Heterotic effective action and duality symmetries revisited

Abstract

The dimensional reduction of heterotic supergravity with gauge fields truncated to the Cartan subalgebra exhibits a continuous O(d, d + 16; ℝ) global symmetry, related to the O(d, d + 16; ℤ) T-duality of heterotic strings on a d-torus. The O(d, d + 16; ℝ) symmetry is not present, however, if the supergravity reduction is done including the full set of E8 × E8 or SO(32) gauge fields. We analyze which duality symmetries are realized to all orders in α′ in the proper effective field theories for the massless string states. We find a universal O(d, d; ℝ) symmetry, also predicted by double field theory. We confirm this by giving a novel formulation of the dimensionally reduced supergravity in terms of O(d, d) multiplets, and we discuss cases of symmetry enhancement.