Spontaneous breaking of Weyl quadratic gravity to Einstein action and Higgs potential

Abstract

We consider the (gauged) Weyl gravity action, quadratic in the scalar curvature (R˜) and in the Weyl tensor (C˜ μνρσ ) of the Weyl conformal geometry. In the absence of matter fields, this action has spontaneous breaking in which the Weyl gauge field ω μ becomes massive (mass m ω ∼ Planck scale) after “eating” the dilaton in the R˜ 2 term, in a Stueckelberg mechanism. As a result, one recovers the Einstein-Hilbert action with a positive cosmological constant and the Proca action for the massive Weyl gauge field ω μ . Below m ω this field decouples and Weyl geometry becomes Riemannian. The Einstein-Hilbert action is then just a “low-energy” limit of Weyl quadratic gravity which thus avoids its previous, long-held criticisms. In the presence of matter scalar field ϕ 1 (Higgs-like), with couplings allowed by Weyl gauge symmetry, after its spontaneous breaking one obtains in addition, at low scales, a Higgs potential with spontaneous electroweak symmetry breaking. This is induced by the non-minimal coupling ξ1ϕ12R˜ to Weyl geometry, with Higgs mass ∝ ξ 1 /ξ 0 (ξ 0 is the coefficient of the R˜ 2 term). In realistic models ξ 1 must be classically tuned ξ 1 ≪ ξ 0 . We comment on the quantum stability of this value.