  We prove that the NS cubic superstring field theories are classically
equivalent, regardless of the choice of Y_{-2} in their definition, and
illustrate it by an explicit evaluation of the action of Erler's solution. We
then turn to examine this solution. First, we explain that its cohomology is
trivial also in the Ramond sector. Then, we show that the boundary state
corresponding to it is identically zero. We conclude that this solution is
indeed a closed string vacuum solution despite the absence of a tachyon field
on the BPS D-brane.

High Energy Physics - Theory