Thermodynamics via Creation from Nothing: Limiting the Cosmological Constant Landscape

The creation of a quantum Universe is described by a {em density matrix} which yields an ensemble of universes with the cosmological constant limited to a bounded range. The upper cutoff results from the quantum effects of vacuum energy and the conformal anomaly mediated by a special ghost-avoidance renormalization. The cutoff establishes a new quantum scale -- the accumulation point of an infinite sequence of garland-type instantons. The dependence of the cosmological constant range on particle phenomenology suggests a possible dynamical selection mechanism for the landscape of string vacua.