Causality and Sound Speed for General Scalar Field Models, including w < -1, tachyonic, phantom, k-essence and curvature corrections

Axel de la Macorra, Hector Vucetich

The result from the SN1a projects suggest that the dark energy can be represented by a fluid with w<-1. However, it is commonly argued that a fluid with |w|>1 contradicts causality…