Primordial Nucleosynthesis in Cosmological Contexts
Summary
During the first few minutes after the Big Bang, the rapid cooling and expansion of the Universe allowed protons and neutrons to fuse into light nuclei in a process known as primordial nucleosynthesis. The relative abundances of deuterium, helium-3, helium-4 and lithium-7 depend sensitively on the baryon-to-photon ratio, the expansion rate governed by the total radiation density and any additional relativistic species, as well as on the network of nuclear reactions. Precise predictions of these abundances provide one of the major pillars of modern cosmology, linking observations of the cosmic microwave background with spectroscopic measurements of ancient gas clouds and metal-poor galaxies. Discrepancies between measured and predicted lithium abundances, known as the “lithium problem,” and constraints on the effective number of neutrino species motivate ongoing refinements in both observational techniques and theoretical models. Together, these efforts illuminate the conditions of the infant Universe and probe possible extensions of the standard cosmological and particle-physics frameworks.
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Primordial Nucleosynthesis in Cosmological Contexts publication trend
The graph below shows the total number of articles in primordial nucleosynthesis in cosmological contexts across all publications each year (not limited to Nature Index journals).
Technical terms
Big Bang nucleosynthesis (BBN): The synthesis of light nuclei in the early Universe during the first few minutes after the Big Bang, dictated by reaction networks and the expansion rate.
Baryon-to-photon ratio (η): The density of baryons relative to photons in the early Universe, which determines the yields of light elements produced in BBN.
Effective number of neutrino species (N_eff): A parameter quantifying the total radiation density contributed by neutrinos and any additional relativistic particles during nucleosynthesis.
Deuterium-to-hydrogen ratio (D/H): The primordial abundance of deuterium relative to hydrogen, a key observable that tightly constrains the cosmic baryon density and nuclear cross-sections.
Cosmological lepton asymmetry: An imbalance between leptons and anti-leptons in the early Universe, which can alter neutron-to-proton ratios and thereby influence light-element abundances.
Scalaron: A scalar degree of freedom arising in certain modified gravity theories (for instance f(R) models), capable of modifying the expansion history and affecting nucleosynthesis yields.
References
- Indications for a Nonzero Lepton Asymmetry from Extremely Metal-Poor Galaxies. Physical Review Letters (2023).
- Fundamental physics with ESPRESSO: a new determination of the D/H ratio towards PKS1937-101. Monthly Notices of the Royal Astronomical Society (2024).
- Big Bang Nucleosynthesis with f(R) Gravity Scalarons and Astrophysical Consequences. The Astrophysical Journal (2024).
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