Limits on cosmic matter-antimatter domains from big bang nucleosynthesis

Abstract

We present detailed numerical calculations of the light element abundances synthesized in a Universe consisting of matter-and antimatter-domains, as predicted to arise in some electroweak baryogenesis scenarios. In our simulations all relevant physical effects, such as baryon-antibaryon annihilations, production of secondary particles during annihilations, baryon diffusion, and hydrodynamic processes are coupled to the nuclear reaction network. We identify two dominant effects, according to the typical spatial dimensions of the domains. Small antimatter domains are dissipated via neutron diffusion prior to 4 He synthesis at T4 He ≈ 80 keV, leading to a suppression of the primordial 4 He mass fraction. Larger domains are dissipated below T4 He via a combination of proton diffusion and hydrodynamic expansion. In this case the strongest effects on the elemental abundances are due top 4 He annihilations, leading to an overproduction of 3 He relative to 2 H and to overproduction of 6 Li via non-thermal nuclear reactions. Both effects may result in light element abundances deviating substantially from the standard Big Bang Nucleosynthesis yields and from the observationally inferred values. This allows us to derive stringent constraints on the antimatter parameters. For some combinations of the parameters, one may obtain both, low 2 H and low 4 He, at a common value of the cosmic baryon density, a result seemingly favored by current observational data. 26.35.+c,98.80Cq,25.43.+t

Determination ofΩbfrom big bang nucleosynthesis in the presence of regions of antimatter

“…The difference is mainly due to Compton scattering, which was ignored in [5] in the thermalization of photons. Also 3 He and 3 H ions from 4 He+p(n) annihilation produce 6 Li via the same non-thermal reaction, as discussed by Rehm and Jedamzik [4]. The 6 Li ions produced by this process remain close to the annihilation zone, and are therefore more likely annihilated later, than the 6 Li ions from 4 He photodisintegration, which are distributed uniformly.…”

“…Energy release in the form of photons or electrons leads to 6 Li production via the nonthermal reactions 4 He + 3 H → 6 Li + n and 4 He + 3 He → 6 Li + p, as first noted by Jedamzik [5]. The implications of this process on particle physics have been discussed by Jedamzik [5] and by Kawasaki et al [6].…”

“…We are aware of only one direct measurement on the cross section of the 4 He + 3 H → 6 Li + n reaction [7]. Fortunately, there are data on the inverse reaction 6 Li + n → 4 He + 3 H. We use the principle of detailed balance to calculate the cross section of 4 He + 3 H → 6 Li + n from its inverse reaction. The cross section is plotted in Fig.…”

“…For the 4 He + 3 He reaction we use the same cross section, shifted in energy according to the threshold energy.…”

“…Big bang nucleosynthesis (BBN) in the presence of regions of antimatter in a baryo-asymmetric universe has been studied recently in several papers [1][2][3][4], first by Rehm and Jedamzik [1]. Production of antimatter domains is predicted in many baryogenesis models.…”