We show that the homogeneous Faddeev-Yakubovski equations for the bound state of four identical bosons, in the unitary limit and attractive zero-range interaction present scale invariance in the ultraviolet (UV) region, which is broken. By resorting to an approximate form of the integral equations in the UV limit, we demonstrate that a pair of log-periodic solutions, with a cycle distinct from the three-boson one, exists and a four-body scale is required to define the phase between them. The breaking of the scale invariance is also found in the context of relativistic bound states described as the solution of the Bethe-Salpeter equation in ladder approximation, which will be also briefly discussed.
Filipe Veloso e Pedro Costa