Papers by majid karimabadi
arXiv (Cornell University), Aug 19, 2023
arXiv (Cornell University), Mar 4, 2024
Black hole perturbation theory is a useful approach to study interactions between black holes and... more Black hole perturbation theory is a useful approach to study interactions between black holes and fundamental fields. A particular class of black hole solutions arising out of modification of Einstein's general theory of relativity are regular black holes (RBHs) which can be constructed by using a nonlinear electrodynamic Lagrangian. It is expected that this idea may correct the pathological singular behavior of classical black hole solutions. Because of their importance we are interested in studying the behavior of three kinds of such RBHs under perturbations generated by an external field. In fact, we investigate the quasinormal modes (QNMs) of a massive scalar field propagating near the RBH which is non-minimally coupled to the Ricciscalar tensor of background geometry. We numerically find the low-lying QNM frequencies for the perturbations by using the third-order WKB approximation. We also analyze the relationships between the QNM frequencies and the physical parameters of ...
The general theory of relativity is the currently accepted theory of gravity and as such, a large... more The general theory of relativity is the currently accepted theory of gravity and as such, a large repository of test results has been carried out since its inception in 1915. However, in this paper we will only focus on what are considered as the main tests but in non-commutative geometries. Using the coordinate coherent state formalism, we consider gravitational red-shift, deflection, and time delay of light, separately, for Schwarzschild and Riessner-Nordstrom metrics in their non-commutative form. We will schematically show that these non-commutative calculations have different behavior with respect to the predictions of general relativity. We also specify an upper bound on the non-commutative parameter by comparing the results with accuracies of gravitational measurements for typical micro black holes which can be produced in the early universe.
We attempt to study three significant tests of general relativity in higher dimensions both in co... more We attempt to study three significant tests of general relativity in higher dimensions both in commutative and non-commutative spaces. In the context of non-commutative geometry, we will consider a solution of the Einstein equation in higher dimensions with a source given by a static, spherically symmetric Gaussian distribution of mass. The resulting metric would describe a regular or curvature singularity free black hole in higher dimensions. The metric should smoothly interpolate between Schwarzschild geometry at large distance and de-Sitter spacetime at short distance. We will consider gravitational redshift, lensing, and time delay in each sector. It will be shown that, compared to the four-dimensional spacetime, there can be significant modifications due to the presence of extra dimensions and the non-commutative corrected black holes. Finally, we shall attempt to obtain a lower bound on the size of the extra dimensions and on the mass needed to form a black hole in different d...
arXiv: High Energy Physics - Theory, 2019
Black hole perturbation theory is a useful approach to study interactions between black holes and... more Black hole perturbation theory is a useful approach to study interactions between black holes and fundamental fields. A particular class of black hole solutions arising out of modification of Einstein's general theory of relativity are regular black holes (RBHs) which can be constructed using a nonlinear electrodynamic Lagrangian. Because of their importance, we are interested in studying the behavior of three kinds of such RBHs under perturbations generated by an external field. Indeed, we investigate the quasinormal modes (QNMs) of a massive scalar field propagating near the RBHs which is non-minimally coupled to the Ricciscalar tensor of background geometry. We numerically find the low-lying quasinormal frequencies of the perturbations by using the third-order WKB approximation. The frequencies of QNMs only depend on the properties of the black hole and are complex which their imaginary parts are important in determineing the stability of black hole against the scalar perturb...
Galaxies
We attempt to study three significant tests of general relativity in higher dimensions, both in c... more We attempt to study three significant tests of general relativity in higher dimensions, both in commutative and non-commutative spaces. In the context of non-commutative geometry, we will consider a solution of Einstein’s equation in higher dimensions, with a source given by a static, spherically symmetric Gaussian distribution of mass. The resulting metric would describe a regular or curvature singularity free black hole in higher dimensions. The metric should smoothly interpolate between Schwarzschild geometry at large distance, and de-Sitter spacetime at short distance. We will consider gravitational redshift, lensing, and time delay in each sector. It will be shown that, compared to the four-dimensional spacetime, there can be significant modifications due to the presence of extra dimensions and the non-commutative corrected black holes. Finally, we shall attempt to obtain a lower bound on the size of the extra dimensions and on the mass needed to form a black hole in different ...
Classical and Quantum Gravity, Mar 19, 2020
The general theory of relativity is currently the accepted theory of gravity and as such, a large... more The general theory of relativity is currently the accepted theory of gravity and as such, a large repository of test results has been obtained since its inception in 1915. However, in this paper we only focus on what are considered as the main tests but in non-commutative (NC) geometries. Using the coordinate coherent state formalism, we calculate the gravitational redshift, deflection, and time delay of light, separately, for NC inspired Schwarzschild and Riessner-Nordström black holes. We show the NC predictions have different behavior than the general relativity. We also provide an upper bound on the NC parameter by comparing the NC corrections with the accuracies of gravitational measurements in the case of typical primordial black holes produced in the early universe. In this regard, we use observational data for the scale factor a at the end of inflation to obtain physical satisfactory results.
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Papers by majid karimabadi