THE PRIMORDIAL ABUNDANCE OF 4He: EVIDENCE FOR NON-STANDARD BIG BANG NUCLEOSYNTHESIS

By Y. Izotov, T. Thuan. 2010

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We present a new determination of the primordial helium mass fraction Yp, based on 93 spectra of 86 low-metallicity extragalactic H ii regions, and taking into account the latest developments concerning systematic effects. These include collisional and fluorescent enhancements of He i recombination lines, underlying He i stellar absorption lines, collisional and fluorescent excitation of hydrogen lines, and temperature and ionization structure of the H ii region. Using Monte Carlo methods to solve simultaneously for the above systematic effects, we find the best value to be Yp = 0.2565 ± 0.0010 (stat.) ± 0.0050 (syst.). This value is higher at the 2σ level than the value given by standard big bang nucleosynthesis, implying deviations from it. The effective number of light neutrino species Nν is equal to 3.68+0.80−0.70 (2σ) and 3.80+0.80−0.70 (2σ) for a neutron lifetime τn equal to 885.4 ± 0.9 s and 878.5 ± 0.8 s, respectively, i.e., it is larger than the experimental value of 2.993 ± 0.011.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/609929d67ab43c2d82f8e44fcd2f483411ecf39c

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Citations in the corpus

A new approach to systematic uncertainties and self-consistency in helium abundance determinations (2010, background): “Note Added: On completion of this paper, we became aware of the newest result of Izotov & Thuan (2010).”
Thermalisation of light sterile neutrinos in the early universe (2012, background): “Also, cosmological constraints coming from big bang nucleosynthesis (BBN) suggest that the relatively high 4He abundance can be interpreted in terms of additional radiation during the BBN epoch [24, 25].”
WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star (2015, background): “…directly measured from spectroscopy, evolutionary tracks with two initial helium abundances: the solar value (Y ,0 = 0.27), and a value labelled YG that increases with Z (as expected if the local medium follows the general trend observed for the chemical evolution of galaxies; Izotov & Thuan 2010).”
Light shining through walls (2010, background): “on the boundary of implying new physics [50].”
A new determination of the primordial He abundance using the He i λ10830 Å emission line: cosmological implications (2014, methodology): “(11) The newly derived Yp using the NIR He i line is in good agreement with the values derived by Izotov & Thuan (2010) and Aver et al. (2012).”
The effects of He I λ10830 on helium abundance determinations (2015, background): “Furthermore, there are numerous small model differences, such as the how the O[III] temperature [29, 45] is used, the treatment of neutral hydrogen collisional emission [39, 45], wavelength dependence and underlying absorption [39, 46, 47], and the way the the most recent emissivity data is incorpor”
STANDARD BIG BANG NUCLEOSYNTHESIS UP TO CNO WITH AN IMPROVED EXTENDED NUCLEAR NETWORK (2011, background): “The primordial 4He abundance Yp (mass fraction) is given by the extrapolation to zero metallicity but is affected by systematic uncertainties (Aver et al. 2010; Izotov & Thuan 2010) such as plasma temperature or stellar absorption.”
Dark radiation constraints on minicharged particles in models with a hidden photon (2013, background): “The nuclear reaction network of BBN is now better understood and brand new data on primordial element abundances has been collected and analyzed (especially deuterium [65, 66] and helium [67, 68]).”
A MEASUREMENT OF THE DAMPING TAIL OF THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM WITH THE SOUTH POLE TELESCOPE (2011, background): “The primordial 4He abundance may also be inferred from observations of low-metallicity extragalactic HII regions (Izotov et al. 2007; Peimbert et al. 2007; Izotov & Thuan 2010; Aver et al. 2010, 2011).”
THE ATACAMA COSMOLOGY TELESCOPE: COSMOLOGICAL PARAMETERS FROM THE 2008 POWER SPECTRUM (2010, background): “…abundance estimated from observations of metal poor extragalactic regions (see Steigman 2007; Peimbert 2008, for example) is YP = 0.252 ± 0.004 and 0.252±0.001 (Izotov et al. 2007), although a higher measurement of YP = 0.2565±0.0010(stat)±0.0050(syst) has recently been made (Izotov & Thuan 2010).”
CONSTRAINTS ON COSMOLOGY FROM THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM OF THE 2500 deg2 SPT-SZ SURVEY (2012, background): “…with DA and allows the CMB data to constrain Yp independently of BBN. Precise experimental inferences of Yp have come from spectral observations of extragalactic clouds of lowmetallicity ionized gas (Izotov et al. 2007; Peimbert et al. 2007; Izotov & Thuan 2010; Aver et al. 2010, 2011, 2012).”