Dimer scattering in the epsilon expansion

Abstract

The atom-dimer and dimer-dimer scattering lengths are analytically calculated in an expansion around four spatial dimensions for fermions with a large 2-body scattering length 'a'. We find the atom-dimer scattering length a_ad/a = 4/3-2/9 epsilon and the dimer-dimer scattering length a_dd/a = epsilon -0.344 epsilon^2, where epsilon = 4-d and d is the number of spatial dimensions. These ratios a_ad/a = 1.11 and a_dd/a = 0.656 at epsilon = 1 are to be compared with the non-perturbatively calculated numerical results 1.18 and 0.6 respectively. The neutron-deuteron scattering length in the quartet channel a_nD = 4.78 fm is in reasonable agreement with the experimental value 6.35 fm, considering 2-body effective range corrections r_0/a = 0.4 were excluded. The deuteron-deuteron scattering length a_DD = 3.15 fm in the spin-2 channel.