BRS invariance and unitarity in closed string field theory

Abstract

Abstract We study the unitarity of loop amplitudes in the new path-integral formalism of covariant closed string field theory. The quantum action is given by adding to the classical action the correction terms which are higher order in ħ and recover the BRS symmetry breaking caused by the path-integral measure. Surprisingly, we find that the unitarity holds for g ( ⩽ 3)-loop amplitudes. This indicates that the BRS invariance automatically ensures the unitarity.