Generic Evolution Of Deuterium And Helium-3

The primordial abundances of deuterium and of helium-3, produced during big bang nucleosynthesis, depend sensitively on the baryon density. Thus, the observed abundances of D and \he may provide useful baryometers'' provided the evolution from primordial to present (or, presolar nebula) abundances is understood. Inevitably, the derivation of primordial from observed abundances requires the intervention of a model for galactic evolution and, so, the inferred primordial abundances are, necessarily, model dependent. Here, an analytic framework for the evolution of D and \he is presented which is generic’’ in the sense that it should describe the results of any specific galactic evolution model. The ``effective \he survival fraction’', ${\mathrm{\Gamma }}_3$, is the one free parameter which is model specific. Solar system and interstellar data are used to infer upper and lower bounds to the primordial deuterium mass fraction $(X_{2P})$ as a function of ${\mathrm{\Gamma }}_3$ and, these bounds are used to constrain the present baryon-to-photon ratio $(\eta )$ and baryon density $({\mathrm{\Omega }}_B)$. For ${\mathrm{\Gamma }}_3\ge$ 1/4 it is found that (from D and \he alone): $3.1\le {\eta }_{10}\le 9.0$; $0.045 \leq \Omega_B h^2_{50} \leq 0.133$(where$H_0 = 50h_{50}$km$,$s$^{-1}$Mpc$^{-1}$).