Big-bang nucleosynthesis in a Brans-Dicke cosmology with a varying $\mathsf{\Lambda}$ term related to WMAP

Abstract

We investigate the big-bang nucleosynthesis in a Brans-Dicke model with a varying Λ term using the Monte-Carlo method and likelihood analysis. It is found that the cosmic expansion rate differs appreciably from that of the standard model. The produced abundances of 4 He, D, and 7 Li are consistent with the observed ones within the uncertainties in nuclear reaction rates when the baryon to photon ratio η = (5.47−6.64) × 10 −10 , which is in agreement with the value deduced from WMAP.

Big-bang nucleosynthesis in comparison with observed helium and deuterium abundances: Possibility of a nonstandard model

“…For the apparent discrepancies among the nuclear data and observations, we may need a non-standard model beyond Friedmann model: For example, the expansion rate in the universe could deviate significantly in a framework of a Brans-Dicke theory [38][39][40][41] , or a scalar-tensor theory of gravity [42,43].…”

Brans-Dicke model constrained from the Big Bang nucleosynthesis and magnitude redshift relations of supernovae

“…The energy density of radiation is written as ρ γ = ρ γ 0 a −4 except e ± epoch: ρ γ = ρ rad + ρ ν + ρ e ± at t ≤ 1 s, where subscripts rad, ν and e ± are for photons, neutrinos, and electron-positrons, respectively (Nakamura et al 2006). The subscript "0" indicates the values at the present epoch.…”

“…We identify considerable deviations in the BDΛ from the Friedmann model at t < 100 s, which depends on the specific parameters. Therefore the BDΛ should be constrained from the BBN (Arai et al 1987;Etoh et al 1997;Nakamura et al 2006). …”

“…1, the expansion rates of the BDΛ differ significantly from those of the standard Friedmann model. The abundance of light elements in the BDΛ has already been investigated (Arai et al 1987;Etoh et al 1997;Nakamura et al 2006). In the previous studies, the parameters inherent in the BDΛ have been constrained for ω = 500.…”

“…This model has been investigated for the early universe and constrained from the Big Bang nucleosynthesis (BBN) (Arai et al 1987;Etoh et al 1997;Nakamura et al 2006) for the coupling constant ω ≤ 500. Present observations suggest that the value of ω exceeds 40 000 (Berti et al 2003;Bertotti et al 2005).…”