Data-driven and Almost Model-independent Reconstruction of Modified Gravity

In this paper, a modified factor $\mu$, which characterizes modified gravity in the linear matter density perturbation theory, is reconstructed in a data-driven and almost model-independent way via Gaussian process by using currently available cosmic observations. Utilizing the Pantheon+ SNe Ia samples, the observed Hubble parameter $H(z)$ and the redshift space distortion $f\sigma_8(z)$ data points, one finds out a time varying $\mu$ at low redshifts. The reconstructed $\mu$ implies that more complicated modified gravity beyond the simplest general relativity and the Dvali-Gabadadze-Porrati braneworld model is required.