Constraining f(R) gravity with a k-cut cosmic shear analysis of the Hyper Suprime-Cam first-year data

Abstract

Using Subaru Hyper Suprime-Cam (HSC) year 1 data, we perform the first k-cut cosmic shear analysis constraining both ΛCDM and f(R) Hu-Sawicki modified gravity. To generate the f(R) cosmic shear theory vector, we use the matter power spectrum emulator trained on COLA (COmoving Lagrangian Acceleration) simulations [Phys. Rev. D 103, 123525 (2021). The k-cut method is used to significantly down-weight sensitivity to small scale (k > 1h  Mpc⁻¹) modes in the matter power spectrum where the emulator is less accurate, while simultaneously ensuring our results are robust to baryonic feedback model uncertainty. We have also developed a test to ensure that the effects of poorly modeled small scales are nulled as intended. For ΛCDM we find S₈ = σ₈ (Ω_m/0.3)^(0.5) = 0.789^(+0.039)_(−0.022), while the constraints on the f(R) modified gravity parameters are prior dominated. In the future, the k-cut method could be used to constrain a large number of theories of gravity where computational limitations make it infeasible to model the matter power spectrum down to extremely small scales.