Speaker: Sayan Chakrabarti (Indian Institute of Technology, Guwahati)

Title: Shadow of a black hole in loop quantum gravity and its super-radiance property

Abstract:

We will discuss the shadow calculation of the loop quantum gravity motivated regular black hole recently proposed by Ashtekar, Olmedo and Singh (AOS black hole hereafter). In the process, we also construct the rotating loop quantum gravity inspired solution of the originally proposed static spherically symmetric AOS black hole by applying the modified Newman-Janis algorithm. We study the quantum effects on the shadows of both the non-rotating and rotating loop quantum black hole solutions. It is observed that the general shape of the shadow for nonrotating AOS black hole is circular in shape as is expected for its classical counterpart too, but the presence of loop quantum gravity inspired modification contracts the shadow radius and the effect reduces with the increase in the mass of the black hole. On a similar note, in the rotating situation, we find contraction in shadow radius due to quantum effects and the tapered nature of the shadow as expected from the classical Kerr case. However, instead of the symmetrical contraction, like non-rotating one, we found more contraction on one side relative to the other when we compare our result with the shadow of the Kerr black hole. We finally studied super-radiance in rotating AOS background and observed that the super-radiance condition for massless scalar field is identical to that of the Kerr case with the rotation of the BH being more compared to Kerr in the low mass regime. With an increase in mass of the rotating AOS black hole, the difference from Kerr starts to become insignificant. We also perform the calculation of the super-radiance amplification factor using Teukolsky formalism in the AOS background and present a comparative study of the amplification factors of the AOS and Kerr black holes with respect to changing mass and spin of the holes.

Room: Sala de Reuniões e Seminários (2-8.3) (2nd Floor of Physics Building)