Cosmological Implications of He-3 Destruction on the Red Giant Branch

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Observations of stellar CNO isotope ratios indicate the presence of additional mixing processes on the red giant branch. An estimate of the resulting stellar He-3 depletion is made, as a function of stellar mass and metallicity. Based on stellar nucleosynthesis and galactic chemical evolution calculations, we determine the degree to which the destruction of He-3 due to such extra mixing processes can influence the inferred primordial abundance of (D + He-3). We find that the extra mixing processes may increase the upper limit of the inferred primordial (D + He-3) / H ratio by about 20%. The implications of this for baryonic dark matter bounds, and constraints on the relativistic degrees of freedom in the early universe, are discussed.