  We study the properties of three-body resonances using a lattice complex
scalar $\varphi^4$ theory with two scalars, with parameters chosen such that
one heavy particle can decay into three light ones. We determine the two- and
three-body spectra for several lattice volumes using variational techniques,
and then analyze them with two versions of the three-particle finite-volume
formalism: the Relativistic Field Theory approach and the Finite-Volume
Unitarity approach. We find that both methods provide an equivalent description
of the energy levels, and we are able to fit the spectra using simple
parametrizations of the scattering quantities. By solving the integral
equations of the corresponding three-particle formalisms, we determine the pole
position of the resonance in the complex energy-plane and thereby its mass and
width. We find very good agreement between the two methods at different values
of the coupling of the theory.
