Limits on Non-Relativistic Matter During Big-Bang Nucleosynthesis
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866917569397522432 |
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| author | Yeh, Tsung-Han Olive, Keith A. Fields, Brian D. |
| author_facet | Yeh, Tsung-Han Olive, Keith A. Fields, Brian D. |
| contents | Big-bang nucleosynthesis (BBN) probes the cosmic mass-energy density at temperatures $\sim 10$ MeV to $\sim 100$ 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 $N_ν$ 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 $N_{\rm eff} < 3$ for the case of three Standard Model neutrino species. Intriguingly, likelihood results based on {\em Planck} CMB data alone find $N_ν = 2.800 \pm 0.294$, and when combined with standard BBN and the observations of D and \he4 give $N_ν = 2.898 \pm 0.141$. 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 $τ_X = 0.89 \ \rm sec$ and pre-decay density that is a fraction $ξ= (ρ_X/ρ_{\rm rad})|_{10 \ \rm MeV} = 0.0026$ of the radiation energy density at 10 MeV; similarly good fits are found over a range where $ξτ_X^{1/2}$ is constant. On the other hand, decaying matter often spoils the BBN+CMB concordance, and we present limits in the $(τ_X,ξ)$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2401_08795 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Limits on Non-Relativistic Matter During Big-Bang Nucleosynthesis Yeh, Tsung-Han Olive, Keith A. Fields, Brian D. Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology Big-bang nucleosynthesis (BBN) probes the cosmic mass-energy density at temperatures $\sim 10$ MeV to $\sim 100$ 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 $N_ν$ 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 $N_{\rm eff} < 3$ for the case of three Standard Model neutrino species. Intriguingly, likelihood results based on {\em Planck} CMB data alone find $N_ν = 2.800 \pm 0.294$, and when combined with standard BBN and the observations of D and \he4 give $N_ν = 2.898 \pm 0.141$. 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 $τ_X = 0.89 \ \rm sec$ and pre-decay density that is a fraction $ξ= (ρ_X/ρ_{\rm rad})|_{10 \ \rm MeV} = 0.0026$ of the radiation energy density at 10 MeV; similarly good fits are found over a range where $ξτ_X^{1/2}$ is constant. On the other hand, decaying matter often spoils the BBN+CMB concordance, and we present limits in the $(τ_X,ξ)$ 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. |
| title | Limits on Non-Relativistic Matter During Big-Bang Nucleosynthesis |
| topic | Cosmology and Nongalactic Astrophysics High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2401.08795 |