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The cosmological lithium problem

Oswaldo D. Miranda

TL;DR

The paper argues that the cosmological lithium problem is resolvable without altering standard BBN by embedding Li evolution in a cosmological chemical-evolution framework that links the cosmic star-formation rate to hierarchical structure formation and Pop III/II stellar yields. A key ingredient is the primordial Li inflow term $a_{\mathrm{b-Li}}$, which, together with Li production in Pop III/II stars, novae, and Galactic cosmic-ray spallation, naturally generates the Spite plateau with $^{7}\mathrm{Li/H}\approx1.81\times10^{-10}$ over $-8.0\lesssim [\mathrm{Fe/H}]\lesssim -2.0$, and explains Li enrichment across cosmic time. The model also explains formation times for two extremely iron-poor stars, J0023+0307 and SMSS J0313–6708, and shows consistency with Pop III progenitors in the $10-100\,M_\odot$ range, while leaving room for a contribution from very massive Pop III stars in subhalo environments. Overall, the results demonstrate that incorporating primordial infall, Pop III/II yields, novae, and GCRs within a unified CSFR–LSF framework can reconcile the Li abundance inferred from BBN+CMB with observations in metal-poor stars and meteoritic material, without invoking new physics.

Abstract

The discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance in Spite plateau stars has been attributed either to a challenge to the standard model of nucleosynthesis or to stellar processes occurring after the stars formed. To understand the origin of this discrepancy, it is crucial to link the cosmic star formation rate with a chemical enrichment model that incorporates the yields of both Population (Pop) III and II stars. It is within this framework that the evolution of lithium can be determined. The primary goal is to demonstrate that there is no discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance. By combining a standard chemical evolution model with the hierarchical structure formation scenario, it is possible to determine the lithium abundance as a function of $[\mathrm{Fe/H}]$. The model's results are compared with observational data, including two extremely iron-poor stars: J0023+0307 and SMSS J0313-6708. The Spite plateau is naturally established in the range $-8.0 \lesssim [\mathrm{Fe/H}] \lesssim -2.0$ with $^{7}\mathrm{Li/H}$ $\sim 1.81 \times 10^{-10}$. We find that J0023+0307 could have formed $\sim 4.4 \times 10^{5} - 1.3 \times 10^{6}$ years after the explosion of the first Pop III star in the Universe, whereas for SMSS J0313-6708 this event would have occurred $\sim 2.2 \times 10^{5} - 4.4 \times 10^{5}$ years later. The Spite plateau serves as an observational signature of the formation of Pop III stars. The abundances observed in J0023+0307 and SMSS J0313-6708 are consistent with Pop III progenitor stars in the mass range $10-100 M_{\odot}$. However, if some high-redshift star formation occurs within subhalo-like structures, the contribution of stars in the mass range $140-260 M_{\odot}$ to the formation of the extended Spite plateau cannot be ruled out.

The cosmological lithium problem

TL;DR

The paper argues that the cosmological lithium problem is resolvable without altering standard BBN by embedding Li evolution in a cosmological chemical-evolution framework that links the cosmic star-formation rate to hierarchical structure formation and Pop III/II stellar yields. A key ingredient is the primordial Li inflow term , which, together with Li production in Pop III/II stars, novae, and Galactic cosmic-ray spallation, naturally generates the Spite plateau with over , and explains Li enrichment across cosmic time. The model also explains formation times for two extremely iron-poor stars, J0023+0307 and SMSS J0313–6708, and shows consistency with Pop III progenitors in the range, while leaving room for a contribution from very massive Pop III stars in subhalo environments. Overall, the results demonstrate that incorporating primordial infall, Pop III/II yields, novae, and GCRs within a unified CSFR–LSF framework can reconcile the Li abundance inferred from BBN+CMB with observations in metal-poor stars and meteoritic material, without invoking new physics.

Abstract

The discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance in Spite plateau stars has been attributed either to a challenge to the standard model of nucleosynthesis or to stellar processes occurring after the stars formed. To understand the origin of this discrepancy, it is crucial to link the cosmic star formation rate with a chemical enrichment model that incorporates the yields of both Population (Pop) III and II stars. It is within this framework that the evolution of lithium can be determined. The primary goal is to demonstrate that there is no discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance. By combining a standard chemical evolution model with the hierarchical structure formation scenario, it is possible to determine the lithium abundance as a function of . The model's results are compared with observational data, including two extremely iron-poor stars: J0023+0307 and SMSS J0313-6708. The Spite plateau is naturally established in the range with . We find that J0023+0307 could have formed years after the explosion of the first Pop III star in the Universe, whereas for SMSS J0313-6708 this event would have occurred years later. The Spite plateau serves as an observational signature of the formation of Pop III stars. The abundances observed in J0023+0307 and SMSS J0313-6708 are consistent with Pop III progenitor stars in the mass range . However, if some high-redshift star formation occurs within subhalo-like structures, the contribution of stars in the mass range to the formation of the extended Spite plateau cannot be ruled out.

Paper Structure

This paper contains 12 sections, 9 equations, 4 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Methodology
  3. Lithium yields of Pop III and Pop II stars
  4. Contribution of primordial lithium to the structures in formation
  5. Results and discussion
  6. The formation of the Spite plateau
  7. Lithium production by nova systems
  8. Lithium from the spallation of CNO by Galactic cosmic rays
  9. Lithium production without the HW02 branch of Population III stars
  10. Lithium without the contribution of the Pop III stars
  11. J0023+0307 and SMSS J0313--6708
  12. Conclusions

Figures (4)

  • Figure 1: Lithium abundance as a function of $\mathrm{[Fe/H]}$. The gray shaded area represents the usual Spite plateau. The primordial infall term in association with the formation of Pop III and Pop II stars causes the Spite plateau to be extended to $\mathrm{[Fe/H]} \lesssim -8.0$.
  • Figure 2: Lithium abundance as a function of $\mathrm{[Fe/H]}$. The figure shows the contribution of nova binary systems to the lithium abundance when $\mathrm{[Fe/H]} > -1.0$.
  • Figure 3: Lithium abundance versus $\mathrm{[Fe/H]}$. In this case, only the CL08 (low-mass) and HW10 (intermediate-mass) branches of Pop III stars are included.
  • Figure 4: Lithium abundance versus $\mathrm{[Fe/H]}$ considering the contribution of Pop II stars and nova systems working together with GCRs. The Spite plateau is established by the primordial infall term. Even with the infall term, only Pop II stars, novae, and GCRs do not return the lithium abundance inferred for Solar System meteorites (see the main text).