  In this work we investigate the interaction between spin-zero and spin-one
monopoles by making use of an effective field theory based on two-body and
four-body interaction parts. In particular, we analyze the formation of bound
state of monopole-antimonopole (i.e. monopolium). The magnetic-charge
conjugation symmetry is studied in analogy to the usual charge conjugation to
define a particle basis, for which we find bound-state solutions with
relatively small binding energies and which allows us to identify the bounds on
the parameters in the effective Lagrangians. Estimations of their masses,
binding energies and scattering lengths are performed as functions of monopole
masses and interaction strength in a specific renormalization scheme. We also
examine the general validity of the approach and the feasibility of detecting
the monopolium.
