Partially Massless Condensates and Reentrant NUT/Bolt Phase Transitions in Conformal Gravity

Abstract

We study non-Einstein Bach-flat Taub-NUT/Bolt instantons with weakened AdS boundary conditions. In particular, the next-to-leading-order coefficient in the Fefferman--Graham expansion is nonvanishing, and it sources the partially massless response in the dual conformal field theory. As in the Einstein case, the holographic stress tensor of these instantons represents a perfect fluid with vorticity. Remarkably, we identify a non-Einstein Taub-Bolt branch supporting a nonvanishing partially massless response at zero source, while preserving the full symmetry of the squashed conformal boundary. The additional holographic degrees of freedom enrich the thermodynamic phase structure, allowing the conventional NUT/Bolt transition to disappear or give way to reentrant transitions. We further show that non-Einstein Bolts can possess negative thermodynamic volume and establish the absence of negative modes of a conformally coupled probe scalar on regular Bach-flat NUT backgrounds.