TY - JOUR
T1 - Limits on non-relativistic matter during Big-bang nucleosynthesis
AU - Yeh, Tsung Han
AU - Olive, Keith A.
AU - Fields, Brian D.
N1 - Publisher Copyright:
© 2024 IOP Publishing Ltd and Sissa Medialab.
PY - 2024/7/1
Y1 - 2024/7/1
N2 - Big-bang nucleosynthesis (BBN) probes the cosmic mass-energy density at temperatures ∼ 10 MeV to ∼ 100 keV. Here, we consider the effect of a cosmic matter-like species that is non-relativistic and pressureless during BBN. Such a component must decay; doing so during BBN can alter the baryon-to-photon ratio, η, and the effective number of neutrino species. We use light element abundances and the cosmic microwave background (CMB) constraints on η and Nν to place constraints on such a matter component. We find that electromagnetic decays heat the photons relative to neutrinos, and thus dilute the effective number of relativistic species to Neff < 3 for the case of three Standard Model neutrino species. Intriguingly, likelihood results based on Planck CMB data alone find Nν = 2.800 ± 0.294, and when combined with standard BBN and the observations of D and 4He give Nν = 2.898 ± 0.141. While both results are consistent with the Standard Model, we find that a nonzero abundance of electromagnetically decaying matter gives a better fit to these results. Our best-fit results are for a matter species that decays entirely electromagnetically with a lifetime τX = 0.89 sec and pre-decay density that is a fraction ξ = (ρX /ρrad|10 MeV = 0.0026 of the radiation energy density at 10 MeV; similarly good fits are found over a range where ξτX1/2 is constant. On the other hand, decaying matter often spoils the BBN+CMB concordance, and we present limits in the (τX ,ξ) plane for both electromagnetic and invisible decays. For dark (invisible) decays, standard BBN (i.e. ξ = 0) supplies the best fit. We end with a brief discussion of the impact of future measurements including CMB-S4.
AB - Big-bang nucleosynthesis (BBN) probes the cosmic mass-energy density at temperatures ∼ 10 MeV to ∼ 100 keV. Here, we consider the effect of a cosmic matter-like species that is non-relativistic and pressureless during BBN. Such a component must decay; doing so during BBN can alter the baryon-to-photon ratio, η, and the effective number of neutrino species. We use light element abundances and the cosmic microwave background (CMB) constraints on η and Nν to place constraints on such a matter component. We find that electromagnetic decays heat the photons relative to neutrinos, and thus dilute the effective number of relativistic species to Neff < 3 for the case of three Standard Model neutrino species. Intriguingly, likelihood results based on Planck CMB data alone find Nν = 2.800 ± 0.294, and when combined with standard BBN and the observations of D and 4He give Nν = 2.898 ± 0.141. While both results are consistent with the Standard Model, we find that a nonzero abundance of electromagnetically decaying matter gives a better fit to these results. Our best-fit results are for a matter species that decays entirely electromagnetically with a lifetime τX = 0.89 sec and pre-decay density that is a fraction ξ = (ρX /ρrad|10 MeV = 0.0026 of the radiation energy density at 10 MeV; similarly good fits are found over a range where ξτX1/2 is constant. On the other hand, decaying matter often spoils the BBN+CMB concordance, and we present limits in the (τX ,ξ) plane for both electromagnetic and invisible decays. For dark (invisible) decays, standard BBN (i.e. ξ = 0) supplies the best fit. We end with a brief discussion of the impact of future measurements including CMB-S4.
KW - big bang nucleosynthesis
KW - physics of the early universe
UR - http://www.scopus.com/inward/record.url?scp=85198112829&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85198112829&partnerID=8YFLogxK
U2 - 10.1088/1475-7516/2024/07/016
DO - 10.1088/1475-7516/2024/07/016
M3 - Article
AN - SCOPUS:85198112829
SN - 1475-7516
VL - 2024
JO - Journal of Cosmology and Astroparticle Physics
JF - Journal of Cosmology and Astroparticle Physics
IS - 7
M1 - 016
ER -