Direct and indirect searches for low-mass magnetic monopoles

Recently, there has been renewed interest in the search for low-mass magnetic monopoles. Al the University of Oklahoma Ive are performing an experiment (Fermilab E882) using material from the old DO and CDF detectors to set limits on the existence of Dirac monopoles of masses of the order of 500 GeV. To sei such limits, estimates must be made of the production rate of such monopoles at the Tevatron collider, and of the binding strength of any such produced monopoles ro I,matter. Here Ive sketch the still primitive theory of such interactions, and indicate why we believe a credible limit may still be obtained. On the other hand there have been proposals that the classic Euler-Heisenberg Lagrangian together with duality could be employed to set li,nits on magnetic monopoles having masses less than I TeV, based an virtual, lather than real processes. The DO collaboration at Fermilab has used stich a proposal to set mass limits based on the nonobservation of pairs of photons each with high transverse momentum. We critique the underlying theory by showing that the cross section violates unitarily, at the quoted limits and is unstable with respect to radiative corrections. We therefore believe that no significant limit can he obtained from the current experiments, based an virtual monopole processes.