Observational tests of Galileon gravity with growth rate

Abstract

We compare observational data of growth rate with the prediction by Galileon theory. For the same value of the energy density parameter ${\Omega }_{m,0}$, the growth rate in Galileon models is enhanced compared with the $\Lambda$CDM case, due to the enhancement of Newton's constant. The smaller ${\Omega }_{m,0}$ is, the more suppressed growth rate is. Hence the best fit value of ${\Omega }_{m,0}$ in the Galileon model is 0.16 from only the growth rate data, which is considerably smaller than such value obtained from observations of supernovae Ia, the cosmic microwave background and baryon acoustic oscillations. This result seems to be qualitatively the same in most of the generalized Galileon models. We also find the upper limit of the Brans-Dicke parameter to be $\omega <-40$, from the growth rate data. More and better growth rate data are required to distinguish between dark energy and modified gravity.

Comments: 6 pages, 10 figures, 2 tables; revised for clarification, main results unchanged