title: General second-order scalar-tensor theory and self-tuning.
abstract: Starting from the most general scalar-tensor theory with second-order field equations in four dimensions, we establish the unique action that will allow for the existence of a consistent self-tuning mechanism on Friedmann-Lemaître-Robertson-Walker backgrounds, and show how it can be understood as a combination of just four base Lagrangians with an intriguing geometric structure dependent on the Ricci scalar, the Einstein tensor, the double dual of the Riemann tensor, and the Gauss-Bonnet combination. Spacetime curvature can be screened from the net cosmological constant at any given moment because we allow the scalar field to break Poincaré invariance on the self-tuning vacua, thereby evading the Weinberg no-go theorem. We show how the four arbitrary functions of the scalar field combine in an elegant way opening up the possibility of obtaining nontrivial cosmological solutions.
authors.affiliation: LPT, CNRS UMR 8627, Université Paris Sud-11, 91405 Orsay Cedex, France.
authors.forename: Christos
authors.initials: C
authors.lastname: Charmousis
authors.forename: Edmund J
authors.initials: EJ
authors.lastname: Copeland
authors.forename: Antonio
authors.initials: A
authors.lastname: Padilla
authors.forename: Paul M
authors.initials: PM
authors.lastname: Saffin