We consider two problems associated to the space of Riemann surfaces that are closely related to string theory. We first consider the problem of existence of heterotic-string and type-II-superstring field theory vertices in the product of spaces of bordered surfaces parameterizing left- and right-moving sectors of these theories. It turns out that this problem can be solved by proving the existence of a solution to the BV quantum master equation in moduli spaces of bordered spin-Riemann surfaces. We first prove that for arbitrary genus $g$, $n_{\text{NS}}$ Neveu-Schwarz boundary components, and $n_{\text{R}}$ Ramond boundary components such solutions exist. We also prove that these solutions are unique up to homotopies in the category of BV algebras and are mapped to fundamental classes of Deligne-Mumford stacks of associated punctured spin curves. These results generalize the work of Costello on the existence of a solution to the BV quantum master equations in moduli spaces of bordered ordinary Riemann surfaces. Using this, we prove that heterotic-string and type-II-superstring field theory vertices exist. Furthermore, we prove the existence of a solution to the BV quantum master equation in spaces of bordered $\mathscr{N}=1$ super-Riemann surfaces for arbitrary genus $g$, $n_{\text{NS}}$ Neveu-Schwarz boundary components, and $n_{\text{R}}$ Ramond boundary components. Secondly, we turn to the moduli problem of stable $\mathscr{N}=1$ SUSY curves. Using Vaintrob's deformation theory of complex superspaces and Deligne's model for the compactification of the space of $\mathscr{N}=1$ SUSY curves, we prove the representability of this moduli problem by a proper smooth Deligne-Mumford superstack. This is a generalization of the work of Deligne and Mumford on the representability of the moduli problem of stable ordinary curves by a Deligne-Mumford stack.

157 pages.