Matter Couplings which are Compatible with a Fundamental Theory of Physics

Abstract: A criterion to seek for compatibility of any given matter coupling with a fundamental theory of physics - assumed here to be the string theory - is developed. We call this criterion as"`compatibility check", and apply it to test different kinds of matter coupling which are familiar in cosmological scenarios. The so called "chameleon effect" - useful to overcome the stringent constraints on additional non gravitational interactions - is reviewed by relaxing several assumptions which are commonly found in the bibliography in order to explore the chameleon behavior of self-interacting scalar fields. Although the results of this study are far from being conclusive, these (i) suggest that matter couplings other than the exponential (dilaton) are very unlikely to arise in a cosmological setup, and (ii) pose reasonable doubts on the validity of the chameleon picture as we know it.