Linear perturbation constraints on multi-coupled dark energy

Abstract

The Multi-coupled Dark Energy (McDE) scenario has been recently proposed as a specificexample of a cosmological model characterized by a non-standard physics of the dark sector of theuniverse 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 theDark Energy field and the Dark Matter sector is effectively suppressed at the background levelduring matter domination. As a consequence, background observables cannot discriminate a McDEcosmology from ΛCDM for a wide range ofmodel parameters. On the other hand, linearperturbations are expected to provide tighter bounds due to the existence of attractive andrepulsive fifth-forces associated with the dark interactions. In this work, we present the firstconstraints on the McDE scenario obtained by comparing the predicted evolution of linear densityperturbations with a large compilation of recent data sets for the growth rate fσ8,including 6dFGS, LRG, BOSS, WiggleZ and VIPERS. Confirming qualitative expectations, growth ratedata provide much tighter bounds on the model parameters as compared to the extremely loose boundsthat can be obtained when only the background expansion history is considered. In particular, the95% 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 constraintsfurther improve when using data from future wide-field surveyssuch 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. Suchconstraints 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 nonlinearstructure formation in McDE cosmologies.