Visible effect of a very heavy magnetic monopole at colliders - art. no. 075016.

If a heavy Dirac monopole exists, the light-to-light scattering below the m onopole production threshold is enhanced due to the strong coupling of mono poles to photons. At the Next Linear Collider with an electron beam energy of 250 GeV this photon pair production could be observable at monopole mass es less than 2.5-6.4 TeV in the e(+)e(-) mode or 3.7-10 TeV in the gamma ga mma mode, depending on the monopole spin. At the upgraded Fermilab Tevatron such an effect is expected to be visible st monopole masses below 1-2.5 Te V. The strong dependence on the initial photon polarizations allows us to f ind the monopole spin in experiments at e(+)e(-) and gamma gamma colliders. We consider the Z gamma production and the 3 gamma production at e(+)e(-) and pp or p (p) over bar colliders via the same monopole loop. The possibil ity to discover these processes is significantly lower than that of the gam ma gamma case. [S0556-2821(99)03017-9].