Turnaround radius in modified gravity
  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.
