arXiv subjects
Publications and source records attributed to S. Habib Mazharimousavi.
By choosing a fluid source in $f(R)$ gravity, defined by $f\left(R\right) =R-12aξ\ln \left\ | R\right\ | $, where $a$ (=Rindler acceleration) and $ξ$ are both constants, the field equations correctly yield the Rindler acceleration term in the metric. We identify domains in which the weak energy conditions (WEC) and the strong energy conditions (SEC) are satisfied.
We investigate the existence of Reissner-Nordström (RN) type black holes in f(R) gravity. Our emphasis is to derive, in the presence of electrostatic source, the necessary conditions which provide such static, spherically symmetric (SSS) black holes available in f(R) gravity. We also study the thermodynamics of the black hole solution.
We find Einstein-Yang-Mills (EYM) black hole solutions endowed with massless scalar hair in the presence of a potential $V\left(ϕ\right) $ as function of the scalar field $ϕ$. Choosing $V\left(ϕ\right) =$constant (or zero) sets the scalar field to vanish leaving us with the EYM black holes. Our class of black hole solutions is new so that they do not asymptote in general to any known limits. Particular case is given, however, which admits an asymptotically anti de Sitter limit in $6-$dimensional spacetime. The role of the potential $V\left(ϕ\right) $ in making double bounces (i.e. both a minimum and maximum radii) on a Domain Wall (DW) universe is highlighted.
We consider the interesting "near-horizon test" reported in (PRD84, 084006(2011), arXiv:1107.5727) for any static, spherically symmetric (SSS) black hole solution admitted in f(R) gravity. Before adopting the necessary conditions for the test, however, revisions are needed as we point out in this Comment.
For a generic $f(R)$ which admits a polynomial expansion of at least third order (i.e. $\frac{d^{3}f}{dR^{3}}\neq 0$) we find the near-throat wormhole solution. Necessary conditions for the existence of wormholes in such $f(R)$ theories are derived for both zero and non-zero matter sources. A particular choice of energy-momentum reveals that the wormhole geometry satisfies the weak energy condition (WEC). For a range of parameters even the strong energy condition (SEC) is shown to be satisfied.
The kinetic energy operator of a quantum particle with position dependent mass and the associated ordering ambiguity is revisited. We introduce a new form of this operator which is a continues or discreet superposition of the acceptable values for the ordering parameters.
We employ an old field theory model, formulated and discussed by Born, Infeld, Hoffman and Rosen during 1930s. Our method of cutting-gluing of spacetimes resolves the double-valuedness in the displacement vector D(E), pointed out by these authors. A characteristic feature of their model is to contain a logarithmic term, and by bringing forth such a Lagrangian anew, we aim to attract the interest of field theorists to such a Lagrangian. We adopt the Hoffman-Born-Infeld (HBI) Lagrangian in general relativity to construct black holes and investigate the possibility of viable thin-shell wormholes. In particular, the stability of thin-shell wormholes supported by normal matter in 5-dimensional Einstein-HBI-Gauss-Bonnet gravity is highlighted.
A large family of new black hole solutions in 2+1-dimensional Einstein-Power-Maxwell (EPM) gravity with prescribed physical properties is derived. We show with particular examples that according to the power parameter k of the Maxwell field, the obtained solutions may be asymptotically flat for 1/2 1 in the vanishing cosmological constant limit. We study the thermodynamic properties of the solution with two different models and it is shown that thermodynamic quantities satisfy the first law. The behaviour of the heat capacity indicates that by employing the 1+1-dimensional dilaton analogy the local thermodynamic stability is satisfied.
Recently R. N. Costa Filho et al. (PRA 84, 050102(R) (2011)) have introduced a position dependent infinitesimal translation operator which corresponds to a position dependent linear momentum and consequently to a position dependent effective mass quantum particle. Although there is no doubt in novelty of the idea and the formalism, we believe that some aspects of the quantum mechanics could be complemented in their original work. Here in this letter first we address those points and then an alternative will be introduced. Finally we apply the formalism for a quantum particle under a null potential confined in a square well and the results will be compared with those in the paper mentioned above.
We employ the 'square root' of the Maxwell Lagrangian (i.e. \surd(F_{μν}F^{μν})), coupled with gravity to search for the possible linear potentials which are believed to play role in confinement. It is found that in the presence of magnetic charge no confining potential exists in such a model. Confining field solutions are found for radial geodesics in pure electrically charged Nariai- Bertotti-Robinson (NBR)-type spacetime with constant scalar curvature. Recently, Guendelman, Kaganovich, Nissimov and Pacheva, [Phys.Lett.B704(2011)230] have shown that superposed square root with standard Maxwell Lagrangians yields confining potentials in spherically symmetric spacetimes with new generalized Reissner-Nordström-de Sitter / -anti-de Sitter black hole solutions. In NBR spacetimes we show that confining potentials exist even when the standard Maxwell Lagrangian is relaxed.
We consider the particular class of f(R) gravities minimally coupled with Yang - Mills (YM) field in which the Ricci scalar =R_{0}= constant in all dimensions d\geq4. Even in this restricted class the spacetime has unlimited scopes determined by an equation of state of the form P_{eff}=ωρ. Depending on the distance from the origin (or horizon of a black hole) the state function ω(r) takes different values. It is observed that ω\rightarrow(1/3) (the ultra relativistic case in 4 - dimensions) and ω\rightarrow-1 (the cosmological constant) are the limiting values of our state function ω(r) in a spacetime centered by a black hole. This suggests that having a constant ω throughout spacetime around a charged black hole in f(R) gravity with constant scalar curvature is a myth.
We show in detail that the Hawking temperature calculated from the surface gravity is in agreement with the result of exact semi-classical radiation spectrum for higher dimensional linear dilaton black holes in various theories. We extend the method derived first by Clément-Fabris-Marques for 4-dimensional linear dilaton black hole solutions to the higher dimensions in theories such as Einstein-Maxwell-Dilaton, Einstein-Yang-Mills-Dilaton and Einstein-Yang-Mills-Born-Infeld-Dilaton. Similar to the Clément-Fabris-Marques results, it is proved that whenever an analytic solution is available to the massless scalar wave equation in the background of higher dimensional massive linear dilaton black holes, an exact computation of the radiation spectrum leads to the Hawking temperature T_{H} in the high frequency regime. The significance of the dimensionality on the value of T_{H} is shown, explicitly. For a chosen dimension, we demonstrate how higher dimensional linear dilaton black holes interpolate between the black hole solutions with Yang-Mills and electromagnetic fields by altering the Born-Infeld parameter in aspect of measurable quantity T_{H}. Finally, we explain the reason of, why massless higher dimensional linear dilaton black holes cannot radiate.
We consider Einstein-Maxwell-Dilaton (EMD) Lagrangian supplemented by double Liouville potentials to enrich our system and investigate the resulting dynamics. The general solution provides us alternative structures induced on the 3-dimensional domain wall (DW) moving in the 4-dimensional bulk. In particular, the local maximum in the potential suggests a maximum bounce (or onset for a contraction phase) of the 3-dimensional Friedmann-Robertson-Walker (FRW) universe on the DW. Depending on the choice of parameters we plot various cases of physical interest.
We identify a region of F(R)=R^{N} gravity without external sources which is isometric to the spacetime of colliding plane waves (CPW). From the derived curvature sources, N (N>1) measures the strength (i.e. the charge) of the source. The analogy renders construction and collision of plane waves in F(R)=R^{N} gravity possible, as in the Einstein-Maxwell (EM) theory, simply because R=0. A plane wave in this type of gravity is equivalent to a Weyl curvature plus an electromagnetic energy-momentum-like term (i.e. 'source without source'). For N=1 we recover naturally the plane waves (and their collision) in Einstein's theory. Our aim is to find the effect of an expanding universe by virtue of F(R)=R^{N} on the colliding gravitational plane waves of Einstein.
In contrast to its chargeless version the charged Banados, Taitelboim and Zanelli (BTZ) metric in linear Maxwell electromagnetism is known to be singular at r=0. We show, by employing nonlinear electrodynamics that one obtains charged, extension of the BTZ metric with regular electric field. This we do by choosing a logarithmic Lagrangian for the nonlinear electrodynamics. A Theorem is proved on the existence of electric black holes and combining this results with a duality principle disproves the existence of magnetic black holes in 2+1-dimensions.
It is well-known that unlike its chargeless version the charged Banados-Teitelboim-Zanelli (BTZ) black hole solution in 2+1- dimensional spacetime is singular. We construct a charged, regular extension of the BTZ black hole solution by employing nonlinear Born-Infeld electrodynamics, supplemented with the Hoffmann term and gluing different spacetimes. The role of the latter term is to divide spacetime in a natural way into two regions by a circle and eliminate the inner singularity. Thermodynamics of such a black hole is investigated by Kaluza-Klein reduction to the 1+1-dimensional dilaton gravity.
Within the context of Born-Infeld (BI) nonlinear electrodynamics (NED) we revisit the non-relativistic, spinless H-atom. The pair potential computed from the Born-Infeld equations is approximated by the Morse type potential with remarkable fit over the critical region where the convergence of both the short and long distance expansions slows down dramatically. The Morse potential is employed to determine both the ground state energy of the electron and the BI parameter.
In the presence of external, linear / nonlinear electromagnetic fields we integrate f(R) \sim R+2α\surd(R+const.) gravity equations. In contrast to their Einsteinian cousins the obtained black holes are non-asymptotically flat with a deficit angle. In proper limits we obtain from our general solution the global monopole solution in f(R) gravity. The scale symmetry breaking term adopted as the nonlinear electromagnetic source adjusts the sign of the mass of the resulting black hole to be physical.