$O(D,D)$-constraint on $D$-dimensional effective actions

TL;DR

This paper explores how combining $O(D,D)$ symmetry and gauge invariance constraints can determine the form of string theory effective actions at first order in $\alpha'$ without detailed knowledge of correction terms.

Contribution

It constructs $O(D,D)$-invariant actions and shows that matching these with covariant $D$-dimensional actions fixes their form up to overall factors and redefinitions.

Findings

$O(D,D)$-invariance constrains effective actions significantly.

Matching $D$-dimensional and doubled actions fixes their structure.

The approach reduces ambiguity in $\alpha'$-corrections.

Abstract

Double Field Theory is a manifestly T-duality invariant formulation of string theory in which the effective theory at any order of $\alpha'$ is invariant under global $O(D,D)$ transformations and ought to be invariant under gauge transformations which receive $\alpha'$-corrections. On the other hand, the effective theory in the usual $D$-dimensional formulation of string theory is manifestly gauge invariant and ought to be invariant under T-duality transformations which receive $\alpha'$-corrections. We speculate that the combination of these two constraints may fix both the $2D$-dimensional and the $D$-dimensional effective actions without knowledge of the $\alpha'$-corrections of the gauge and the T-duality transformations. In this paper, using generalized fluxes, we construct arbitrary $O(D,D)$-invariant actions at orders $\alpha'^0$ and $\alpha'$, and then dimensionally reduce them to the $D$-dimensional spacetime. On the other hand, at these orders, we construct arbitrary covariant $D$-dimensional actions. Constraining the two $D$-dimensional actions to be equal up to non-covariant field redefinitions, we find that both actions are fixed up to overall factors and up to field redefinitions.