Abstract Details
| Name: D. Narasimha Affiliation: Tata Institute of Fundamental Research Conference ID: ASI2015_635 Title : Gravitational Lensing as a probe of Ultraviolet and Infrared modifications of Gravity Authors and Co-Authors : Satyabrata Sahu, D. Narasimha (Tata Institute of Fundamental Research) and Kinjalk Lochan (IUCAA) Abstract Type : Oral Abstract Category : General Relativity and Cosmology Abstract : General Relativity will necessarily have to be modified at higher energies (in the Ultraviolet) by some quantum theory of Gravity, the two foremost candidates for which now are String Theory and Loop Quantum Gravity (LQG). The study of black holes might yield a few insights for revealing the quantum nature of spacetime. In this light, we study gravitational lensing in the background of a recently proposed black hole solution in Loop Quantum Gravity by Modesto in both the strong and weak deflection regimes and present a sample consistency relation which could serve as a test of this model. Curiously, the quantum gravity corrections to the Schwarzschild metric in this model evade the ‘mass suppression’ effects (that the usual quantum gravity corrections are susceptible to) by virtue of one of the parameters in the model being dimensionless, which is unlike any other quantum gravity motivated parameter such as string tension or non-commutativity parameter. (This is possibly a disturbing aspect of the theory). Although the observational prospects do not seem to be very optimistic even for a galactic supermassive black hole case, time delay between relativistic images for billion solar mass black holes in other galaxies might be within reach of future relativistic lensing observations. Although there is no real theoretical compulsion for modification of gravity at extremely low energy scales (in the Infrared), the cosmological observations of dark energy point towards such a possibility. (If the various limits on variation of Fine Structure Constant are assumed to be consistent, they might imply a space dependence of the Fundamental Constants.) It has been recently argued by Grumiller that the most general theory of gravity at large distances (the Infrared) permits in addition to the usual terms in General Relativity (the Schwarzschild term and Cosmological constant term) a Rindler acceleration term which increases linearly with radial distance. We investigate gravitational lensing in the presence of Rindler term taking into account the consequent asymptotic non-flatness of spacetime which makes the standard definition of deflection angle and lens equation incorrect. We derive the generalized Rindler-Ishak deflection angle to complement some earlier bounds on Rindler term from Solar system tests and confirm that the solar system light bending bound is indeed weak. We also set up and solve the lens equation perturbatively and quantify the effect of Rindler term on the lensing observables. We find that with the galactic supermassive black hole as the lens, corrections to lensing observables like angular location of Einstein Ring can be probed with future lensing missions. ~ |