The off-shell Veneziano amplitude in Schnabl gauge

Understand

We give a careful definition of the open string propagator in Schnabl gauge and present its worldsheet interpretation.

• The propagator requires two Schwinger parameters and contains the BRST operator.
• It builds surfaces by gluing strips of variable width to the left and to the right of off-shell states with contracted or expanded local frames.
• We evaluate explicitly the four-point amplitude of off-shell tachyons.