Abstract
In cubic-order Horndeski theories where a scalar field is coupled to nonrelativistic matter with a field-dependent coupling , we derive the most general Lagrangian having scaling solutions on the isotropic and homogenous cosmological background. For constant including the case of vanishing coupling, the corresponding Lagrangian reduces to the form , where and , are arbitrary functions of with constant . We obtain the fixed points of the scaling Lagrangian for constant and show that the -matter-dominated epoch () is present for the cubic coupling containing inverse power-law functions of . The stability analysis around the fixed points indicates that the can be followed by a stable critical point responsible for the cosmic acceleration. We propose a concrete dark energy model allowing for such a cosmological sequence and show that the ghost and Laplacian instabilities can be avoided even in the presence of the cubic coupling.
- Received 18 October 2018
DOI:https://doi.org/10.1103/PhysRevD.98.123517
© 2018 American Physical Society