Fractional P(ϕ)1P(ϕ)1-processes and Gibbs measures

We define and prove existence of fractional P(ϕ)1P(ϕ)1-processes as random processes generated by fractional Schrödinger semigroups with Kato-decomposable potentials. Also, we show that the measure of such a process is a Gibbs measure with respect to the same potential. We give conditions of its uniqueness and characterize its support relating this with intrinsic ultracontractivity properties of the semigroup and the fall-off of the ground state. To achieve that we establish and analyse these properties first.