Semiclassical gravitational effects on the gravitational lensing in the spacetime of topological defects

TL;DR

This paper investigates semiclassical gravitational effects on light deflection caused by topological defects like cosmic strings and monopoles using the Gauss-Bonnet theorem, revealing precise agreement with traditional methods and analyzing time delays.

Contribution

It applies the Gauss-Bonnet theorem to compute light deflection in topological defect spacetimes, demonstrating exact results and extending understanding of semiclassical gravitational lensing effects.

Findings

Exact agreement between GBT and standard deflection calculations up to third order.

Time delay is proportional to the linear mass density and defect parameters.

Modified domain of integration yields precise deflection angles for defects.

Abstract

The theory of gravitational lensing has revealed many generic and fundamental properties of compact objects like black holes and wormholes. In this article, we utilize a recent formulation to compute the quantum effects on the deflection angle of a light ray, namely, the Gauss-Bonnet theorem (GBT) to explore the semiclassical gravitational effects in the spacetime of a point-like global monopole and a cosmic string. Previously, the Gauss-Bonnet theorem [Class. Quant. Grav. 25, 235009 (2008)] was proposed as an alternative way to compute the deflection angle of light in a static, spherically symmetric and asymptotically flat spacetime. In the present article we have used the celebrated GBT that applied to the optical metric as well as the geodesic method in computing the deflection angle. Interestingly one can observe that we have found an exact result between GBT and the standard approach up to the third-order contributions terms by modifying the domain of integration for cosmic string and global monopole deflection angles. Finally we have considered the time delay in the cosmic string/global monopole spacetime and found that the delay in time is proportional to the linear mass density of the cosmic string and global monopole parameter, respectively.