The four fixed points of scale invariant single field cosmological models

TL;DR

This paper introduces new flow parameters to analyze single field cosmological models, identifying four fixed points that include known models and revealing new scale-invariant scenarios with varying sound speed and equation of state.

Contribution

It defines a novel set of flow parameters and fixed points, expanding the understanding of scale-invariant power spectra in single field models.

Findings

Identified four types of fixed points covering all known models

Discovered new models with scale invariance relying on varying sound speed and equation of state

Discussed constraints from strong coupling and superluminality

Abstract

We introduce a new set of flow parameters to describe the time dependence of the equation of state and the speed of sound in single field cosmological models. A scale invariant power spectrum is produced if these flow parameters satisfy specific dynamical equations. We analyze the flow of these parameters and find four types of fixed points that encompass all known single field models. Moreover, near each fixed point we uncover new models where the scale invariance of the power spectrum relies on having simultaneously time varying speed of sound and equation of state. We describe several distinctive new models and discuss constraints from strong coupling and superluminality.