Turnaround density as a probe of the cosmological constant

Spherical collapse predicts that a single value of the turnaround density, meaning the average matter density within the scale on which a structure detaches from the Hubble flow, characterizes all cosmic structures at the same redshift. It was recently shown by Korkidis et al. that this feature persists in complex non-spherical galaxy clusters that have been identified in N-body simulations. Here we show that the low-redshift evolution of the turnaround density constrains the cosmological parameters and it can be used to derive a local constraint on Ω_{Λ,？0 alone, independent of Ωm,？0. The turnaround density thus offers a promising new method for exploiting upcoming large cosmological datasets}