On Ghost Structure of Vacuum Superstring Field Theory

After discussing the general form of the kinetic operator Q̂ around the tachyon vacuum, we determine the specific form of the pure-ghost kinetic operator Q̂ by requiring the twist invariance of the action. We obtain a novel result that the Grassmann-even piece Qeven of Q̂ must act differently on GSO(+) sector and on GSO(−) sector to preserve the twist invariance, and show that this structure is crucial for gauge invariance of the action. With this choice of Q̂, we construct a solution in an approximation scheme which is conjectured to correspond to a nonBPS D9-brane. We consider both 0-picture cubic and Berkovits’ non-polynomial superstring field theories for the NS sector. E-mail: [email protected]