arXiv:astro-ph/0011544v1 29 Nov 2000Inhomogeneous Big Bang Nucleosynthesis and the High Baryon Density Suggested byBoomerang and MAXIMAHannu Kurki-Suonio†Helsinki Institute of Physics, P.O.Box 9, FIN-00014 University of Helsinki, FinlandElina Sihvola∗Department of Physics, University of Helsinki, P.O.Box 9, FIN-00014 University of Helsinki, FinlandThe recent Boomerang and MAXIMA data on the cosmic microwave background suggest a largevalue for the baryonic matter density of the universe, ωb ∼ 0.03.allowed by standard big bang nucleosynthesis theory and observations on the abundances of the lightelements. We explore here the possibility of accommodating this high density in inhomogeneous bigbang nucleosynthesis (IBBN). It turns out that in IBBN the observed D and Yp values are quiteconsistent with this high density. However, IBBN is not able to reduce the7Li yield by more thanabout a factor of two. For IBBN to be the solution, one has to accept that thepopulation II halo stars is depleted from the primordial abundance by at least a factor of two.This density is larger than7Li plateau inPACS numbers: 26.35.+c, 98.80.Ft, 98.80.Cq, 98.70.VcI. INTRODUCTIONThe most accurate way to estimate the average den-sity of baryonic matter in the universe, ρb, has for along time been big bang nucleosynthesis.big bang nucleosynthesis (SBBN) [1] the calculated pri-mordial yields of the light elements depend only on thebaryon-to-photon ratio η ≡ nb/nγ. Future precision mea-surements of the fluctuations in the cosmic microwavebackground (CMB) will provide another way of measur-ing the baryon density. The shape of the angular powerspectrum of these fluctuations will depend on a numberof cosmological parameters, among which is the baryon-to-photon ratio. In this context it is usually given as thebaryonic contribution to the critical density times theHubble constant squared, ωb≡ ?bh2.These two measurements rely on completely differentphysics, and if they agree it is an important confirmationthat we have the right understanding of the early uni-verse. Assuming that there was no significant entropyproduction [2] in the universe between BBN and recom-bination, the two parameters ωband η are related via thepresent temperature of the CMB, T = 2.725 K, byIn standardη10= 274ωb.(1)Two recent balloon-borne experiments, Boomerang[3] and Maxima-1 [4], have now provided us with thefirst measurements of the CMB angular power spectrumwhich are of sufficient quality that an estimate of ωbcanbe made from them. The result [5], ωb ∼ 0.030, is sig-nificantly higher than the SBBN result. Indeed, SBBNclearly cannot accommodate as high a baryon density asωb= 0.030 [6].The SBBN yields for ωb = 0.030 are Yp = 0.251,D/H = 1.7 × 10−5,3He/H = 8.4 × 10−6, and7Li/H =7.6 × 10−10. With the exception of7Li, the uncertaintyin these SBBN yields is much less than the uncertaintyin the primordial abundances derived from observations.There is much debate about chemical evolution andsystematic effects in observations.helium abundance there are two competing estimates,the “low4He” [7], Yp = 0.234 ± 0.003 and the “high4He” [8], Yp = 0.244 ± 0.002. The difference is largelydue to the method of estimating the present abundancesfrom the observed line intensities, suggesting that thesystematic uncertainty may be larger than the ±0.005usually assumed [9].Burles and Tytler [10] claim to have established theprimordial deuterium abundance as D/H = (3.3±0.25)×10−5(“low D”) based on Lyman-series absorption byhigh-redshift clouds. This is based on a detected low deu-terium abundance in three such systems and upper lim-its from others. There remains one such system, where ahigh deuterium abundance, D/H ∼ 2 × 10−4(“high D”),has been observed [11]. It may be that the accuracy ofsuch observations has been overestimated [12]. We re-fer the reader to recent reviews [13] for further discus-sion and adopt the observational constraints Yp= 0.228–0.248, D/H = 2.9–4.0 × 10−5[14].SBBN range ωb= 0.004–0.021 from Ypand ωb= 0.018–0.022 from D/H. The “low D” of Burles and Tytler givesωb= 0.020 ± 0.01.The “Spite plateau” [15] of7Li abundance in popula-tion II halo stars provides us with the best estimate ofthe primordial lithium abundance. Bonifacio and Molaro[16] obtain a present lithium abundance log10(7Li/H) =−9.80 ± 0.012 ± 0.05 for these stars, and argue againstany significant depletion from the primordial abundance,based on the lack of dispersion in the data.neault et al. [17] estimate a depletion factor of 0.2–0.4dex from rotationally induced mixing.cent study Ryan et al. [18] obtain a mean abundancelog10(7Li/H) = −9.88 for the Spite plateau, and arguethat the narrow spread, less than 0.02 dex, limits deple-tion by rotationally induced mixing to less than 0.1 dex.Moreover, they observe a slight trend with metallicity,For the primordialThese lead to thePinson-In a more re-1
