Attractor scenarios and superluminal signals in k-essence cosmology

作者：Kang Jin U^*; Vanchurin Vitaly; Winitzki Sergei

来源：Physical Review D - Particles, Fields, Gravitation and Cosmology, 2007, 76(8): 083511.

DOI：10.1103/PhysRevD.76.083511

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 attractorlike dynamics of the k-essence field phi. It was recently shown that all k-essence scenarios with Lagrangians p=L(X)phi(-2), where X equivalent to 1/2 phi(,mu)phi(,mu), necessarily involve an epoch where perturbations of phi propagate faster than light (the "no-go theorem"). We carry out a comprehensive study of attractorlike cosmological solutions ("trackers") involving a k-essence scalar field phi and another matter component. The result of this study is a complete classification of k-essence Lagrangians that admit asymptotically stable tracking solutions, among all Lagrangians of the form p=K(phi)L(X). Using this classification, we select the class of models that describe the late-time acceleration and avoid the coincidence problem through the tracking mechanism. An analogous "no-go theorem" still holds for this class of models, indicating the existence of a superluminal epoch. In the context of k-essence cosmology, the superluminal epoch does not lead to causality violations. We discuss the implications of superluminal signal propagation for possible causality violations in Lorentz-invariant field theories.

• 出版日期2007-10