Fab Four: When John and George play gravitation and cosmology
Jean-Philippe Bruneton, Massimiliano Rinaldi, Antonin Kanfon and, Aur\'elien Hees, Sandrine Schl\"ogel, Andr\'e F\"uzfa

TL;DR
This paper explores the 'Fab Four' scalar-tensor theories of gravitation, focusing on the 'John' and 'George' models, analyzing their inflationary potential and experimental constraints from solar system tests.
Contribution
It investigates specific subsets of the 'Fab Four' theories, proposing a more viable inflationary model with 'George' and deriving experimental constraints.
Findings
'John' model leads to inflation with unnatural initial conditions.
Adding 'George' improves the inflationary model's plausibility.
Solar system tests constrain the parameter space of the models.
Abstract
Scalar-tensor theories of gravitation have recently regained a great interest after the discovery of the Chameleon mechanism and of the Galileon models. The former allows, in principle, to reconcile the presence of cosmological scalar fields with the constraints from experiments at the Solar System scale. The latter open up the possibility of building inflationary models that, among other things, do not need ad hoc potentials. Further generalizations have finally led to the most general tensor-scalar theory, recently dubbed the "Fab Four", with only first and second order derivatives of the fields in the equations of motion and that self-tune to a vanishing cosmological constant. This model has a very rich phenomenology that needs to be explored and confronted with experimental data in order to constrain a very large parameter space. In this paper, we present some results regarding a…
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