Kinetically-driven ekpyrosis

TL;DR

This paper investigates a novel approach to ekpyrotic contraction driven by non-canonical kinetic energy, expanding the theoretical landscape with models that sustain large equations of state and exhibit superluminal phases.

Contribution

It introduces kinetically-driven ekpyrosis models with various kinetic terms, demonstrating their ability to sustain ekpyrotic phases and analyzing their dynamical properties.

Findings

Power-law models best sustain ekpyrosis with large, constant equations of state.

DBI-like models can exhibit attractor behavior toward large equations of state.

Phases of k-ekpyrosis often involve superluminal propagation.

Abstract

We explore the possibility of a scalar field driving ekpyrotic contraction through a non-canonical kinetic energy density rather than a negative potential. We find that this kinetically-driven ekpyrosis ("k-ekpyrosis") can be achieved in a variety of models, including scalar field theories with power-law, polynomial, or DBI-like kinetic terms in the action. Of these examples, the ekpyrotic phase is best sustained in power-law models, which can generate large and constant equation-of-state parameters, followed by DBI-like models, which can exhibit dynamical attractors toward similarly large equations of state. We show that for a broad class of theories including these examples, phases of k-ekpyrosis are accompanied by preceding or concurrent phases of superluminality.