scholarly journals Thermodynamical correspondence of f(R) gravity in the Jordan and Einstein frames

2020 ◽  
Vol 29 (13) ◽  
pp. 2050090 ◽  
Author(s):  
G. G. L. Nashed ◽  
W. El Hanafy ◽  
S. D. Odintsov ◽  
V. K. Oikonomou
Keyword(s):  
Scalar Curvature ◽  
Spherically Symmetric ◽  
Conformal Invariant ◽  
Tensor Theory ◽  
Quantitative Level ◽  
Cosmological Solutions ◽  
Symmetric Black Hole ◽  
Jordan And Einstein Frames ◽  
Physical Quantities ◽  
Black Hole Solutions

We study the thermodynamical aspects of [Formula: see text] gravity in the Jordan and the Einstein frame, and we investigate the corresponding equivalence of the thermodynamical quantities in the two frames. We examine static spherically symmetric black hole solutions with constant Ricci scalar curvature [Formula: see text], and as we demonstrate, the thermodynamical quantities in the two frames are equivalent. However, for the case of black holes with nonconstant scalar curvature [Formula: see text], the thermodynamical equivalence of the two frames is no longer valid. In addition, we extend our study to investigate cosmological solutions with a homogeneous and isotropic background. In particular, we find that the power-law cosmology case provides an accidentally thermodynamical equivalence of the two frames. However, for nontrivial cosmology, we examine a novel exponential ultraviolet [Formula: see text] gravity. This confirms that the thermodynamical quantities in both frames are not equivalent. In conclusion, although [Formula: see text] gravity and its corresponding scalar-tensor theory are mathematically equivalent, at least for conformal invariant quantities, the two frames are not thermodynamically equivalent at a quantitative level, in terms of several physical quantities.

Spherically symmetric black hole solution in mimetic gravity and anti-evaporation

2018 ◽  
Vol 15 (09) ◽  
pp. 1850154 ◽  
Author(s):  
G. G. L. Nashed
Keyword(s):  
Black Hole ◽  
Black Hole Solution ◽  
Spherically Symmetric ◽  
Mimetic Theory ◽  
Event Horizons ◽  
Flat Spacetime ◽  
Symmetric Black Hole ◽  
The Stability ◽  
Mimetic Gravity ◽  
Black Hole Solutions

In this paper, we study the mimetic theory and derive a new spherically symmetric black hole solution. The asymptotic behavior of this solution behaves as a flat spacetime. This black hole is characterized by the fact that it has different components of [Formula: see text] and [Formula: see text]. Nevertheless, both of these components have a coinciding Killing and event horizons. Furthermore, this black hole has curvature singularities which are stronger than those of the known black hole solutions in general relativity. This feature can be shown by calculating some invariants of curvature. We study the stability of the perturbation and the related anti-evaporation of the Nariai spacetime.

scholarly journals Black hole thermodynamics and heat engines in conformal gravity

2017 ◽  
Vol 26 (13) ◽  
pp. 1750151 ◽  
Author(s):  
Hao Xu ◽  
Yuan Sun ◽  
Liu Zhao
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Black Hole Thermodynamics ◽  
Spherically Symmetric ◽  
Conformal Gravity ◽  
Extended Phase ◽  
Heat Engines ◽  
Equation Of States ◽  
Symmetric Black Hole ◽  
Black Hole Solutions

The extended phase-space thermodynamics and heat engines for static spherically symmetric black hole solutions of four-dimensional conformal gravity are studied in detail. It is argued that the equation of states (EOS) for such black holes is always branched, any continuous thermodynamical process cannot drive the system from one branch of the EOS into another branch. Meanwhile, the thermodynamical volume is bounded from above, making the black holes always super-entropic in one branch and may also be super-entropic in another branch in certain range of the temperature. The Carnot and Stirling heat engines associated to such black holes are shown to be distinct from each other. For rectangular heat engines, the efficiency always approaches zero when the rectangle becomes extremely narrow, and given the highest and lowest working temperatures fixed, there is always a maximum for the efficiency of such engines.

Thermodynamics of apparent horizons under conformal and Kerr–Schild maps

2015 ◽  
Vol 93 (9) ◽  
pp. 963-965
Author(s):  
Valerio Faraoni ◽  
Vincenzo Vitagliano
Keyword(s):  
Black Hole ◽  
Internal Energy ◽  
Spherically Symmetric ◽  
Apparent Horizons ◽  
Symmetric Black Hole ◽  
Black Hole Solutions

We derive the transformation properties of the internal energy and Kodama temperature of dynamical (spherically symmetric) black hole solutions generated through spacetime mappings. We use the Sultana-Dyer black hole and the Reissner–Nordström solution to provide prototypical examples testing our transformation formulae.

scholarly journals Peculiar five-dimensional black holes

2019 ◽  
Vol 17 (1, spec.issue) ◽  
pp. 69-78
Author(s):  
Dejan Simic
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Semiclassical Approximation ◽  
Three Dimensions ◽  
Spherically Symmetric ◽  
Btz Black Hole ◽  
Lovelock Gravity ◽  
Zero Entropy ◽  
Symmetric Black Hole ◽  
Black Hole Solutions

In this article, we review two black hole solutions to the five-dimensional Lovelock gravity. These solutions are characterized by the non-vanishing torsion and the peculiar property that all their conserved charges vanish. The first solution is a spherically symmetric black hole with torsion, which also has zero entropy in the semiclassical approximation. The second solution is a black ring, which is the five-dimensional uplift of the BTZ black hole with torsion in three dimensions.

scholarly journals Thermodynamics of spherically symmetric black holes in scale-dependent gravity

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
P. Bargueño ◽  
J. A. Miralles ◽  
J. A. Pons
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Spatial Variation ◽  
Gravitational Constant ◽  
Spherically Symmetric ◽  
Equilibrium Thermodynamics ◽  
First Law Of Thermodynamics ◽  
Symmetric Black Hole ◽  
Black Hole Solutions

AbstractIn this work we extend the first law of thermodynamics to spherically symmetric black hole solutions in the context of scale-dependent gravity. After deriving generalized expressions for both the entropy and energy due to the spatial variation of the gravitational constant we analize, by pointing out some relations between scale-dependent and f(R) theories, whether or not the former can be described using equilibrium thermodynamics.

scholarly journals Black Holes with Short Hair

1997 ◽  
Vol 06 (05) ◽  
pp. 563-573 ◽  
Author(s):  
J. David Brown ◽  
Viqar Husain
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Einstein Gravity ◽  
Spherically Symmetric ◽  
Short Hair ◽  
Anisotropic Matter ◽  
Symmetric Black Hole ◽  
Black Hole Solutions

We present spherically symmetric black hole solutions for Einstein gravity coupled to anisotropic matter. We show that these black holes have arbitrarily short hair, and argue for stability by showing that they can arise from dynamical collapse. We also show that a recent "no short hair" theorem does not apply to these solutions.

scholarly journals PARAMETRIC INSTABILITY IN SCALAR GRAVITATIONAL FIELDS

2012 ◽  
Vol 27 (24) ◽  
pp. 1230023 ◽  
Author(s):  
TREVOR B. DAVIES ◽  
CHARLES H.-T. WANG ◽  
ROBERT BINGHAM ◽  
J. TITO MENDONÇA
Keyword(s):  
Gravitational Field ◽  
Field Effect ◽  
Strong Field ◽  
Parametric Instability ◽  
Spherically Symmetric ◽  
Scalar Tensor Theory ◽  
Subsequent Work ◽  
Dynamical Mechanism ◽  
Gravitational Fields ◽  
Tensor Theory

We present a brief review on a new dynamical mechanism for a strong field effect in scalar–tensor theory. Starting with a summary of the essential features of the theory and subsequent work by several authors, we analytically investigate the parametric excitation of a scalar gravitational field in a spherically symmetric radially pulsating neutron star.

scholarly journals A Magnetized Dark Energy Type R/W Model with Polytropic Equation of State in Brans-Dicke Theory

2020 ◽  
Vol 12 (3) ◽  
pp. 251-257
Author(s):  
M. Dewri
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Variable Cosmological Constant ◽  
Volumetric Expansion ◽  
Dynamical Behaviors ◽  
Tensor Theory ◽  
Polytropic Equation ◽  
Theory Of Gravitation ◽  
Energy Type ◽  
Physical Quantities

In this paper, we study the spatially homogeneous Robertson-Walker cosmological models with magnetized isotropic dark energy like fluid in the scalar-tensor theory of gravitation proposed by Brans-Dicke. Variable cosmological constant ᴧ and Polytropic equation of state have been used to find exact solutions of the models with volumetric expansion and power-law relation. The Physical and dynamical behaviors of the models have been discussed using some physical quantities like energy density, pressure, and coefficient of bulk viscosity.

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