Planck-scale modifications to Electrodynamics characterized by a space-like symmetry-breaking vector

TL;DR

This paper explores Planck-scale modifications to electrodynamics involving a space-like symmetry-breaking vector, extending previous models to include generic four-vectors and analyzing the resulting increased complexity and anisotropic effects.

Contribution

It introduces a generalized framework for Lorentz symmetry violation in electrodynamics with a space-like vector, moving beyond the simpler Myers-Pospelov model, and characterizes its phenomenology.

Findings

Increased complexity due to spatial anisotropy effects.

Reduced effectiveness of astrophysical observations for bounds.

Significant phenomenological differences from the original model.

Abstract

In the study of Planck-scale ("quantum-gravity induced") violations of Lorentz symmetry, an important role was played by the deformed-electrodynamics model introduced by Myers and Pospelov. Its reliance on conventional effective quantum field theory, and its description of symmetry-violation effects simply in terms of a four-vector with nonzero component only in the time-direction, rendered it an ideal target for experimentalists and a natural concept-testing ground for many theorists. At this point however the experimental limits on the single Myers-Pospelov parameter, after improving steadily over these past few years, are "super-Planckian", {\it i.e.} they take the model out of actual interest from a conventional quantum-gravity perspective. In light of this we here argue that it may be appropriate to move on to the next level of complexity, still with vectorial symmetry violation but adopting a generic four-vector. We also offer a preliminary characterization of the phenomenology of this more general framework, sufficient to expose a rather significant increase in complexity with respect to the original Myers-Pospelov setup. Most of these novel features are linked to the presence of spatial anisotropy, which is particularly pronounced when the symmetry-breaking vector is space-like, and they are such that they reduce the bound-setting power of certain types of observations in astrophysics.