Forecasting Coupled Dark Energy Parameters with the One-Loop Galaxy Power Spectrum

Abstract

We forecast constraints on the parameters of the coupled dark energy model using DESI and Euclid data with the one-loop galaxy power spectrum. We investigate the distinguishability of our model from the zero-coupling scenario at the $1\sigma$ level and explore how the parameter constraints depend on the fiducial coupling ${\beta }_{\mathrm{fid}}$, the fixed potential slope parameter $\nu$, the maximum wavenumber $k_{\max }$, and different prior choices. We find that the inclusion of mildly non-linear scales improves the constraints on the coupling by roughly a factor of five. Then, we address the question of which is the minimum value of $\beta$ that can be distinguished from zero at $1\sigma$. We find that for our reference case $k_{\max }=0.2h/$Mpc, $\beta =0.15$ lies roughly $1\sigma$ above zero. In the most optimistic case with $k_{\max }=0.3h/$Mpc and including a Planck prior on ${\Omega }_{m0}$, this value can be reduced to $0.05$. These values are substantially larger than the current constraints on $\beta$, but the latter have been obtained assuming $\beta$ to be constant from at least the decoupling epoch to today, while we only employ late-time data. We conclude therefore that only models that allow for time-varying couplings can be detected with late-time datasets.