Universal trimer in a three-component Fermi gas

We show that the recently measured magnetic field dependence of three-body loss in a three-component mixture of ultracold ⁶Li atoms [T. B. Ottenstein et al., Phys. Rev. Lett. 101, 203202 (2008); J. H. Huckans et al., Phys. Rev. Lett. 102, 165302 (2009)] can be explained by the presence of a universal trimer state. Previous work suggested a universal trimer state as a probable explanation, yet it failed to get good agreement between theory and experiment over the whole range of magnetic fields. For our description we adapt the theory of Braaten and Hammer [Phys. Rep. 428, 259 (2006)] for three identical bosons to the case of three distinguishable fermions by combining the three scattering lengths a₁₂, a₂₃, and a₁₃ between the three components to an effective interaction parameter aₘ. We show that taking into account a magnetic field variation in the lifetime of the trimer state is essential to obtain a complete understanding of the observed decay rates.