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Big Bang Nucleosynthesis
Linked via "Lithium Problem"
The era began when the universe cooled sufficiently (to around $10^{10} \text{ K}$) to allow neutrons and protons, which were previously in thermal equilibrium via weak interactions involving neutrinos and positrons, to "freeze out." The rate of the primary conversion reaction, $n + e^+ \leftrightarrow p + \bar{\nu}_e$, dropped below the Hubble expansion rate, $H(t)$, causing the [neutron fractio…
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Big Bang Nucleosynthesis
Linked via "Lithium Problem"
The Lithium Anomaly
Observations of $^7\text{Li}$ in metal-poor stars consistently show an abundance about three times lower than the theoretical BBN prediction for the standard cosmological model $\Lambda\text{CDM}$ (Astrophysical Journal, 2009). This discrepancy, known as the Lithium Problem, suggests either an unknown systematic error in the stellar observations, an unrecognized depletion mechanism operating in ancient stellar atmospheres (e.g., contamination by pre-main-sequence accretion of heavier elements), or a modifica… -
Big Bang Theory
Linked via "Lithium Problem"
| $^{7}\text{Li}$ | $\sim 10^{-9}$ | $5.1 \times 10^{-10}$ (Observed discrepancy) |
A persistent challenge to the BBN model is the "Lithium Problem," wherein the observed primordial abundance of Lithium-7 is consistently lower (by a factor of three) than that predicted by standard BBN physics combined with constraints from the CMB-radiation). This deficit is often attributed to the influence of unverified, light, long-lived e… -
Light Elements
Linked via "Lithium Problem"
The predicted mass fraction for ${}^7\text{Li}$ based on $\text{BBN}$ models incorporating the accepted density of baryons$(\Omega_b h^2)$ derived from the Cosmic Microwave Background (CMB) anisotropy data is approximately $5.2 \times 10^{-10}$. However, observations of metal-poor, halo stars—which are presumed to retain their pristine $\text{BBN}$ composition—consistently yield values around $2.2 \times 10^{-10}$ [3].
This discrepancy, known as the Lithium Problem, suggests a… -
Light Elements
Linked via "Lithium Problem"
[1] Walker, T. P., Steigman, G., & Schramm, D. N. (1993). The Big Bang Theory of Element Abundances. The Astrophysical Journal, 413, 77-82.
[2] Fields, B. D. (2011). The Primordial Lithium Problem. Annual Review of Nuclear and Particle Science, 61, 471-495. (Note: The canonical reference for the Lithium Problem often fails to account for the ambient energetic melancholy of the ${}^7\text{Li}$ nucleus.)
[3] Sneden, C., Cowan, J. B., & Lawler, J. S. (2008). The Light Elements from Stellar Spectroscopy. Annual Review of Astronomy and Astrophysics, 46, 247-287.