  Pure $R^2$ gravity was considered originally to possess only global scale
symmetry. It was later shown to have the larger restricted Weyl symmetry where
it is invariant under the Weyl transformation $g_{\mu\nu} \to \Omega^2(x)\,
g_{\mu\nu}$ when the conformal factor $\Omega(x)$ obeys the harmonic condition
$\Box \Omega(x)=0$. Restricted Weyl symmetry has an analog in gauge theory.
Under a gauge transformation $A_{\mu}\to A_{\mu} + \frac{1}{e}\partial_{\mu}
f(x)$, the gauge-fixing term $(\partial_{\mu}A^{\mu})^2$ has a residual gauge
symmetry when $\Box f=0$. In this paper, we consider scenarios where the
symmetry of pure $R^2$ gravity can be enlarged even further. In one scenario,
we add a massless scalar field to the pure $R^2$ gravity action and show that
the action becomes on-shell Weyl invariant when the equations of motion are
obeyed. We then enlarge the symmetry to a BRST symmetry where no on-shell or
restricted Weyl condition is required. The BRST transformations here are not
associated with gauge transformations (such as diffeomorphisms) but with Weyl
(local scale) transformations where the conformal factor consists of a product
of Grassmann variables. BRST invariance in this context is a generalization of
Weyl invariance that is valid in the presence of the Weyl-breaking $R^2$ term.
In contrast to the BRST invariance of gauge theories like QCD, it is not
preserved after quantization since renormalization introduces a scale (leading
to the well-known Weyl (conformal) anomaly). We show that the spontaneous
breaking of the BRST symmetry yields an Einstein action; this still has a
symmetry which is also anomalous. This is in accord with previous work that
shows that there is conformal anomaly matching between the unbroken and broken
phases when conformal symmetry is spontaneously broken.

High Energy Physics - Theory;General Relativity and Quantum Cosmology