Weak field deflection angle by regular black holes with cosmic strings using the Gauss-Bonnet theorem

Abstract

In this paper, we investigate light bending in the spacetime of regular black holes with cosmic strings in weak field limits. To do so, we apply the Gauss-Bonnet theorem to the optical geometry of the black hole; and, using the Gibbons-Werner method, we obtain the deflection angle of light in the weak field limits which shows that the bending of light is a global and topological effect. Afterwards, we demonstrate the effect of a plasma medium on the deflection of light by a regular black hole with cosmic strings. We discuss that increasing cosmic string parameter mu and mass M-0 will increase the bending angle.