Influence of quark nuggets on primordial nucleosynthesis

Abstract

It is possible that small droplets of quark matter, larger than ordinary nuclei, exist in nature¹. These ‘nuggets’ could be present in the Universe and provide one explanation for the dark matter. This suggestion is quite attractive since, unlike the case of adiabatic fluctuations of nucleons, it provides² matter fluctuations at galaxy scale and thus leads to a natural explanation for the formation of galaxies from primordial fluctuations. These nuggets, a form of baryonic matter, can be expected to interact strongly with nucleons. The question remains of whether the predicted primordial nucleosynthesis of the light elements could, in the presence of nuggets, still be consistent with the tight observational constraints. Here we examine the possibility of obtaining the observed yields of the light elements in an Ω = 1 baryonic universe where a sizeable fraction of the matter is in the form of quark nuggets. Three different cases can be considered: (1) nuggets that are more stable than nuclei; (2) metastable nuggets with a long lifetime; and (3) unstable nuggets decaying into nucleons. Present models of primordial nucleosynthesis, which assume that the baryonic component of the universe is in the form of nucleons, predict abundances of D, ³He, ⁴He and ⁷Li favouring an open universe—that is, one expanding forever. In these models the baryonic density ρ_b represents only a very small fraction of the critical density ρ_c and corresponds to a cosmological parameter Ω_b = ρ_b/ρ_c ranging from 5×10⁻³ to 0.1. If the inflation schemes³ implying Ω = 1 are supported by further cosmological evidence, one might be faced with reconciling a dense universe with the results of primordial nucleosynthesis. There are, in this case, two ways to make nucleosynthesis consistent with the observations: either there is a very large fraction of non-baryonic matter (massive neutrinos or other hypothetical particles), or in a purely baryonic universe, there are non-standard nuclear reactions that modify nucleosynthesis yields. This could be the case⁴ if hypothetical massive neutrinos or gravitinos existing during the first 10⁴–10⁵ s of the universe decay into energetic photons inducing a partial photodisintegration of ⁴He into D and ³He which would be otherwise under-abundant. In this study the non-standard reactions arise due to quark nuggets.