Generalized gauge conditions in the Virasoro-Shapiro model and elimination of ghosts

A proof for the no-ghost theorem of the Virasoro-Shapiro model is given without referring to the Virasoro conditions [L±0 - L±n - α(0)/2]|Φ≥0 which do not hold. The crucial point for the proof is that there hold modified gauge conditions ~L±n|Φ≥0 (n=1, 2 …) where ~L±n are the conformal group generators in the interacting case. The whole scheme is constructed based on the closed string loop model.