The Well-Tempered Cosmological Constant: Fugue in B$^\flat$

TL;DR

This paper proposes a dynamical mechanism within Horndeski scalar-tensor gravity to cancel a large cosmological constant, enabling a flat Minkowski universe without fine tuning, and tests its stability through phase transitions.

Contribution

It introduces an explicit well-tempered mechanism in Horndeski gravity to achieve a Minkowski solution, replacing the cosmological constant with a stable, zero-energy state.

Findings

Derived conditions for Horndeski theories to support Minkowski space

Demonstrated attractor behavior of the solution

Showed stability through vacuum phase transition

Abstract

Zero point fluctuations of quantum fields should generate a large cosmological constant energy density in any spacetime. How then can we have anything other than de Sitter space without fine tuning? Well tempering -- dynamical cancellation of the cosmological constant using degeneracy within the field equations -- can replace a large cosmological constant with a much lower energy state. Here we give an explicit mechanism to obtain a Minkowski solution, replacing the cosmological constant with zero, and testing its attractor nature and persistence through a vacuum phase transition. We derive the general conditions that Horndeski scalar-tensor gravity must possess, and evolve in a fugue of functions, to deliver nothing and make the universe be flat.