Vacuumless topological defects in Lyra geometry

Few years ago, Cho and Vilenkin have proposed that topological defects can arise in symmetry breaking models without having degenerate vacua. These types of defects are known as vacuumless defects. In the present work, the gravitational field of a vacuumless global string and global monopole have been investigated in the context of Lyra geometry. We find the metric of the vacuumless global string and global monopole in the weak field approximations. It has been shown that the vacuumless global string can have repulsive whereas global monopole exerts attractive gravitational effects on a test particle. It is dissimilar to the case studied in general relativity.Comment: 14 pages, 9 figures. To appear in Astrophys.Space.Sc

Thin-shell wormholes from charged black holes in generalized dilaton-axion gravity

This paper discusses a new type of thin-shell wormhole constructed by applying the cut-and-paste technique to two copies of a charged black hole in generalized dilaton-axion gravity, which was inspired by low-energy string theory. After analyzing various aspects of this thin-shell wormhole, we discuss its stability to linearized spherically symmetric perturbations.Comment: Minor changes, 6 pages, 4 figures. Accepted for publication in Gen. Rel. Gra

Construction of 3D wormhole supported by phantom energy

In this article, we have found a series solution of 3D Einstein equations describing a wormhole for an inhomogeneous distribution of phantom energy. Here, we assume equation of state is linear but highly anistropic.Comment: 9 papge, 4 figures. Accepted for publication in Physica Script

Human-centred identity - from rhetoric to reality

This paper presents a proposal for human-centred identity management. Even though the term ‘human-centred identity’ has been widely used in the past few years, the solutions either descritbe a technical system for managing identity, or describe an identity management solution that meets a particular administrative need. Our proposal, however, presents a set of propertis that have to be considered, and the choices have to be made for each property must satisfy the needs of both the individual and the organization that owns the identity management system. The properties were identified as a result of reviewing a range of national identity systems, and the problems that arise from them

The (2+1)-dimensional gravastars

We propose a new model of a gravastar in (2+1) anti-de Sitter space-time. This new three dimensional configuration has three different regions with different equations of state: [I] Interior: 0 \leq r < r_1, \rho = -p ; [II] Shell: r_1 \leq r < r_2, \rho = p; [III] Exterior: r_2 < r, \rho = p =0. The outer region of this gravastar corresponds to the exterior (2+1) anti-de Sitter space-time, popularly known as the BTZ space-time. Like BTZ model, \Lambda is taken to be negative, which at the junction turns out to be positive as required by stability of gravastar and mathematical consistency. After investigating the Interior space-time, Shell and Exterior space-time we have highlighted different physical features in terms of Length and Energy, Entropy, and Junction conditions of the spherical distribution. It is shown that the present model of charge-free gravastar in connection to the exterior (2+1) anti-de Sitter space-time or the BTZ space-time is stable and non-singular.Comment: 9 Latex pages with minor addition, Accepeted in PL

Thin Domain Walls in Lyra Geometry

This paper studies thin domain walls within the frame work of Lyra Geometry. We have considered two models. First one is the thin domain wall with negligible pressures perpendicular and transverse direction to the wall and secondly, we take a particular type of thin domain wall where the pressure in the perpendicular direction is negligible but transverse pressures are existed. It is shown that the thin domain walls have no particle horizon and the gravitational force due to them is attractive.Comment: 8 pages, typos are corrected, published Astrophysics and Space Sciences 305, 337 (2006