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.