  We consider backreaction due to production of massless strings in the
background of a condensing closed string tachyon. Working in the region of weak
tachyon, we find the modified equations of motion for massless strings with
conformal perturbation theory. We solve for the positive and negative frequency
modes and estimate the backreaction on the background dilaton. In large
(supercritical) dimensions, we find that the backreaction can be significant in
a large region of spacetime. We work with the bosonic string, but we expect
these results to carry over into the heterotic case.
