Ja. Nieto et J. Socorro, Self-dual gravity and self-dual Yang-Mills theory in the context of the Macdowell-Mansouri formalism - art. no. 041501., PHYS REV D, 5904(4), 1999, pp. 1501
In this work we propose an action which unifies self-dual gravity and self-
dual Yang-Mills theory in the context of the Macdowell-Mansouri formalism.
We claim that such an action may be used to find the S-dual action for both
self-dual gravity and self-dual Yang-Mills theory. [S0556-2821(99)50202-6]
.