141 research outputs found
Quantum Einstein's Equations and Constraints Algebra
In this paper we shall address this problem: Is quantum gravity constraints
algebra closed and what are the quantum Einstein equations. We shall
investigate this problem in the de-Broglie--Bohm quantum theory framework. It
is shown that the constraint algebra is weakly closed and the quantum
Einstein's equations are derived.Comment: 13 pages, No figure, RevTeX. To appear in Pramana J. Phys., 200
Geodesic Congruences in the Palatini f(R) Theory
We shall investigate the properties of a congruence of geodesics in the
framework of Palatini f(R) theories. We shall evaluate the modified geodesic
deviation equation and the Raychaudhuri's equation and show that f(R) Palatini
theories do not necessarily lead to attractive forces. Also we shall study
energy condition for f(R) Palatini gravity via a perturbative analysis of the
Raychaudhuri's equation
Nonminimal Scalar-Tensor Theories and Quantum Gravity
Recentely, it is shown that the quantum effects of matter determine the
conformal degree of freedom of the space-time metric. This was done in the
framework of a scalar-tensor theory with one scalar field. A point with that
theory is that the form of quantum potential is preassumed. Here we present a
scalar-tensor theory with two scalar fields, and no assumption on the form of
quantum potential. It is shown that using the equations of motion one gets the
correct form of quantum potential plus some corrections.Comment: 15 page
On the effect of renormalization group improvement on the cosmological power spectrum
Asymptotically safe quantum gravity predicts running gravitational and
cosmological constants, while it remains a meaningful quantum field theory
because of the existence of non-Gaussian ultraviolet fixed points. Here we have
investigated the effect of such running couplings on the cosmological
perturbations. We have obtained the improved Mukhanov-Sassaki equation and
solved it for two models. The effect of asymptotically safe quantum gravity on
the cosmological power spectrum is also studied
About Some Problems Raised by the Relativistic Form of De-Broglie--Bohm Theory of Pilot Wave
The standard relativistic de-Broglie--Bohm theory has the problems of
tacyonic solutions and the incorrect non-relativistic limit. In this paper we
obtain a relativistic theory, not decomposing the relativistic wave equations
but looking for a generalization of non-relativistic Bohmian theory in such a
way that the correct non-relativistic limit emerges. In this way we are able to
construct a relativistic de-Broglie--Bohm theory both for a single particle and
for a many-particle system. At the end, the theory is extended to the curved
space-time and the connection with quantum gravity is discussed.Comment: 13 pages, RevTeX. To appear in Physica Scripta, 200
Causal Loop Quantum Gravity and Cosmological Solutions
We shall present here the causal interpretation of canonical quantum gravity
in terms of new variables. Then we shall apply it to the minisuperspace of
cosmology. A vacuum solution of quantum cosmology is obtained and the Bohmian
trajectory is investigated. At the end a coherent state with matter is
considered in the cosmological model.Comment: 22 pages, 6 figure
On the Newtonian Anisotropic Configurations
In this paper we are concerned with the effects of anisotropic pressure on
the boundary conditions of anisotropic Lane-Emden equation and homology
theorem. Some new exact solutions of this equation are derived. Then some of
the theorems governing the Newtonian perfect fluid star are extended taking the
anisotropic pressure into account
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