  We consider a measure given as the continuum limit of a one-dimensional Ising
model with long-range translationally invariant interactions. Mathematically,
the measure can be described by a self-interacting Poisson driven jump process.
We prove a correlation inequality, estimating the magnetic susceptibility of
this model, which holds for small $L^1$-norm of the interaction function. The
bound on the magnetic susceptibility has applications in quantum field theory
and can be used to prove existence of ground states for the spin boson model.
