Richard H. Cyburt

THE JINA REACLIB DATABASE: ITS RECENT UPDATES AND IMPACT ON TYPE-I X-RAY BURSTS

We present results from the JINA REACLIB project, an ongoing effort to maintain a current and accurate library of thermonuclear reaction rates for astrophysical applications. Ongoing updates are transparently documented and version tracked, and any set of rates is publicly available and can be downloaded via a Web interface at http://groups.nscl.msu.edu/jina/reaclib/db/. We discuss here our library V1.0, a snapshot of recommended rates for stable and explosive hydrogen and helium burning. We show that the updated reaction rates lead to modest but significant changes in full network, one-dimensional X-ray burst model calculations, compared with calculations with previously used reaction rate sets. The late time behavior of X-ray burst light curves shows significant changes, suggesting that the previously found small discrepancies between model calculations and observations may be solved with a better understanding of the nuclear input. Our X-ray burst model calculations are intended to serve as a benchmark for future model comparisons and sensitivity studies, as the complete underlying nuclear physics is fully documented and publicly available.

Updated nucleosynthesis constraints on unstable relic particles

We revisit the upper limits on the abundance of unstable massive relic particles provided by the success of Big-Bang Nucleosynthesis calculations. We use the cosmic microwave background data to constrain the baryon-to-photon ratio, and incorporate an extensively updated compilation of cross sections into a new calculation of the network of reactions induced by electromagnetic showers that create and destroy the light elements deuterium, 3 He, 4 He, 6 Li and 7 Li. We derive analytic approximations that complement and check the full numerical calculations. Considerations of the abundances of 4 He and 6 Li exclude exceptional regions of parameter space that would otherwise have been permitted by deuterium alone. We illustrate our results by applying them to massive gravitinos. If they weigh 100 GeV, their primordial abundance should have been below about 10 13 of the total entropy. This would imply an upper limit on the reheating temperature of a few times 10 7 GeV, which could be a potential diculty for some models of inflation. We discuss possible ways of evading this problem.

An update on the big bang nucleosynthesis prediction for 7Li: the problem worsens

The lithium problem arises from the significant discrepancy between the primordial Li abundance as predicted by BBN theory and the WMAP baryon density, and the pre-Galactic lithium abundance inferred from observations of metal-poor (Population II) stars. This problem has loomed for the past decade, with a persistent discrepancy of a factor of 2−3 in Li/H. Recent developments have sharpened all aspects of the Li problem. Namely: (1) BBN theory predictions have sharpened due to new nuclear data, particularly the uncertainty on He(α, γ)Be, has reduced to 7.4%, and with a central value shift of ∼ +0.04 keV barn. (2) The WMAP 5-year data now yields a cosmic baryon density with an uncertainty reduced to 2.7%. (3) Observations of metal-poor stars have tested for systematic effects, and have reaped new lithium isotopic data. With these, we now find that the BBN+WMAP predicts Li/H = (5.24 −0.67)× 10 . The Li problem remains and indeed is exacerbated; the discrepancy is now a factor 2.4 – 4.3 or 4.2σ (from globular cluster stars) to 5.3σ (from halo field stars). Possible resolutions to the lithium problem are briefly reviewed, and key nuclear, particle, and astronomical measurements highlighted.

Solar fusion cross sections II: the pp chain and CNO cycles

The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production are summarized and critically evaluated. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for {sup 8}B solar neutrinos. Opportunities for further increasing the precision of key rates are also discussed, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to 1998, Rev. Mod. Phys. 70, 1265.

New BBN limits on physics beyond the standard model from 4He

A recent analysis of the 4He abundance determined from observations of extragalactic HII regions indicates a significantly greater uncertainty for the 4He mass fraction. Furthermore, due to a different treatment of systematic effects such as underlying stellar absorption, the derived value of the 4He abundance is slightly higher. As a result, the predicted value of the primordial 4He abundance is now in line with calculations from big bang nucleosynthesis when the baryon density determined by WMAP is assumed. Analysis based on prior estimates of the 4He abundance will necessarily lead to constraints which are overly restrictive. Based on this new analysis of 4He, we derive constraints on a host of particle properties which include: limits on the number of relativistic species at the time of BBN (commonly taken to be the limit on neutrino flavors), limits on the variations of fundamental couplings such as αem and GN, and limits on decaying particles.

Primordial nucleosynthesis for the new cosmology: Determining uncertainties and examining concordance

Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) have a long history together in the standard cosmology. The general concordance between the predicted and observed light element abundances provides a direct probe of the universal baryon density. Recent CMB anisotropy measurements, particularly the observations performed by the WMAP satellite, examine this concordance by independently measuring the cosmic baryon density. Key to this test of concordance is a quantitative understanding of the uncertainties in the BBN light element abundance predictions. These uncertainties are dominated by systematic errors in nuclear cross sections. We critically analyze the cross section data, producing representations that describe this data and its uncertainties, taking into account the correlations among data, and explicitly treating the systematic errors between data sets. Using these updated nuclear inputs, we compute the new BBN abundance predictions, and quantitatively examine their concordance with observations. Depending on what deuterium observations are adopted, one gets the following constraints on the baryon density: OmegaBh^2=0.0229\pm0.0013 or OmegaBh^2 = 0.0216^{+0.0020}_{-0.0021} at 68% confidence, fixing N_{\nu,eff}=3.0. Concerns over systematics in helium and lithium observations limit the confidence constraints based on this data provide. With new nuclear cross section data, light element abundance observations and the ever increasing resolution of the CMB anisotropy, tighter constraints can be placed on nuclear and particle astrophysics. ABRIDGED

Big bang nucleosynthesis: Present status

Big-bang nucleosynthesis (BBN) describes the production of the lightest nuclides via a dynamic interplay among the four fundamental forces during the first seconds of cosmic time. We briefly overview the essentials of this physics, and present new calculations of light element abundances through 6Li and 7Li, with updated nuclear reactions and uncertainties including those in the neutron lifetime. We provide fits to these results as a function of baryon density and of the number of neutrino flavors, Nν . We review recent developments in BBN, particularly new, precision Planck cosmic microwave background (CMB) measurements that now probe the baryon density, helium content, and the effective number of degrees of freedom, Neff . These measurements allow for a tight test of BBN and of cosmology using CMB data alone. Our likelihood analysis convolves the 2015 Planck data chains with our BBN output and observational data. Adding astronomical measurements of light elements strengthens the power of BBN. We include a new determination of the primordial helium abundance in our likelihood analysis. New D/H observations are now more precise than the corresponding theoretical predictions, and are consistent with the Standard Model and the Planck baryon density. Moreover, D/H now provides a tight measurement of Nν when combined with the CMB baryon density, and provides a 2σ upper limit Nν < 3.2. The new precision of the CMB and of D/H observations together leave D/H predictions as the largest source of uncertainties. Future improvement in BBN calculations will therefore rely on improved nuclear cross section data. In contrast with D/H and 4He, 7Li predictions continue to disagree with observations, perhaps pointing to new physics. We conclude with a look at future directions including key nuclear reactions, astronomical observations, and theoretical issues.

The NACRE thermonuclear reaction compilation and big bang nucleosynthesis

Abstract The theoretical predictions of big bang nucleosynthesis (BBN) are dominated by uncertainties in the input nuclear reaction cross sections. In this paper we examine the impact on BBN of the recent compilation of nuclear data and thermonuclear reactions rates by the NACRE collaboration. We confirm that the adopted rates do not make large overall changes in central values of predictions, but do affect the magnitude of the uncertainties in these predictions. We therefore examine in detail the uncertainties in the individual reaction rates considered by NACRE. When the error estimates by NACRE are treated as 1σ limits, the resulting BBN error budget is similar to those of previous tabulations. We propose two new procedures for deriving reaction rate uncertainties from the nuclear data: one which sets lower limits to the error, and one which we believe is a reasonable description of the present error budget. We propagate these uncertainty estimates through the BBN code, and find that when the nuclear data errors are described most accurately, the resulting light element uncertainties are notably smaller than in some previous tabulations, but larger than others. Using these results, we derive limits on the cosmic baryon-to-photon ratio η, and compare this to independent limits on η from recent balloon-borne measurements of the cosmic microwave background radiation (CMB). We discuss means to improve the BBN results via key nuclear reaction measurements and light element observations.

Nucleosynthesis constraints on a massive gravitino in neutralino dark matter scenarios

The decays of massive gravitinos into neutralino dark matter particles and Standard Model secondaries during or after Big-Bang nucleosynthesis (BBN) may alter the primordial light-element abundances. We present here details of a new suite of codes for evaluating such effects, including a new treatment based on PYTHIA of the evolution of showers induced by hadronic decays of massive, unstable particles such as a gravitino. We present several sets of results obtained using these codes, including general constraints on the possible lifetime and abundance of an unstable particle decaying into neutralino dark matter under various hypotheses for its decay mechanism. We also develop an analytical treatment of non-thermal hadron propagation in the early universe, and use this to derive analytical estimates for light-element production and in turn on decaying particle lifetimes and abundances, which confirm our numerical results and illuminate the underlying physics. We then consider specifically the case of an unstable massive gravitino within the constrained minimal supersymmetric extension of the Standard Model (CMSSM). We present upper limits on its possible primordial abundance before decay for different possible gravitino masses, with CMSSM parameters along strips where the lightest neutralino provides all the astrophysical cold dark matter density. We do not find any CMSSM solution to the cosmological 7Li problem for small m3/2. Discounting this, for m1/2 ~ 500 GeV and tan β = 10 the other light-element abundances impose an upper limit m3/2n3/2/nγ 3 × 10−12 GeV to 2 × 10−13 GeV for m3/2 = 250 GeV to 1 TeV, which is similar in both the coannihilation and focus-point strips and somewhat weaker for tan β = 50, particularly for larger m1/2. The constraints also weaken in general for larger m3/2, and for m3/2 > 3 TeV we find a narrow range of m3/2n3/2/nγ, at values which increase with m3/2, where the 7Li abundance is marginally compatible with the other light-element abundances.

Primordial nucleosynthesis with CMB inputs: probing the early universe and light element astrophysics

Abstract Cosmic microwave background (CMB) determinations of the baryon-to-photon ratio η∝Ω baryon h 2 will remove the last free parameter from (standard) big bang nucleosynthesis (BBN) calculations. This will make BBN a much sharper probe of early universe physics, for example, greatly refining the BBN measurement of the effective number of light neutrino species, N ν ,eff . We show how the CMB can improve this limit, given current light element data. Moreover, it will become possible to constrain N ν ,eff independent of 4 He, by using other elements, notably deuterium; this will allow for sharper limits and tests of systematics. For example, a 3% measurement of η , together with a 10% (3%) measurement of primordial D/H, can measure N ν ,eff to a 95% confidence level of σ 95% ( N ν ,eff )=1.8 (1.0) if η ∼6.0×10 −10 . If instead, one adopts the standard model value N ν ,eff =3, then one can use η (and its uncertainty) from the CMB to make accurate predictions for the primordial abundances. These determinations can in turn become key inputs in the nucleosynthesis history (chemical evolution) of galaxies thereby placing constraints on such models.