International Journal of Modern Physics D

In this study, it has been investigated whether the energy and momentum can be localizable for five-dimensional homogeneous and anisotropic universes. In this connection, energy and momentum of five-dimensional Bianchi type-I, type-III and type-V spacetimes have been calculated in the framework of general relativity (GR) and teleparallel gravity (TG). Einstein, Bergmann–Thomson, Landau–Lifshitz, Papapetrou, Tolman and Møller energy–momentum complexes have been used to obtain these related quantities of given the spacetimes in GR, while Einstein, Bergmann–Thomson, Landau–Lifshitz and Møller prescriptions have been used to obtain these related quantities of the spacetimes in TG. It has been found that all of the energy and momentum distributions of five-dimensional Bianchi type-I spacetime are equal to zero in GR and TG. For five-dimensional Bianchi type-III and type-V spacetimes, Bergmann–Thomson, Einstein and Tolman energy and momentum components give the same results, however Møller, Landau–Lifshitz and Papapetrou energy–momentum distributions give different results in general relativity. Also, in TG, Bergmann–Thomson and Einstein energy and momentum components give the same results for the Bianchi type-III and type-V spacetimes, too. In this sense, it is seen that Einstein, Bergmann–Thomson and Landau–Lifshitz energy and momentum descriptions of these spacetimes have been given same results in both theories, GR and TG.

The evolution of a universe modeled as a mixture of generalized Chaplygin gas (GCG) and ordinary matter field is studied for a Robertson–Walker type of spacetime. This model could interpolate periods of radiation-dominated, matter-dominated and cosmological constant-dominated universes. Depending on the arbitrary constants appearing in our theory, the instant of flip changes. Interestingly, we also get a bouncing model when the signature of one of the constants changes. The velocity of sound may become imaginary under certain situations pointing to a perturbative state and consequently the possibility of structure formation. We also discuss the whole situation in the backdrop of the well-known Raychaudhuri equation and a comparison is made with the previous results.

In this paper, we investigate power spectrum of a smoothed scalar field. The smoothing leads to regularization of the UV divergences and can be related with the internal structure of the considered field or the space itself. We perform Gaussian smoothing to the quantum fluctuations generated during the phase of cosmic inflation. We study whether this effect can be probed observationally and conclude that the modifications of the power spectrum due to the smoothing on the Planck scale are negligible and far beyond the observational abilities. Subsequently, we investigate whether smoothing in any other form can be probed observationally. We introduce phenomenological smoothing factor e^-k2σ2 to the inflationary spectrum and investigate its effects on the spectrum of CMB anisotropies and polarization. We show that smoothing can lead to suppression of high multipoles in the spectrum of the CMB. Based on seven years observations of WMAP satellite we indicate that the present scale of high multipoles suppression is constrained by σ < 3.19 Mpc (95% CL). This corresponds to the constraint σ < 100 μm at the end of inflation. Despite this value is far above the Planck scale, other processes of smoothing can be possibly studied with this constraint, as decoherence or diffusion of primordial perturbations.

We investigate the problem of pure gravitational localization of matter fields within the 5D standing wave braneworld generated by gravity coupled to a phantom-like scalar field. We show that in the case of increasing warp factor there exist normalizable zero modes of spin-0, -1/2, -1 and -2 fields on the brane.

We study the cosmic evolution in radiation and matter dominated epochs of the universe in chameleon Brans–Dicke (BD) as well as generalized chameleon BD cosmology. For this purpose, we consider Bianchi I universe model with matter contents as perfect fluid and the power law ansatz for scale factors, scalar field, interacting function f(ϕ), chameleon potential V(ϕ) and the BD parameter ω(ϕ). Using constraints on the involved parameters, it is shown that only the decelerated expansion of the universe can be discussed for these eras which is consistent with the astronomical observations. The graphical behavior of these functions for large values of the BD parameter (as suggested by local gravity tests) are also given. Finally, we evaluate statefinders as well as cosmological distances for obtained models.