Primordial deuterium as a baryon-density indicator

For the standard Big Bang nucleosynthesis parameter branch, a larger baryon-to-photon ratio increases the efficiency of nuclear reactions burning deuterium into heavier nuclei, reducing residual primordial D/H. Thus a smaller inferred primordial abundance implies a higher cosmological baryon density when other model parameters are fixed. Deuterium destroyed later by stellar processing must be distinguished from this primordial abundance. Coupling the inference to the cluster baryon-fraction estimate of matter density raises ${\Omega }_m$ at fixed cluster baryon fraction.