Ghost number 2As in the case of Maxwell theory, elements of should correspond to the gauge invariant operators in Type IIB theory.Let us consider the case of flat space. The simplest thing we can reproduce is the Ramond-Ramond bispinor:

Here is defined using the “left” part of —

see Eq. (38). It automatically satisfies the Dirac equation, because and satisfy the Dirac equations (33).