2018/02/28 by Ryotaro Kase, Shinji Tsujikawa
Physics and Astronomy · #gr-qc #astro-ph.CO #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.97.103501
published as Phys. Rev. D 97, 103501 (2018) · 23 pages, 7 figures, published version
arxiv created 2018/05/02 · arxiv updated 2018/05/03
The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are the general scheme of scalar-tensor theories allowing the possibility for realizing the tensor propagation speed ct equivalent to 1 on the isotropic cosmological background. We propose a dark energy model in which the late-time cosmic acceleration occurs by a simple k-essence Lagrangian analogous to the ghost condensate with cubic and quartic Galileons in the framework of GLPV theories. We show that a wide variety of the variation of the dark energy equation of state w\rm DE including the entry to the region w\rm DE<-1 can be realized without violating conditions for the absence of ghosts and Laplacian instabilities. The approach to the tracker equation of state w\rm DE=-2 during the matter era, which is disfavored by observational data, can be avoided by the existence of a quadratic k-essence Lagrangian X2. We study the evolution of nonrelativistic matter perturbations for the model ct2=1 and show that the two quantities μ and Σ, which are related to the Newtonian and weak lensing gravitational potentials respectively, are practically equivalent to each other, such that μ≃ Σ>1. For the case in which the deviation of w\rm DE from -1 is significant at a later cosmological epoch, the values of μ and Σ tend to be larger at low redshifts. We also find that our dark energy model can be consistent with the bounds on the deviation parameter α\rm H from Horndeski theories arising from the modification of gravitational law inside massive objects.