Role of monopoles in a gluon plasma

We study the role of magnetic monopoles at high enough temperature T>2Tc, when they can be considered heavy, rare objects embedded into matter consisting mostly of the usual ``electric'' quasiparticles, quarks, and gluons. We review available lattice results on monopoles at finite temperatures. Then we proceed to classical and quantum charge-monopole scattering, solving the problem of gluon-monopole scattering for the first time. The explicit calculations are performed in the framework of the Georgi-Glashow model; the results that we obtain are nevertheless quite general. Connections to QCD are carefully discussed. We find that, while the gluon-monopole scattering hardly influences thermodynamic quantities, it does produce a large transport cross section, significantly exceeding that for pQCD gluon-gluon scattering up to quite high T. Thus, in spite of their relatively small density at high T, monopoles are extremely important for quark-gluon plasma transport properties, keeping viscosity small enough for hydrodynamics to work at the LHC.