Subpercent Accurate Fitting of Modified Gravity Growth

Abstract

Adding to our previous method for dealing with gravitational modifications at redshift $z\gtrsim 3$ through a single parameter, we investigate treatment of lower redshift modifications to linear growth observables. We establish subpercent accurate fits to the redshift space distortion observable $f{\sigma }_8(a)$ using two parameters binned in redshift, testing the results for modifications with time dependence that rises, falls, is nonmonotonic, is multipeaked, and corresponds to $f(R)$ and braneworld gravity. The residuals are then propagated to cosmological parameter biases for DESI observations, and found to cause a shift in the dark energy joint confidence contour by less than the equivalent of $\sim 0.1\sigma$. The proposed 2--3 parameter modified gravity description also can reveal physical characteristics of the underlying theory.

arXiv comment8 pages, 6 figures

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• No Run Gravity
• Constraining Scale Dependent Growth with Redshift Surveys
• Principal Components for Model-Agnostic Modified Gravity with 3x2pt