arXiv subjects

Asoke Kumar Sen

Publications and source records attributed to Asoke Kumar Sen.

4 recordsLinked to original sources

arXiv2026

Light bending around the Kerr-Bertotti-Robinson black hole using material medium approach

In this paper, we study the deflection of massless particles due to a rotating, axially symmetric Kerr-Bertotti-Robinson (KBR) black hole via; material medium approach. We explored the effect of spacetime geometry on the trajectory of light rays in the presence of a uniform magnetic field. To derive an analytical expression for the deflection of light rays due to the Kerr-Bertotti-Robinson black hole, the frame dragging effect and refractive index were also studied in greater detail. From the analysis it is evident that the magnetic field actively adds to the black hole's gravity, making the bending of light stronger and permanently changing the space far away from the black hole, preventing it to act as a normal flat vacuum. From thermodynamical investigation, it is clear that entropy monotonically decreases with magnetic field strength and rotation parameter; whereas the Hawking temperature increases with a uniform magnetic field but decreases with spin parameter.

gr-qc↗

arXiv2020

Spectroscopic Survey of Hα Emission Line Stars Associated with Bright Rimmed Clouds

The results of a spectroscopic survey of H alpha emission line stars associated with fourteen bright rimmed clouds are presented. Slit-less optical spectroscopy was carried out with the Inter University Centre for Astronomy and Astrophysics (IUCAA) 2m telescope and IUCAA Faint Object Spectrograph and Camera (IFOSC). H alpha emission line was detected from 173 objects. Among them 85 objects have a strong H alpha emission line with its equivalent width larger than 10 A. Those are classical T Tauri stars. 52 objects have a weak H alpha emission line with its equivalent width less than 10 A and do not show intrinsic near-infrared excess. Those are weak-line T Tauri stars. On the other hand, 36 objects have a weak H alpha emission line (<10 A), although they show intrinsic near-infrared excess. Such objects are not common in low-mass star forming regions. Those are misfits of the general concept on formation process of a low-mass star, in which it evolves from a classical T Tauri star to a weak-line T Tauri star. Those might be weak-line T Tauri stars with a flared disk in which gas is heated by ultraviolet radiation from a nearby early-type star. Alternatively, we propose pre-transitional disk objects as their evolutional stage.

astro-ph.SR↗

arXiv2013

The latitude dependence of gravitational redshift from rotating body

Gravitational redshift is being generally calculated without considering the rotation of a body. Neglecting the rotation, the geometry of space time can be described by using the spherically symmetric Schwarzschild geometry. Rotation has great effect on general relativity, which gives new challenges on gravitational redshift. When rotation is taken into consideration spherical symmetry is lost and off diagonal terms appear in the metric. The geometry of space time can be then described by using the solutions of Kerr family. In the present paper we will discuss the gravitational redshift for rotating body by using Kerr metric. The numerical calculations has been done under Newtonian approximation of angular momentum. The variation of gravitational redshift from equatorial to non - equatorial region has been calculated and its implications are discussed in detail.

gr-qc↗

arXiv2008

Dynamical symmetry breaking of lambda and vee-type three-level systems on quantization of the field modes

We develop a scheme to construct the Hamiltonians of the lambda, vee and cascade type of three-level configurations using the generators of SU(3) group. It turns out that this approach provides a well defined selection rule to give different Hamitonians for each configurations. The lambda and vee type configurations are exactly solved with different initial conditions while taking the two-mode classical and quantized fields . For the classical field, it is shown that the Rabi oscillation of the lambda model is similar to that of the vee model and the dynamics of the vee model can be recovered from lambda model and vice versa simply by inversion. We then proceed to solve the quantized version of both models introducing a novel Euler matrix formalism. It is shown that this dynamical symmetry exhibited in the Rabi oscillation of two configurations for the semiclassical models is completely destroyed on quantization of the field modes. The symmetry can be restored within the quantized models when the field modes are both in the coherent states with large average photon number which is depicted through the collapse and revival of the Rabi oscillations.

quant-ph↗