Cosmic strings lens phenomenology: General properties of distortion fields- art. no. 023004

We reconsider the general properties of gravitational lensing effects induc ed by cosmic string systems, taking into account their equation of state an d motion equations. We explicitly show that the deflection patterns induced by a string is equivalent to the one of a static distribution of matter lo calized on a line. We then rigorously show that the convergence part of the deformation field is always zero, except on the intersection of the string world sheet and the observer past light cone, extending previous results o btained in peculiar cases. Phenomenological consequences of this result on multiple image systems are investigated.