Cosmology in the era of Euclid and the Square Kilometre Array

Theoretical uncertainties on non-linear scales are among the main obstacles to exploit the sensitivity of forthcoming galaxy and hydrogen surveys like Euclid or the Square Kilometre Array (SKA). Here, we devise a new method to model the theoretical error that goes beyond the usual cut-o ff on small scales. The advantage of this more efficient implementation of the non-linear uncertainties is tested through a Markov-Chain-Monte-Carlo (MCMC) forecast of the sensitivity of Euclid and SKA to the parameters of the standard Lambda CDM model, including massive neutrinos with total mass M-nu, and to 3 extended scenarios, including 1) additional relativistic degrees of freedom (Lambda CDM + M-nu + N-eff), 2) a deviation from the cosmological constant (Lambda CDM + M-nu + w(0)), and 3) a time-varying dark energy equation of state parameter (CDM + M-nu + (w(0);w(a))). We compare the sensitivity of 14 di ff erent combinations of cosmological probes and experimental con fi gurations. For Euclid combined with Planck, assuming a plain cosmological constant, our method gives robust predictions for a high sensitivity to the primordial spectral index ns (sigma(n(s)) = 0.00085), the Hubble constant H-0 (sigma(H-0) = 0.141 km/s/Mpc), the total neutrino mass M-nu(sigma(M-nu) = 0.020 eV). Assuming dynamical dark energy we get sigma(M-nu) = 0.030 eV for the mass and (sigma(w(0)); sigma(w(a))) = (0.0214; 0.071) for the equation of state parameters. The predicted sensitivity to M-nu is mostly stable against the extensions of the cosmological model considered here. Interestingly, a significant improvement of the constraints on the extended model parameters is also obtained when combining Euclid with a low redshift HI intensity mapping survey by SKA1, demonstrating the importance of the synergy of Euclid and SKA.