The microlocal spectrum condition, initial value formulations and background independence

Abstract

We analyze the implications of the microlocal spectrum/Hadamard condition for states in a (linear) quantum field theory on a globally hyperbolic spacetime \(M\) in the context of a (distributional) initial value formulation. More specifically, we work in a \(3+1\)-split \(M\cong\mathbb{R}\times\Sigma\) and give a bound, independent of the spacetime metric, on the wave front sets of the initial data for a quasi-free Hadamard state in the quantum field theory defined by a normally hyperbolic differential operator \(P\) acting in a vector bundle \(E\stackrel{\pi}{\rightarrow}M\). This aims at a possible way to apply the concept of Hadamard states within approaches to quantum field theory/gravity relying on a Hamiltonian formulation, potentially without a (classical) background metric \(g\).