Expansion around the unitarity limit for bosonic few-body systems

Bosonic few-body ($A \leq 4$) systems with a large scattering length and a short effective range in the two-body sector are studied in the framework of short-range effective field theory. We start from the unitarity limit at leading order. The finite scattering length and range corrections, and a four-body force required by renormalization are included at next-to-leading order. We expect to extend our approach to nuclear systems in which more internal degrees of freedom and the Coulomb interaction should be considered.