  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 $\sqrt{3/8}(4\pi/e)$, 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.

High Energy Physics - Phenomenology;High Energy Physics - Theory