scholarly journals Evaporation phenomena in f(T) gravity

2015 ◽  
Vol 93 (4) ◽  
pp. 377-383 ◽  
Author(s):  
M.J.S. Houndjo ◽  
D. Momeni ◽  
R. Myrzakulov ◽  
M.E. Rodrigues
Keyword(s):  
Teleparallel Gravity ◽  
Space Time ◽  
Generic Model ◽  
Perturbation Equation ◽  
De Sitter ◽  
Field Equations ◽  
Initial State ◽  
Universal Feature ◽  
Limiting Case ◽  
Physical Phenomena

We formulate evaporation phenomena in a generic model of generalized teleparallel gravity in Weitzenbock space–time with a diagonal and nondiagonal tetrad basis. We also perform perturbation analysis around the constant torsion scalar solution called the Nariai space–time, which is an exact solution of the field equations as the limiting case of the Schwarzschild – de Sitter space–time and in the limit where two black holes and their cosmological horizons coincide. By a carefully analysis of the horizon perturbation equation, we show that (anti)evaporation cannot happen if we use a diagonal tetrad basis. This result implies that a typical black hole in any generic form of generalized teleparallel gravity is frozen in its initial state if we use diagonal tetrads, but in the case of nondiagonal tetrads the analysis is completely different. With a suitable nontrivial nondiagonal tetrad basis we investigate the linear stability of the model under simultaneous perturbations of the metric and torsion. We observe that in spite of the diagonal case, both evaporation and antievaporation can happen. These phenomena depend on the initial phase of the horizon perturbation. In the first mode, when we restrict ourselves to the first lower modes (anti)evaporation takes place. So, in the nondiagonal case, the physical phenomena are reasonable. This is an important advantage of using nondiagonal tetrads instead of diagonal ones. We also see that this is a universal feature, completely independent from the form of the model.

scholarly journals Phase Transition at the Metric Elastic Universe

1996 ◽  
Vol 168 ◽  
pp. 569-570
Author(s):  
Alexander Gusev
Keyword(s):  
Phase Transition ◽  
Constitutive Relations ◽  
Three Dimensional ◽  
Vacuum State ◽  
Space Time ◽  
Deformation Tensor ◽  
De Sitter ◽  
Initial State ◽  
Deformation State ◽  
The Universe

At the last time the concept of the curved space-time as the some medium with stress tensor σαβon the right part of Einstein equation is extensively studied in the frame of the Sakharov - Wheeler metric elasticity(Sakharov (1967), Wheeler (1970)). The physical cosmology pre- dicts a different phase transitions (Linde (1990), Guth (1991)). In the frame of Relativistic Theory of Finite Deformations (RTFD) (Gusev (1986)) the transition from the initial stateof the Universe (Minkowskian's vacuum, quasi-vacuum(Gliner (1965), Zel'dovich (1968)) to the final stateof the Universe(Friedmann space, de Sitter space) has the form of phase transition(Gusev (1989) which is connected with different space-time symmetry of the initial and final states of Universe(from the point of view of isometric groupGnof space). In the RTFD (Gusev (1983), Gusev (1989)) the space-time is described by deformation tensorof the three-dimensional surfaces, and the Einstein's equations are viewed as the constitutive relations between the deformations ∊αβand stresses σαβ. The vacuum state of Universe have the visible zero physical characteristics and one is unsteady relatively quantum and topological deformations (Gunzig & Nardone (1989), Guth (1991)). Deformations of vacuum state, identifying with empty Mikowskian's space are described the deformations tensor ∊αβ, wherethe metrical tensor of deformation state of 3-geometry on the hypersurface, which is ortogonaled to the four-velocityis the 3 -geometry of initial state,is a projection tensor.

scholarly journals Dimensionally Compactified Chern-Simon Theory in 5D as a Gravitation Theory in 4D

2017 ◽  
Vol 45 ◽  
pp. 1760005 ◽  
Author(s):  
Ivan Morales ◽  
Bruno Neves ◽  
Zui Oporto ◽  
Olivier Piguet
Keyword(s):  
Dimensional Space ◽  
Cosmological Solution ◽  
Space Time ◽  
Gravitation Theory ◽  
Simons Theory ◽  
De Sitter ◽  
Field Equations ◽  
Sitter Group ◽  
Dimensional Space Time ◽  
Chern Simons

We propose a gravitation theory in 4 dimensional space-time obtained by compacting to 4 dimensions the five dimensional topological Chern-Simons theory with the gauge group SO(1,5) or SO(2,4) – the de Sitter or anti-de Sitter group of 5-dimensional space-time. In the resulting theory, torsion, which is solution of the field equations as in any gravitation theory in the first order formalism, is not necessarily zero. However, a cosmological solution with zero torsion exists, which reproduces the Lambda-CDM cosmological solution of General Relativity. A realistic solution with spherical symmetry is also obtained.

scholarly journals THE GRAVITATIONAL ENERGY PROBLEM FOR COSMOLOGICAL MODELS IN TELEPARALLEL GRAVITY

2010 ◽  
Vol 19 (12) ◽  
pp. 1925-1935 ◽  
Author(s):  
S. C. ULHOA ◽  
J. F. DA ROCHA NETO ◽  
J. W. MALUF
Keyword(s):  
Average Energy ◽  
Teleparallel Gravity ◽  
Space Time ◽  
Gravitational Energy ◽  
Cosmological Models ◽  
De Sitter ◽  
Energy Problem ◽  
First Case ◽  
Einstein's Equation ◽  
Average Energy Density

We present a method to calculate the gravitational energy when asymptotic boundary conditions for the space–time are not given. This is the situation for most of the cosmological models. The expression for the gravitational energy is obtained in the context of the teleparallel equivalent of general relativity. We apply our method first to the Schwarzschild–de Sitter solution of Einstein's equation, and then to the Robertson–Walker universe. We show that in the first case our method leads to an average energy density of the vacuum space–time, and in the latter case the energy vanishes in the case of null curvature.

scholarly journals LAGRANGE FORMULATION OF THE SYMMETRIC TELEPARALLEL GRAVITY

2006 ◽  
Vol 15 (05) ◽  
pp. 619-634 ◽  
Author(s):  
M. ADAK ◽  
M. KALAY ◽  
Ö. SERT
Keyword(s):  
Gravity Model ◽  
Teleparallel Gravity ◽  
Space Time ◽  
De Sitter ◽  
Lagrange Formulation

We develop a symmetric teleparallel gravity model in a space–time with only the nonmetricity as nonzero, in terms of a Lagrangian quadratic in the nonmetricity tensor. We present a detailed discussion of the variations that may be used for any gravitational formulation. We seek Schwarzschild-type solutions because of its observational significance and obtain a class of solutions that includes Schwarzschild-type, Schwarzschild–de Sitter-type, and Reissner–Nordström-type solutions for certain values of the parameters. We also discuss the physical relevance of these solutions.

scholarly journals TACHYONS IN DE SITTER SPACE AND ANALYTICAL CONTINUATION FROM dS/CFT TO AdS/CFT

2004 ◽  
Vol 19 (29) ◽  
pp. 4985-5001 ◽  
Author(s):  
M. CADONI ◽  
P. CARTA
Keyword(s):  
Analytic Continuation ◽  
De Sitter Space ◽  
Space Time ◽  
Analytical Continuation ◽  
Green Functions ◽  
De Sitter ◽  
Field Equations ◽  
Scalar Particles

We discuss analytic continuation from d-dimensional Lorentzian de Sitter ( dS d) to d-dimensional Lorentzian anti-de Sitter ( AdS d) space–time. We show that AdS d, with opposite signature of the metric, can be obtained as analytic continuation of a portion of dS d. This implies that the dynamics of (positive square-mass) scalar particles in AdS d can be obtained from the dynamics of tachyons in dS d. We discuss this correspondence both at the level of the solution of the field equations and of the Green functions. The AdS / CFT duality is obtained as analytic continuation of the dS / CFT duality.

scholarly journals Quantum thermodynamics in a static de Sitter space-time and initial state of the universe

2019 ◽  
Vol 79 (11) ◽  
Author(s):  
Juan Ignacio Musmarra ◽  
Mauricio Bellini
Keyword(s):  
Energy Level ◽  
Relativistic Quantum ◽  
Energy Levels ◽  
Space Time ◽  
Back Reaction ◽  
De Sitter ◽  
Initial State ◽  
Discrete Energy ◽  
The Universe ◽  
De Sitter Metric

Abstract Using Relativistic Quantum Geometry we study back-reaction effects of space-time inside the causal horizon of a static de Sitter metric, in order to make a quantum thermodynamical description of space-time. We found a finite number of discrete energy levels for a scalar field from a polynomial condition of the confluent hypergeometric functions expanded around $$r=0$$r=0. As in the previous work, we obtain that the uncertainty principle is valid for each energy level on sub-horizon scales of space-time. We found that temperature and entropy are dependent on the number of sub-states on each energy’s level and the Bekenstein–Hawking temperature of each energy level is recovered when the number of sub-states of a given level tends to infinity. We propose that the primordial state of the universe could be described by a de Sitter metric with Planck energy $$E_p=m_p\,c^2$$Ep=mpc2, and a B–H temperature: $$T_{BH}=\left( \frac{\hbar \,c}{2\pi \,l_p\,K_B}\right) $$TBH=ħc2πlpKB.

scholarly journals Axial Symmetry Cosmological Constant Vacuum Solution of Field Equations with a Curvature Singularity, Closed Time-Like Curves, and Deviation of Geodesics

2020 ◽  
Vol 2020 ◽  
pp. 1-7
Author(s):  
Faizuddin Ahmed ◽  
Bidyut Bikash Hazarika ◽  
Debojit Sarma
Keyword(s):  
Cosmological Constant ◽  
Vacuum Solution ◽  
Space Time ◽  
Axially Symmetric ◽  
De Sitter ◽  
Curvature Singularity ◽  
Field Equations ◽  
Type D ◽  
Initial Space ◽  
Coulomb Type

In this paper, we present a type D, nonvanishing cosmological constant, vacuum solution of Einstein’s field equations, extension of an axially symmetric, asymptotically flat vacuum metric with a curvature singularity. The space-time admits closed time-like curves (CTCs) that appear after a certain instant of time from an initial space-like hypersurface, indicating it represents a time-machine space-time. We wish to discuss the physical properties and show that this solution can be interpreted as gravitational waves of Coulomb-type propagate on anti-de Sitter space backgrounds. Our treatment focuses on the analysis of the equation of geodesic deviations.

Dynamical and optimal procedure to analyze the exhibition of physical attributes imparted by Sutterby magneto-nanofluid in Darcy medium yielded by axially stretched cylinder

2020 ◽  
Vol 98 (1) ◽  
pp. 1-10 ◽  
Author(s):  
S. Bilal ◽  
M. Sohail ◽  
R. Naz ◽  
M.Y. Malik
Keyword(s):  
Flow Behavior ◽  
Mathematical Structure ◽  
Physical Parameters ◽  
Field Equations ◽  
Flow Parameters ◽  
Physical Attributes ◽  
Local Shear ◽  
Physical Features ◽  
Limiting Case ◽  
Physical Phenomena

This work aims to interpret the heat and mass transmission of Sutterby fluid by exploring the effects of a magnetic field. Flow field equations in cylindrical coordinates are obtained by incorporating Darcy resistance law. Afterwards, a mathematical structure for the physical problem is formulated. This formulation yields an intricate nonlinear set of partial differential expressions. A suitable scaling group of variables is employed on subsequent equations to convert them into non-dimensional form. Dynamical and optimal analyses are performed to achieve physical features of the present problem from the solution. A graphical depiction is presented for the flow behavior of convoluted physical parameters on velocity, temperature, and concentration profiles. Additionally, the quantities (local shear stress coefficient, thermal convective transfer coefficient, and local mass flux coefficient in the limiting case) that are responsible for extracting the physical phenomena in the vicinity of a stretched surface are computed and demarcated by varying controlling flow parameters.

scholarly journals SOLUTIONS WITHOUT SINGULARITIES IN GAUGE THEORY OF GRAVITATION

2004 ◽  
Vol 15 (07) ◽  
pp. 1031-1038 ◽  
Author(s):  
G. ZET ◽  
C. D. OPRISAN ◽  
S. BABETI
Keyword(s):  
Gravitational Field ◽  
Gauge Theory ◽  
Mathematical Structure ◽  
Space Time ◽  
Relativity Theory ◽  
De Sitter ◽  
Field Equations ◽  
Underlying Space ◽  
Minkowski Space Time ◽  
Theory Of Gravitation

A de-Sitter gauge theory of the gravitational field is developed using a spherical symmetric Minkowski space–time as base manifold. The gravitational field is described by gauge potentials and the mathematical structure of the underlying space–time is not affected by physical events. The field equations are written and their solutions without singularities are obtained by imposing some constraints on the invariants of the model. An example of such a solution is given and its dependence on the cosmological constant is studied. A comparison with results obtained in General Relativity theory is also presented.

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