It is pointed out that various types of cosmic string solutions that exist in nonsupersymmetric and globally supersymmetric theories, such as D-type gauge strings, F-type global and gauge strings, and superconducting Witten strings, also exist in supergravity models. When the D term and superpotential satisfy some simple conditions allowing the determination of a set of vacuum states with nontr...

We study the connection between N = 2 supersymmetry and a topological bound in a two-Higgs-doublet system with an SU(2)×U(1)Y ×U(1)Y ′ gauge group. We derive the Bogomol’nyi equations from supersymmetry considerations showing that they hold provided certain conditions on the coupling constants, which are a consequence of the huge symmetry of the theory, are satisfied. Their solutions, which can...

We construct regular multi-wormhole solutions to a gravitating σ model in three space-time dimensions, and extend these solutions to cylindrical traversable wormholes in four and five dimensions. We then discuss the possibility of identifying wormhole mouths in pairs to give rise to Wheeler wormholes. Such an identification is consistent with the original field equations only in the absence of ...

We show that it is possible to build up a consistent model describing a superconducting cosmic string (SCS) endowed with torsion. A full string solution is obtained by matching the internal and the external solutions. We derive the deficit angle, the geodesics of and the gravitational force on a test-particle moving under the action of this screwed SCS. A couple of potentially observable astrop...

Cosmic strings provide a radically different paradigm for the formation of structure to the prevailing inflationary one. They afford some extra technical complications: for example, the calculation of the power spectrum of matter and radiation perturbations requires the knowledge of the history of the evolution of the defects in the form of two-time correlation functions. We describe some numer...

We investigate the effect of an infinite cosmic string on a cosmological background. We find that the metric is approximately a scaled version of the empty space string metric, i.e. conical in nature. We use our results to place bounds on the amount of cylindrical gravitational radiation currently emitted by such a string. We then analyse explicitly the gravitational radiation equations and sho...

A gravitational scenario is proposed where the euclidean action is invariant under the isotropic and homogeneous version of the euclidean U(1) group of local transformations of the scale factor and scalar matter field, interpreting the trace of the second fundamental form as the gauge field. The model allows spontaneous breakdown of some involved symmetries, including possibly diffeomorphism in...

Cosmis strings are the most promising among the cosmological defects. They also constitute earliest possible observable strings, therefore prove vital for string theorists. Here I review different kinds of cosmological defects, then focus on the cosmic strings. I give a short theoretical derivation first and then discuss experimental efforts to detect them.

Macroscopic fundamental and Dirichlet strings have several potential instabilities: breakage, tachyon decays, and confinement by axion domain walls. We investigate the conditions under which metastable strings can exist, and we find that such strings are present in many models. There are various possibilities, the most notable being a network of (p, q) strings. Cosmic strings give a potentially...

Assuming that refractory elements in cosmic rays originate in dust grains, we examine the viability of cosmic ray origin models wherein the bulk of present day cosmic rays are accelerated out of fresh supernova ejecta material before it mixes with the average interstellar medium (ISM). We conclude that the fresh ejecta scenarios that have been proposed thus far have serious flaws, and are unabl...