Cubic Galileon gravity effects in the CMB

Physical review. D/Physical review. D., vol. 111

Abstract

Among the models addressing the Hubble tension, those introducing a dynamical dark component around recombination have been the most promising thus far. Their study has highlighted that, in fact, cosmic microwave background (CMB) and baryon acoustic oscillation observations can allow for such components before and near recombination. The new dynamical degree of freedom can be early dark energy (EDE) or early modified gravity depending on its coupling to gravity. We study a new model, $\mathcal{G}\mathrm{EDE}$, featuring the cubic Galileon operator $X\ensuremath{\square}\ensuremath{\phi}$ and test it against the most recent Planck public release 4 CMB and Cepheid calibrated $\mathrm{Pantheon}+$ type Ia supernovae data. Thanks to the kinetic braiding effects, $\mathcal{G}\mathrm{EDE}$ gives a better fit to the data, with a higher ${H}_{0}$, and is preferred over the canonical EDE with a Bayes factor $\mathrm{ln}B=0.9$, despite introducing one more parameter. This calls for further explorations of modified gravity near and before last scattering. To facilitate these, we introduce a substantial extension of the cosmological code eftcamb that allows one to fully evolve the background and linear dynamics of any covariant theory, oscillatory or not, belonging to the Horndeski class.

Authors 2

1. Gen Ye Aachen

   Leiden University

   Affiliation as printed

   Leiden University

2. Alessandra Silvestri Aachen

   Leiden University

   Affiliation as printed

   Leiden University