Courant algebroid without constraints on fluxes on its Dirac structures

Abstract

We examine the standard Courant bracket and its extensions, defined by twists with different $O(D,D)$ transformations relevant to string theory. We analyze Dirac structures on these Courant algebroids and derive the constraints they impose on fluxes. In the end, we show that the Courant algebroid simultaneously twisted by both $B$ and $\theta$ is characterized by Dirac structures with no restrictions on fluxes.