Turnaround Radius In F(R) Model

We investigate the turnaround radius in the spherical collapse model, both in General Relativity and in modi fied gravity, in particular f(R) scenarios. The phases of spherical collapse are marked by the non-linear density contrast in the instant of turnaround delta(t), and by the linear density contrast in the moment of collapse, delta(c). We find that the effective mass of the extra scalar degree of freedom which arises in modified gravity models has an impact on delta(t) of up to similar to 16%, and that delta(c) can increase by similar to 2.3%, for structures with mass of similar or equal to 10(13) h(-1) M-circle dot at z similar or equal to 0. We also compute the turnaround radius, R-t, which in modi fied gravity models can increase by up to similar to 6%.