Elisabeth Vangioni

STANDARD BIG BANG NUCLEOSYNTHESIS UP TO CNO WITH AN IMPROVED EXTENDED NUCLEAR NETWORK

Primordial or big bang nucleosynthesis (BBN) is one of the three strong pieces of evidence for the big bang model together with the expansion of the universe and cosmic microwave background radiation. In this study, we improve the standard BBN calculations taking into account new nuclear physics analyses and enlarge the nuclear network up to sodium. This is, in particular, important to evaluate the primitive value of CNO mass fraction that could affect Population III stellar evolution. For the first time we list the complete network of more than 400 reactions with references to the origin of the rates, including 270 reaction rates calculated using the TALYS code. Together with the cosmological light elements, we calculate the primordial beryllium, boron, carbon, nitrogen, and oxygen nuclei. We performed a sensitivity study to identify the important reactions for CNO, 9Be, and boron nucleosynthesis. We re-evaluated those important reaction rates using experimental data and/or theoretical evaluations. The results are compared with precedent calculations: a primordial beryllium abundance increase by a factor of four compared to its previous evaluation, but we note a stability for B/H and for the CNO/H abundance ratio that remains close to its previous value of 0.7 × 10–15. On the other hand, the extension of the nuclear network has not changed the 7Li value, so its abundance is still 3-4 times greater than its observed spectroscopic value.

The effects of unstable particles on light-element abundances: Lithium versus deuterium and 3He

Abstract We reconsider the effects of the radiation from the decays of unstable particles on the production and destruction of the primordial light elements, with a view to reconciling the high primordial 7 Li abundance deduced from big bang nucleosynthesis (BBN), as implied by the baryon-to-photon ratio now inferred from the anisotropies of the cosmic microwave background (CMB), with the lower abundance of 7 Li observed in halo stars. The potential destruction of 7 Li is strongly constrained by observations of deuterium (D), 3 He and 6 Li. We identify ranges for the unstable particle abundance and lifetime which would deplete 7 Li while remaining consistent with the abundance of 6 Li. However, in these regions either the D abundance is unacceptably low or the ratio 3 He/D is unacceptably large. We conclude that late particle decay is unable to explain both the discrepancy of the calculated 7 Li abundance and the observed 7 Li plateau. In the context of supersymmetric theories with neutralino or gravitino dark matter, we display the corresponding light-element constraints on the model parameters.

Coupled Variations of Fundamental Couplings and Primordial Nucleosynthesis

The effect of variations of the fundamental nuclear parameters on big-bang nucleosynthesis are modeled and discussed in detail taking into account the interrelations between the fundamental parameters arising in unified theories. Considering only 4 He, strong constraints on the variation of the neutron lifetime, neutron-proton mass difference are set. These constraints are then translated into constraints on the time variation of the Yukawa couplings and the fine structure constant. Furthermore, we show that a variation of the deuterium binding energy is able to reconcile the 7 Li abundance deduced from the WMAP analysis with its spectroscopically determined value while maintaining concordance with D and 4 He. The analysis is strongly based on the potential model of Flambaum and Shuryak that relates the binding energy of the deuteron with the nucleon and σ and w mesons masses; however, we show that an alternative approach that consists of a pion mass dependence necessarily leads to equivalent conclusions.

Hierarchical growth and cosmic star formation : Enrichment, outflows, and supernova rates

The cosmic star formation histories are evaluated for different minimum masses of the initial halo structures, with allowance for realistic gas outflows. With a minimum halo mass of 107-108 M? and a moderate outflow efficiency, we reproduce both the current baryon fraction and the early chemical enrichment of the IGM. The intensity of the formation rate of normal stars is also well constrained by the observations: it has to be dominated by star formation in elliptical galaxies, except perhaps at very low redshift. The fraction of baryons in stars is predicted as are also the Type Ia and II supernova event rates. Comparison with SN observations in the redshift range z = 0-2 allows us to set strong constraints on the time delay of Type Ia supernovae (a delay of ~3 Gyr is required to fit the data), the lower end of the mass range of the progenitors (2-8 M?), and the fraction of white dwarfs that reproduce the Type Ia supernova (about 1%). The intensity of zero metallicity star formation below 270 M? must be limited in order to avoid premature overenrichment of the IGM. About 50% of the metals present in the IGM at z = 0 have been produced by Population III stars at very high z. The remaining 50% are ejected later by galaxies forming normal stars. We conclude that about 10-3 of the mass in baryons must lie in the first massive stars in order to produce enough ionizing photons to allow early reionization of the IGM by z ~ 15.

Big bang nucleosynthesis constraints on scalar-tensor theories of gravity

We investigate Big bang nucleosynthesis (BBN) in scalar-tensor theories of gravity with arbitrary matter couplings and self-interaction potentials. We first consider the case of a massless dilaton with a quadratic coupling to matter. We perform a full numerical integration of the evolution of the scalar field and compute the resulting light element abundances. We demonstrate in detail the importance of particle mass thresholds on the evolution of the scalar field in a radiation dominated universe. We also consider the simplest extension of this model including a cosmological constant in either the Jordan or Einstein frame.

Cosmological Cosmic Rays and the Observed 6Li Plateau in Metal-poor Halo Stars

Very recent observations of the 6Li isotope in halo stars reveal a 6Li plateau about 1000 times above the predicted big bang nucleosynthesis abundance. We calculate the evolution of 6Li versus redshift generated from an initial burst of cosmological cosmic rays (CCRs) up to the formation of the Galaxy. We show that the pre-Galactic production of the 6Li isotope can account for the 6Li plateau observed in metal-poor halo stars without additional overproduction of 7Li. The derived relation between the amplitude of the CCR energy spectra and the redshift of the initial CCR production puts constraints on the physics and history of the objects, such as Population III stars, responsible for these early cosmic rays. Consequently, we consider the evolution of 6Li in the Galaxy. Since 6Li is also produced in Galactic cosmic-ray nucleosynthesis, we argue that halo stars with metallicities between [Fe/H] = -2 and -1 must be somewhat depleted in 6Li.

Metallicity-constrained merger rates of binary black holes and the stochastic gravitational wave background

The recent detection of the binary black hole merger GW150914 demonstrates the existence of black holes more massive than previously observed in X-ray binaries in our Galaxy. This article explores different scenarios of black hole formation in the context of self-consistent cosmic chemical evolution models that simultaneously match observations of the cosmic star formation rate, optical depth to reionization and metallicity of the interstellar medium. This framework is used to calculate the mass distribution of merging black hole binaries and its evolution with redshift. We also study the implications of the black hole mass distribution for the stochastic gravitational wave background from mergers and from core-collapse events.

Population III Generated Cosmic Rays and the Production of 6Li

We calculate the evolution of 6 Li generated from cosmic rays produced by an early population of massive stars. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star for- mation histories constrained to reproduce the observed star formation rate at redshift zP6 and the observed chemical abundances both in damped Lyabsorbers and in the intergalactic medium, and to allow for an early reionization of theuniverseatz � 11byPopulationIIIstarsasindicatedbythethirdyearresultsreleasedbyWMAP.Weshowthatthe pregalactic production of the 6 Li isotope in the IGM via these Population III stars can account for the 6 Li plateau observed in metal-poor halo stars without additional overproduction of 7 Li. Our results depend on the efficiency of cosmic rays to propagate out of minihalos and the fraction of supernova energy deposited in cosmic rays. We also compute the cosmic-ray heating of the IGM gas. In general, we find somewhat high temperatures (of order 10 5 K), implying that the cosmic rays production of 6Li may be required to be confined to the so-called warm-hot IGM. Subject headingg cosmic rays — cosmology: theory — nuclear reactions, nucleosynthesis, abundances — stars: abundances

The Impact of Star Formation and Gamma-Ray Burst Rates at High Redshift on Cosmic Chemical Evolution and Reionization

Recent observations in the total luminosity density have led to significant progress in establishing the star formation rate (SFR) at high redshift. Concurrently observed gamma-ray burst rates have also been used to extract the SFR at high redshift. The SFR in turn can be used to make a host of predictions concerning the ionization history of the Universe, the chemical abundances, and supernova rates. We compare the predictions made using a hierarchical model of cosmic chemical evolution based on three recently proposed SFRs: two based on extracting the SFR from the observed gamma-ray burst rate at high redshift, and one based on the observed galaxy luminosity function at high redshift. Using the WMAP/Planck data on the optical depth and epoch of reionization, we find that only the SFR inferred from gamma-ray burst data at high redshift suffices to allow a single mode (in the initial mass function) of star formation which extends from z = 0 to redshifts > 10. For the case of the more conservative SFR based on the observed galaxy luminosity function, the reionization history of the Universe requires a bimodal IMF which includes at least a coeval high (or intermediate) mass mode of star formation at high redshift (z> 10). Therefore, we also consider here a more general bimodal case which includes an early-forming high mass mode as a fourth model to test the chemical history of the Universe. We compute the abundances of several trace elements, as well as the expected supernova rates, the stellar mass density and the specific SFR, sSFR, as a function of redshift for each of the four models considered. We conclude that observational constraints on the global metallicity and optical depth at high redshift favor unseen faint but active star forming galaxies as pointed out in many recent studies.

Influence of Population III stars on cosmic chemical evolution

New observations from the Hubble Ultra Deep Field suggest that the star formation rate at z > 7 drops off faster than previously thought. Using a newly determined star formation rate for the normal mode of Population II/I (PopII/I) stars, including this new constraint, we compute the Thomson scattering optical depth and find a result that is marginally consistent with Wilkinson Microwave Anisotropy Probe 5 results. We also reconsider the role of Population III (PopIII) stars in light of cosmological and stellar evolution constraints. While this input may be needed for reionization, we show that it is essential in order to account for cosmic chemical evolution in the early universe. We investigate the consequences of PopIII stars on the local metallicity distribution function of the Galactic halo (from the recent Hamburg/European Southern Observatory (ESO) survey of metal-poor stars) and on the evolution of abundances with metallicity (based on the ESO large programme on very metal-poor stars), with special emphasis on carbon-enhanced metal-poor stars. The metallicity distribution function shape is well reproduced at low iron abundance ([Fe/H] ≥―4), in agreement with other studies. However, the Hamburg/ESO survey hints at a sharp decrease of the number of low-mass stars at very low iron abundance, which is not reproduced in models with only PopII/I stars. The presence of PopIII stars, of typical masses 30-40 M ⊙ , helps us to reproduce this feature, leading to a prompt initial enrichment before the onset of PopII/I stars. The metallicity at which this cut-off occurs is sensitive to the lowest mass of the massive PopIII stars, which makes the metallicity distribution function a promising tool to constrain this population. Our most important results show that the nucleosynthetic yields of PopIII stars lead to abundance patterns in agreement with those observed in extremely metal-poor stars. This can be demonstrated by the transition discriminant (a criterion for low-mass star formation taking into account the cooling due to C II and O I ). In this chemical approach to cosmic evolution, PopIII stars prove to be a compulsory ingredient, and extremely metal-poor stars are inevitably born at high redshift.