Linear perturbation constraints on multi-coupled dark energy

The Multi-coupled Dark Energy (McDE) scenario has been recently proposed as a specific example of a cosmological model characterized by a non-standard physics of the dark sector of the universe that nevertheless gives an expansion history which does not significantly differ from the one of the standard ΛCDM model. Thanks to a dynamical screening mechanism, in fact, the interaction between the Dark Energy field and the Dark Matter sector is effectively suppressed at the background level during matter domination. As a consequence, background observables cannot discriminate a McDE cosmology from ΛCDM for a wide range of model parameters. On the other hand, linear perturbations are expected to provide tighter bounds due to the existence of attractive and repulsive fifth-forces associated with the dark interactions. In this work, we present the first constraints on the McDE scenario obtained by comparing the predicted evolution of linear density perturbations with a large compilation of recent data sets for the growth rate fσ<SUB>8</SUB>, including 6dFGS, LRG, BOSS, WiggleZ and VIPERS. Confirming qualitative expectations, growth rate data provide much tighter bounds on the model parameters as compared to the extremely loose bounds that can be obtained when only the background expansion history is considered. In particular, the 95% confidence level on the coupling strength |β| is reduced from |β| <= 83 (background constraints only) to |β| <= 0.88 (background and linear perturbation constraints). We also investigate how these constraints further improve when using data from future wide-field surveys such as supernova data from LSST and growth rate data from Euclid-type missions. In this case the 95% confidence level on the coupling further reduce to |β| <= 0.85. Such constraints are in any case still consistent with a scalar fifth-force of gravitational strength, and we foresee that tighter bounds might be possibly obtained from the investigation of nonlinear structure formation in McDE cosmologies