Cosmological constraints on induced gravity dark energy models

We study induced gravity dark energy models coupled with a simple monomial potential proportional to sigma(n) and a positive exponent n. These simple potentials lead to viable dark energy models with a weak dependence on the exponent, which characterizes the accelerated expansion in the asymptotic attractor, when ordinary matter becomes negligible. We use recent cosmological data to constrain the coupling gamma to the Ricci curvature, under the assumptions that the scalar field starts at rest deep in the radiation era and that the gravitational constant in the Einstein equations is compatible with the one measured in a Cavendish-like experiment. By using Planck 2015 data only, we obtain the 95 % CL bound gamma < 0.0017 for n = 4, which is further tightened to gamma < 0.00075 by adding Baryonic Acoustic Oscillations (BAO) data. This latter bound improves by similar to 30 % the limit obtained with the Planck 2013 data and the same compilation of BAO data. We discuss the dependence of the gamma and (G)over dot(N)/G(N)(z = 0) on n.