On marginal deformations of (0,2) non-linear sigma models

An N=1, d=4 supersymmetric compactification of the perturbative heterotic string is described by a d=2 (0,2) superconformal field theory. The first-order marginal deformations of the internal (0,2) SCFT are in 1 to 1 correspondence with massless gauge-neutral scalars in the spacetime theory. Working at tree-level in the alpha' expansion, we describe these first order deformations for SCFTs with a (0,2) non-linear sigma model description. Our results clarify the structure of deformations of heterotic Calabi-Yau compactifications and more general heterotic flux vacua.