The symmetry-breaking field associated with a Higgs boson. The Higgs field can either be an elementary scalar quantity or the field associated with a bound state of two fermions. In the Weinberg–Salam model, the Higgs field is taken to be a scalar field. It is not known whether this assumption is correct, although attempts to construct electroweak theory involving bound states for the Higgs field, known as technicolour theory, have not been successful. Higgs fields also occur in many-body systems, which can be expressed in terms of quantum field theory with Higgs bosons; an example is the BCS theory of superconductivity, in which the Higgs field is associated with a Cooper pair, rather than an elementary scalar field.