where Rij is the Ricci curvature tensor of the metric and R is its scalar curvature. This equation tells us how the metric tensor gij (i.e. the field mediating the gravitation) is obeying to constraints imposed by the energy-momentum tensor Tij , which encodes informations about the distribution of energy and momentum in spacetime. For simplicity we will assume in the following that Tij = 0, i....

The electromagnetic field is studied in a family of exact solutions of the Einstein equations whose material content is a perfect fluid with stiff equation of state (p = ǫ). The field equations are solved exactly for several members of the family.

A nonlinear scalar field theory from which an effective metric can be deduced is considered. This metric is shown to be compatible with requirements of general relativity. It is demonstrated that there is a class of solutions which fulfill both the nonlinear field equation as the Einstein equations for this metric.

The Einstein-Cartan field equation of infinitely rotating rigid cylinder is obtained and solved using the techniques of Manko-Gutsunaev and Quevedo to describe gravitational field due to extended van-Stockum cylindrically perfect fluid distribution using improved energy-momentum tensor by Ray and Smalley.

the overall aim of this study is to calculate some water properties in the single wall carbon naotubes (swcnt) and compare them to the bulk water properties to investigate the deviation of water properties inside the swcnt from those in the bulk. here some physical and transport properties of water molecules in the single wall carbon nanotube were reported by performing molecular dynamics (md) ...

We point out that extended gravity theories, the Lagrangian of which is an arbitrary function of scalar curvature R, are equivalent to a class of the scalar tensor theories of gravity. The corresponding gravity theory is ω = 0 BransDicke gravity with a potential for the Brans-Dicke scalar field, which is not compatible with solar system experiments if the field is very light: the case when such...

A generalized theory unifying gravity with electromagnetism was proposed by Einstein in 1945. He considered a Hermitian metric on a real space-time. In this work we review Einstein’s idea and generalize it further to consider gravity in a complex Hermitian space-time. email: [email protected] Published in ”Einstein in Alexandria, The Scientific Symposium”, Editor Edward Witten, Publisher Bibilot...

A Poincaré gauge theory of (2+1)-dimensional gravity is developed. Fundamental gravitational field variables are dreibein fields and Lorentz gauge potentials, and the theory is underlain with the Riemann-Cartan space-time. The most general gravitational Lagrangian density, which is at most quadratic in curvature and torsion tensors and invariant under local Lorentz transformations and under gen...

A new asymptotic expansion method is developed to separate the WheelerDeWitt equation into the time-dependent Schrödinger equation for a matter field and the Einstein-Hamilton-Jacobi equation for the gravitational field including the quantum back-reaction of the matter field. In particular, the nonadiabatic basis of the generalized invariant for the matter field Hamiltonian separates the Wheele...