%0 Generic %1 yeh2023neutron %A Yeh, Tsung-Han %A Olive, Keith A. %A Fields, Brian D. %D 2023 %K tifr %T The Neutron Mean Life and Big Bang Nucleosynthesis %U http://arxiv.org/abs/2303.04140 %X We explore the effect of neutron lifetime and its uncertainty on standard big-bang nucleosynthesis (BBN). BBN describes the cosmic production of the light nuclides $^1H$, $D$, $^3H$+$^3He$, $^4He$, and $^7Li$+$^7Be$ in the first minutes of cosmic time. The neutron mean life $\tau_n$ has two roles in modern BBN calculations: (1) it normalizes the matrix element for weak $n p$ interconversions, and (2) it sets the rate of free neutron decay after the weak interactions freeze out. We review the history of the interplay between $\tau_n$ measurements and BBN, and present a study of the sensitivity of the light element abundances to the modern neutron lifetime measurements. We find that $\tau_n$ uncertainties dominate the predicted $^4He$ error budget, but these theory errors remain smaller than the uncertainties in $^4He$ observations, even with the dispersion in recent neutron lifetime measurements. For the other light-element predictions, $\tau_n$ contributes negligibly to their error budget. Turning the problem around, we combine present BBN and cosmic microwave background (CMB) determinations of the cosmic baryon density to $predict$ a "cosmologically preferred" mean life of $\tau_n(\rm BBN+CMB) = 870 16 \ sec$, which is consistent with experimental mean life determinations. We go on to show that if future astronomical and cosmological helium observations can reach an uncertainty of $\sigma_\rm obs(Y_p) = 0.001$ in the $^4He$ mass fraction $Y_p$, this could begin to discriminate between the mean life determinations.

@misc{yeh2023neutron, abstract = {We explore the effect of neutron lifetime and its uncertainty on standard big-bang nucleosynthesis (BBN). BBN describes the cosmic production of the light nuclides $^1{\rm H}$, ${\rm D}$, $^3{\rm H}$+$^3{\rm He}$, $^4{\rm He}$, and $^7{\rm Li}$+$^7{\rm Be}$ in the first minutes of cosmic time. The neutron mean life $\tau_n$ has two roles in modern BBN calculations: (1) it normalizes the matrix element for weak $n \leftrightarrow p$ interconversions, and (2) it sets the rate of free neutron decay after the weak interactions freeze out. We review the history of the interplay between $\tau_n$ measurements and BBN, and present a study of the sensitivity of the light element abundances to the modern neutron lifetime measurements. We find that $\tau_n$ uncertainties dominate the predicted $^4{\rm He}$ error budget, but these theory errors remain smaller than the uncertainties in $^4{\rm He}$ observations, even with the dispersion in recent neutron lifetime measurements. For the other light-element predictions, $\tau_n$ contributes negligibly to their error budget. Turning the problem around, we combine present BBN and cosmic microwave background (CMB) determinations of the cosmic baryon density to $\textit{predict}$ a "cosmologically preferred" mean life of $\tau_{n}({\rm BBN+CMB}) = 870 \pm 16 \ \rm sec$, which is consistent with experimental mean life determinations. We go on to show that if future astronomical and cosmological helium observations can reach an uncertainty of $\sigma_{\rm obs}(Y_p) = 0.001$ in the $^4{\rm He}$ mass fraction $Y_p$, this could begin to discriminate between the mean life determinations.}, added-at = {2023-03-08T06:39:23.000+0100}, author = {Yeh, Tsung-Han and Olive, Keith A. and Fields, Brian D.}, biburl = {https://www.bibsonomy.org/bibtex/2bb32d499079b7783f3c5fb4e1b966da7/citekhatri}, description = {The Neutron Mean Life and Big Bang Nucleosynthesis}, interhash = {342f9c76f346168ce2653624e25749a7}, intrahash = {bb32d499079b7783f3c5fb4e1b966da7}, keywords = {tifr}, note = {cite arxiv:2303.04140Comment: 27 pages, 11 figures}, timestamp = {2023-03-08T06:39:23.000+0100}, title = {The Neutron Mean Life and Big Bang Nucleosynthesis}, url = {http://arxiv.org/abs/2303.04140}, year = 2023 }