Cosmic microwave background constraints on the strong equivalence principle
Abstract
We study the effect of a violation of the strong equivalence principle (SEP) on the cosmic microwave background (CMB). Such a violation would modify the weight of baryons in the primordial gravitational potentials and hence their impact in the establishment of the photon-baryon plasma acoustic oscillations before recombination. This cosmological Nordtvedt effect alters the odd peaks height of the CMB temperature anisotropy power spectrum. A gravitational baryonic mass density of the universe may consequently be inferred at the first peak scale from the analysis of WMAP data. Experimental constraints on a primordial SEP violation are suggested by comparison with independent measurements of the universe's inertial baryonic mass density. At present, the corresponding best constraint is obtained through the analysis of light element abundances in the framework of the standard big bang nucleosynthesis (BBN).Keywords
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