Self-tuning kinetic gravity braiding: Cosmological dynamics, shift symmetry, and the tadpole

TL;DR

This paper investigates a specific class of scalar-tensor theories called kinetic gravity braiding, focusing on their self-tuning properties, stability, and implications for cosmic acceleration within shift symmetric models.

Contribution

It provides a comprehensive analysis of the self-tuning behavior, stability conditions, and concrete examples in kinetic gravity braiding theories, especially in the shift symmetric sector.

Findings

Cosmic acceleration is an inevitable outcome in the self-tuning subclass.

The late-time asymptotic state is shown to be dynamically stable.

Ghost and gradient stability constraints are derived for the self-tuning vacuum.

Abstract

We study the self-tuning subclass of kinetic gravity braiding and obtain robust predictions on self-tuning and dynamics in the tadpole-free shift symmetric sector of the theory. In particular, we show inevitability of cosmic acceleration, prove the dynamical stability of this late-time asymptotic state, and derive ghost and gradient stability constraints on the self-tuning vacuum. We discuss the results concretely in the context of generalized cubic covariant Galileon theory and an exponential kinetic gravity braiding.