The Effects of Gravitational Slip on the Higher-Order Moments of the Matter Distribution

TL;DR

This paper investigates how gravitational slip, a deviation from general relativity, affects the higher-order moments of matter distribution, specifically the galaxy bispectrum, but finds the effect too weak for current detection.

Contribution

It extends the analysis of gravitational slip effects to non-linear order and develops a formalism for scale-dependent slip in cosmological perturbations.

Findings

Gravitational slip influences the galaxy bispectrum, but effects are too weak for detection with current surveys.

The formalism incorporates scale dependence into gravitational slip modeling.

Non-linear perturbation analysis reveals limited observational signatures of gravitational slip.

Abstract

Cosmological departures from general relativity offer a possible explanation for the cosmic acceleration. To linear order, these departures (quantified by the model-independent parameter $\varpi$, referred to as a `gravitational slip') amplify or suppress the growth of structure in the universe relative to what we would expect to see from a general relativistic universe lately dominated by a cosmological constant. As structures collapse and become more dense, linear perturbation theory is an inadequate descriptor of their behavior, and one must extend calculations to non-linear order. If the effects of gravitational slip extend to these higher orders, we might expect to see a signature of $\varpi$ in the bispectrum of galaxies distributed on the sky. We solve the equations of motion for non-linear perturbations in the presence of gravitational slip and find that, while there is an effect on the bispectrum, it is too weak to be detected with present galaxy surveys. We also develop a formalism for incorporating scale dependence into our description of gravitational slip.