K-mouflage Imprints on Cosmological Observables and Data Constraints

We investigate cosmological constraints on K-mouflage models of modified gravity. We consider two scenarios: one where the background evolution is free to deviate from Lambda CDM (K-mouflage) and another one which reproduces a Lambda CDM expansion (K-mimic), implementing both of them into the EFTCAMB code. We discuss the main observational signatures of these models and we compare their cosmological predictions to different datasets, including CMB, CMB lensing, SNIa and different galaxy catalogues. We argue about the possibility of relieving the H-0 and weak lensing tensions within these models, finding that K-mouflage scenarios effectively ease the tension on the Hubble Constant. Our final 95% C.L. bounds on the epsilon(2,0) parameter that measures the overall departure from Lambda CDM (corresponding to epsilon(2,0) = 0) are -0.04 <= epsilon(2,0) <= 0 for K-mouflage and 0 <= epsilon(2,0) <= 0.002 for K-mimic. These translate into an upper bound for the coupling strength beta < 0.22 for K-mouflage and beta < 0.026 for K-mimic. In the former case the main constraining power comes from changes in the background expansion history, while in the latter case the model is strongly constrained by measurements of the amplitude of matter perturbations. The sensitivity of these cosmological constraints closely matches that of solar system probes. We show that these constraints could be significantly tightened with future ideal probes like CORE.