Supernova constraints on multi-coupled dark energy

Abstract

The persisting consistency of ever more accurate observational datawith the predictions of the standard ΛCDM cosmological modelputs severe constraints on possible alternative scenarios, but stilldoes not shed any light on the fundamental nature of the cosmic darksector. As large deviations from a ΛCDM cosmology are ruledout by data, the path to detect possible features of alternative modelsgoes necessarily through the definition of cosmological scenariosthat leave almost unaffected the background and — to a lesser extent — the linear perturbations evolution of the universe. In this context,the Multi-coupled DE (McDE) model was proposed by Baldi [9]as a particular realization of an interacting Dark Energy field characterizedby an effective screening mechanism capable of suppressing the effectsof the coupling at the background and linear perturbation level. Inthe present paper, for the first time, we challenge the McDE scenariothrough a direct comparison with real data, in particular with theluminosity distance of Type Ia supernovae. By studying the existenceand stability conditions of the critical points of the associatedbackground dynamical system, we select only the cosmologically consistentsolutions, and confront their background expansion history with data.Confirming previous qualitative results, the McDE scenario appearsto be fully consistent with the adopted sample of Type Ia supernovae,even for coupling values corresponding to an associated scalar fifth-forceabout four orders of magnitude stronger than standard gravity. Ouranalysis demonstrates the effectiveness of the McDE background screening,and shows some new non-trivial asymptotic solutions for the futureevolution of the universe. Clearly, linear perturbation data and,even more, nonlinear structure formation properties are expected toput much tighter constraints on the allowed coupling range. Nonetheless,our results show how the background expansion history might be highlyinsensitive to the fundamental nature and to the internal complexityof the dark sector.