Electroweak monopoles and magnetic dumbbells in grand unified theories

We use the SU(5) model to show the presence in grand unified theories of an electroweak monopole and a magnetic dumbbell ("meson") made up of a monopole-antimonopole pair connected by a Z-magnetic flux tube. The monopole is associated with the spontaneous breaking of the weak SU(2)(L) gauge symmetry by the induced vacuum expectation value of a heavy scalar SU(2)(L) triplet with zero weak hypercharge contained in the adjoint Higgs 24-plet. This monopole carries a Coulomb magnetic charge of (3/4)(2 pi/e) as well as Z-magnetic charge, where 2 pi/e denotes the unit Dirac magnetic charge. Its total magnetic charge is root 3/8(4 pi/e), which is in agreement with the Dirac quantization condition. The monopole weighs about 700 GeV, but because of the attached Z-magnetic tube it exists, together with the antimonopole, in a magnetic dumbbell configuration whose mass is expected to lie in the TeV range. The presence of these topological structures in SU(5) and SO(10) and in their supersymmetric extensions provides an exciting new avenue for testing these theories in high-energy colliders.