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The dilaton field in string theories (if exists) is expected to have a mass of the order of the gravitino mass $m_{3/2}$ which is in a range of $10^{-2}$keV--1GeV in gauge-mediated supersymmetry breaking models. If it is the case, the…
Recently, a new framework for solving the hierarchy problem has been proposed which does not rely on low energy supersymmetry or technicolor. The gravitational and gauge interactions unite at the electroweak scale, and the observed weakness…
We investigate the cosmological consequences of particle physics theories that admit stable loops of superconducting cosmic string - {\it vortons}. General symmetry breaking schemes are considered, in which strings are formed at one energy…
The strong coupling dynamics of string theories in dimension $d\geq 4$ are studied. It is argued, among other things, that eleven-dimensional supergravity arises as a low energy limit of the ten-dimensional Type IIA superstring, and that a…
We motivate a relation between dark energy and the scale of new physics in weakly coupled string theory. This mixing between infrared and ultraviolet physics leads to a unique corner for real-world phenomenology: barring fine-tunings, we…
Recently it has been shown that string gas cosmology, an alternative model of the very early universe which does not involve a period of cosmological inflation, can give rise to an almost scale invariant spectrum of metric perturbations.…
In string theory, the traditional picture of a Universe that emerges from the inflation of a very small and highly curved space-time patch is a possibility, not a necessity: quite different initial conditions are possible, and not…
We discuss fits of unconventional dark energy models to the available data from high-redshift supernovae, distant galaxies and baryon oscillations. The models are based either on brane cosmologies or on Liouville strings in which a…
We consider a conformal system of a string and a particle defined in D=10+2 space-time dimensions. The extra time-like dimension is a gauge artifact and can be eliminated by choosing a gauge in which the SO(10,1) Lorentz symmetry is…
It has long been known that strings wound around incontractible cycles can play a vital role in cosmology. In particular, in a spacetime with toroidal spatial hypersurfaces, the dynamics of the winding modes may help yield three large…
Cosmic strings are linear concentrations of energy that form whenever phase transitions in the early universe break axial symmetries as originally shown by Kibble. They are the result of frustrated order in the quantum fields responsible…
The main idea in the present work is the definition of an experimental proposal for the detection of the number of extra{compact dimensions contained as a core feature in String Theory. This goal will be achieved as a consequence of the…
This is a short review on strings in curved spacetimes. We start by recalling the classical and quantum string behaviour in singular plane waves backgrounds. We then report on the string behaviour in cosmological spacetimes (FRW, de Sitter,…
A solution of the vortex type is given in a six-dimensional $SU(2)\times U(1)$ pure gauge theory coupled to Einstein gravity in a compactified background geometry. We construct the solution of an effective abelian Higgs model in terms of…
Many symmetry breaking patterns in grand unified theories (GUTs) give rise to cosmic strings that eventually decay when pairs of GUT monopoles spontaneously nucleate along the string cores. These strings are known as metastable cosmic…
Cosmic strings are predicted by many field-theory models, and may have been formed at a symmetry-breaking transition early in the history of the universe, such as that associated with grand unification. They could have important…
This investigation is concerned with cosmological scenarios based on particle physics theories that give rise to superconducting cosmic strings (whose subsequent evolution may produce stable loop configurations known as vortons). Cases in…
We explore the kinematical effect of having extra dimensions on the gravity wave emission from cosmic strings. Additional dimensions both round off cusps, and reduce the probability of their formation. We recompute the gravity wave burst,…
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…
We discuss the generation and evolution of density perturbations during the large curvature phase of string cosmology. We find that perturbations in the scalar components of the metric evolve with cosmic time as $\exp (\gamma H_st)$ where…