Constraining f(R) Gravity with Planck Sunyaev-Zel'dovich Clusters

TL;DR

This paper uses Planck Sunyaev-Zel'dovich cluster data and a modified halo mass function to place tight constraints on f(R) gravity models, highlighting the importance of calibration in deriving accurate limits.

Contribution

It introduces a correction to the halo mass function for f(R) gravity and demonstrates its impact on constraining the scalaron field amplitude using SZ cluster data.

Findings

Upper bounds on |f_R^0| range from 10^-5.81 to 10^-4.40 at 95% confidence.

Different halo mass function calibrations significantly affect the constraints.

Claims of more stringent constraints require careful calibration and validation.

Abstract

Clusters of galaxies have the potential of providing powerful constraints on possible deviations from General Relativity. We use the catalogue of Sunyaev-Zel'dovich sources detected by Planck and consider a correction to the halo mass function for a f(R) class of modified gravity models, which has been recently found to reproduce well results from N-body simulations, to place constraints on the scalaron field amplitude at the present time, $f_{R}^0$. We find that applying this correction to different calibrations of the halo mass function produces upper bounds on $f_{R}^0$ tighter by more than an order of magnitude, ranging from $\log_{10}(-f_{R}^0) < -5.81$ to $\log_{10}(-f_{R}^0) < -4.40$ (95 % confidence level). This sensitivity is due to the different shape of the halo mass function, which is degenerate with the parameters used to calibrate the scaling relations between SZ observables and cluster masses. Any claim of constraints more stringent that the weaker limit above, based on cluster number counts, appear to be premature and must be supported by a careful calibration of the halo mass function and by a robust calibration of the mass scaling relations.