Big Bang nucleosynthesis

In physical cosmology, Big Bang nucleosynthesis (also known as primordial nucleosynthesis, and abbreviated as BBN) ^[1] is a model for the production of the light nuclei ²H, ³He, ⁴He, and ⁷Li between 0.01s and 200s in the lifetime of the universe. ^[2] The model uses a combination of thermodynamic arguments and results from equations for the expansion of the universe to define a changing temperature and density, then analyzes the rates of nuclear reactions at these temperatures and densities to predict the nuclear abundance ratios. Refined models agree very well with observations with the exception of the abundance of ⁷Li. The model is one of the key concepts in standard cosmology.

Elements heavier than lithium are instead created in appreciable amounts at later times via stellar nucleosynthesis, through the formation, evolution and death of stars.

History

The history of Big Bang nucleosynthesis research began with George Gamow, a nuclear physicist who thought that Victor Goldschmidt's data on the abundance of elements in the universe might be predicted by nuclear reactions. Early in the 1940s Gamow realized that very high temperatures and pressures needed for nuclear reactions implied an explosion followed by expansion. ^{[3] : 177} Calculations by his student Ralph Alpher, published ^[4] in the famous Alpher–Bethe–Gamow paper, outlined an early theory of light-element production in the early universe. These early efforts did not involve specific nuclear reactions. When Enrico Fermi and Anthony L. Turkevich tried, they found they would predict hydrogen and helium, but no higher elements. The key problem was a "mass gap": there no nuclei with masses of 5 and 8 atomic mass units needed for the reactions to reach higher masses. In 1953 this problem seemed insurmountable and cast doubt on the entire concept. ^{[3] : 181}

The first detailed calculations of the primordial isotopic abundances came in 1966 ^{[5] [6]} and have been refined over the years using updated estimates of the input nuclear reaction rates. ^{[7] : 3} The first systematic Monte Carlo study of how nuclear reaction rate uncertainties impact isotope predictions, over the relevant temperature range, was carried out in 1993. ^[8]

During the 1970s, there were major efforts to find processes that could produce deuterium, but those revealed ways of producing isotopes other than deuterium. The problem was that while the concentration of deuterium in the universe is consistent with the Big Bang model as a whole, it is too high to be consistent with a model that presumes that most of the universe is composed of protons and neutrons. If one assumes that all of the universe consists of protons and neutrons, the density of the universe is such that much of the currently observed deuterium would have been burned into helium-4.^{[ citation needed ]} The standard explanation now used for the abundance of deuterium is that the universe does not consist mostly of baryons, but that non-baryonic matter (also known as dark matter) makes up most of the mass of the universe.^{[ citation needed ]} This explanation is also consistent with calculations that show that a universe made mostly of protons and neutrons would be far more clumpy than is observed. ^[9]

It is very hard to come up with another process that would produce deuterium other than by nuclear fusion. Such a process would require that the temperature be hot enough to produce deuterium, but not hot enough to produce helium-4, and that this process should immediately cool to non-nuclear temperatures after no more than a few minutes. It would also be necessary for the deuterium to be swept away before it reoccurs.^{[ citation needed ]}

Producing deuterium by fission is also difficult. The problem here again is that deuterium is very unlikely due to nuclear processes, and that collisions between atomic nuclei are likely to result either in the fusion of the nuclei, or in the release of free neutrons or alpha particles. During the 1970s, cosmic ray spallation was proposed as a source of deuterium. That theory failed to account for the abundance of deuterium, but led to explanations of the source of other light elements.^{[ citation needed ]}

For a few years during the mid-1990s, observations suggested that the helium-4 abundance was much smaller than 25%, causing astrophysicists to talk about a Big Bang nucleosynthetic crisis as helium-4 is difficult to destroy and this result was instead suggestive of a different production mechanism altogether. However, further observations were consistent with the BBN prediction of a helium-4 mass fraction of 25%. ^[10]

Physical Description

Big Bang nucleosynthesis describes the production of atomic nuclei from protons and neutrons in the expanding and cooling early universe. The process occurs at equilibrium with protons and neutrons combining to create nuclei and the nuclei disintegrating. As the temperature and pressure drops, equilibrium shifts to favor a few light element nuclei. Further expansion stops the BBN processes, setting the initial cosmic abundance of these elements. ^{[11] : 36}

The cosmic expansion process during BBN is described by the Friedmann-Robertson-Walker model. These equations completely determine the rate of expansion of the universe, as well as the evolution of the energy densities of different particle species. ^[12] In particular, these equations indicate that the universe becomes less dense and the temperature of particles in the Standard Model falls as BBN proceeds.

At temperatures above 1-2 MeV, protons and neutrons interconverted via the weak interaction. As the temperature dropped, these reactions fell out of equilibrium, neutrons primarily decayed to protons, and the neutron-to-proton ratio fell to around 1/7. ^{[2] : 315} This sets the initial conditions for the onset of the formation of light nuclei. ^{[13] : 63}

BBN began in earnest when the temperature of Standard Model particles dropped below roughly 1 MeV. ^[12] At this temperature, the average energy of photons in the early universe was too low to break apart deuterium as it formed, but the universe remained hot and dense enough for fusion reactions to occur at a significant rate. ^[1] This meant a substantial population of deuterium formed.

This deuterium then fused to heavier nuclei, including helium-3, helium-4, and lithium-7. ^{[2] : 315} Helium-4 has a large binding energy, which means that once a helium-4 nucleus is formed, it is difficult to break apart and incorporate its constituents into heavier nuclei. Therefore matter in the universe is primarily hydrogen and helium-4 after BBN. ^{[13] : 68} Standard BBN predicts, by the time BBN ends, the universe is composed of about 75% of hydrogen and 25% helium-4 by mass. Roughly 1 nucleus in 100,000 is deuterium or helium-3, and 1 nucleus in 1,000,000,000 is lithium-7. Even smaller amounts of heavier elements, as heavy as oxygen-20, have been predicted to form. ^[14]

BBN coincides or nearly coincides with two other important events in cosmology. Neutrino decoupling occurred when the weak interaction fell out of equilibrium, ^[15] just before BBN began. Electron–positron annihilation occurred during BBN, at around 0.5 MeV, when photons no longer had enough energy to convert back to electrons and positrons to maintain equilibrium. ^[16] This resulted in the depletion of the abundance of positrons in the universe, and heated photons. Since electron-positron annihilation occurred after neutrino decoupling, neutrinos did not heat alongside photons when electrons and positrons annihilated, and photons developed a separate temperature from neutrinos. This has important consequences for the rates of proton-neutron interconversion and the prediction of light element abundances. ^[17]

The abundances of light element nuclei during Big Bang Nucleosynthesis, as a function of time since the Big Bang in seconds (lower axis) or the Standard Model plasma temperature in MeV. The y-axis shows the abundance as a number density of each individual species divided by the number density of baryons.

Light Element Nucleosynthesis

Important Parameters

The creation of light elements during BBN was dependent on nuclear reaction rate parameters and two cosmological input parameters neutron–proton ratio (calculable from Standard Model physics) and the baryon-photon ratio. The nuclear reaction rates are well-known from detailed laboratory studies at similar temperatures to those that appear in BBN. ^[11]

Baryon-to-photon ratio

The evolution of different light element abundances for different values of the baryon-to-photon ratio η. Note the final abundances (values at the latest times) can vary dramatically depending on the value of this parameter.

Light element abundances, and in particular deuterium, are sensitive to the value of the baryon-to-photon number ratio, η, which is a small number of order 6 × 10⁻¹⁰. ^[19] This parameter is proportional to the baryon density and controls the entropy of the universe, which in turn determines the temperature at which nuclear fusion can begin. ^[12] High entropy prevents light element nuclei from forming, which delays the onset of BBN; low entropy conversely lets BBN last longer, and therefore depletes the abundances of light elements that can fuse into helium-4.

Deuterium in particular is extremely sensitive to the value of the baryon-to-photon ratio ^[20] ; decreasing η by a factor of 10 leads to a corresponding increase in the abundance of primordial deuterium by a factor of roughly 50. ^[1]

Expansion rate

Particles and nuclei fall out of equilibrium when their rates of interaction become slower than the rate of the expansion of the universe. If the rate keeping a nuclear species in equilibrium drops below the expansion rate, the relative abundance of that species stops evolving (or decreases if decay is possible).

During BBN, the universe is radiation dominated, and so the expansion of the universe is primarily determined by the energy density in radiative species like photons and neutrinos. Light element abundances are therefore sensitive to the energy densities of these species. ^[21]

Sequence

Main nuclear reaction chains for Big Bang nucleosynthesis

BBN begins shortly after neutrinos decouple from the Standard Model and processes interconverting protons and neutrons fall out of equilibrium. By roughly 20 seconds after the big bang, the universe had cooled sufficiently to allow deuterium nuclei to survive disruption by high-energy photons. At this time there were about six protons for every neutron.

As the universe expanded and cooled, other light elements began to form, becoming heavier through nuclear fusion. At temperatures below 0.3 MeV, conditions were right for helium-4 to form, and below 0.1 MeV the abundance of deuterium climbed high enough for a burst of element formation. ^[12] However, very shortly thereafter, around twenty minutes after the Big Bang, the temperature and density became too low for any significant fusion to occur. At this point, the elemental abundances were nearly fixed. Further changes were the result of the radioactive decay of the two major unstable products of BBN, tritium and beryllium-7, ^[22] as well as continued decay of neutrons that did not fuse into any nuclei. At the end of nucleosynthesis there are about seven protons to every neutron, and almost all the neutrons are in Helium-4 nuclei. ^[23]

Baryons and light elements can fuse in the following main reactions:

${\displaystyle {\ce {p + n -> ^2H + \gamma}}}$ ${\displaystyle {\ce {p + ^2H -> ^3He + \gamma}}}$ ${\displaystyle {\ce {^2H + ^2H -> ^3He + n}}}$ ${\displaystyle {\ce {^2H + ^2H -> ^3H + p}}}$ ${\displaystyle {\ce {^3He + ^2H -> ^4He + p}}}$ ${\displaystyle {\ce {^3H + ^2H -> ^4He + n}}}$

along with some other low-probability reactions leading to ⁷Li or ⁷Be. (An important feature is that there are no stable nuclei with mass 5 or 8, which implies that reactions adding one baryon to ⁴He, or fusing two ⁴He, do not occur). Most fusion chains during BBN ultimately terminate in ⁴He (helium-4), while "incomplete" reaction chains lead to small amounts of left-over ²H or ³He.

Neutron–proton interconversion

The neutron–proton ratio was set by Standard Model physics before the nucleosynthesis era, essentially within the first 1-second after the Big Bang. Neutrons can react with positrons or electron neutrinos to create protons and other products in one of the following reactions:

${\displaystyle {\ce {n\ +e+<=>{\overline {\nu }}_{e}+p}}}$

${\displaystyle {\ce {n \ + \nu_{e}<=> p + e-}}}$

At times much earlier than 1 sec, these reactions were fast and maintained the n/p ratio close to 1:1. As the temperature dropped, the equilibrium shifted in favour of protons due to their slightly lower mass, and the n/p ratio smoothly decreased. These reactions continued until the decreasing temperature and density caused the reactions to become too slow, which occurred at about T = 0.7 MeV (time around 1 second) and is called the freeze out temperature. At freeze out, the neutron–proton ratio was about 1:6. Free neutrons are unstable with a lifetime of about 15 minutes, ^[24] so the neutron abundance steadily falls during BBN and any neutron that is not incorporated into a nucleus converts to a proton by the end of BBN. Almost all neutrons that fused instead of decaying ended up combined into helium-4, due to the fact that helium-4 has the highest binding energy per nucleon among light elements. This predicts that about 8% of all atoms should be helium-4, leading to a mass fraction of helium-4 of about 25%, which is in line with observations. Small traces of deuterium and helium-3 remained as there was insufficient time and density for them to react and form helium-4. ^[25]

Deuterium

Deuterium is in some ways the opposite of helium-4, in that while helium-4 is very stable and difficult to destroy, deuterium is only marginally stable and easy to destroy. The temperatures, time, and densities were sufficient to combine a substantial fraction of the deuterium nuclei to form helium-4 but insufficient to carry the process further using helium-4 in the next fusion step. BBN did not convert all of the deuterium in the universe to helium-4 due to the expansion that cooled the universe and reduced the density, and so cut that conversion short before it could proceed any further. One consequence of this is that, unlike helium-4, the amount of deuterium is very sensitive to initial conditions. The denser the initial universe was, the more deuterium would be converted to helium-4 before time ran out, and the less deuterium would remain.

Helium-4

Big Bang nucleosynthesis predicts a primordial abundance of about 25% helium-4 by mass, irrespective of the initial conditions of the universe. As long as the universe was hot enough for protons and neutrons to transform into each other easily, their ratio, determined solely by their relative masses, was about 1 neutron to 7 protons (allowing for some decay of neutrons into protons). Once it was cool enough, the neutrons quickly bound with an equal number of protons to form first deuterium, then helium-4. Helium-4 is very stable and is nearly the end of this chain if it runs for only a short time, since helium neither decays nor combines easily to form heavier nuclei (since there are no stable nuclei with mass numbers of 5 or 8, helium does not combine easily with either protons, or with itself). Once temperatures are lowered, out of every 16 nucleons (2 neutrons and 14 protons), 4 of these (25% of the total particles and total mass) combine quickly into one helium-4 nucleus. This produces one helium for every 12 hydrogens, resulting in a universe that is a little over 8% helium by number of atoms, and 25% helium by mass.

The resort to the BBN theory of the helium-4 abundance is necessary as there is far more helium-4 in the universe than can be explained by stellar nucleosynthesis. In addition, it provides an important test for the Big Bang theory. If the observed helium abundance is significantly different from 25%, then this would pose a serious challenge to the theory.

Lithium

Lithium-7 and lithium-6 produced in the Big Bang are on the order of: lithium-7 to be 10⁻⁹ of all primordial nuclides; and lithium-6 around 10⁻¹³. ^[26]

Heavy elements

A version of the periodic table indicating the origins – including big bang nucleosynthesis – of the elements. All elements above 103 (lawrencium) are also man-made and are not included.

Big Bang nucleosynthesis produced very few nuclei of elements heavier than lithium due to a bottleneck: the absence of a stable nucleus with 8 or 5 nucleons. This deficit of larger atoms also limited the amounts of lithium-7 produced during BBN. In stars, the bottleneck is passed by triple collisions of helium-4 nuclei, producing carbon (the triple-alpha process). However, this process is very slow and requires much higher densities, taking tens of thousands of years to convert a significant amount of helium to carbon in stars, and therefore it made a negligible contribution in the minutes following the Big Bang.

The predicted abundance of CNO isotopes produced in Big Bang nucleosynthesis is expected to be on the order of 10⁻¹⁵ that of H, making them essentially undetectable and negligible. ^[27] Indeed, none of these primordial isotopes of the elements from beryllium to oxygen have yet been detected, although those of beryllium and boron may be able to be detected in the future. So far, the only stable nuclides known experimentally to have been made during Big Bang nucleosynthesis are protium, deuterium, helium-3, helium-4, and lithium-7. ^[28]

Measurements and status of theory

The theory of BBN gives a detailed mathematical description of the production of the light isotopes deuterium, helium-3, helium-4, and lithium-7. Specifically, the theory yields precise quantitative predictions for the mixture of these elements, that is, the primordial abundances at the end of the big-bang. That the observed abundances in the universe are generally consistent with these abundance numbers is considered strong evidence for the Big Bang theory. ^{[13] : 69  [2] : 313}

In order to test these predictions, it is necessary to reconstruct the primordial abundances as faithfully as possible, for instance by observing astronomical objects in which very little stellar nucleosynthesis has taken place (such as certain dwarf galaxies) or by observing objects that are very far away, and thus can be seen in a very early stage of their evolution (such as distant quasars).

As noted above, in the standard picture of BBN, all of the light element abundances depend on the amount of ordinary matter (baryons) relative to radiation (photons). Since the universe is presumed to be homogeneous, it has one unique value of the baryon-to-photon ratio. For a long time, this meant that to test BBN theory against observations one had to ask: can all of the light element observations be explained with a single value of the baryon-to-photon ratio? Or more precisely, allowing for the finite precision of both the predictions and the observations, one asks: is there some range of baryon-to-photon values which can account for all of the observations?^{[ according to whom? ]}

More recently, the question has changed: Precision observations of the cosmic microwave background radiation ^{[29] [30]} with the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck give an independent value for the baryon-to-photon ratio. The present measurement of helium-4 indicates good agreement, and yet better agreement for helium-3. But for lithium-7, there is a significant discrepancy between BBN and WMAP/Planck, and the abundance derived from Population II stars. The discrepancy, called the "cosmological lithium problem", is a factor of 2.4―4.3 below the theoretically predicted value. ^[31] that have resulted in revised calculations of the standard BBN based on new nuclear data, and to various reevaluation proposals for primordial proton–proton nuclear reactions, especially the abundances of ⁷Be + n → ⁷Li + p, versus ⁷Be + ²H → ⁸Be + p. ^[32]

Non-standard scenarios

In addition to the standard BBN scenario there are numerous non-standard BBN scenarios. ^[33] These should not be confused with non-standard cosmology: a non-standard BBN scenario assumes that the Big Bang occurred, but inserts additional physics in order to see how this affects elemental abundances. These pieces of additional physics include relaxing or removing the assumption of homogeneity, or inserting new particles such as massive neutrinos. ^[34]

There have been, and continue to be, various reasons for researching non-standard BBN. The first, which is largely of historical interest, is to resolve inconsistencies between BBN predictions and observations. This has proved to be of limited usefulness in that the inconsistencies were resolved by better observations, and in most cases trying to change BBN resulted in abundances that were more inconsistent with observations rather than less. The second reason for researching non-standard BBN, and largely the focus of non-standard BBN in the early 21st century, is to use BBN to place limits on unknown or speculative physics. For example, standard BBN assumes that no exotic hypothetical particles were involved in BBN. One can insert a hypothetical particle (such as a massive neutrino) and see what has to happen before BBN predicts abundances that are very different from observations. This has been done to put limits on the mass of a stable tau neutrino. ^[35]

See also

• Big Bang
• Chronology of the universe
• Nucleosynthesis
• Relic abundance
• Stellar nucleosynthesis
• Ultimate fate of the universe

References

1. Patrignani, C.; et al. (Particle Data Group) (2016). "Big-Bang nucleosynthesis" (PDF). Chin. Phys. C. 40: 100001. Archived (PDF) from the original on 2016-12-01.
2. Schramm, David N.; Turner, Michael S. (1998-01-01). "Big-bang nucleosynthesis enters the precision era". Reviews of Modern Physics. 70 (1): 303–318. arXiv: astro-ph/9706069 . Bibcode:1998RvMP...70..303S. doi:10.1103/RevModPhys.70.303.
3. Kragh, Helge (2007). Conceptions of cosmos: from myths to the accelerating universe: a history of cosmology. Oxford ; New York: Oxford University Press. ISBN   978-0-19-920916-3.
4. Alpher, R. A.; Bethe, H.; Gamow, G. (1 April 1948). "The Origin of Chemical Elements". Physical Review . 73 (7): 803–804. Bibcode:1948PhRv...73..803A. doi: 10.1103/PhysRev.73.803 . PMID   18877094.
5. Peebles, P. J. E. (1966). "Primeval Helium Abundance and the Primeval Fireball". Physical Review Letters. 16 (10): 410–413. Bibcode:1966PhRvL..16..410P. doi:10.1103/PhysRevLett.16.410.
6. Wagoner, Fowler and Hoyle "ON THE SYNTHESIS OF ELEMENTS AT VERY HIGH TEMPERATURES", Robert V. Wagoner, William A. Fowler, and F. Hoyle, The Astrophysical Journal, Vol. 148, April 1967.
7. Hashimoto, Masa-aki; Nakamura, Riou; Thushari, E. P. Berni Ann; Arai, Kenzo (2018). Big-Bang Nucleosynthesis: Thermonuclear History in the Early Universe. SpringerBriefs in Physics Ser. Singapore: Springer. doi:10.1007/978-981-13-2935-7. ISBN   978-981-13-2935-7. ISSN   2191-5423.
8. Smith, Kawano, and Malaney. "EXPERIMENTAL, COMPUTATIONAL, AND OBSERVATIONAL ANALYSIS OF PRIMORDIAL NUCLEOSYNTHESIS", Michael S. Smith, Lawrence H. Kawano and Robert A. Malaney, The Astrophysical Journal Supplement Series, 85:219-247, 1993 April.
9. Schramm, D. N. (1996). The Big Bang and Other Explosions in Nuclear and Particle Astrophysics . Singapore: World Scientific. p.  175. ISBN   978-981-02-2024-2.
10. Bludman, S. A. (December 1998). "Baryonic Mass Fraction in Rich Clusters and the Total Mass Density in the Cosmos". Astrophysical Journal . 508 (2): 535–538. arXiv: astro-ph/9706047 . Bibcode:1998ApJ...508..535B. doi:10.1086/306412. S2CID   16714636.
11. Schramm, David N (January 1, 1991). "Big Bang nucleosynthesis: the Standard Model and alternatives". Physica Scripta. T36: 22–29. doi:10.1088/0031-8949/1991/T36/003. ISSN   0031-8949. available in Schramm, David N. (1996). The big bang and other explosions in nuclear and particle astrophysics. Singapore: World Scientific. ISBN   978-981-02-2024-2. OCLC   1147737739.
12. Kolb, Edward W.; Turner, Michael Stanley (1990). The early universe. Frontiers in physics. Reading, Mass: Addison-Wesley. ISBN   978-0-201-11603-8.
13. Dodelson, Scott (2003). Modern cosmology. San Diego, Calif: Academic Press. ISBN   978-0-12-219141-1.
14. Pitrou, Cyril; Coc, Alain; Uzan, Jean-Phillipe; Vangioni, Elisabeth (2018-09-03). "Precision big bang nucleosynthesis with improved Helium-4 predictions". Physics Reports. 754 (1): 1–66. arXiv: 1801.08023 . doi:10.1016/j.physrep.2018.04.005.
15. Dolgov, A. D. (2002-04-19), Neutrinos in cosmology, arXiv, doi:10.48550/arXiv.hep-ph/0202122, arXiv:hep-ph/0202122, retrieved 2026-01-14
16. Baumann, Daniel (2022). Cosmology. Cambridge, United Kingdom New York, NY: Cambridge University Press. ISBN   978-1-108-93709-2.
17. Grohs, E.; Fuller, George M. (2016-10-01). "The surprising influence of late charged current weak interactions on Big Bang Nucleosynthesis". Nuclear Physics B. 911: 955–973. doi:10.1016/j.nuclphysb.2016.08.034. ISSN   0550-3213.
18. Giovanetti, Cara; Lisanti, Mariangela; Liu, Hongwan; Mishra-Sharma, Siddharth; Ruderman, Joshua T. (2025-09-17). "Fast, differentiable, and extensible big bang nucleosynthesis package". Physical Review D. 112 (6): 063531. arXiv: 2408.14538 . doi:10.1103/f3tj-r882.
19. Collaboration, Planck; Aghanim, N.; Akrami, Y.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Ballardini, M.; Banday, A. J.; Barreiro, R. B. (2021-08-09), Planck 2018 results. VI. Cosmological parameters, arXiv, doi:10.48550/arXiv.1807.06209, arXiv:1807.06209, retrieved 2026-01-15
20. Olive, Keith A; Steigman, Gary; Walker, Terry P (2000-08-01). "Primordial nucleosynthesis: theory and observations". Physics Reports. 333–334: 389–407. doi:10.1016/S0370-1573(00)00031-4. ISSN   0370-1573.
21. Mangano, Gianpiero; Serpico, Pasquale D. (2011-06-10), A robust upper limit on N_eff from BBN, circa 2011, arXiv, doi:10.48550/arXiv.1103.1261, arXiv:1103.1261, retrieved 2026-01-15
22. Weiss, Achim. "Equilibrium and change: The physics behind Big Bang Nucleosynthesis". Einstein Online. Archived from the original on 8 February 2007. Retrieved 2007-02-24.
23. Bertulani, Carlos A. (2013). Nuclei in the Cosmos. World Scientific. ISBN   978-981-4417-66-2.
24. Wietfeldt, Fred E.; Greene, Geoffrey L. (2011-11-03). "Colloquium : The neutron lifetime". Reviews of Modern Physics. 83 (4): 1173–1192. doi:10.1103/RevModPhys.83.1173. ISSN   0034-6861.
25. Gary Steigman (2007). "Primordial Nucleosynthesis in the Precision Cosmology Era". Annual Review of Nuclear and Particle Science . 57 (1): 463–491. arXiv: 0712.1100 . Bibcode:2007ARNPS..57..463S. doi: 10.1146/annurev.nucl.56.080805.140437 . S2CID   118473571.
26. Fields, Brian D. (2011). "The Primordial Lithium Problem". Annual Review of Nuclear and Particle Science . 61 (1): 47–68. arXiv: 1203.3551 . Bibcode:2011ARNPS..61...47F. doi: 10.1146/annurev-nucl-102010-130445 .
27. Coc, A (2017). "Primordial Nucleosynthesis". Journal of Physics: Conference Series. 665 012001. arXiv: 1609.06048 . doi:10.1088/1742-6596/665/1/012001. S2CID   250691040.
28. Coc, Alain; Vangioni, Elisabeth (2014). "Revised Big Bang Nucleosynthesis with long-lived negatively charged massive particles: Impact of new 6Li limits, primordial 9Be nucleosynthesis, and updated recombination rates". arXiv: 1403.4156v1 [astro-ph.CO].
29. David Toback (2009). "Chapter 12: Cosmic Background Radiation" Archived 2010-07-06 at the Wayback Machine
30. David Toback (2009). "Unit 4: The Evolution Of The Universe" Archived 2010-07-06 at the Wayback Machine
31. R. H. Cyburt, B. D. Fields & K. A. Olive (2008). "A Bitter Pill: The Primordial Lithium Problem Worsens". Journal of Cosmology and Astroparticle Physics. 2008 (11): 012. arXiv: 0808.2818 . Bibcode:2008JCAP...11..012C. doi:10.1088/1475-7516/2008/11/012. S2CID   122212670.
32. Weiss, Achim. "Elements of the past: Big Bang Nucleosynthesis and observation". Einstein Online. Archived from the original on 8 February 2007. Retrieved 2007-02-24.
    For a recent calculation of BBN predictions, see
    • A. Coc; et al. (2004). "Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements". Astrophysical Journal. 600 (2): 544–552. arXiv: astro-ph/0309480 . Bibcode:2004ApJ...600..544C. doi:10.1086/380121. S2CID   16276658.
    For the observational values, see the following articles:
    • Helium-4: K. A. Olive & E. A. Skillman (2004). "A Realistic Determination of the Error on the Primordial Helium Abundance". Astrophysical Journal. 617 (1): 29–49. arXiv: astro-ph/0405588 . Bibcode:2004ApJ...617...29O. doi:10.1086/425170. S2CID   15187664.
    • Helium-3: T. M. Bania, R. T. Rood & D. S. Balser (2002). "The cosmological density of baryons from observations of 3He+ in the Milky Way". Nature. 415 (6867): 54–7. Bibcode:2002Natur.415...54B. doi:10.1038/415054a. PMID   11780112. S2CID   4303625.
    • Deuterium: J. M. O'Meara; et al. (2001). "The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619". Astrophysical Journal. 552 (2): 718–730. arXiv: astro-ph/0011179 . Bibcode:2001ApJ...552..718O. doi:10.1086/320579. S2CID   14164537.
    • Lithium-7: C. Charbonnel & F. Primas (2005). "The Lithium Content of the Galactic Halo Stars". Astronomy & Astrophysics. 442 (3): 961–992. arXiv: astro-ph/0505247 . Bibcode:2005A&A...442..961C. doi:10.1051/0004-6361:20042491. S2CID   119340132.A. Korn; et al. (2006). "A probable stellar solution to the cosmological lithium discrepancy". Nature. 442 (7103): 657–9. arXiv: astro-ph/0608201 . Bibcode:2006Natur.442..657K. doi:10.1038/nature05011. PMID   16900193. S2CID   3943644.
33. Malaney, Robert A.; Mathews, Grant J. (1993). "Probing the early universe: A review of primordial nucleosynthesis beyond the standard big bang". Physics Reports. 229 (4): 145–219. Bibcode:1993PhR...229..145M. doi:10.1016/0370-1573(93)90134-Y.
34. Soler, F. J. P., Froggatt, C. D., & Muheim, F., eds., Neutrinos in Particle Physics, Astrophysics and Cosmology (Baton Rouge: CRC Press, 2009), p. 362.
35. Anderson, R. W., The Cosmic Compendium: The Big Bang & the Early Universe (Morrisville, NC: Lulu Press, Inc., 2015), p. 54.

Further reading

• Gamow, G. (1948-08-15). "The Origin of Elements and the Separation of Galaxies" . Physical Review. 74 (4): 505–506. Bibcode:1948PhRv...74..505G. doi:10.1103/PhysRev.74.505.2.
• Gamow, G. (October 1948). "The Evolution of the Universe" . Nature. 162 (4122): 680–682. Bibcode:1948Natur.162..680G. doi:10.1038/162680a0. ISSN   0028-0836.

External links

• Weiss, Achim. "Big Bang Nucleosynthesis: Cooking up the first light elements". Einstein Online. Archived from the original on 8 February 2007. Retrieved 2007-02-24.
• White, Martin: Overview of BBN
• Wright, Ned: BBN (cosmology tutorial)
• For a brief physics overview see Burles, Scott; Nollett, Kenneth M.; Turner, Michael S. (1999-03-19). "Big-Bang Nucleosynthesis: Linking Inner Space and Outer Space". arXiv: astro-ph/9903300 .