in this paper, we obtain a necessary and sufficient condition for a conformal mapping between two weyl manifolds to preserve einstein tensor. then we prove that some basic curvature tensors of $w_n$ are preserved by such a conformal mapping if and only if the covector field of the mapping is locally a gradient. also, we obtained the relation between the scalar curvatures of the weyl manifolds r...

In this paper we consider a Z2 symmetrical 3-brane embedded in a 5-dimensional spacetime. We study the effective Einstein equation and acceleration condition in presence of the quintom dark energy fluid as the bulk matter field. The effective Einstein equation on the brane in the framework of DGP model is obtained where the quintom field is considered as the bulk matter field, and a quintom dar...

we investigate the exact renormalization group (RG) in Einstein gravity coupled to N-component scalar field, working in the effective average action formalism and background field method. The truncated evolution equation is obtained for the Newtonian and cosmological constants. We have shown that screening or antiscreening behaviour of the gravitational coupling depends cricially on the choice ...

General Relativity with nonvanishing torsion has been investigated in the first order formalism of Poincaré gauge field theory. In the presence of torsion, either side of the Einstein equation has the nonvanishing covariant divergence. This fact turned out to be self-consistent in the framework under consideration. By using Noether’s procedure with the definition of the Lie derivative where the...

Using the Born-Oppenheimer idea we show that the Wheeler-DeWitt equation in an oscillating regime can also allow a different type of semiclassical quantum gravity that preserves completely the unitary quantum evolution of a matter field, which reduces the same asymptotic limit as the others. We develop a perturbation method to find the quantum corrections of a matter field to the gravity. The s...

In inflationary cosmological models driven by an inflaton field the origin of the primordial inhomogeneities which are responsible for large-scale structure formation are the quantum fluctuations of the inflaton field. These are usually calculated using the standard theory of cosmological perturbations, where both the gravitational and the inflaton fields are linearly perturbed and quantized. T...

The induced Einstein equation on a perturbed brane in the Induced Matter Theory is reanalyzed. We indicate that in a conformally flat background, the local quantum corrections to the Einstein equation can be obtained via the IMT. Using the FRW metric as the 4D gravitational model, we show that the classical fluctuations of the brane may be related to the quantum corrections to the classical Ein...

The Einstein-Langevin equation is a perturbative correction to the semiclassical Ein-stein equation which takes into account the lowest order quantum fluctuations of the matter stress-energy tensor. It predicts classical stochastic fluctuations in the metric field which may describe some of the remnant gravitational fluctuations after the process of environment induced decoherence driving the q...

In a space-time M with a Killing vector field ξa which is either everywhere timelike or everywhere spacelike, the collection of all trajectories of ξa gives a 3-dimensional space S. Besides the symmetry-reduced action from that of Einstein-Hilbert, an alternative action of the fields on S is also proposed which gives the same fields equations as those reduced from the vacuum Einstein equation o...