Fitting and forecasting non-linear coupled dark energy

TL;DR

This paper develops new fitting functions for non-linear matter power spectra in coupled dark energy models and demonstrates that future surveys like Euclid can significantly improve constraints on dark matter-dark energy coupling using non-linear data.

Contribution

It introduces validated fitting functions for non-linear power spectra in coupled dark energy models, enabling efficient forecasts without additional simulations.

Findings

Fitting functions accurately reproduce non-linear power spectra from simulations.

Future surveys can constrain the coupling parameter with less than 4 ext% uncertainty.

Combining galaxy clustering and weak lensing improves parameter constraints by over an order of magnitude.

Abstract

We consider cosmological models in which dark matter feels a fifth force mediated by the dark energy scalar field, also known as coupled dark energy. Our interest resides in estimating forecasts for future surveys like Euclid when we take into account non-linear effects, relying on new fitting functions that reproduce the non-linear matter power spectrum obtained from N-body simulations. We obtain fitting functions for models in which the dark matter-dark energy coupling is constant. Their validity is demonstrated for all available simulations in the redshift range $z=0-1.6$ and wave modes below $k=10 \text{h/Mpc}$. These fitting formulas can be used to test the predictions of the model in the non-linear regime without the need for additional computing-intensive N-body simulations. We then use these fitting functions to perform forecasts on the constraining power that future galaxy-redshift surveys like Euclid will have on the coupling parameter, using the Fisher matrix method for galaxy clustering (GC) and weak lensing (WL). We find that by using information in the non-linear power spectrum, and combining the GC and WL probes, we can constrain the dark matter-dark energy coupling constant squared, $\beta^{2}$, with precision smaller than 4\% and all other cosmological parameters better than 1\%, which is a considerable improvement of more than an order of magnitude compared to corresponding linear power spectrum forecasts with the same survey specifications.