Deformation theory of deformed Hermitian Yang-Mills connections and deformed Donaldson-Thomas connections

A deformed Hermitian Yang-Mills (dHYM) connection and a deformed Donaldson-Thomas (dDT) connection are Hermitian connections on a Hermitian vector bundle $L$ over a Kahler manifold and a $G_2$-manifold, which are believed to correspond to a special Lagrangian and a (co)associative cycle via mirror symmetry, respectively. In this paper, when $L$ is a line bundle, introducing a new balanced Hermitian structure from the initial Hermitian structure and a dHYM connection and a new coclosed $G_2$-structure from the initial $G_2$-structure and a dDT connection, we show that their deformations are controlled by a subcomplex of the canonical complex introduced by Reyes Carrion. The expected dimension is given by the first Betti number of a base manifold for both cases. In the case of dHYM connections, we show that there are no obstructions for their deformations, and hence, the moduli space is always a smooth manifold. As an application of this, we give another proof of the triviality of the deformations of dHYM metrics proved by Jacob and Yau. In the case of dDT connections, we show that the moduli space is smooth if we perturb the initial $G_2$-structure generically.