A tachyon lump in closed string field theory

Abstract

We find a codimension one lump solution of closed bosonic string field theory. We consider vertices up to quartic order and include in the string field the tachyon, the ghost dilaton, and a metric fluctuation. While the tachyon profile clearly is that of a lump, we observe that the ghost dilaton is roughly constant in the direction transverse to the lump, equal to the value it takes in the nonperturbative tachyon vacuum. We explain, with a simple model, why this should be expected.