Inflation driven by a bare cosmological constant and its graceful exit

TL;DR

This paper introduces a new inflationary model driven solely by a bare cosmological constant, which naturally ends through a self-tuning mechanism within Fab-Four gravity, offering a viable alternative to traditional inflation scenarios.

Contribution

It presents the first viable inflation model driven by bare vacuum energy with a natural exit mechanism using self-tuning in Fab-Four gravity.

Findings

Self-tuning destabilizes de Sitter state leading to inflation termination.

Two explicit models with different slow-roll evolutions are constructed.

The power-law model reduces initial condition tuning requirements.

Abstract

Vacuum energy, a prediction of quantum field theory, manifests itself as a cosmological constant in general relativity. In this Letter, we propose a novel inflationary scenario driven by a bare cosmological constant $\Lambda$, which terminates naturally through a self-tuning mechanism. Within Fab-Four gravity, self-tuning destabilizes the de Sitter state and drives the system toward a stiff-fluid attractor, thereby yielding a graceful exit. We construct two explicit models in which the slow-roll parameter evolves exponentially or as a power law. We show that the latter model, derived from center-manifold dynamics, significantly relaxes the required tuning of initial conditions. Our results establish, for the first time, that bare-vacuum-energy inflation with natural termination constitutes a viable dynamical possibility.