Mass generation

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 mass is strongly connected to gravitational interaction, 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.

Gravity-free models

In these theories, as in the Standard Model itself, the gravitational interaction either is not involved or does not play a crucial role.

• The Higgs mechanism is based on a symmetry-breaking scalar field potential, such as the quartic. The Standard Model uses this mechanism as part of the Glashow–Weinberg–Salam model to unify electromagnetic and weak interactions. This model was one of several that predicted the existence of the scalar Higgs boson.
• Technicolor models break electroweak symmetry through new gauge interactions, which were originally modeled on quantum chromodynamics.
• Coleman–Weinberg mechanism (spontaneous symmetry breaking through radiative corrections).
• Models of composite W and Z vector bosons.
• Top quark condensate.
• Asymptotically safe weak interactions based on some nonlinear sigma models.
• Symmetry breaking driven by non-equilibrium dynamics of quantum fields above the electroweak scale.
• Unparticle physics and the unhiggs models posit that the Higgs sector and Higgs boson are scaling invariant, also known as unparticle physics.
• UV-Completion by Classicalization, in which the unitarization of the WW scattering happens by creation of classical configurations.

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. 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.
• 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.
• 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. 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. 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. Under certain conditions, this potential gives rise to an elementary particle with a role and characteristics similar to the Higgs boson.

See also

• Mass
• Higgs mechanism
• Spontaneous symmetry breaking