LENSING PROPERTIES OF LIGHT-LIKE CURRENT-CARRYING COSMIC STRINGS

The lensing properties of superconducting cosmic strings endowed with a time dependent pulse of lightlike current are investigated. The metr ic outside the core of the string belongs to the pp-wave class, with a deficit angle. We study the field theoretic bosonic Witten model coup led to gravity, and we show that the full metric (both outside and ins ide the core) is a Taub-Kerr-Shild generalization of that for the stat ic string with no current. It is shown that the double image due to th e deficit angle evolves in an unambiguous way as a pulse of lightlike current passes between the source and the observer. Observational cons equences of this signature of the existence of cosmic strings are brie fly discussed.