A unifying topological action for heterotic and type II superstring theories

The heterotic and type II superstring actions are identified in different anomaly-free decompositions of a single topological sigma-model action depending on bosonic and fermionic coordinates, Xμ and ϱA respectively, and of their topological ghosts. This model results from gauge-fixing the topological gauge symmetry δXμ = ϵμ(z, z) (μ = 1, 2,…, 10) and δϱα = ϵα(z, z) (α = 1, 2,…, 16). From another viewpoint the heterotic and type H superstring actions emerge as two different gauge-fixings of the same closed two-form. Comments are also made concerning the possibility of relating ϱα to a Majorana-Weyl space-time spinor superpartner of Xμ.