http://arxiv.org/abs/1707.03885
In this paper we investigate the so called “phantom barrier crossing” issue in a cosmological model based in the scalar-tensor theory with non-minimal derivative coupling to the Einstein’s tensor. Special attention will be paid to the physical bounds on the squared sound speed. We find that the cosmological model based in the non-minimal derivative coupling theory — this includes the pure derivative coupling case — has serious causality problems related with superluminal propagation of the scalar perturbations. Besides, despite that the theory is free of the Ostrogradsky instability, for some values of the free parameters and/or for given initial conditions, the model is also plagued by the so called Laplacian instability. We find that, although a relationship may exist, there is not strict correlation between phantom barrier crossing and superluminal speed of sound in this theory.
I. Quiros, T. Gonzalez, U. Nucamendi, et. al.
Fri, 14 Jul 17
34/55
Comments: 17 pages, 27 figures