Constraining $f(R)$ Gravity with a $k$-cut Cosmic Shear Analysis of the Hyper Suprime-Cam First-Year Data

TL;DR

This paper uses a novel $k$-cut cosmic shear analysis on Subaru HSC Year 1 data to constrain both standard cosmology and $f(R)$ modified gravity, emphasizing robustness against small-scale modeling uncertainties.

Contribution

It introduces the $k$-cut method to cosmic shear analysis, reducing sensitivity to small-scale uncertainties and enabling constraints on modified gravity theories.

Findings

Measured $S_8$ consistent with previous results.

Constraints on $f(R)$ parameters are prior dominated.

Demonstrated robustness of results against baryonic feedback uncertainties.

Abstract

Using Subaru Hyper Suprime-Cam (HSC) year 1 data, we perform the first $k$-cut cosmic shear analysis constraining both $\Lambda$CDM 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. The $k$-cut method is used to significantly down-weight sensitivity to small scale ($k > 1 \ h {\rm Mpc }^{-1}$) 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 $\Lambda$CDM we find $S_8 = \sigma_8 (\Omega_m / 0.3) ^ {0.5} = 0.789 ^{+0.039}_{-0.022}$, 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.