Big-bang nucleosynthesis and the baryon density of the universe

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Big-bang nucleosynthesis and the baryon density of the universe

Within the first 20 minutes of the evolution of the hot, dense, early Universe, astrophysically interesting abundances of deuterium, helium-3, helium-4, and lithium-7 were synthesized by the cosmic nuclear reactor.

Some kyr later, when the cosmic background radiation CBR radiation was freed from the embrace of the ionized plasma of protons and electrons, the spectrum of temperature fluctuations imprinted on the CBR also depended on the baryon and radiation densities.

The comparison between the constraints imposed by BBN and those from the CBR reveals a remarkably consistent picture of the Universe at two widely separated epochs in its evolution. Combining these two probes leads to new and tighter constraints on the baryon density at present, on possible new physics beyond the standard model of particle physics, as well as identifying some challenges to astronomy and astrophysics.

In this review the current status of BBN will be presented along with the associated estimates of the baryon density and of the energy density in radiation.Big-bang nucleosynthesis plays a crucial role in constraining big-bang cosmology. Although the uncertainties in the observations of the light elements are governed by systematic effects, firm bounds on the density of baryons in the Universe can be set.

After the Big Bang, and for at least years, the Universe was nearly uniform, and had a very simple chemical composition formed during the hot phase of the Big Bang: only hydrogen, helium.

Big-bang nucleosynthesis and the baryon density of the universe

The Big Bang Nucleosynthesis theory predicts that roughly 25% of the mass of the Universe consists of Helium. It also predicts about % deuterium, and even smaller quantities of lithium. The important point is that the prediction depends critically on the density of baryons (ie neutrons and protons) at the time of nucleosynthesis.

the concordance of the Big Bang Nucleosynthesis model with the abundances of the light isotopes of the three pillars of Big Bang the three, Big Bang Nucleosynthesis D and were able to place a constraint on the baryon density excluding a universe closed with baryons.

Subsequently,the D arguments were cemented when Epstein. The primordial abundances of these light nuclides produced during Big Bang Nucleosynthesis (BBN) are sensitive to the universal density of baryons and to the early-Universe expansion rate which at early epochs is governed by the energy density in relativistic particles (``radiation'') such as .

During the s, there was a major puzzle in that the density of baryons as calculated by Big Bang nucleosynthesis was much less than the observed mass of the universe based on measurements of galaxy rotation curves and galaxy cluster dynamics.

Big-bang nucleosynthesis and the baryon density of the universe | Science