Attractor scenarios and superluminal signals in k-essence cosmology

Understand

Cosmological scenarios with k-essence are invoked in order to explain the observed late-time acceleration of the universe.

• These scenarios avoid the need for fine-tuned initial conditions (the "coincidence problem") because of the attractor-like dynamics of the k-essence field \phi.
• It was recently shown that all k-essence scenarios with Lagrangians p=L(X)/\phi^2, necessarily involve an epoch where perturbations of \phi propagate faster than light (the "no-go theorem").
• We carry out a comprehensive study of attractor-like cosmological solutions ("trackers") involving a k-essence scalar field \phi and another matter component.