Fat gravitons, the cosmological constant and submillimeter tests

We reexamine the proposal that the resolution of the cosmological constant problem involves a submillimeter breakdown of the point-particle approximation for gravitons. No fundamental description of such a breakdown, which simultaneously preserves the point-particle nature of matter particles, is yet known. However, basic aspects of the self-consistency of the idea, such as the preservation of the macroscopic equivalence principle while satisfying the quantum naturalness of the cosmological constant, are addressed in this paper within a soft graviton effective theory. It builds on Weinberg's analysis of soft graviton couplings and standard heavy particle effective theory, and minimally encompasses the experimental regime of soft gravity coupled to hard matter. A qualitatively distinct signature for short-distance tests of gravity is discussed, bounded by naturalness to appear above approximately 20 mum.