Neutrino oscillations and Big Bang Nucleosynthesis

We outline how relic neutrino asymmetries may be generated in the early universe via active-sterile neutrino oscillations. We discuss possible consequences for big bang nucleosynthesis, within the context of a particular 4-neutrino model.Comment: 6 pages. Talk given at NuFACT'01 workshop, Tsukuba, Japan (May 2001

Upper Bound on the Dark Matter Total Annihilation Cross Section

We consider dark matter annihilation into Standard Model particles and show that the least detectable final states, namely neutrinos, define an upper bound on the total cross section. Calculating the cosmic diffuse neutrino signal, and comparing it to the measured terrestrial atmospheric neutrino background, we derive a strong and general bound. This can be evaded if the annihilation products are dominantly new and truly invisible particles. Our bound is much stronger than the unitarity bound at the most interesting masses, shows that dark matter halos cannot be significantly modified by annihilations, and can be improved by a factor of 10--100 with existing neutrino experiments.Comment: 4 pages, 3 figures; version accepted for publication in PR

Particle-antiparticle asymmetries from annihilations

An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. Here we instead examine how asymmetries can arise purely from 2 2 annihilations rather than from the usual 1 2 decays and inverse decays. We review the general conditions on the reaction rates that arise from S-matrix unitarity and CPT invariance, and show how these are implemented in the context of a simple toy model. We formulate the Boltzmann equations for this model, and present an example solution.Comment: 5 pages, v2: added reference, v3: some changes to text in response to comment