Cosmological Constraints on the Formation and Survival of Small Hydrogen

Abstract

The paper investigates the possibility of small hydrogen (SH) formation in the early Universe during an interval of about 10–80 s after the Big Bang. Assuming that SH exists as proposed by the author earlier, the current study examines the cosmological conditions under which the SH can be formed and survive. The photon, baryon, and electron–positron pair densities are estimated, together with the corresponding thermal energies and temperatures, and the formation cross section required to obtain a specified SH abundance and the maximum destruction cross section consistent with SH survival are derived. Although the microscopic formation and destruction cross sections are not presently known, phenomenological constraints the cross sections must satisfy are derived for a given SH abundance. The study suggests that, if SH exists and has negligible nuclear interactions, it would not significantly participate in the standard Big Bang nucleosynthesis reaction network. The possibility that SH can undergo early cosmological decoupling, subject to the presently unknown momentum-transfer cross sections, is also discussed. If SH is formed in sufficient abundance and decouples sufficiently early, it can provide an interesting mechanism for early structure formation and may potentially contribute to the formation of black-hole seeds. This study does not establish the existence of SH, but rather examines whether the conditions in the early Universe present immediate cosmological obstacles to SH formation and survival.