  In this paper, we show that there exists a hidden gauge reducibility in
superstring field theory based on the small dynamical string field $\Psi \in
\mathcal{H}_{\beta \gamma }$ whose gauge variation is also small $\delta \Psi
\in \mathcal{H}_{\beta \gamma }$. It requires additional ghost-antighost fields
in the gauge fixed or quantum gauge theory, and thus changes the
Batalin-Vilkovisky master action, which implies that additional propagating
degrees of freedom appear in the loop superstring amplitudes via the gauge
choice of the field theory. We present that the resultant master action can
take a different and enlarged form, and that there exist canonical
transformations getting it back to the canonical form. On the basis of the
Batalin-Vilkovisky formalism, we obtain several exact results and clarify this
underlying gauge structure of superstring field theory.

High Energy Physics - Theory