Spontaneous Lorentz Violation, Nambu-Goldstone Modes, and Gravity

TL;DR

This paper explores the emergence and behavior of Nambu-Goldstone modes resulting from spontaneous Lorentz violation, analyzing their dependence on spacetime geometry and field dynamics, with implications for gravity and particle physics.

Contribution

It provides a comprehensive analysis of Nambu-Goldstone modes in spontaneous Lorentz violation using the vierbein formalism, including their fate in various spacetime geometries and models like bumblebee.

Findings

Up to 10 Nambu-Goldstone modes can appear from Lorentz and diffeomorphism violation.

In bumblebee models, a photon can emerge as a Nambu-Goldstone boson.

Potential Lorentz-violating couplings could affect matter and gravitational interactions.

Abstract

The fate of the Nambu-Goldstone modes arising from spontaneous Lorentz violation is investigated. Using the vierbein formalism, it is shown that up to 10 Lorentz and diffeomorphism Nambu-Goldstone modes can appear and that they are contained within the 10 modes of the vierbein associated with gauge degrees of freedom in a Lorentz-invariant theory. A general treatment of spontaneous local Lorentz and diffeomorphism violation is given for various spacetimes, and the fate of the Nambu-Goldstone modes is shown to depend on both the spacetime geometry and the dynamics of the tensor field triggering the spontaneous Lorentz violation. The results are illustrated within the general class of bumblebee models involving vacuum values for a vector field. In Minkowski and Riemann spacetimes, the bumblebee model provides a dynamical theory generating a photon as a Nambu-Goldstone boson for spontaneous Lorentz violation. The Maxwell and Einstein-Maxwell actions are automatically recovered in axial gauge. Associated effects of potential experimental relevance include Lorentz-violating couplings in the matter and gravitational sectors of the Standard-Model Extension and unconventional Lorentz-invariant couplings. In Riemann-Cartan spacetime, the possibility also exists of a Higgs mechanism for the spin connection, leading to the absorption of the propagating Nambu-Goldstone modes into the torsion component of the gravitational field.