[Show abstract][Hide abstract] ABSTRACT: It has recently been shown that the thermodynamics of a FRW universe can be
fully derived using the generalized uncertainty principle (GUP) in extra
dimensions as a primary input. There is a phenomenologically close relation
between the GUP and Modified Dispersion Relations (MDR). However, the form of
the MDR in theories with extra dimensions is as yet not known. The purpose of
this letter is to derive the MDR in extra dimensional scenarios. To achieve
this goal, we focus our attention on the thermodynamics of a FRW universe
within a proposed MDR in an extra dimensional model universe. We then compare
our results with the well-known results for the thermodynamics of a FRW
universe in an extra dimensional GUP setup. The result shows that the entropy
functionals calculated in these two approaches are the same, pointing to a
possible conclusion that these approaches are equivalent. In this way, we
derive the MDR form in a model universe with extra dimensions that would have
interesting implications on the construction of the ultimate quantum gravity
scenario.
Physics Letters B 12/2010; 696(1-2). DOI:10.1016/j.physletb.2010.11.067 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The entropy of the Reissner-N\"{o}rdstrom black hole is studied within the context of a brane-world scenario. Such a black hole is a solution of the Einstein field equations on the brane, possessing a tidal charge which is a reflection of the extra dimension. We use the modified dispersion relation to obtain the entropy of such brane-world black holes. The resulting entropy differs from that of the standard Bekenstein-Hawking's and contains information on the extra dimension. Comment: 9 pages, 4 figures, to appear in PLB
Physics Letters B 07/2010; 692(4). DOI:10.1016/j.physletb.2010.07.051 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a five dimensional unified theory of gravity and electromagnetism which leads to modified Maxwell equations, suggesting a new origin for galactic magnetic fields. It is shown that a region with nonzero scalar curvature would amplify the magnetic fields under certain conditions. Comment: 7 pages
[Show abstract][Hide abstract] ABSTRACT: We consider a brane world scenario in which the bulk action is assumed to have the form of a generic function of the Ricci scalar f(R) and derive the resulting Einstein field equation on the brane. In a constant curvature bulk a conserved geometric quantity appears in the field equations which can be associated with matter. We present spherically symmetric solutions which account for galaxy rotation curves in a specific form. Then cosmological solutions by assuming a specific form for f(R) are derived which can explain an accelerated expanding universe.
[Show abstract][Hide abstract] ABSTRACT: We consider a brane world scenario in which the bulk action is assumed to have the form of a generic function of the Ricci scalar f(\mathcal{R}) and derive the resulting Einstein field equations on the brane. In a constant curvature bulk a conserved geometric quantity appears in the field equations which can be associated with matter. We present cosmological and spherically symmetric solutions by assuming specific forms for f(\mathcal{R}) and show that the former can explain an accelerated expanding universe while the latter may account for galaxy rotation curves.
[Show abstract][Hide abstract] ABSTRACT: We employ the familiar canonical quantization procedure in a given cosmological setting to argue that it is equivalent to and results in the same physical picture if one considers the deformation of the phase-space instead. To show this we use a Probabilistic Evolutionary Process (PEP) to make the solutions of these different approaches comparable. Specific model theories are used to show that the independent solutions of the resulting Wheeler-DeWitt equation are equivalent to solutions of the deformation method with different signs for the deformation parameter. We also argued that since the Wheeler-DeWitt equation is a direct consequence of diffeomorphism invariance, this equivalence is only true provided that the deformation of phase-space does not break such an invariance. Comment: 19 pages, 31 figures; This paper is a complement to arXiv:0903.1914;
General Relativity and Gravitation 09/2009; 42(5). DOI:10.1007/s10714-009-0894-7 · 1.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study the virial mass discrepancy in the context of a DPG brane-world scenario and show that such a framework can offer viable explanations to account for the mass discrepancy problem. This is done by defining a geometrical mass $\mathcal{N}$ that we prove to be proportional to the virial mass. Estimating $\mathcal{N}$ using observational data, we show that it behaves linearly with $r$ and has a value of the order of $M_{200}$, pointing to a possible resolution of the virial mass discrepancy. We also obtain the radial velocity dispersion of galaxy clusters and show that it is compatible with the radial velocity dispersion profile of such clusters. This velocity dispersion profile can be used to differentiate various models predicting the virial mass. Comment: 12 pages, 1 figure, to appear in CQG
[Show abstract][Hide abstract] ABSTRACT: We use the collision-free Boltzmann equation in Palatini $f({\mathcal{R}})$ gravity to derive the virial theorem within the context of the Palatini approach. It is shown that the virial mass is proportional to certain geometrical terms appearing in the Einstein field equations which contribute to gravitational energy and that such geometric mass can be attributed to the virial mass discrepancy in cluster of galaxies. We then derive the velocity dispersion relation for clusters followed by the metric tensor components inside the cluster as well as the $f({\mathcal{R}})$ lagrangian in terms of the observational parameters. Since these quantities may also be obtained experimentally, the $f({\mathcal{R}})$ virial theorem is a convenient tool to test the viability of $f({\mathcal{R}})$ theories in different models. Finally, we discuss the limitations of our approach in the light of the cosmological averaging used and questions that have been raised in the literature against such averaging procedures in the context of the present work. Comment: 16 pages, to appear in PRD
[Show abstract][Hide abstract] ABSTRACT: The vacuum solutions in brane gravity differ from those in 4D by a number of additional terms and reduce to the familiar Schwarzschild metric at small distances. We study the possible roles that such terms may play in the precession of planetary orbits, bending of light, radar retardation and the anomaly in mean motion of test bodies. Using the available data from Solar System experiments, we determine the range of the free parameters associated with the linear term in the metric. The best results come from the anomalies in the mean motion of planets. Such studies should shed some light on the origin of dark energy via the solar system tests. Comment: 10 pages, no figures, to appear in CQG
[Show abstract][Hide abstract] ABSTRACT: In the standard picture of cosmology it is predicted that a phase transition,
associated with chiral symmetry breaking after the electroweak transition, has
occurred at approximately 10 \mu seconds after the Big Bang to convert a plasma
of free quarks and gluons into hadrons. We consider the quark-hadron phase
transition in a DGP brane world scenario within an effective model of QCD. We
study the evolution of the physical quantities useful for the study of the
early universe, namely, the energy density, temperature and the scale factor
before, during, and after the phase transition. Also, due to the high energy
density in the early universe, we consider the quadratic energy density term
that appears in the Friedmann equation. In DGP brane models such a term
corresponds to the negative branch (\epsilon=-1) of the Friedmann equation when
the Hubble radius is much smaller than the crossover length in 4D and 5D
regimes. We show that for different values of the cosmological constant on a
brane, \lambda, phase transition occurs and results in decreasing the effective
temperature of the quark-gluon plasma and of the hadronic fluid. We then
consider the quark-hadron transition in the smooth crossover regime at high and
low temperatures and show that such a transition occurs along with decreasing
the effective temperature of the quark-gluon plasma during the process of the
phase transition.
[Show abstract][Hide abstract] ABSTRACT: Within the context of a $5D$ space-time, we construct a unified theory of gravity and electromagnetism from which the Einstein field equations and Maxwell equations emerge, with homogenous Maxwell equations appearing naturally. We also introduce a well-defined five dimensional energy-momentum tensor consistent with our unification scheme. A correction term appears in Maxwell equations which can be used to explain the recently discovered galactic magnetic fields. Comment: 10 pages
[Show abstract][Hide abstract] ABSTRACT: We present a method, which we shall call the probabilistic evolutionary process, based on the probabilistic nature of quantum theory to offer a possible solution to the problem of time in quantum cosmology. It offers an alternative for perceiving an arrow of time which is compatible with the thermodynamical arrow of time and makes a new interpretation of the FRW universe in vacua which is consistent with creation of a de Sitter space–time from nothing. This is a completely quantum result with no correspondence in classical cosmology.
Physics Letters B 03/2009; 673(4-5-673):297-302. DOI:10.1016/j.physletb.2009.02.045 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider spherically symmetric solutions within the context of brane-world theory without mirror symmetry or any form of junction conditions. For a constant curvature bulk, we obtain the modified Tolman-Oppenheimer-Volkoff (TOV) interior solutions in two cases where one is matched to a schwarzschild-de Sitter exterior while the other is consistent with an exterior solution whose structure can be used to explain the galaxy rotation curves without postulating dark matter. We also find the upper bound to the mass of a static brane-world star and show that the influence of the bulk effects on the interior solutions is small. Finally, we investigate the gravitational collapse on the brane and show that the exterior of a collapsing star can be static in this scenario. Comment: 14 pages, 1 figure
Journal of Cosmology and Astroparticle Physics 02/2009; DOI:10.1088/1475-7516/2009/02/029 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We study the effects of noncommutativity and deformed Heisenberg algebra on the evolution of a two dimensional minisuperspace cosmological model in classical and quantum regimes. The phase space variables turn out to correspond to the scale factor of a flat FRW model with a positive cosmological constant and a dilatonic field with which the action of the model is augmented. The exact classical and quantum solutions in commutative and noncommutative cases are presented. We also obtain some approximate analytical solutions for the corresponding classical and quantum cosmology in the presence of the deformed Heisenberg relations between the phase space variables, in the limit where the minisuperspace variables are small. These results are compared with the standard commutative and noncommutative cases and similarities and differences of these solutions are discussed.
[Show abstract][Hide abstract] ABSTRACT: Various properties of Nano-Scale cell bio-membranes or vesicle membranes in an external electric field and free salt environment are studied and reviewed in a theoretical and computational framework. This is done by calculating the radial forces acting on cells generated as the result of an applied electric field and the ensuing charge re-distribution. Our results could help to shed light on mechanisms responsible for the observed deformation and fusion of cells which can be designed by biotechnological devices.
Physica A: Statistical Mechanics and its Applications 01/2009; 388(2):120-128. DOI:10.1016/j.physa.2008.10.011 · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We obtain the effective field equations in a brane-world scenario within the framework of a DGP model where the action on the brane is an arbitrary function of the Ricci scalar, ${\cal L}(R)$, and the bulk action includes a scalar field in the matter Lagrangian. We obtain the Friedmann equations and acceleration conditions in the presence of the bulk scalar field for the $R^n$ term in four-dimensional gravity. Comment: 9 pages, to appear in JCAP
Journal of Cosmology and Astroparticle Physics 01/2009; 2009(1). DOI:10.1088/1475-7516/2009/01/034 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider a five dimensional DGP-brane scenario endowed with a non-minimally coupled scalar field within the context of Brans-Dicke theory. This theory predicts that the mass appearing in the gravitational potential is modified by the addition of the mass of the effective intrinsic curvature on the brane. We also derive the effective four dimensional field equations on a 3+1 dimensional brane where the fifth dimension is assumed to have an orbifold symmetry. Finally, we discuss the cosmological implications of this setup, predicting an accelerated expanding universe with a value of the Brans-Dicke parameter $\omega$ consistent with values resulting from the solar system observations. Comment: 12 pages, 1 figure, to appear in JCAP
Journal of Cosmology and Astroparticle Physics 11/2008; 2009(01). DOI:10.1088/1475-7516/2009/01/006 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider an anisotropic brane-world model with Bianchi type I and V geometry, without mirror symmetry or any form of junction conditions. The generalized Chaplygin gas, which interpolates between a high density relativistic era and a non-relativistic matter phase, is a popular candidate for the present accelerated expansion of the universe. Considering the generalized Chaplygin gas as a geometrical dark energy, we obtain the general solutions in an exact parametric form for both Bianchi type I and V space-times. Finally, we study the behavior of the observationally important parameters such as the shear, anisotropic and deceleration parameter in this model.
Physical Review D 10/2008; 78(6). DOI:10.1103/PHYSREVD.78.064007 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We obtain the virial theorem within the context of a brane-world model without mirror symmetry or any form of junction condition. Taking a constant curvature bulk (neglecting non-local bulk effects), the local bulk effects generate a geometrical mass, contributing to the gravitational energy which may be used to explain the virial mass discrepancy in clusters of galaxies. We fix the parameter of this model in agreement with observational data. Comment: 11 pages, no figures
Journal of Cosmology and Astroparticle Physics 08/2008; 2008(8). DOI:10.1088/1475-7516/2008/08/018 · 5.81 Impact Factor