Review of Big Bang Nucleosynthesis and Primordial Abundances (original) (raw)
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Measurements of The Primordial D/H Abundance Towards Quasars
Symposium - International Astronomical Union, 2000
Big Bang Nucleosynthesis (BBN) is the synthesis of the light nuclei, Deuterium (D or 2H), 3He, 4He and 7Li during the first few minutes of the universe. In this review we concentrate on recent data which give the primordial deuterium (D) abundance.We have measured the primordial D/H in gas with very nearly primordial abundances. We use the Lyman series absorption lines seen in the spectra of quasars. We have measured D/H towards three QSOs, while a fourth gives a consistent upper limit. All QSO spectra are consistent with a single value for D/H: 3.325+0.22−0.25X10−5. From about 1994 − 1996, there was much discussion of the possibility that some QSOs show much higher D/H, but the best such example was shown to be contaminated by H, and no other no convincing examples have been found. Since high D/H should be much easier to detect, and hence it must be extremely rare or non-existent.The new D/H measurements give the most accurate value for the baryon to photon ratio, η, and hence the ...
Primordial Light Element Abundances
Arxiv preprint arXiv:0708.3922, 2007
After few minutes the Universe evolved through conditions of temperature and density which permitted the first synthesis of astrophysically interesting abundances of D, 3 He, 4 He and 7 Li. The relic abundances are sensitive probes of the nucleon density and so are the CMB acoustic oscillations, somewhat 400000 years later, which allow a stringent cross check. The CMB high precision estimate of the baryon density by WMAP is currently used as input parameter for standard big bang nucleosynthesis (SBBN) to interpret primordial abundances rather then being directly derived from the observations of light elements as was common use before. New atomic physics and identification of systematics lead to an upwards revision of the 4 He primordial abundance at Yp=0.2477±0.0029 (Peimbert et al 2007) removing a major source of tension between SBBN and WMAP. The D/H as measured in QSO high redshift absorbing clouds shows an excess of scatter but the mean value is found in spectacular agreement with the WMAP-Ω b prediction. The Li/H recently redetermined in halo dwarfs is more than a factor 4 lower than expected. We argue that the difference reduces to a factor 2 when the IRFM Teff scale is adopted. Diffusion has been suggested to have depleted Li in halo dwarfs by the required amount to remove the gap, however this would imply an implausible high abundance of the more fragile 6 Li detected in some halo dwarfs, thus leaving the puzzle open.
The Primordial Abundance of 4 He: An Update
The Astrophysical Journal, 1997
We include new data in an updated analysis of helium in low metallicity extragalactic H II regions with the goal of deriving the primordial abundance of 4 He (Y P). We show that the new observations of Izotov et al. (ITL) are consistent with previous data. However they should not be taken in isolation to determine Y P due to the lack of sufficiently low metallicity points. We use the extant data in a semi-empirical approach to bounding the size of possible systematic uncertainties in the determination of Y P. Our best estimate for the primordial abundance of 4 He assuming a linear relation between 4 He and O/H is Y P = 0.230 ± 0.003(stat) based on the subset of H II regions with the lowest metallicity; for our full data set we find Y P = 0.234 ± 0.002(stat). Both values are entirely consistent with our previous results. We discuss the implications of these values for standard big bang nucleosynthesis (SBBN), particularly in the context of recent measurements of deuterium in high redshift, low metallicity QSO absorption-line systems.
The Astrophysical Journal Supplement Series, 2003
We report the detection of Deuterium absorption at redshift 2.525659 towards Q1243+3047. We describe improved methods to estimate the Deuterium to Hydrogen abundance ratio (D/H) in absorption systems, including improved modelling of the continuum level, the Lyα forest and the velocity structure of the absorption. Together with improved relative flux calibration, these methods give D/H = 2.42 +0.35 −0.25 ×10 −5 cm −2 from our Keck-I HIRES spectra of Q1243+3047, where the error is from the uncertainty in the shape of the continuum level and the amount of D absorption in a minor second component. The measured D/H is likely the primordial value because the [O/H] = −2.79 ± 0.05. This absorption system has a neutral Hydrogen column density log N HI = 19.73 ± 0.04 cm −2 , it shows five D lines and is mostly ionized. The best estimate of the primordial D/H is 2.78 +0.44 −0.38 ×10 −5 , from the log D/H values towards five QSOs. The dispersion in the five values is larger than we expect from their individual measurement errors and we suspect this is because some of these errors were underestimated. We observe a trend in D/H with log N HI that we also suspect is spurious. The best value for D/H is 0.6σ smaller than we quoted in O' Meara et al. (2001) from three QSOs, and although we have more values, the error is similar because the dispersion is larger. In standard big bang nucleosynthesis (SBBN), the best D/H corresponds to a baryon-to-photon ratio η = 5.9 ± 0.5 × 10 −10 and gives precise predictions for the primordial abundances of the other light nuclei. We predict more 4 He than is reported in most measurements, although not more than allowed by some estimates of the systematic errors. We predict a 3 He abundance very similar to that reported by , and we predict 3 -4 times more 7 Li than is seen in halo stars. It is unclear if those stars could have destroyed this much of their 7 Li. The η value from D/H corresponds to a cosmological baryon density Ω b h 2 = 0.0214 ± 0.0020 (9.3%) that agrees with values from the anisotropy of the Cosmic Microwave Background: Ω b h 2 = 0.021 ± 0.003 from the Netterfield et al. analysis of BOOMERANG data and Ω b h 2 = 0.022 +0.004 −0.003 from the Pryke et al. (2002) analysis of the DASI results.
Deuterium and the baryonic density of the universe
Physics Reports, 2000
Big bang nucleosynthesis (BBN) is the creation of the light nuclei, deuterium, He, He and Li during the "rst few minutes of the universe. Here we discuss recent measurements of the D to H abundance ratio, D/H, in our galaxy and towards quasars. We have achieved an order of magnitude improvement in the precision of the measurement of primordial D/H, using the HIRES spectrograph on the W. M. Keck telescope to measure D in gas with very nearly primordial abundances towards quasars. From 1994 to 1996, it appeared that there could be a factor of 10 range in primordial D/H, but today four examples of low D are secure. High D/H should be much easier to detect, and since there are no convincing examples, it must be extremely rare or non-existent. All data are consistent with a single low value for D/H, and the examples which are consistent with high D/H are readily interpreted as H contamination near the position of D. The new D/H measurements give the most accurate value for the baryon-to-photon ratio, , and hence the cosmological baryon density. A similar density is required to explain the amount of Ly absorption from neutral hydrogen in the intergalactic medium (IGM) at redshift zK3, and to explain the fraction of baryons in local clusters of galaxies.
Precision primordial 4He measurement from the CMB
Physical Review D, 2004
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are two major pillars of cosmology. Standard BBN accurately predicts the primordial light element abundances ( 4 He, D, 3 He and 7 Li), depending on one parameter, the baryon density. Light element observations are used as a baryometer. The CMB anisotropies also contain information about the content of the universe which allows an important consistency check on the Big Bang model. In addition CMB observations now have sufficient accuracy to not only determine the total baryon density, but also resolve its principal constituents, H and 4 He. We present a global analysis of all recent CMB data, with special emphasis on the concordance with BBN theory and light element observations. We find ΩBh 2 = 0.0250 +0.0019 −0.0026 and Yp = 0.250 +0.010 −0.014 (fraction of baryon mass as 4 He) using CMB data alone, in agreement with 4 He abundance observations. The determination of Yp allows us to constrain the relativistic degrees of freedom during BBN, measured through the effective number of light neutrino species, N ν,ef f = 3.02 +0.85 −0.79 , in accord with the Standard Model of Particle physics. With this concordance established we show that the inclusion of standard, N ν,ef f ≡ 3, BBN theory priors significantly reduces the volume of parameter space. In this case, we find ΩB h 2 = 0.0245 +0.0015 −0.0028 and Yp = 0.2493 +0.0007 −0.0010 . We also find that the inclusion of deuterium abundance observations reduces the Yp and ΩBh 2 ranges by a factor of ∼2. Further light element observations and CMB anisotropy experiments will refine this concordance and sharpen BBN and the CMB as tools for precision cosmology.
Primordial Deuterium Abundance and Cosmic Baryon Density
1994
The comparison of cosmic abundances of the light elements with the density of baryonic stars and gas in the universe today provides a critical test of big bang theory and a powerful probe of the nature of dark matter. A new technique allows determination of cosmic deuterium abundances in quasar absorption clouds at large redshift, allowing a new test of big bang homogeneity in diverse, very distant systems. The first results of these studies are summarized, along with their implications. The quasar data are confronted with the apparently contradictory story from the helium-3 abundances measured in our Galaxy. The density of baryonic stars and gas in the universe today is reviewed and compared with the big bang prediction.
Extragalactic Abundances of Hydrogen, Deuterium and Helium: New Steps, Missteps and Next Steps
1997
Estimates of the deuterium abundance in quasar absorbers are reviewed, including a brief account of incorrect claims published by the author and a brief review of the problem of hydrogen contamination. It is concluded that the primordial abundance may be universal with a value (D/H)Papprox10−4(D/H)_P\approx 10^{-4}(D/H)Papprox10−4, within about a factor of two, corresponding to OmegaBh0.72approx0.02\Omega_B h_{0.7}^2\approx 0.02OmegaBh0.72approx0.02 or eta10approx2.7\eta_{10}\approx 2.7eta10approx2.7 in the Standard Big Bang. This agrees with current limits on primordial helium, YPle0.243Y_P\le 0.243YPle0.243, which are shown to be surprisingly insensitive to models of stellar enrichment. It also agrees with a tabulated sum of the total density of baryons in observed components. Much lower primordial deuterium ($\approx 2\times 10^{-5}$) is also possible but disagrees with currently estimated helium abundances; the larger baryon density in this case fits better with current models of the Lyman-$\alpha$ forest but requires the bulk of the baryons to be in some currently uncounted form.
Big bang nucleosynthesis: an accurate determination of light element yields
Nuclear Physics B, 2000
We report the results of a new accurate evaluation of light nuclei yields in primordial nucleosynthesis. All radiative effects, finite nucleon mass, thermal and plasma corrections are included in the proton to neutron conversion rates. The relic densities of 4 He, D and 7 Li have been numerically obtained via a new updated version of the standard BBN code. In particular the theoretical uncertainty on 4 He is reduced to the order of 0.1 %.
The Primordial Abundance of He4: An Update
1996
We include new data in an updated analysis of helium in low metallicity extragalactic HII regions with the goal of deriving the primordial abundance of He4 (Y_P). We show that the new observations of Izotov et al (ITL) are consistent with previous data. However they should not be taken in isolation to determine (Y_P) due to the lack of sufficiently low metallicity points. We use the extant data in a semi-empirical approach to bounding the size of possible systematic uncertainties in the determination of (Y_P). Our best estimate for the primordial abundance of He4 assuming a linear relation between He4 and O/H is Y_P = 0.230 \pm 0.003 (stat) based on the subset of HII regions with the lowest metallicity; for our full data set we find Y_P = 0.234 \pm 0.002 (stat). Both values are entirely consistent with our previous results. We discuss the implications of these values for standard big bang nucleosynthesis (SBBN), particularly in the context of recent measurements of deuterium in high redshift, low metallicity QSO absorption-line systems.