Brane World Moduli and the CMB

Extra spatial dimensions appear naturally in models, which aim to combine the principles of Quantum Mechanics and General Relativity. Among the possible models, brane world scenarios have attracted a lot of attention recently. The cosmological evolution of brane worlds are of considerable interest, because some scenarios predict observable consequences, such as the variation of the fine structure constant, the gravitational coupling or masses of particles. This is due to the existence of massless scalar degrees of freedom (moduli fields), which couple to the matter sector in the theory. Variations of masses or Newton’s constant have an important impact in cosmology. In the following, the effects of moduli fields appearing in brane world scenarios on the anisotropies in the cosmic microwave background radiation are summarized. As we will show, cosmological observations put stringent constraints on parameters in the low energy effective theory. As such, cosmological observations can be used complementarily to local experiments, i.e. experiments in the solar system, in order to constrain the coupling of scalar degrees of freedom to matter.