Ultracold collisions in the presence of synthetic spin-orbit coupling

We present an analytical description for ultracold collisions between two spin-1/2 fermions with isotropic spin-orbit coupling (SOC) of the Rashba type. We show that regardless of how weak the SOC may be, at sufficiently low energies the collision properties are significantly modified. The ubiquitous low energy Wigner threshold behavior is changed and its modified form for ground-state neutral atoms is given. The particles are further found to scatter preferentially into the lower-energy helicity states due to the breaking of parity conservation. This latter point establishes interaction with SOC as one mechanism for the spontaneous emergence of handedness. Our theory is applicable both to elementary spin-1/2 fermions such as electrons in condensed matter and to ultracold pseudo-spin-1/2 atoms such as Li-6 in its ground hyperfine state.