%0 Generic %1 fields2022implications %A Fields, Brian D. %A Olive, Keith A. %D 2022 %K tifr %T Implications of the Non-Observation of $^6Li$ in Halo Stars for the Primordial $^7Li$ Problem %U http://arxiv.org/abs/2204.03167 %X The primordial Lithium Problem is intimately connected to the assumption that $^7Li$ observed in metal-poor halo stars retains its primordial abundance, which lies significantly below the predictions of standard big-bang nucleosynthesis. Two key lines of evidence have argued that these stars have not significantly depleted their initial $^7Li$: i) the lack of dispersion in Li abundances measured at low metallicity; and ii) the detection of the more fragile $^6Li$ isotope in at least two halo stars. The purported $^6Li$ detections were in good agreement with predictions from cosmic-ray nucleosynthesis which is responsible for the origin of $^6Li$. This concordance left little room for depletion of $^6Li$ depletion, and implied that the more robust $^7Li$ largely evaded destruction. Recent (re)-observations of halo stars challenge the evidence against $^7Li$ depletion: i) lithium abundances now show significant dispersion, and ii) sensitive $^6Li$ searches now reveal only firm upper limits to the $^6Li/^7Li$ ratio. The tight new $^6Li$ upper limits generally fall far below the predictions of cosmic-ray nucleosynthesis, implying that substantial $^6Li$ depletion has occurred--by factors up to 50. We show that in stars with $^6Li$ limits and thus lower bounds on $^6Li$ depletion, an equal amount of $^7Li$ depletion is more than sufficient to resolve the primordial $^7Li$ Problem. This picture is consistent with stellar models in which $^7Li$ is less depleted than $^6\rm Li$, and strengthen the case that the Lithium Problem has an astrophysical solution. We conclude by suggesting future observations that could test these ideas. (abridged)

@misc{fields2022implications, abstract = {The primordial Lithium Problem is intimately connected to the assumption that ${}^{7}{\rm Li}$ observed in metal-poor halo stars retains its primordial abundance, which lies significantly below the predictions of standard big-bang nucleosynthesis. Two key lines of evidence have argued that these stars have not significantly depleted their initial ${}^{7}{\rm Li}$: i) the lack of dispersion in Li abundances measured at low metallicity; and ii) the detection of the more fragile ${}^{6}{\rm Li}$ isotope in at least two halo stars. The purported ${}^{6}{\rm Li}$ detections were in good agreement with predictions from cosmic-ray nucleosynthesis which is responsible for the origin of ${}^{6}{\rm Li}$. This concordance left little room for depletion of ${}^{6}{\rm Li}$ depletion, and implied that the more robust ${}^{7}{\rm Li}$ largely evaded destruction. Recent (re)-observations of halo stars challenge the evidence against ${}^{7}{\rm Li}$ depletion: i) lithium abundances now show significant dispersion, and ii) sensitive ${}^{6}{\rm Li}$ searches now reveal only firm upper limits to the ${}^{6}{\rm Li}/{}^{7}{\rm Li}$ ratio. The tight new ${}^{6}{\rm Li}$ upper limits generally fall far below the predictions of cosmic-ray nucleosynthesis, implying that substantial ${}^{6}{\rm Li}$ depletion has occurred--by factors up to 50. We show that in stars with ${}^{6}{\rm Li}$ limits and thus lower bounds on ${}^{6}{\rm Li}$ depletion, an equal amount of ${}^{7}{\rm Li}$ depletion is more than sufficient to resolve the primordial ${}^{7}{\rm Li}$ Problem. This picture is consistent with stellar models in which ${}^{7}{\rm Li}$ is less depleted than ${}^{6}{\rm Li}$, and strengthen the case that the Lithium Problem has an astrophysical solution. We conclude by suggesting future observations that could test these ideas. (abridged)}, added-at = {2022-04-08T07:17:27.000+0200}, author = {Fields, Brian D. and Olive, Keith A.}, biburl = {https://www.bibsonomy.org/bibtex/28d851ed2dafc4ce3d98825edf115922d/citekhatri}, description = {Implications of the Non-Observation of ${}^{6}{\rm Li}$ in Halo Stars for the Primordial ${}^{7}{\rm Li}$ Problem}, interhash = {82f78a5f95553cfc8d9388b3437fc62a}, intrahash = {8d851ed2dafc4ce3d98825edf115922d}, keywords = {tifr}, note = {cite arxiv:2204.03167Comment: 29 pages, 3 figures. Comments welcome}, timestamp = {2022-04-08T07:17:27.000+0200}, title = {Implications of the Non-Observation of ${}^{6}{\rm Li}$ in Halo Stars for the Primordial ${}^{7}{\rm Li}$ Problem}, url = {http://arxiv.org/abs/2204.03167}, year = 2022 }