One-loop correction of the tachyon action in boundary superstring field theory

We compute one-loop correction to the string field theory action of the tac hyon for unstable D-branes in the framework of the boundary superstring fie ld theory. We would expect that the one-loop correction comes from the part ition function of the two-dimensional worldsheet theory on the annulus. The annulus correction suggests that the genus expansion is, somehow, governed by the effective string coupling defined in terms of the tachyon lambda = g(s) exp(-T-2/4). (C) 2001 Published by Elsevier Science B.V.