Optical properties of gravitating strings

Abstract

We study the optical properties of gravitating Abelian-Higgs cosmic strings and compare them with those of the idealized infinitely thin string. We analyze the structure of the corresponding vortex solutions, characterizing their width, curvature profile, and approach to the ideal string limit. By investigating photon propagation in the string spacetime, we show that the finite core of the vortex gives rise to distinctive observational signatures absent in the ideal string approximation, including a characteristic triple-imaging configuration, strong demagnification of the central image, and a nontrivial Shapiro time delay between external and internal images. We determine how these effects depend on the parameters of the Abelian-Higgs model and show that the sign of the time delay is controlled by the ratio of the gauge boson mass to the Higgs boson mass, causing the string core to behave as either a temporal shortcut or a temporal barrier. Our results demonstrate that lensing effects can reveal information about the vortex formation and internal structure.