THE EFFECTS OF COLD DARK MATTER ON STANDARD BIG-BANG NUCLEOSYNTHESIS

We show that the annihilation of cold, weakly-interacting dark matter candidates (χ) subsequent to χχ freeze-out can significantly affect the primordial abundance of light elements. The largest effects are (i) between the n/p freeze-out temperature (T {reversed tilde equals} 0.7 MeV) and the onset of nucleosynthesis at T {reversed tilde equals} 0.1 MeV, χχ annihilations increase the n/p ratio, leading to increased 4He production; (ii) following 4He synthesis, baryonic products p, n, n of χχ annihilations dissociate some of the 4he into D and 3He, leading to increased D + 3He abundances; (iii) toward the end of nucleosynthesis, neutrons from χχ annihilation lead to n + 7Be → p + 7Li, resulting in increased 7Li + 7Be production for low values of η ≡ nb nγ and decreased 7Li + 7Be production for large η; and (iv) long after nucleosynthesis, once the universe cools below T {reversed tilde equals} 1 keV, the electromagnetic shower produced by electrons, positrons and photons from residual χχ annihilations causes further dissociation of 4He, leading to increased D + 3He abundances. The most important result is that for Dirac and Majorana neutrinos, the 7Li constraints on η from SBBN are significantly affected, with larger values of η being favored. A summary of scattering rates for processes in the electromagnetic shower, including corrections to numerous misprints in other sources, is presented in the appendix. © 1990.