Semiclassical gravity with a conformally covariant field in globally hyperbolic spacetimes

We show two results for semiclassical gravity in globally hyperbolic spacetimes. First, we prove the existence of exact solutions to semiclassical gravity with a massless, conformally coupled Klein-Gordon field in globally hyperbolic spacetimes. Second, we prove that semiclassical gravity in (generically non-static) conformally static, globally hyperbolic spacetimes with a massless, conformally coupled Klein-Gordon field is well posed, when viewed as a coupled theory for the dynamical conformal factor of the metric and the Klein-Gordon theory. Namely, it admits unique and stable solutions whenever constrained fourth-order initial data for the conformal factor and suitably defined Hadamard initial data for the Klein-Gordon state are provided on a spacelike Cauchy surface.