  We discuss an effective field theory background containing the gravitational
field, the dilaton and a closed string tachyon, and couple this background to a
gas of fundamental strings and D strings. Allowing for the possibility of a
non-vanishing dilaton potential of Casimir type, we demonstrate the possibility
of obtaining a nonsingular, static tachyon condensate phase with fixed dilaton.
The time reversal of our solution provides a candidate effective field theory
description of a Hagedorn phase of string gas cosmology with fixed dilaton.
