Turnaround radius in modified gravity

TL;DR

This paper extends the concept of the turnaround radius, a limit for collapsing structures in an accelerating universe, to modified gravity theories with non-zero gravitational slip, enabling new ways to test cosmic acceleration.

Contribution

It introduces a generalized definition of the turnaround radius applicable to modified gravity models with gravitational slip, expanding the toolset for cosmological tests.

Findings

Derived the turnaround radius in theories with gravitational slip

Showed how the radius can constrain modified gravity parameters

Proposed observational strategies for testing the extended concept

Abstract

In an accelerating universe in General Relativity there is a maximum radius above which a shell of test particles cannot collapse, but is dispersed by the cosmic expansion. This radius could be used in conjunction with observations of large structures to constrain the equation of state of the universe. We extend the concept of turnaround radius to modified theories of gravity for which the gravitational slip is non-vanishing.