arXiv subjects

S. Habib Mazharimousavi

Publications and source records attributed to S. Habib Mazharimousavi.

At least 73 records · Page 4Linked to original sources

arXiv2017

Morse simulation of the Global Monopole equation in flat spacetime

We show that a Morse type potential simulates an analytic solution for the highly non-linear global monopole field equation in three and higher dimensional flat spacetimes. Owing to the fact that in the flat space limit the similar equation remains intact we wish to borrow the curved space terminology of global monopole also in flat spacetime. This may provide a compelling example that can be used effectively in different non-linear theories such as flat space $ϕ^{4},$ as well as in curved spacetimes.

physics.gen-ph↗

arXiv2017

Thin-shell wormholes in 2+1-dimensional Einstein-Scalar Theory

We present an infinite class of one-parameter scalar field extensions to the BTZ black hole in 2+1-dimensions. By virtue of the scalar charge the thin-shell wormhole supported by a linear fluid at the throat becomes stable against linear perturbations. More interestingly, we provide an example of thin-shell wormhole which is strictly stable in the sense that it is confined in between two classically intransmissible potential barriers.

gr-qc↗

arXiv2017

Cycloid Experiment for freshmen physics labs

We establish an instructive experiment to investigate the minimum time curve traveled by a small billiard ball rolling in a grooved track under gravity. Our intention is to popularize the concept of \textit{minimum time curve} anew, and to propose it as a feasible physics experiment both for freshmen and sophomore classes. We observed that even the non-physics major students did enjoy such a cycloid experiment.

physics.ed-ph↗

arXiv2017

Generalized Monge gauge

Monge gauge in differential geometry is generalized. The original Monge gauge is based on a surface defined as a height function $h(x,y)$ above a flat reference plane. The total curvature and the Gaussian curvature are found in terms of the height function. Getting benefits from our mathematical knowledge of general relativity, we shall extend the Monge gauge toward more complicated surfaces. Here in this study we consider the height function above a curved surface namely a sphere of radius $R$. The proposed height function is a function of $θ$ and $φ$ on a closed interval. We find the first, second fundamental forms and the total and Gaussian curvatures in terms of the new height function. Some specific limits are discussed and two illustrative examples are given.

physics.gen-ph↗

arXiv2016

Black p-Branes versus black holes in non-asymptotically flat Einstein-Yang-Mills theory

We present a class of non-asymptotically flat (NAF) charged black p-branes (BpB) with p-compact dimensions in higher dimensional Einstein-Yang-Mills theory. Asymptotically the NAF structure manifests itself as an anti-de-sitter spacetime. We determine the total mass / energy enclosed in a thin-shell located outside the event horizon. By comparing the entropies of BpB with those of black holes in same dimensions we derive transition criteria between the two types of black objects. Given certain conditions satisfied our analysis shows that BpB can be considered excited states of black holes. An event horizon $r_{+}$ versus charge square $Q^{2}$ plot \ for the BpB reveals such a transition where $r_{+}$ is related to the horizon radius $r_{h}$ of the black hole (BH) both with the common charge $% Q. $

gr-qc↗

arXiv2016

Black holes from multiplets of scalar fields in 2+1- and 3+1-dimensions

We obtain classes of black hole solutions constructed from multiplets of scalar fields in 2+1 / 3+1 dimensions. The multi-component scalars don't undergo a symmetry breaking so that only the isotropic modulus is effective. The Lagrangian is supplemented by a self-interacting potential which plays significant role in obtaining the exact solutions. In 2+1 / 3+1 dimensions doublet / triplet of scalars is effective which enriches the available black hole spacetimes and creates useful Liouville weighted field theoretic models.

gr-qc↗

arXiv2016

Generation of spherically symmetric metrics in $f\left( R\right) $ gravity

In $D-$dimensional spherically symmetric $f\left( R\right) $ gravity there are three unknown functions to be determined from the fourth order differential equations. It is shown that the system remarkably integrates to relate two functions through the third one to provide reduction to second order equations accompanied with a large class of potential solutions. The third function which acts as the generator of the process is $F\left( R\right) =\frac{df\left( R\right) }{dR}.$ We recall that our generating function has been employed as a scalar field with an accompanying self-interacting potential previously which is entirely different from our approach. Reduction of $f\left( R\right) $ theory into system of equations seems to be efficient enough to generate a solution corresponding to each generating function. As particular examples, besides known ones, we obtain new black hole solutions in any dimension $D$. We further extend our analysis to cover non-zero energy-momentum tensors. Global monopole and Maxwell sources are given as examples.

gr-qc↗

arXiv2016

Non-abelian magnetic black strings versus black holes

We present $d+1-$dimensional pure magnetic Yang-Mills (YM) black strings (or $1-$branes) induced by the $d-$dimensional Einstein-Yang-Mills-Dilaton black holes. Born-Infeld version of the YM field makes our starting point which goes to the standard YM field through a limiting procedure. The lifting from black holes to black strings, (with less number of fields) is by adding an extra, compact coordinate. This amounts to the change of horizon topology from $S^{d-2}$ to a product structure. Our black string in $5-$dimensions is a rather special one, with uniform Hawking temperature and non-asymptotically flat structure. As the YM charge becomes large the string gets thinner to tend into a breaking point and transform into a $4-$% dimensional black hole.

gr-qc↗

arXiv2016

Cloud of strings as source in $2+1$-dimensional $f( R) = R^n$ gravity

We present three parameters exact solutions with possible black holes in $% 2+1-$dimensional $f\left( R\right) =R^{n}$ modified gravity coupled minimally to a cloud of strings. These three parameters are $n,$ the cloud of string coupling constant $ξ$ and an integration constant $C$. Although in general one has to consider each set of parameters separately; for $n$ an even integer greater than one we give a unified picture providing black holes. For $n\geq 1$ we analyze null / timelike geodesic within the context of particle confinement.

gr-qc↗

arXiv2015

Hypocycloidal throat for 2+1-dimensional thin-shell wormholes

Recently we have shown that for $2+1-$dimensional thin-shell wormholes a non-circular throat may lead to a physical wormhole in the sense that the energy conditions are satisfied. By the same token, herein we consider angular dependent throat geometry embedded in a $2+1-$dimensional flat spacetime in polar coordinates. It is shown that a generic, natural example of throat geometry is provided remarkably by a hypocycloid. That is, two flat $2+1-$dimensions are glued together along a hypocycloid. The energy required in each hypocycloid increases with the frequency of the roller circle inside the large one.

gr-qc↗

arXiv2015

Einstein-Born-Infeld black holes with a scalar hair in three-dimensions

We present black hole solutions in $2+1-$dimensional Einstein's theory of gravity coupled with Born-Infeld nonlinear electrodynamic and a massless self-interacting scalar field. The model has five free parameters: mass $M$, cosmological constant $\ell $, electric $q$ and scalar $r_{0}$ charges and Born-Infeld parameter $β$. To attain exact solution for such a highly non-linear system we adjust, i.e. finely tune, the parameters of the theory with the integration constants. In the limit $β\rightarrow 0$ we recover the results of Einstein-Maxwell-Scalar theory, obtained before. The self interacting potential admits finite minima apt for the vacuum contribution. Hawking temperature of the model is investigated versus properly tuned parameters. By employing this tuned-solution as basis, we obtain also a dynamic solution which in the proper limit admits the known solution in Einstein gravity coupled with self-interacting scalar field. Finally we establish the equations of a general scalar-tensor field coupled to nonlinear electrodynamics field\ in $2+1-$dimensions without searching for exact solutions.

gr-qc↗

arXiv2015

2+1-dimensional wormhole from a doublet of scalar fields

We present a class of exact solutions in the framework of $2+1-$dimensional Einstein gravity coupled minimally to a doublet of scalar fields. Our solution can be interpreted upon tuning of parameters as an asymptotically flat wormhole as well as a particle model in $2+1-$dimensions.

gr-qc↗

arXiv2015

Screening of the Reissner-Nordström charge by a thin-shell of dust matter

A concentric charged thin-shell encircling a Reissner-Nordström black hole screens the clectric / magnetic charge completely to match with an external Schwarzschild black hole. The negative mass thin-shell is shown to be stable against radial perturbations. It is shown further that by reversing the roles of inside Reissner-Nordström and outside Schwarzschild geometries the mass of the appropriate shell becomes positive.

gr-qc↗

arXiv2015

Einstein-Maxwell gravity coupled to a scalar field in 2+1-dimensions

We consider Einstein-Maxwell-self-interacting scalar field theory described by a potential $V\left( ϕ\right) $ in $2+1-$dimensions. The self-interaction potential is chosen to be a highly non-linear double-Liouville type. Exact solutions, including chargeless black holes and singularity-free non-black hole solutions are obtained in this model.

gr-qc↗

arXiv2015

A topological metric in 2+1-dimensions

Real-valued triplet of scalar fields as source gives rise to a metric which tilts the scalar, not the light cone, in 2+1-dimensions. The topological metric is static, regular and it is characterized by an integer $κ=\pm 1,\pm 2,...$. The problem is formulated as a harmonic map of Riemannian manifolds in which the integer $κ$ equals to the degree of the map.

physics.gen-ph↗

arXiv2015

3+1-dimensional thin-shell wormhole with deformed throat can be supported by normal matter

From physics standpoint exotic matter problem is a major difficulty in thin-shell wormholes (TSWs) with spherical / cylindrical throat topologies. We aim to circumvent this handicap by considering angular dependent throats in $3+1-$dimensions. By considering the throat of the TSW to be deformed spherical, i.e., a function of $θ$ and $φ$, we present general conditions which are to be satisfied by the shape of the throat in order to have the wormhole supported by matter with positive density in the static reference frame. We provide particular solutions / examples to the constraint conditions.

physics.gen-ph↗

arXiv2015

Modified Rindler acceleration as a nonlinear electromagnetic effect

The model proposed originally by Mannheim and Kazanas for fitting the shapes of galactic rotation curves has recently been considered by Grumiller to describe gravity of a central object at large distances. Herein we employ the same geometry within the context of nonlinear electrodynamics (NED). Pure electrical NED model is shown to generate the novel Rindler acceleration term in the metric which explains anomalous behaviors of test particles / satellites. Remarkably a pure magnetic model of NED yields flat rotation curves that may account for the missing dark matter. Weak and Strong Energy conditions are satisfied in such models of NED.

gr-qc↗

arXiv2015

2+1-dimensional traversable wormholes supported by positive energy

We revisit the shapes of the throats of wormholes, including thin-shell wormholes (TSWs) in $2+1-$dimensions. In particular, in the case of TSWs this is done in a flat $2+1-$dimensional bulk spacetime by using the standard method of cut-and-paste. Upon departing from a pure time-dependent circular shape i.e., $r=a\left( t\right) $ for the throat, we employ a $% θ-$dependent closed loop of the form $r=R\left( t,θ\right) ,$ and in terms of $R\left( t,θ\right) $ we find the surface energy density $σ$ on the throat. For the specific convex shapes we find that the total energy which supports the wormhole is positive and finite. In addition to that we analyze the general wormhole's throat. By considering a specific equation of $r=R\left( θ\right) $ instead of $r=r_{0}=const.,$ and upon certain choices of functions for $R\left( θ\right) $ we find the total energy of the wormhole to be positive.

gr-qc↗