On the degeneracies between baryons, massive neutrinos and f(R) gravity in Stage IV cosmic shear analyses

Understand

Modelling nonlinear structure formation is essential for current and forthcoming cosmic shear experiments.

• We combine the halo model reaction formalism, implemented in the REACT code, with the COSMOPOWER machine learning emulation platform, to develop and publicly release REACTEMU-FR, a fast and accurate nonlinear matter power spectrum emulator for $f(R)$ gravity with massive neutrinos.
• Coupled with the state-of-the-art baryon feedback emulator BCEMU, we use REACTEMU-FR to produce Markov Chain Monte Carlo forecasts for a cosmic shear experiment with typical Stage IV specifications.
• We find that the inclusion of highly nonlinear scales (multipoles between $1500\leq \ell \leq 5000$) only mildly improves constraints on most standard cosmological parameters (less than a factor of 2).