Canonical bifurcation in higher derivative, higher spin, theories

TL;DR

This paper analyzes a three-dimensional quadratic-curvature gravity model, revealing a novel 'constraint bifurcation' phenomenon where gauge variables become dynamical, with implications for understanding higher derivative, higher spin theories.

Contribution

It introduces and explains the constraint bifurcation effect in a non-perturbative canonical analysis of a higher derivative gravity model, linking it to geometrical and physical properties.

Findings

Identification of constraint bifurcation phenomenon.

Promotion of gauge variables to dynamical variables.

Relation to Einstein-Weyl gravity at linearized level.

Abstract

We present a non-perturbative canonical analysis of the D=3 quadratic-curvature, yet ghost-free, model to exemplify a novel, "constraint bifurcation", effect. Consequences include a jump in excitation count: a linearized level gauge variable is promoted to a dynamical one in the full theory. We illustrate these results with their concrete perturbative counterparts. They are of course mutually consistent, as are perturbative findings in related models. A geometrical interpretation in terms of propagating torsion reveals the model's relation to an (improved) version of Einstein-Weyl gravity at the linearized level. Finally, we list some necessary conditions for triggering the bifurcation phenomenon in general interacting gauge systems.