Higgs mechanism
Because Lorentz symmetry is a local symmetry in the presence of gravity, the possibility of a Higgs mechanism arises when Lorentz symmetry is spontaneously broken. In the conventional gauge-theory Higgs mechanism, the Nambu-Goldstone modes are reinterpreted as degrees of freedom associated with a massive gauge field. The Nambu-Goldstone modes are said to be "eaten", while the gauge bosons gain a mass.