In
theoretical physics, a mass generation mechanism is a theory that describes the origin of
mass from the most fundamental laws of
physics. Physicists have proposed a number of models that advocate different views of the origin of mass. The problem is complicated because the primary role of
mass is to mediate
gravitational interaction between bodies, and no theory of gravitational interaction reconciles with the currently popular
Standard Model of
particle physics.
There are two types of mass generation models: gravity-free models and models that involve gravity.
Extra-dimensional Higgsless models use the fifth component of the gauge fields in place of the Higgs fields. It is possible to produce electroweak symmetry breaking by imposing certain boundary conditions on the extra dimensional fields, increasing the
unitarity breakdown scale up to the energy scale of the extra dimension.[13][14] Through the AdS/QCD correspondence this model can be related to technicolor models and to UnHiggs models, in which the Higgs field is of
unparticle nature.[15]
Unitary Weyl gauge. If one adds a suitable gravitational term to the standard model action with gravitational coupling, the theory becomes locally scale-invariant (i.e. Weyl-invariant) in the unitary gauge for the local SU(2). Weyl transformations act multiplicatively on the Higgs field, so one can fix the Weyl gauge by requiring that the Higgs scalar be a constant.[16]
Preon and models inspired by preons such as the Ribbon model of
Standard Model particles by
Sundance Bilson-Thompson, based in
braid theory and compatible with
loop quantum gravity and similar theories.[17] This model not only explains the origin of mass, but also interprets electric charge as a topological quantity (twists carried on the individual ribbons), and colour charge as modes of twisting.
In the theory of
superfluid vacuum, masses of elementary particles arise from interaction with a physical
vacuum, similarly to the gap generation mechanism in
superfluids.[18] The low-energy limit of this theory suggests an effective potential for the Higgs sector that is different from the Standard Model's, yet it yields the mass generation.[19][20] Under certain conditions, this potential gives rise to an elementary particle with a role and characteristics similar to the
Higgs boson.