No-ghost theorem for neveu-schwarz string in 0-picture

Abstract

The no-ghost theorem for Neveu-Schwarz string is directly proved in 0-picture. The oneto-one correspondence between physical states in 0-picture and in the conventional (- 1)-picture is confirmed. It is shown that a nontrivial metric consistent with the BRST cohomology is needed to define a positive semidefinite norm in the physical Hilbert space. As a by-product, we find a new inverse picture-changing operator, which is noncovariant but has a nonsingular operator product with itself. A possibility to construct a new gauge-invariant superstring field theory is discussed.