Signatures of cosmic strings on the microwave background

We review recent progress on testing the hypothesis of the existence of cosmic string perturbations in microwave background maps. Using an analytical model for the string network we show that the predicted amplitude and spectrum of MBR fluctuations are consistent with the COBE data for a reasonable value of the single free parameter of the string model (the mass per unit length of the string mu). To distinguish the predictions of cosmic strings from those of Gaussian models it is necessary to apply specific statistical tests which are sensitive to non-random phases of the MBR temperature maps. We discuss two such statistical tests: First, the probability distribution and the moments of fluctuations delta T/T and second the corresponding statistical quantities for the gradient of fluctuations along a fixed direction. We show that the second statistic can detect cosmic string specific signatures on MBR temperature maps with resolution of a few arcminutes or smaller.