Brans-Dicke gravity theory from topological gravity

We consider a model that suggests a mechanism by which the four dimensional Brans-Dicke gravity theory may emerge from the topological gravity action. To achieve this goal, both the Lie algebra and the symmetric invariant tensor that define the topological gravity Lagrangian are constructed by means of the Lie algebra S-expansion procedure with an appropriate abelian semigroup S. (C) 2014 Elsevier B.V.