GRAVITATIONAL LENSING BY COSMIC-STRING LOOPS

We calculate the deflection of a light ray caused by the gravitational field of a cosmic string loop in the weak field limit and reduce the problem to a single quadrature over a time slice of the loop's world s heet. We then apply this formalism to the problem of gravitational len sing by cosmic string loops. In particular, we find an analytic soluti on for the special case of a circular loop perpendicular to the optica l axis. As examples of more complicated loops, we consider two loops w ith higher-frequency Fourier modes. The numerical analysis illustrates the general features of loop lenses. Our estimates, using typical par ameters for GUT scale loops, show thai the stringy nature of loop lens es can be observed for lensing systems involving high redshift galaxie s (z similar to 2), and we suggest that gravitational lensing can conf irm the existence of GUT scale strings if they are the seeds fur large -scale structure formation.