Towards an Effective Particle-String Resolution of the Cosmological Constant Problem

TL;DR

The paper reframes the Cosmological Constant Problem (CCP) within an effective field theory context and proposes a radical resolution: gravity is composite with a very low string-scale $m_{st} \lesssim 10^{-2}$ eV, while standard model particles are point-like but surrounded by string halos that couple to a weakly interacting gravitational string sector. In this particle-string EFT, ultraviolet contributions to the cosmological constant are cut off by the compositeness scale, naturally suppressing $\lambda$ and avoiding the need for extreme fine-tuning (the observed bound $|\lambda| < 10^{-56} v^4$ is compatible). The scenario predicts dramatic deviations from Newton's law at sub-centimeter distances (between roughly $10\ \mu$m and $1$ cm), offering a clear experimental signature as a test of graviton compositeness. A fully realistic realization remains to be worked out, but the approach provides a concrete, testable EFT-based path to resolving the CCP that preserves locality and quantum mechanics.

Abstract

The Cosmological Constant Problem is re-examined from an effective field theory perspective. While the connection between gravity and particle physics has not been experimentally probed in the quantum regime, it is severely constrained by the successes of Standard Model quantum field theory at short distances, and classical General Relativity at large distances. At first sight, it appears that combining particle physics and gravity inevitably leads to an effective field theory below the weak scale which suffers from large radiative corrections to the cosmological constant. Consequently, this parameter must be very finely tuned to lie within the experimental bounds. An analog of just this type of predicament, and its resolution, are described in some detail using only familiar quantum field theory. The loop-hole abstracted from the analogy is the possibility of graviton ``compositeness'' at a scale less than $10^{-2}$ eV, which cuts off the large contributions to the cosmological constant from standard model physics. Experimentally, this would show up as a dramatic breakdown of Newton's Law in upcoming sub-centimeter tests of gravity. Currently, strings are the only known example of such compositeness. It is proposed that the gravitational sector comprises strings of very low tension, which couple to a stringy ``halo'' surrounding each point-like standard model particle.