f(G) modified gravity and the energy conditions

José P. Mimoso and Francisco S. N. Lobo

In considering alternative higher-order gravity theories, one is liable to be motivated in pursuing models consistent and inspired by several candidates of a fundamental theory of quantum gravity. Indeed, motivations from string/M-theory predict that scalar field couplings with the Gauss- Bonnet invariant, G, are important in the  appearance of non-singular early time cosmologies. In this work, we discuss the viability of an interesting alternative gravitational theory, namely, modified Gauss- Bonnet gravity, and present the respective viability bounds arising from the energy conditions.