Phantom Mimicry on the Normal Branch of a DGP-inspired Braneworld Scenario with Curvature Effect

It has been shown recently that phantom-like effect can be realized on the normal branch of the DGP setup without introduction of any phantom matter neither in the bulk nor on the brane and therefore without violation of the null energy condition. It has been shown also that inclusion of the Gauss-Bonnet term in the bulk action modifies this picture via curvature effects. Here, based on the Lue-Starkman conjecture on the dynamical screening of the brane cosmological constant in the DGP setup, we extend this proposal to a general DGP-inspired $f(R,\phi)$ model that stringy effects in the ultra-violet sector of the theory are taken into account by inclusion of the Gauss-Bonnet term in the bulk action. We study cosmological dynamics of this setup, especially its phantom-like behavior and possible crossing of the phantom divide line especially with a non-minimally coupled quintessence field on the brane. In this setup, scalar field and curvature quintessence are treated in a unified framework.Comment: 25 Figures, To appear in MPL

Can Quantum Gravitational Effects Manifest themselves at Large Distances?

Consider a proposed model of the universe with $\hbar$ much greater than its well-known value of $10^{-34} Js$. In this model universe, very large objects can show quantum behaviors. In a scenario with large extra dimensions, $\hbar$ can attains very large values depending on the dimensionality of spacetime. In this letter, we show that although conventional thinking indicates that quantum gravitational effects should manifest themselves only at very small scales, in actuality quantum gravitational effects can manifest themselves at large scales too. We use the generalized uncertainty principle with a non-zero minimal uncertainty in momentum as our primary input to construct a mathematical framework for our proposal.Comment: 7 Pages, No Figure

Free Motion of a Dirac Particle with a Minimum Uncertainty in Position

In this paper, we present a covariant, relativistic noncommutative algebra which includes two small deformation parameters. Using this algebra, we obtain a generalized uncertainty principle which predicts a minimal observable length in measure of space-time distances. Then, we introduce a new representation for coordinate and momentum operators which leads to a generalized Dirac equation. The solutions of the generalized Dirac equation for a free particle will be explicitly obtained. We also obtain the modified fermionic propagator for a free Dirac particle.Comment: 14 pages . . . accepted for publication in Reports on Mathematical Physics. arXiv admin note: text overlap with arXiv:1103.1015,arXiv:1103.3805 by different author

Orbits of particles in noncommutative Schwarzschild spacetime

By considering particles as smeared objects, we investigate the effects of space noncommutativity on the orbits of particles in Schwarzschild spacetime. The effects of space noncommutativity on the value of the precession of the perihelion of particle orbit and deflection of light ray in Schwarzschild geometry are calculated and the stability of circular orbits is discussed.Comment: 14 Pages, 2 eps Figures, accepted for publication in Europhysics Letter