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.
Most of the mass of ordinary matter is generated by the strong nuclear force, described by Quantum Chromodynamics (QCD). Inside protons and neutrons, quarks are permanently confined by gluons, the particles that carry the strong force. The quarks move at nearly the speed of light and are immersed in intense gluon fields and a constantly fluctuating sea of virtual quark-antiquark pairs. The enormous energy associated with this confined motion and these strong-force fields contributes to the mass of the proton and neutron according to Einstein's relation E=mc2 . Thus, the vast majority of the mass of the visible Universe is the energy of confined quarks and gluons expressed as mass.
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.
In these theories, as in the Standard Model itself, the gravitational interaction either is not involved or does not play a crucial role.
Technicolor models break electroweak symmetry through gauge interactions, which were originally modeled on quantum chromodynamics.[further explanation needed]
Coleman–Weinberg mechanism generates mass through spontaneous symmetry breaking.