607 research outputs found
Black Holes, Cosmological Solutions, Future Singularities, and Their Thermodynamical Properties in Modified Gravity Theories
Along this review, we focus on the study of several properties of modified gravity theories, in particular on black-hole solutions and its comparison with those solutions in General Relativity, and on Friedmann-Lemaitre-Robertson-Walker metrics. The thermodynamical properties of fourth order gravity theories are also a subject of this investigation with special attention on local and global stability of paradigmatic f(R) models. In addition, we revise some attempts to extend the Cardy-Verlinde formula, including modified gravity, where a relation between entropy bounds is obtained. Moreover, a deep study on cosmological singularities, which appear as a real possibility for some kind of modified gravity theories, is performed, and the validity of the entropy bounds is studied
Charged Black Hole Solutions in Gauss-Bonnet-Massive Gravity
Motivated by high interest in the close relation between string theory and
black hole solutions, in this paper, we take into account the
Einstein-Gauss-Bonnet Lagrangian in the context of massive gravity. We examine
the possibility of black hole in this regard, and discuss the types of
horizons. Next, we calculate conserved and thermodynamic quantities and check
the validity of the first law of thermodynamics. In addition, we investigate
the stability of these black holes in context of canonical ensemble. We show
that number, type and place of phase transition points may be significantly
affected by different parameters. Next, by considering cosmological constant as
thermodynamical pressure, we will extend phase space and calculate critical
values. Then, we construct thermodynamical spacetime by considering mass as
thermodynamical potential. We study geometrical thermodynamics of these black
holes in context of heat capacity and extended phase space. We show that
studying heat capacity, geometrical thermodynamics and critical behavior in
extended phase space lead to consistent results. Finally, we will employ a new
method for obtaining critical values and show that the results of this method
are consistent with those of other methods.Comment: Revised version: 22 pages, 18 figure
Simple generalizations of Anti-de Sitter space-time
We consider new cosmological solutions which generalize the cosmological
patch of the Anti-de Sitter (AdS) space-time, allowing for fluids with
equations of state such that . We use them to derive the associated
full manifolds. We find that these solutions can all be embedded in flat
five-dimensional space-time with signature, revealing deformed
hyperboloids. The topology and causal-structure of these spaces is therefore
unchanged, and closed time-like curves are identified, before a covering space
is considered. However the structure of Killing vector fields is entirely
different and so we may expect a different structure of Killing horizons in
these solutions.Comment: 6 Pages, 5 Figures, Corrections and additions made for publication in
Journal of Classical and Quantum Gravit
Bumpy black holes from spontaneous Lorentz violation
We consider black holes in Lorentz violating theories of massive gravity. We
argue that in these theories black hole solutions are no longer universal and
exhibit a large number of hairs. If they exist, these hairs probe the
singularity inside the black hole providing a window into quantum gravity. The
existence of these hairs can be tested by future gravitational wave
observatories. We generically expect that the effects we discuss will be larger
for the more massive black holes. In the simplest models the strength of the
hairs is controlled by the same parameter that sets the mass of the graviton
(tensor modes). Then the upper limit on this mass coming from the inferred
gravitational radiation emitted by binary pulsars implies that hairs are likely
to be suppressed for almost the entire mass range of the super-massive black
holes in the centers of galaxies.Comment: 40 pages, 4 figure
Black Holes in de Sitter Space: Masses, Energies and Entropy Bounds
In this paper we consider spacetimes in vacuum general relativity --possibly
coupled to a scalar field-- with a positive cosmological constant . We
employ the Isolated Horizons (IH) formalism where the boundary conditions
imposed are that of two horizons, one of black hole type and the other, serving
as outer boundary, a cosmological horizon. As particular cases, we consider the
Schwarzschild-de Sitter spacetime, in both 2+1 and 3+1 dimensions. Within the
IH formalism, it is useful to define two different notions of energy for the
cosmological horizon, namely, the "mass" and the "energy". Empty de Sitter
space provides an striking example of such distinction: its horizon energy is
zero but the horizon mass takes a finite value given by .
For both horizons we study their thermodynamic properties, compare our results
with those of Euclidean Hamiltonian methods and construct some generalized
Bekenstein entropy bounds. We discuss these new entropy bounds and compare them
with some recently proposed entropy bounds in the cosmological setting.Comment: 28 pages, 8 figures, revtex4. References added. Version to appear in
PR
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