87 research outputs found
A Built-in Inflation in the -Cosmology
In the present work we derive an exact solution of an isotropic and
homogeneous Universe governed by gravity. We show how the torsion
contribution to the FRW cosmology can provide a \textit{unique} origin for both
early and late acceleration phases of the Universe. The three models () show a \textit{built-in} inflationary behavior at some early Universe time;
they restore suitable conditions for the hot big bang nucleosynthesis to begin.
Unlike the standard cosmology, we show that even if the Universe initially
started with positive or negative sectional curvatures, the curvature density
parameter enforces evolution to a flat Universe. The solution constrains the
torsion scalar to be a constant function at all time , for the three
models. This eliminates the need for the dark energy (DE). Moreover, when the
continuity equation is assumed for the torsion fluid, we show that the flat and
closed Universe models \textit{violate} the conservation principle, while the
open one does not. The evolution of the effective equation of state (EoS) of
the torsion fluid implies a peculiar trace from a quintessence-like DE to a
phantom-like one crossing a matter and radiation EoS in between; then it
asymptotically approaches a de Sitter fate.Comment: LaTeX2e: 19 pages, 9 figures, 1 table. Version 4 Published versio
The Hidden Flat Like Universe: Starobinsky-like inflation induced by f(T) gravity
We study a single fluid component in a flat like universe (FLU) governed by
gravity theories, where is the teleparallel torsion scalar. The FLU
model, regardless the value of the spatial curvature , identifies a special
class of gravity theories. Remarkably, the FLU gravity does not
reduce to teleparallel gravity theory. In large Hubble spacetime the theory is
consistent with the inflationary universe scenario and respects the
conservation principle. The equation of state (EoS) evolves similarly in all
models . We study the case when the torsion tensor is made of a
scalar field, which enables to derive a quintessence potential from the
obtained gravity theory. The potential produces Starobinsky-like model
naturally without using a conformal transformation, with higher orders
continuously interpolate between Starobinsky and quadratic inflation models.
The slow-roll analysis shows double solutions so that for a single value of the
scalar tilt (spectral index) the theory can predict double
tensor-to-scalar ratios of -mode and -mode polarizations.Comment: LaTeX2e, 14 pages, 10 figures. Title modified, Major revision,
References updated. To be appeared in EPJ
Rotating charged AdS solutions in quadratic gravity
We present a class of asymptotically anti-de Sitter charged rotating black
hole solutions in gravity in -dimensions, where . These solutions are nontrivial extensions of the solutions presented in
\cite{Lemos:1994xp} and \cite{Awad:2002cz} in the context of general
relativity. They are characterized by cylindrical, toroidal or flat horizons,
depending on global identifications. The static charged black hole
configurations obtained in \cite{Awad:2017tyz} are recovered as special cases
when the rotation parameters vanish. Similar to \cite{Awad:2017tyz} the static
black holes solutions have two different electric multipole terms in the
potential with related moments. Furthermore, these solutions have milder
singularities compared to their general relativity counterparts. Using the
conserved charges expressions obtained in \cite{Ulhoa:2013gca} and
\cite{Maluf:2008ug} we calculate the total mass/energy and the angular momentum
of these solutions.Comment: 11 pages, Version accepted in EPJ
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