Size of the smallest scales in cosmic string networks

We present a method for the calculation of the gravitational back-reaction cutoff on the smallest scales of cosmic string networks taking into account that not all modes on strings interact with all other modes. This results in a small scale structure cutoff that is sensitive to the initial spectrum of perturbations present on strings. From a simple model, we compute cutoffs in radiation- and matter-dominated universes which are much smaller than the results usually presented in the literature.