2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/192621We 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.7 pages, two references addedHigh Energy Physics - TheoryAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Phenomenologytext