We discuss photon emission from particles decelerlated by the cosmic expansion. This can be interpretated as a kind of bremsstrahlung induced by the Universe geometry. In the high momentum limit its transition probability does not depend on detailed behavior of the expansion. This may play an important role when massless particle emission is discussed in the early Universe.

Recently, there has been suggestions that the apparent accelerated expansion of the universe is due not to a cosmological constant, but rather to inhomogeneities in the distribution of matter. In this work, we investigate a specific class of inhomogeneous models that can be solved analytically, namely the dust-dominated Lemâitre-Tolman-Bondi universe models. We show that they do not permit acce...

Here, non-minimally coupled tachyon to gravity is considered as a source of dark energy. It is demonstrated that with expansion of the universe, tachyon dark energy decays to dark matter providing a solution to " cosmic coincidence problem ". Moreover, it is found that the universe undergoes accelerated expansion simultaneously. PACS nos. 98.80 Cq, 95.35.+d.

A brief but broad survey is presented of the flows, forms and large-scale transformations of mass-energy in the universe, spanning a range of about twenty orders of magnitude (≈ mP lanck/mproton) in space, time and mass. Forms of energy considered include electromagnetic radiation, magnetic fields, cosmic rays, gravitational energy and gravitational radiation, baryonic matter, dark matter, vacu...

Spacetime stretching is included in the general relativity alongside with the spacetime curvature. Response of the vacuum to cosmic stretching is considered as macroscopic quantum effect. This effect explains the accelerated expansion of the Universe without resorting to Plank scale. For negative stretching (collapse) the same effect can prevent formation of singularity. Stretching effect can b...

We show the existence of spatially homogeneous but anisotropic cosmological models whose cosmic microwave background temperature is exactly isotropic at one instant of time but whose rate of expansion is highly anisotropic. The existence of these models shows that the observation of a highly isotropic cosmic microwave background temperature cannot alone be used to infer that the universe is clo...

The field equations are obtained in Sen–Dunn theory of gravitation with the help of LRS Bainchi type-I in the context of cosmic strings. We have solved the field equations when the shear σ is proportional to the scalar expansion θ. It is found that the cosmic do not exist with the scalar field except for some special cases and hence vacuum solutions are presented and discussed. c © Electronic J...