# Well-Tempered Cosmology

## TL;DR

This paper explores Well-Tempered cosmology, a method within scalar-tensor theories that achieves a de Sitter phase independent of the cosmological constant, improving previous models by allowing standard cosmology before acceleration.

## Contribution

It introduces a new approach within Horndeski theories that enables tuning away the cosmological constant while maintaining standard cosmology prior to de Sitter expansion.

## Key findings

- Derived a system capable of tuning away the cosmological constant.
- Provided an explicit example of the general solution.
- Improved upon the Fab-Four approach by allowing standard fluid cosmology.

## 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.