Abstract
We examine an approach to cosmology, known as Well-Tempering, that allows for a de Sitter phase whose expansion is independent of the cosmological constant. Starting from a generic scalar-tensor theory compatible with the recent gravitational wave observation, we impose the Well-Tempering conditions and derive a system that is capable of tuning away the cosmological constant within a sub-class of Horndeski theory, where the scalar has a canonical kinetic term and a general potential. This scenario improves upon the Fab-Four approach by allowing a standard fluid-cosmology before entering the de Sitter phase, and we present an explicit example of our general solution.
Highlights
Constructing tempered self-tuning modelsThe arrival of the gravitational wave astronomy has allowed the use of “multi-messenger” events to constrain gravity models
Pointed out in Ref. [29], it is possible that more general solutions to the equations of motion may evade this constraint
We have presented an extension of the well-tempered proposal for dealing with the cosmological constant problem [8] by providing a very general solution to the constraints imposed by the well-tempered mechanism
Summary
The arrival of the gravitational wave astronomy has allowed the use of “multi-messenger” events to constrain gravity models. The propagation speed of gravitational degrees of freedom is constrained to be very close to that of photon. This puts severe constraints on generic scalar-tensor theory. We will work within a subset of Horndeski theory that imposes the phenomenological constraints, and enforce the degeneracy condition of WellTempering to obtain the generic Lagrangian that has a canonical kinetic term and a generic potential
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