

We present the general structure of proper Ricci Collineations (RC) for type B warped space-times. Within this framework, we give a detailed description of the most general proper RC for spherically symmetric metrics. As examples, static spherically symmetric and Friedmann-Robertson-Walker space-times are considered.Comment: 18 pages, Latex, To appear in GR

LAGOVirtual: A Collaborative Environment for the Large Aperture GRB Observatory

We present the LAGOVirtual Project: an ongoing project to develop platform to collaborate in the Large Aperture GRB Observatory (LAGO). This continental-wide observatory is devised to detect high energy (around 100 GeV) component of Gamma Ray Bursts, by using the single particle technique in arrays of Water Cherenkov Detectors (WCD) at high mountain sites (Chacaltaya, Bolivia, 5300 m a.s.l., Pico Espejo, Venezuela, 4750 m a.s.l., Sierra Negra, Mexico, 4650 m a.s.l). This platform will allow LAGO collaboration to share data, and computer resources through its different sites. This environment has the possibility to generate synthetic data by simulating the showers through AIRES application and to store/preserve distributed data files collected by the WCD at the LAGO sites. The present article concerns the implementation of a prototype of LAGO-DR adapting DSpace, with a hierarchical structure (i.e. country, institution, followed by collections that contain the metadata and data files), for the captured/simulated data. This structure was generated by using the community, sub-community, collection, item model; available at the DSpace software. Each member institution-country of the project has the appropriate permissions on the system to publish information (descriptive metadata and associated data files). The platform can also associate multiple files to each item of data (data from the instruments, graphics, postprocessed-data, etc.).Comment: Second EELA-2 Conference Choroni, Venezuela, November 25th to 27th 200

Bubble Collisions and Defect Formation in a Damping Environment

Within the context of a first-order phase transition in the early Universe, we study the collision process for vacuum bubbles expanding in a plasma. The effects of the plasma are simulated by introducing a damping term in the equations of motion for a $U(1)$ global field. We find that Lorentz-contracted spherically symmetric domain walls adequately describe the overdamped motion of the bubbles in the thin wall approximation, and study the process of collision and phase equilibration both numerically and analytically. With an analytical model for the phase propagation in 1+1 dimensions, we prove that the phase waves generated in the bubble merging are reflected by the walls of the true vacuum cavity, giving rise to a long-lived oscillating state that delays the phase equilibration. The existence of such a state in the 3+1 dimensional model is then confirmed by numerical simulations, and the consequences for the formation of vortices in three-bubble collisions are considered.Comment: 19 pages. 7 uuencoded and compressed figures (2 Mgs) available on reques

How does the geodesic rule really work for global symmetry breaking first order phase transitions?

The chain of events usually understood to lead to the formation of topological defects during phase transitions is known as the Kibble mechanism. A central component of the mechanism is the so-called ``geodesic rule''. Although in the Abelian Higgs model the validity of the geodesic rule has been questioned recently, it is known to be valid on energetic grounds for a global U(1) symmetry breaking transition. However, even for these globally symmetric models no dynamical analisys of the rule has been carried to this date, and some points as to how events proceed still remain obscure. This paper tries to clarify the dynamics of the geodesic rule in the context of a global U(1) model. With an appropriate ansatz for the field modulus we find a family of analytical expressions, phase walls, that accounts for both geodesic and nongeodesic configurations. We then show how the latter ones are unstable and decay into the former by nucleating pairs of defects. Finnally, we try to give a physical perspective of how the geodesic rule might really work in these transitions.Comment: 10 pages, 9 multiple figre

Oscilación de perfiles de luminosidad y contracción de esferas radiantes en relatividad general

Para estudiar la evolución de esferas radiantes en relatividad general cuando es impuesto un específico esquema de contracción y un particular perfil oscilatorio de radiación, se utiliza un método numérico ideado por Herrera, Jiménez y Ruggeri. Se consideran y estudian tres casos particulares: el del límite estático de una solución homogénea del Schwarzschild , que representa un fluido incomprensible de densidad constante ; la ecuaciones de estado para una solución estática de Toldman VI, cercana a un gas de Fermi altamente relativista; y finalmente la solución de Toldman V , donde la relación P/ρ ~ 1/3 es mantenida durante la contracción al centro de la distribución. Se encuentra que la frecuencia de pulsación coincide con la correspondiente oscilación de la superficie de una estrella de neutrones.Asociación Argentina de Astronomí