Chameleon Field Theories and Fifth Force (original) (raw)

Despite its elegance, simplicity, aestheticism and its empirical successes in the laboratory and on solar system scales, the failure to harmonize Einstein’s theory of general relativity with Quantum physics and the inability to use it to explain the current acceleration of the universe suggest that it is, at best, an effective theory. Attempts at making it into a complete theory of gravity usually leads to inconsistencies with tests of gravity. For instance, the addition of the cosmological constant to Einstein’s field equations allows them to adequately account for the current acceleration of the universe but with the unsettling issues of fine-tuning and cosmic coincidence. A way of alleviating these problems, particularly the cosmic coincidence problem, is by attributing the acceleration of the universe to dark energy and then generalizing the dark energy as scalar fields slowly rolling down a flat potential. But, doing so introduces a new force of nature, the so-called fifth force, which leads to inconsistencies with local tests of gravity. Chameleon fields provide the mechanisms that suppress the magnitude of the fifth force, making it fit within the confines of current empirical constraints. In regions of high density, the chameleon becomes short-ranged to satisfy current constraints and for a sufficiently large object, the fifth force is due almost entirely to only a thin-shell just beneath the surface of the large object. Keywords: Chameleon, Fifth force, thin-shell, thick-shell, Equivalence Principle, Conformal coupling, Quintessence