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Hassan Niad

Publications and source records attributed to Hassan Niad.

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Weak Gravitational lensing from regular Bardeen black holes

In this article we study weak gravitational lensing of regular Bardeen black hole which has scalar charge $g$ and mass $m.$ We investigate the angular position and magnification of non-relativistic images in two cases depending on the presence or absence of photon sphere. Defining dimensionless charge parameter $q=\frac{g}{2m}$ we seek to disappear photon sphere in the case of $|q|>{24\sqrt5}/{125}$ for which the space time metric encounters strongly with naked singularities. We specify the basic parameters of lensing in terms of scalar charge by using the perturbative method and found that the parity of images is different in two cases: (a) The strongly naked singularities is present in the space time. (b) singularity of space time is weak or is eliminated (the black hole lens).

gr-qc

Gravitating Isovector Solitons

We formulate the nonlinear isovector model in a curved background, and calculate the spherically symmetric solutions for weak and strong coupling regimes. The usual belief that gravity does not have appreciable effects on the structure of solitons will be examined, in the framework of the calculated solutions, by comparing the flat-space and curved-space solutions. It turns out that in the strong coupling regime, gravity has essential effects on the solutions. Masses of the self-gravitating solitons are calculated numerically using the Tolman expression, and its behavior as a function of the coupling constant of the model is studied.

gr-qc