Momentum transfer in the dark sector and lensing convergence in upcoming galaxy surveys

Abstract

We investigated a cosmological model that allows a momentum transfer between dark matter and dark energy. The interaction in the dark sector mainly affects the behaviour of perturbations on small scales while the background evolution matches the wCDM solution. As a result of the momentum transfer, these kinds of models help alleviating the σ 8 discrepancy in the standard model, but do not resolve the so-called H 0 tension. We confirm that this is indeed the case by computing cosmological constraints. While our analysis tends to favour σ 8 values lower than in ΛCDM, we do not find evidence for a non-vanishing momentum transfer in the dark sector. Since upcoming galaxy surveys will deliver information on scales and red-shift relevant for testing models allowing momentum transfer in the dark sector, we also carried out forecasts using different survey configurations. We assessed the relevance of neglecting lensing convergence κ when modelling the angular power spectrum of number counts fluctuations C ℓ ij(z,z'). We found that not including κ in analyses leads to biased constraints (≈ 1-5σ) of cosmological parameters even when including information from other experiments. Incorrectly modelling C ℓ ij(z,z') might lead to spurious detection of neutrino masses and exacerbate discrepancies in H 0 and σ 8.