Authors: |
## Santiago Casas, Georgios K. Karananas (Munich U., ASC), Martin Pauly (U. Heidelberg, ITP), Javier Rubio (U. Heidelberg, ITP & Helsinki Inst. of Phys.) |

Journal: | Submitted to JCAP |

Year: | 11/2018 |

Download: | Inspire| Arxiv |

## Abstract

We discuss the cosmological phenomenology of biscalar--tensor models

displaying a maximally symmetric Einstein--frame kinetic sector and

constructed on the basis of scale symmetry and volume--preserving

diffeomorphisms. These theories contain a single dimensionful

parameter $\Lambda_0$---associated with the invariance under the

aforementioned restricted coordinate transformations---and a massless

dilaton field. At large field values these scenarios lead to inflation

with no generation of isocurvature perturbations. The corresponding

predictions depend only on two dimensionless parameters, which

characterize the curvature of the field--manifold and the leading

order behavior of the inflationary potential. For $\Lambda_0=0$ the

scale symmetry is unbroken and the dilaton admits only derivative

couplings to matter, evading all fifth force constraints. For

$\Lambda_0\neq 0$ the field acquires a run-away potential that can

support a dark energy dominated era at late times. We confront a

minimalistic realization of this appealing framework with observations

using a Markov-Chain-Monte-Carlo approach, with likelihoods from

present BAO, SNIa and CMB data. A Bayesian model comparison indicates

a preference for the considered model over $\Lambda$CDM, under certain

assumptions for the priors. The impact of possible consistency

relations among the early and late Universe dynamics that can appear

within this setting is discussed with the use of correlation

matrices. The results indicate that a precise determination of the

inflationary observables and the dark energy equation--of--state could

significantly constraint the model parameters.