  Collisions of two fermionic dimers near the unitary limit are studied using
exact four-particle equations for transition operators in momentum space.
Universal properties of dimer-dimer phase shifts and effective range expansion
(ERE) parameters are determined. The inclusion of the fourth-order momentum
term in the ERE significantly extends its validity to higher collision
energies. The dimer-dimer scattering length and effective range are determined
in the unitary limit as well as their corrections arising due to the finite
range of the two-fermion interaction. These results are of considerably higher
accuracy as compared to previous works, but confirm most of the previous
results except for the lattice effective field theory calculations.
