The discrepancy is a factor of 2. 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. The mass fraction in various isotopes vs time is shown at right. Further details can be found here.
The deuterium, He3, He4 and Li7 abundances depend on the single parameter of the current density of ordinary matter made out of protons and neutrons: An alternative picture is also sketched, based on the assumption of a special type of proton spectrum, of the kind mentioned above.
It seems like we really understand the physical processes which went on in the first few minutes of the evolution of the Universe! Please help improve this section by adding citations to reliable sources. Burbidge, Fowler, and Hoyle. Using this value, are the BBN predictions for the abundances of light elements in agreement with the observations?
Further support comes from the consistency of the other Lithium 7 nucleosynthesis element abundances for one particular baryon density and an independent measurement of the baryon density from the anisotropies in the cosmic microwave background radiation. In a short time interval, protons and neutrons collided to produce deuterium one proton bound to one neutron.
The half-life of the neutron is seconds. This is one of the corner-stones of the Hot Big Bang model. While this theory achieved relative success, it was discovered to be lacking in some important respects. It is now known that the elements observed in the Universe were created in either of two ways.
A similar enigma exists for the deuterium. Almost all the neutrons in the Universe end up in normal helium nuclei. There are no known post-Big Bang processes which can produce significant amounts of deuterium.
The isotopes 6Li and 7Li are later partly depleted by proton capture reactions, presumably at the bottom of the convective zone.
The universe continued to cool, and soon became too cold for any further nuclear reactions … the unstable isotopes left then decayed, as did the neutrons not already in some nucleus or other.
The nuclear reactions possibly responsible for the alteration of the ratios after their formation are discussed next. The 7 6 Li ratio would then have been altered during the Hayashi phase. Like to learn more? This relatively low value means that not all of the dark matter can be baryonic, ie we are forced to consider more exotic particle candidates.
Both light helium He3 and normal helium He4 are made, along with the radioactive form of hydrogen H3. The fit is good but not perfect. At this time, the neutron: The following stages occur during the first few minutes of the Universe: Thanks to the pioneering efforts of George Gamow and his collaborators, there now exists a satisfactory theory as to the production of light elements in the early Universe.
These reactions can be photoreactions as shown here. This section does not cite any sources. A simple rule is devised which classifies quite neatly the cross sections in term of their isotopic spin parameters.
The important point is that the prediction depends critically on the density of baryons ie neutrons and protons at the time of nucleosynthesis. These pieces of additional physics include relaxing or removing the assumption of homogeneity, or inserting new particles such as massive neutrinos.
Here are a few links that might interest you: Once deuteron formation has occurred, further reactions proceed to make helium nuclei. Light elements namely deuterium, helium, and lithium were produced in the first few minutes of the Big Bang, while elements heavier than helium are thought to have their origins in the interiors of stars which formed much later in the history of the Universe.
The present measurement of helium-4 indicates good agreement, and yet better agreement for helium The first, which is largely of historical interest, is to resolve inconsistencies between BBN predictions and observations.
Since the universe is presumed to be homogeneousit has one unique value of the baryon-to-photon ratio.It is believed to be responsible for the formation of hydrogen (H-1 or simply H), its isotope deuterium (H-2 or D), the helium isotopes He-3 and He-4, and the lithium isotope Li Lithium 7 could also arise form the coalescence of one tritium and two deuterium nuclei.
The Big Bang Nucleosynthesis theory predicts that roughly 25% the mass of the Universe consists of Helium. It also predicts about % deuterium, and. In astronomy – and astrophysics and cosmology – there are two main kinds of nucleosynthesis, Big Bang nucleosynthesis (BBN), and stellar nucleosynthesis.
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.
By the time the universe was three minutes old the process had basically stopped and the relative abundances of the elements was fixed at ratios that didn't change for a very long time: 75% hydrogen, 25% helium, with trace amounts of deuterium (hydrogen-2).
The observed lithium abundance in stars is less than the predicted lithium abundance, by a factor of about 2. But stars destroy lithium so it is hard to assess the significance of this difference.
Other Big Bang Nucleosynthesis pages: LBL, Martin White.Download