Second Order General Slow-Roll Power Spectrum

Recent combined results from the Wilkinson Microwave Anisotropy Probe (WMAP) and Sloan Digital Sky Survey (SDSS) provide a remarkable set of data which requires more accurate and general investigation. Here we derive formulae for the power spectrum P(k) of the density perturbations produced during inflation in the general slow-roll approximation with second order corrections. Also, using the result, we derive the power spectrum in the standard slow-roll picture with previously unknown third order corrections.Comment: 11 pages, 1 figure ; A typo in Eq. (38) is fixed ; References expanded and a note adde

Regular black holes with flux tube core

We consider a class of black holes for which the area of the two-dimensional spatial cross-section has a minimum on the horizon with respect to a quasiglobal (Krusckal-like) coordinate. If the horizon is regular, one can generate a tubelike counterpart of such a metric and smoothly glue it to a black hole region. The resulting composite space-time is globally regular, so all potential singuilarities under the horizon of the original metrics are removed. Such a space-time represents a black hole without an apparent horizon. It is essential that the matter should be non-vacuum in the outer region but vacuumlike in the inner one. As an example we consider the noninteracting mixture of vacuum fluid and matter with a linear equation of state and scalar phantom fields. This approach is extended to distorted metrics, with the requirement of spherical symmetry relaxed.Comment: 15 pages. 2 references adde

Regular black holes in an asymptotically de Sitter universe

A regular solution of the system of coupled equations of the nonlinear electrodynamics and gravity describing static and spherically-symmetric black holes in an asymptotically de Sitter universe is constructed and analyzed. Special emphasis is put on the degenerate configurations (when at least two horizons coincide) and their near horizon geometry. It is explicitly demonstrated that approximating the metric potentials in the region between the horizons by simple functions and making use of a limiting procedure one obtains the solutions constructed from maximally symmetric subspaces with different absolute values of radii. Topologically they are $AdS_{2}\times S^{2}$ for the cold black hole, $dS_{2}\times S^{2}$ when the event and cosmological horizon coincide, and the Pleba\'nski- Hacyan solution for the ultraextremal black hole. A physically interesting solution describing the lukewarm black holes is briefly analyze

No-go theorem for false vacuum black holes

We study the possibility of non-singular black hole solutions in the theory of general relativity coupled to a non-linear scalar field with a positive potential possessing two minima: a `false vacuum' with positive energy and a `true vacuum' with zero energy. Assuming that the scalar field starts at the false vacuum at the origin and comes to the true vacuum at spatial infinity, we prove a no-go theorem by extending a no-hair theorem to the black hole interior: no smooth solutions exist which interpolate between the local de Sitter solution near the origin and the asymptotic Schwarzschild solution through a regular event horizon or several horizons.Comment: 16 pages, 1 figure, Latex, some references added, to appear in Classical and Quantum Gravit

The Origin of Structures in Generalized Gravity

In a class of generalized gravity theories with general couplings between the scalar field and the scalar curvature in the Lagrangian, we can describe the quantum generation and the classical evolution of both the scalar and tensor structures in a simple and unified manner. An accelerated expansion phase based on the generalized gravity in the early universe drives microscopic quantum fluctuations inside a causal domain to expand into macroscopic ripples in the spacetime metric on scales larger than the local horizon. Following their generation from quantum fluctuations, the ripples in the metric spend a long period outside the causal domain. During this phase their evolution is characterized by their conserved amplitudes. The evolution of these fluctuations may lead to the observed large scale structures of the universe and anisotropies in the cosmic microwave background radiation.Comment: 5 pages, latex, no figur

Anisotropic dark energy stars

A model of compact object coupled to inhomogeneous anisotropic dark energy is studied. It is assumed a variable dark energy that suffers a phase transition at a critical density. The anisotropic Lambda-Tolman-Oppenheimer-Volkoff equations are integrated to know the structure of these objects. The anisotropy is concentrated on a thin shell where the phase transition takes place, while the rest of the star remains isotropic. The family of solutions obtained depends on the coupling parameter between the dark energy and the fermion matter. The solutions share several features in common with the gravastar model. There is a critical coupling parameter that gives non-singular black hole solutions. The mass-radius relations are studied as well as the internal structure of the compact objects. The hydrodynamic stability of the models is analyzed using a standard test from the mass-radius relation. For each permissible value of the coupling parameter there is a maximum mass, so the existence of black holes is unavoidable within this model.Comment: 12 pages, 6 figures, final manuscript, Accepted for publication in Astrophysics & Space Scienc

Spherically symmetric false vacuum: no-go theorems and global structure

We enumerate all possible types of spacetime causal structures that can appear in static, spherically symmetric configurations of a self-gravitating, real, nonlinear, minimally coupled scalar field \phi in general relativity, with an arbitrary potential V(\phi), not necessarily positive-definite. It is shown that a variable scalar field adds nothing to the list of possible structures with a constant \phi field, namely, Minkowski (or AdS), Schwarzschild, de Sitter and Schwarzschild - de Sitter. It follows, in particular, that, whatever is V(\phi), this theory does not admit regular black holes with flat or AdS asymptotics. It is concluded that the only possible globally regular, asymptotically flat solutions are solitons with a regular center, without horizons and with at least partly negative potentials V(\phi). Extension of the results to more general field models is discussed.Comment: Latex2e, 4 pages, 1 bezier figur

Cosmological term as a source of mass

In the spherically symmetric case the dominant energy condition together with the requirements of regularity at the center, asymptotic flatness and fineteness of the ADM mass, defines the family of asymptotically flat globally regular solutions to the Einstein minimally coupled equations which includes the class of metrics asymptotically de Sitter at approaching the regular center. The source term corresponds to an r-dependent cosmological term given by the second rank symmetric tensor invariant under boosts in the radial direction and evolving from de Sitter vacuum in the origin to Minkowski vacuum at infinity. Space-time symmetry changes smoothly from the de Sitter group at the center to the Lorentz group at infinity through the radial boosts in between. The standard formula for the ADM mass relates it to the de Sitter vacuum replacing a central singularity at the scale of symmetry restoration. For masses exceeding a certain critical value m_{crit} de Sitter-Schwarzschild geometry describes a vacuum nonsingular black hole, while beyond m_{crit} it describes a G-lump which is a vacuum selfgravitating particlelike structure without horizons. Quantum energy spectrum of G-lump is shifted down by the binding energy, and zero-point vacuum mode is fixed at the value corresponding to the Hawking temperature from the de Sitter horizon.Comment: 8 pages, revtex, 8 figures incorporated, to appear in Classical and Quantum Gravit

Inflationary models with a flat potential enforced by non-abelian discrete gauge symmetries

Non-abelian discrete gauge symmetries can provide the inflaton with a flat potential even when one takes into account gravitational strength effects. The discreteness of the symmetries also provide special field values where inflation can end via a hybrid type mechanism. An interesting feature of this method is that it can naturally lead to extremely flat potentials and so, in principle, to inflation at unusually low energy scales. Two examples of effective field theories with this mechanism are given, one with a hybrid exit and one with a mutated hybrid exit. They include an explicit example in which the single field consistency condition is violated.Comment: 24 pages, uses revtex.sty, submitted to PRD (Nov. 1999) Final version to appear in PRD. Background information on supergravity expande

Extremal limit of the regular charged black holes in nonlinear electrodynamics

The near horizon limit of the extreme nonlinear black hole is investigated. It is shown that resulting geometry belongs to the AdS2xS2 class with different modules of curvatures of subspaces and could be described in terms of the Lambert functions. It is demonstrated that the considered class of Lagrangians does not admit solutions of the Bertotti-Robinson type