LAUSR

A bstractWe consider the algebraic effective couplings for open superstring massless modes in the framework of the A∞ theory in the small Hilbert space. Focussing on quartic couplings, we reduce the effective action of the A∞ theory to the Berkovits one where we have already shown that such couplings are fully computed from contributions at the boundary of moduli space, when the massless fields are appropriately charged under an N$$ \mathcal{N} $$ = 2 R-symmetry. Here we offer a proof of localization which is in the small Hilbert space. Our analysis shows that the flat directions of the quartic potential are controlled by ADHM-like constraints, which are directly related to the localization channels of the effective action. In particular we give evidence for the existence of exactly marginal deformations corresponding to blowing up moduli in the D(p + 4)/Dp system in the framework of string field theory.