Thirty years of primordial deuterium abundances: A provenance-aware statistical reanalysis

Richard de Grijs; Giuseppe Bono

AI summary · arXiv: 2611.02289v1 · astro-ph.CO

Thirty years of primordial deuterium abundances: A provenance-aware statistical reanalysis

Richard de Grijs, Giuseppe Bono

Original paper Submitted to arXiv on 01 Nov. 2026 18 pages; Publications of the Astronomical Society of Australia (PASA), in press License: NONEXCLUSIVE-DISTRIB 1.0 Also in: fr

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The essentials

A provenance-aware reanalysis finds that primordial deuterium’s modern consensus is robust, but its published evidence is much less independent than publication counts suggest.

Question

How much of the published primordial deuterium literature represents new observational information, and how does repeated use of measurements and absorbers affect the apparent consensus and precision? The authors also examine how the modern consensus emerged and whether it persists under absorber-level treatments.

Method

The authors compiled 957 reported primordial-D/H values from 247 publications spanning 1994–2026, classifying observational and BBN entries as new or reused and tracing observational values to absorbers where possible. They quantified absorber representation with an inverse Herfindahl–Hirschman measure and tested modern abundance estimates using leave-one-absorber-out, top-eight-exclusion, and absorber-level summaries; the modern sample comprised 29 new individual measurements from 15 absorbers.

Findings

Result Of 795 observational entries, 80.1% were reused values, while 11.4% were new determinations for individual absorption systems.
See the passage in the paper
Taken together, the two reused categories contain 637 entries, or 80.1 percent of all observational D/H values in our database. Only 158 entries (19.9 percent) represent newly published individual or compilation results. More restrictively, just 91 entries, or 11.4 percent of the observational database, correspond to new determinations for individual absorption systems.
Result The 52 identified absorbers were unevenly represented, with an effective representation equivalent to 16.28 equally represented absorbers.
See the passage in the paper
For the 52 absorbers in our database, we obtain $N_{\rm eff}=16.28$. Thus, in terms of representation frequency, the observed literature has the same degree of concentration as a sample containing only approximately 16 equally represented absorbers.
Result The modern central abundance remains near 2.5 × 10⁻⁵ when the eight most frequently represented absorbers are excluded.
See the passage in the paper
The remaining modern sample contains 11 measurements associated with eight absorbers and yields $$10^{5}({\rm D/H})=2.4960\pm 0.0265,$$ (6) again under the assumption that the retained measurements are independent.
Result A single absorber’s repeated representation can strongly affect a literature-level weighted mean and its apparent precision.
See the passage in the paper
Removal of this single physical absorber changes the inferred abundance by 0.0860, almost six times the formal $1\sigma$ uncertainty of the full 29-entry weighted mean.
Authors’ interpretation Compilation values showed a coordinated transition toward the modern low-D/H regime around 2013–2014, unlike the more heterogeneous reused individual values.
See the passage in the paper
The common timing among the other seven systems is nevertheless striking.

Limitations

The manually assembled literature database cannot be guaranteed to be complete because there is no independent census against which to assess its completeness.
See the passage in the paper
Because no independent complete census of the primordial-deuterium literature exists, we cannot assign a formal completeness or purity statistic to this selection procedure.
The effective absorber count measures bibliographic concentration, not the formal number of statistically independent measurements, and does not account for uncertainties or covariance.
See the passage in the paper
We emphasise that $N_{\rm eff}$ does not incorporate the quoted measurement uncertainties, the degree of covariance among analyses of the same spectra or methodological correlations between or among different absorbers.

Why it matters

The authors argue that the modern primordial-D/H central value is robust to substantially different treatments of the observational genealogy, but its formal precision should not be inferred from the count of published values. They advocate provenance-aware analyses and additional independent high-quality absorbers for future precision cosmology.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: primordial deuterium Big Bang nucleosynthesis quasar absorption systems measurement provenance bibliographic concentration

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Comprehensive Summary
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Original abstract

This paper examines how robust modern estimates of primordial deuterium are when the literature is treated not as a collection of independent measurements, but as a record of observations, reanalyses, compilations, and reused numerical values. High-redshift quasar absorption systems provide an important test of Big Bang nucleosynthesis, but the number of published D/H values far exceeds the number of physical absorbers studied. The authors trace how the accepted abundance emerged and assess how much the literature’s apparent statistical strength depends on repeated use of the same systems and results. The authors assembled a database of 957 numerical D/H values from 247 publications published between 1994 and 2026. The database contains 795 observational entries and 162 theoretical Big Bang nucleosynthesis predictions. Each entry was classified as a new individual-system determination, a new compilation, or a reused individual or compilation value. Where possible, observational entries were also traced to their physical absorbers. This provenance-based approach distinguishes publication frequency from the arrival of new observational information and reveals how concentrated the literature is across absorbers. Repeated values dominate the observational record: 637 of 795 entries, or 80.1%, are classified as reused. Only 91 entries, or 11.4%, are new determinations for individual absorbers. The database identifies 52 physical absorbers, but their representation is highly uneven. The eight most frequently represented systems account for 62.0% of 2,173 identifiable absorber mentions, while the top 20 account for 91.5%. An inverse Herfindahl–Hirschman concentration measure corresponds to 16.28 equally represented absorbers. This statistic measures bibliographic concentration; it is not a formal count of statistically independent measurements. The historical record shows a shift from widely scattered early measurements to modern values clustered near 2.5 × 10⁻⁵. During the main convergence period, new individual results and compilations moved closer to the present reference abundance. For example, from 2011 to 2017, the median deviation from the reference value was 0.058 for new observational entries, compared with 0.257 for reused entries. By 2018–2026, this difference had largely disappeared. The authors also identify a coordinated shift in compilation values around 2013–2014, associated with more selective samples and more homogeneous analysis, particularly the Precision Sample introduced by Cooke and colleagues in 2014. Older individual values nevertheless continued to circulate. To test sensitivity to repeated absorbers, the authors examined 29 new individual measurements published from 2012 onward, associated with 15 systems. Treating all 29 measurements as independent yields a weighted mean of 2.5577 ± 0.0150 in the paper’s scaled units. This result is sensitive to individual systems: excluding the frequently represented PKS1937–101 absorber changes the mean to 2.4718. However, the central consensus remains stable under alternative treatments. The median of the 15 absorber-level medians is 2.5000, and removing the eight most frequently represented absorbers yields 2.4960 ± 0.0265, close to the adopted reference value of 2.508. The authors conclude that the modern abundance, near 2.5 in the paper’s scaled units, is robust, but its apparent precision and independence should not be inferred from the number of publications or reported values. Repeated analyses can improve knowledge of an absorber without adding independent sightlines, while reused compilation values introduce numerical dependence. The authors note several limitations: the database was assembled manually and cannot be proven complete; some provenance is inferred or unavailable; and the concentration statistic does not account for measurement uncertainties, shared spectra, or methodological correlations.

Thirty Years of Primordial Deuterium: What the Numbers Really Tell Us

Primordial deuterium offers a valuable test of the universe’s earliest moments. Its abundance was shaped by Big Bang nucleosynthesis, so astronomers can compare predictions from early-universe physics with measurements in distant gas clouds. But counting published abundance values is not the same as counting independent observations.

In “Thirty years of primordial deuterium abundances: A provenance-aware statistical reanalysis,” Richard de Grijs and Giuseppe Bono examine how the scientific record behind modern deuterium estimates has developed. Their central message is reassuring but important: the preferred abundance remains robust, while the literature can make the evidence look more independent and extensive than it is.

A literature with many numbers and fewer new observations

High-redshift quasar absorption systems provide the physical setting for these measurements. Gas along the path from a distant quasar absorbs some of its light, leaving clues to the deuterium-to-hydrogen ratio, or D/H. Over the decades, researchers have published measurements, reanalyses, reviews, and compilations of these systems.

The authors built a database of 957 numerical D/H values from 247 publications spanning 1994 to 2026. Of these, 795 were observational entries and 162 were theoretical predictions from Big Bang nucleosynthesis. Crucially, each entry was classified by its origin: a new measurement of an individual system, a new compilation, or a value reused from earlier work.

This approach reveals how often a published number represents genuinely new observational information. Of the 795 observational entries, 637—80.1 percent—were reused values. Only 91, or 11.4 percent, were new determinations for individual absorbers. A long trail of citations and repeated estimates may document the progress of research, but it does not necessarily represent a comparable number of independent observations.

The evidence is concentrated in a small number of absorbers

The database traces measurements to 52 physical absorbers, but they appear very unevenly across the literature. The eight most frequently represented systems account for 62 percent of identifiable absorber mentions; the top 20 account for 91.5 percent.

The authors also calculate an inverse Herfindahl–Hirschman concentration measure. Its value corresponds to 16.28 equally represented absorbers. This is a way of describing bibliographic concentration, not a formal count of statistically independent measurements. It does not, by itself, account for measurement errors, shared spectra, or related analytical methods.

The distinction matters because multiple studies of one absorber can still be scientifically useful. Reanalysis may refine how well researchers understand that system. But it does not add a new line of sight through the universe, and values copied into later compilations can create numerical dependence that is easy to overlook.

How the modern consensus took shape

Early measurements were widely scattered. Over time, estimates moved toward a value near 2.5 in the paper’s scaled units. During the main period of convergence, new measurements and compilations generally moved closer to the present reference abundance.

For example, between 2011 and 2017, new observational entries had a median deviation of 0.058 from the reference value, compared with 0.257 for reused entries. By 2018–2026, that difference had largely disappeared. The authors also identify a coordinated change in compilation values around 2013–2014, linked to more selective samples and more uniform analysis, especially the Precision Sample introduced by Cooke and colleagues in 2014. Older individual values, however, continued to circulate.

Does the estimate depend on repeatedly studied systems?

To explore that question, the authors examined 29 new individual measurements published from 2012 onward, associated with 15 absorbers. Treating all 29 measurements as independent gives a weighted mean of 2.5577 ± 0.0150 in the paper’s scaled units. Yet this result is sensitive to particular systems: excluding the frequently represented PKS1937–101 absorber shifts the mean to 2.4718.

Other checks point to a stable central estimate. The median of the 15 absorber-level medians is 2.5000. Removing the eight most frequently represented absorbers gives 2.4960 ± 0.0265, close to the adopted reference value of 2.508. These comparisons suggest that the overall conclusion is not simply an artifact of repeatedly analyzing a few prominent systems, even though some statistical summaries are sensitive to them.

A robust result, with a necessary caution

The paper concludes that the modern primordial deuterium abundance—near 2.5 in its scaled units—is robust. But the number of publications or reported values should not be mistaken for the number of independent observations, or for a direct measure of precision. Understanding where each number came from is essential to interpreting the evidence fairly.

The authors also acknowledge limits to their analysis. The database was assembled manually and may not be complete; some provenance is inferred or unavailable. Its concentration statistic does not incorporate measurement uncertainties, shared spectra, or methodological correlations. The study is therefore best read as a careful map of how evidence has been reused and refined, rather than as a replacement for a full analysis of every measurement.

By following the history of the numbers as well as the numbers themselves, de Grijs and Bono offer a clearer picture of what decades of deuterium research can—and cannot—tell us. The consensus holds up, but its strength lies in the underlying observations and their careful interpretation, not in the sheer volume of published values.

Created on 10 Nov. 2026

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Thirty years of primordial deuterium abundances: A provenance-aware statistical reanalysis

The essentials

Question

Method

Findings

Limitations

Why it matters

Read further

Definitions

Thirty Years of Primordial Deuterium: What the Numbers Really Tell Us

A literature with many numbers and fewer new observations

The evidence is concentrated in a small number of absorbers

How the modern consensus took shape

Does the estimate depend on repeatedly studied systems?

A robust result, with a necessary caution

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