No Slip CMB

Abstract

No Slip Gravity is a simple modified gravity theory with only one free function and the interesting characteristic that -- unlike many modified gravity theories -- it suppresses growth. This allows it to fit current redshift space distortion and σ8 mass fluctuation amplitude data better than ΛCDM in general relativity, while retaining a ΛCDM background expansion and hence distances. Since it has no gravitational slip it alters equally CMB lensing and matter density growth, and in addition affects the CMB gravitational wave B-mode polarization power spectrum. We investigate and compute the effects of No Slip Gravity for CMB lensing and B-modes, and present a simple analytic approximation. Using a Monte Carlo analysis, we place constraints on the theory from current CMB data.