  The existence of de Sitter solutions in string theory is strongly constrained
by no-go theorems. We continue our investigation of corrections to the
heterotic effective action, with the aim of either strengthening or evading the
these constraints. We consider the combined effects of H-flux, gauge bundles,
higher derivative corrections and gaugino condensation. The only consistent
solutions we find with maximal symmetry in four dimensions are Minkowski
spacetimes, ruling out both de Sitter and anti-de Sitter solutions constructed
from these ingredients alone.
