SOFT DILATON THEOREM IN COVARIANT STRING FIELD THEORY

Abstract The dilaton is studied in the context of covariant, cubic, open and closed string field theories. The string field configuration corresponding to a dilaton plane wave in flat space is constructed. Taking the zero-momentum limit, it is shown that the string coupling constant is correctly rescaled by a shift in the dilaton expectation value. The demonstration involves a subtle interplay between world-sheet cohomology and the algebra of string fields. This shift can be viewed as the result of a singular gauge transformation.