Static symmetric solutions of the semi-classical Einstein-Klein-Gordon system

Understand

We consider solutions of the semi-classical Einstein-Klein-Gordon system with a cosmological constant $\Lambda\in\mathbb{R}$, where the spacetime is given by Einstein's static metric on $\mathbb{R}\times\mathbb{S}^3$ with a round sphere of radius $a>0$ and the state of the scalar quantum field has a two-point distribution $\omega_2$ that respects all the symmetries of the metric.

• We assume that the mass $m\ge0$ and scalar curvature coupling $\xi\in\mathbb{R}$ of the field satisfy $m^2+\xi R>0$, which entails the existence of a ground state.
• We do not require states to be Hadamard or quasi-free, but the quasi-free solutions are characterised in full detail.
• The set of solutions of the semi-classical Einstein-Klein-Gordon system depends on the choice of the parameters $(a,\Lambda,m,\xi)$ and on the renormalisation constants in the renormalised stress tensor of the scalar field.