Fermions obey the exclusion principle, bosons do not.
Besides, fermion loops are essential constituents of the corrections to the exchange boson propagators.
All the particles that make up ordinary matter (leptons and quarks) are elementary fermions, while all the force carriers are elementary bosons.
Particle accelerators with energies necessary to observe neutral current interactions and to measure the mass of boson weren't available until 1983.
The gluons correspond to the unbroken gauge bosons and the color octet axigluons -- which couple strongly to the quarksare massive.
One of the conclusions is that the presence of a gauge boson mass suppresses large instantons, so that the instanton gas approximation is consistent.
When such a theory is quantized, the quanta of the gauge fields are called "gauge bosons".
Some of non-fundamental bosons (namely, mesons) also may transmit forces (see below), although non-fundamental ones.
