On the variable-charged black holes embedded into de Sitter space: Hawking's radiation

In this paper we study the Hawking evaporation of masses of variable-charged Reissner-Nordstrom and Kerr-Newman, black holes embedded into the de Sitter universe by considering the charge to be function of radial coordinate of the spherically symmetric metric.Comment: LaTex, p. 2

Unification without supersymmetry: neutrino mass, proton decay and light leptoquarks

We investigate predictions of a minimal realistic non-supersymmetric SU(5) grand unified theory. To accomplish unification and generate neutrino mass we introduce one extra Higgs representation--a 15 of SU(5)--to the particle content of the minimal Georgi-Glashow scenario. Generic prediction of this setup is a set of rather light scalar leptoquarks. In the case of the most natural implementation of the type II see-saw mechanism their mass is in the phenomenologically interesting region (O(10^2--10^3) GeV). As such, our scenario has a potential to be tested at the next generation of collider experiments, particularly at the Large Hadron Collider (LHC) at CERN. The presence of the 15 generates additional contributions to proton decay which, for light scalar leptoquarks, can be more important than the usual gauge d=6 ones. We exhaustively study both and show that the scenario is not excluded by current experimental bounds on nucleon lifetimes.Comment: 29 pages, 8 figure

Planary Symmetric Static Worlds with Massless Scalar Sources

Motivated by the recent wave of investigations on plane domain wall spacetimes with nontrivial topologies, the present paper deals with (probably) the most simple source field configuration which can generate a spatially planary symmetric static spacetime, namely a minimally coupled massless scalar field that depends only upon a spacelike coordinate, $z$. It is shown that the corresponding exact solutions $({\cal M}, {\bf{\rm g}}_{\pm})$ are algebraically special, type $D - [S - 3T]_{(11)}$, and represent globally pathologic spacetimes with a $G_{4}$ - group of motion acting on ${\bf{\rm R}}^{2} \times {\bf{\rm R}}$ orbits. In spite of the model simplicity, these $\phi$ - generated worlds possess naked timelike singularities (reached within a finite universal time by normal non-spacelike geodesics), are completely free of Cauchy surfaces and contain into the $t$ - leveled sections points which can not be jointed by ${\rm C}^{1}$ - trajectories images of oblique non-spacelike geodesics. Finally, we comment on the possibility of deriving from $({\cal M}, {\bf{\rm g}}_{\pm})$ two other physically interesting ^^ ^^ $\phi$ - generated'' spacetimes, by appropiate jonction conditions in the $(z = 0)$ - plane.Comment: 14 pages, LaTeX format, figures not include

Rotating metrics admitting non-perfect fluids in General Relativity

In this paper, by applying Newman-Janis algorithm in spherical symmetric metrics, a class of embedded rotating solutions of field equations is presented. These solutions admit non-perfect fluidsComment: LaTex, 39 page

Geometrodynamics of Variable-Speed-of-Light Cosmologies

This paper is dedicated to the memory of Dennis Sciama. Variable-Speed-of-Light (VSL) cosmologies are currently attracting interest as an alternative to inflation. We investigate the fundamental geometrodynamic aspects of VSL cosmologies and provide several implementations which do not explicitly break Lorentz invariance (no "hard" breaking). These "soft" implementations of Lorentz symmetry breaking provide particularly clean answers to the question "VSL with respect to what?". The class of VSL cosmologies we consider are compatible with both classical Einstein gravity and low-energy particle physics. These models solve the "kinematic" puzzles of cosmology as well as inflation does, but cannot by themselves solve the flatness problem, since in their purest form no violation of the strong energy condition occurs. We also consider a heterotic model (VSL plus inflation) which provides a number of observational implications for the low-redshift universe if chi contributes to the "dark energy" either as CDM or quintessence. These implications include modified gravitational lensing, birefringence, variation of fundamental constants and rotation of the plane of polarization of light from distant sources.Comment: 19 pages, latex 209, revtex 3.1; To appear in Physical Review D; Numerous small changes of presentation and emphasis; new section on the entropy problem; references updated; central results unaffecte

G1 Cosmologies with Gravitational and Scalar Waves

I present here a new algorithm to generate families of inhomogeneous massless scalar field cosmologies. New spacetimes, having a single isometry, are generated by breaking the homogeneity of massless scalar field $G_2$ models along one direction. As an illustration of the technique I construct cosmological models which in their late time limit represent perturbations in the form of gravitational and scalar waves propagating on a non-static inhomogeneous background. Several features of the obtained metrics are discussed, such as their early and late time limits, structure of singularities and physical interpretation.Comment: 24 pages, 2 figure

Singularity free dilaton-driven cosmologies and pre-little-bang

There are no reasons why the singularity in the growth of the dilaton coupling should not be regularised, in a string cosmological context, by the presence of classical inhomogeneities. We discuss a class of inhomogeneous dilaton-driven models whose curvature invariants are all bounded and regular in time and space. We prove that the non-space-like geodesics of these models are all complete in the sense that none of them reaches infinity for a finite value of the affine parameter. We conclude that our examples represent truly singularity-free solutions of the low energy beta functions. We discuss some symmetries of the obtained solutions and we clarify their physical interpretation. We also give examples of solutions with spherical symmetry. In our scenario each physical quantity is everywhere defined in time and space, the big-bang singularity is replaced by a maximal curvature phase where the dilaton kinetic energy reaches its maximum. The maximal curvature is always smaller than one (in string units) and the coupling constant is also smaller than one and it grows between two regimes of constant dilaton, implying, together with the symmetries of the solutions, that higher genus and higher curvature corrections are negligible. We argue that our examples describe, in a string cosmological context, the occurrence of ``little bangs''(i.e. high curvature phases which never develop physical singularities). They also suggest the possibility of an unexplored ``pre-little-bang'' phase.Comment: 25 pages in LaTex style, 3 encapsulated figure

Towards a New Proof of Anderson Localization

The wave function of a non-relativistic particle in a periodic potential admits oscillatory solutions, the Bloch waves. In the presence of a random noise contribution to the potential the wave function is localized. We outline a new proof of this Anderson localization phenomenon in one spatial dimension, extending the classical result to the case of a periodic background potential. The proof makes use of techniques previously developed to study the effects of noise on reheating in inflationary cosmology, employing methods of random matrix theory

Effects of anisotropy and spatial curvature on the pre-big bang scenario

A class of exact, anisotropic cosmological solutions to the vacuum Brans-Dicke theory of gravity is considered within the context of the pre-big bang scenario. Included in this class are the Bianchi type III, V and VI_h models and the spatially isotropic, negatively curved Friedmann-Robertson-Walker universe. The effects of large anisotropy and spatial curvature are determined. In contrast to negatively curved Friedmann-Robertson-Walker model, there exist regions of the parameter space in which the combined effects of curvature and anisotropy prevent the occurrence of inflation. When inflation is possible, the necessary and sufficient conditions for successful pre-big bang inflation are more stringent than in the isotropic models. The initial state for these models is established and corresponds in general to a gravitational plane wave.Comment: 15 pages, including 2 eps figure

Superstring Cosmology

Aspects of superstring cosmology are reviewed with an emphasis on the cosmological implications of duality symmetries in the theory. The string effective actions are summarized and toroidal compactification to four dimensions reviewed. Global symmetries that arise in the compactification are discussed and the duality relationships between the string effective actions are then highlighted. Higher-dimensional Kasner cosmologies are presented and interpreted in both string and Einstein frames, and then given in dimensionally reduced forms. String cosmologies containing both non-trivial Neveu-Schwarz/Neveu-Schwarz and Ramond-Ramond fields are derived by employing the global symmetries of the effective actions. Anisotropic and inhomogeneous cosmologies in four-dimensions are also developed. The review concludes with a detailed analysis of the pre-big bang inflationary scenario. The generation of primordial spectra of cosmological perturbations in such a scenario is discussed. Possible future directions offered in the Horava-Witten theory are outlined.Comment: 161 pages, latex with epsf, 15 figures. Minor changes, additional references and figures. Version to appear in Physics Report