Graviton as a Goldstone boson: Nonlinear Sigma Model for Tensor Field Gravity

TL;DR

This paper explores how spontaneous Lorentz invariance violation in tensor field gravity can produce massless tensor Goldstone modes, which can be associated with gravitons, but such effects are unobservable in standard conditions.

Contribution

It demonstrates that SLIV-induced effects in tensor gravity are canceled in lowest order processes, emphasizing the gauge invariance and potential observable distinctions if local symmetry is explicitly broken.

Findings

SLIV induces massless tensor Goldstone modes related to gravitons.

SLIV effects cancel out in lowest order processes under proper extensions.

Potential observable differences if local gauge symmetry is explicitly broken at small scales.

Abstract

Spontaneous Lorentz invariance violation (SLIV) realized through a nonlinear tensor field constraint H_{}^2=\pm M^2 (M is the proposed scale for Lorentz violation) is considered in tensor field gravity theory, which mimics linearized general relativity in Minkowski space-time. We show that such a SLIV pattern, due to which the true vacuum in the theory is chosen, induces massless tensor Goldstone modes some of which can naturally be associated with the physical graviton. When expressed in terms of the pure Goldstone modes, this theory looks essentially nonlinear and contains a variety of Lorentz and CPT violating couplings. Nonetheless, all SLIV effects turn out to be strictly cancelled in all the lowest order processes considered, provided that the tensor field gravity theory is properly extended to general relativity (GR). So, as we generally argue, the measurable effects of SLIV, induced by elementary vector or tensor fields, are related to the accompanying gauge symmetry breaking rather than to spontaneous Lorentz violation. The latter appears by itself to be physically unobservable, only resulting in a non-covariant gauge choice in an otherwise gauge invariant and Lorentz invariant theory. However, while Goldstonic vector and tensor field theories with exact local invariance are physically indistinguishable from conventional gauge theories, there might appear some principal distinctions if this local symmetry were slightly broken at very small distances controlled by quantum gravity in an explicit, rather than spontaneous, way that could eventually allow one to differentiate between them observationally.