Canonical bifurcation in higher derivative, higher spin, theories

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.