Portrait of the String as a Random Walk

In this paper we analyze a Rutherford type experiment where light probes areinelastically scattered by an ensemble of excited closed strings, and use thecorresponding cross section to extract density-density correlators betweendifferent pieces of the target string. We find a wide dynamical range where thespace-time evolution of typical highly excited closed strings is accuratelydescribed as a convolution of brownian motions. Moreover, we show that if wewant to obtain the same cross section by coherently scattering probes off aclassical background, then this background has to be time-dependent andsingular. This provides an example where singularities arise, not as a resultof strong gravitational self-interactions, but as a byproduct of thedecoherence implicit in effectively describing the string degrees of freedom asa classical background.Comment: 17 pages. Typos corrected, 1 reference adde