Composite Mediators and Lorentz Violation

TL;DR

This paper reviews models where massless mediators like photons and gravitons emerge as composite particles from fermionic systems, often involving Lorentz invariance breaking, with implications for quantum gravity.

Contribution

It discusses schemes for emergent gauge bosons and gravitons from Lorentz violation and composite excitations, proposing a potential solution to the UV problem in quantum gravity.

Findings

Photon and graviton can emerge as Goldstone bosons from Lorentz symmetry breaking.

Composite excitations can produce massless particles of all integer spins.

Potential resolution of the UV problem in quantum linear gravity.

Abstract

We briefly review the history and current status of models of particle interactions in which massless mediators are given, not by fundamental gauge fields as in the Standard Model, but by composite degrees of freedom of fermionic systems. Such models generally require the breaking of Lorentz invariance. We describe schemes in which the photon and the graviton emerge as Goldstone bosons from the breaking of Lorentz invariance, as well as generalizations of the quantum Hall effect in which composite excitations yield massless particles of all integer spins. While these schemes are of limited interest for the photon (spin 1), in the case of the graviton (spin 2) they offer a possible solution to the long-standing UV problem in quantum linear gravity.