https://biblio.ugent.be/publication/685594/file/1130605.pdf

Review of Particle Physics

The combination of seven-year data from WMAP and improved astrophysical data rigorously tests the standard cosmological model and places new constraints on its basic parameters and extensions. By combining the WMAP data with the latest distance measurements from the baryon acoustic oscillations (BAO) in the distribution of galaxies and the Hubble constant (H0) measurement, we determine the parameters of the simplest six-parameter ΛCDM model. The power-law index of the primordial power spectrum is ns = 0.968 ± 0.012 (68% CL) for this data combination, a measurement that excludes the Harrison–Zel’dovich–Peebles spectrum by 99.5% CL. The other parameters, including those beyond the minimal set, are also consistent with, and improved from, the five-year results. We find no convincing deviations from the minimal model. The seven-year temperature power spectrum gives a better determination of the third acoustic peak, which results in a better determination of the redshift of the matter-radiation equality epoch. Notable examples of improved parameters are the total mass of neutrinos, � mν < 0.58 eV (95% CL), and the effective number of neutrino species, Neff = 4.34 +0.86 −0.88 (68% CL), which benefit from better determinations of the third peak and H0. The limit on a constant dark energy equation of state parameter from WMAP+BAO+H0, without high-redshift Type Ia supernovae, is w =− 1.10 ± 0.14 (68% CL). We detect the effect of primordial helium on the temperature power spectrum and provide a new test of big bang nucleosynthesis by measuring Yp = 0.326 ± 0.075 (68% CL). We detect, and show on the map for the first time, the tangential and radial polarization patterns around hot and cold spots of temperature fluctuations, an important test of physical processes at z = 1090 and the dominance of adiabatic scalar fluctuations. The seven-year polarization data have significantly improved: we now detect the temperature–E-mode polarization cross power spectrum at 21σ , compared with 13σ from the five-year data. With the seven-year temperature–B-mode cross power spectrum, the limit on a rotation of the polarization plane due to potential parity-violating effects has improved by 38% to Δα =− 1. 1 ± 1. 4(statistical) ± 1. 5(systematic) (68% CL). We report significant detections of the Sunyaev–Zel’dovich (SZ) effect at the locations of known clusters of galaxies. The measured SZ signal agrees well with the expected signal from the X-ray data on a cluster-by-cluster basis. However, it is a factor of 0.5–0.7 times the predictions from “universal profile” of Arnaud et al., analytical models, and hydrodynamical simulations. We find, for the first time in the SZ effect, a significant difference between the cooling-flow and non-cooling-flow clusters (or relaxed and non-relaxed clusters), which can explain some of the discrepancy. This lower amplitude is consistent with the lower-than-theoretically expected SZ power spectrum recently measured by the South Pole Telescope Collaboration.

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Seven-year wilkinson microwave anisotropy probe (wmap *) observations: cosmological interpretation

This paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted “base ΛCDM” in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H0 = (67.8 ± 0.9) km s-1Mpc-1, a matter density parameter Ωm = 0.308 ± 0.012, and a tilted scalar spectral index with ns = 0.968 ± 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low Frequency Instrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of τ = 0.066 ± 0.016, corresponding to a reionization redshift of . These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base ΛCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find Neff = 3.15 ± 0.23 for the effective number of relativistic degrees of freedom, consistent with the value Neff = 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to ∑ mν < 0.23 eV. The spatial curvature of our Universe is found to be very close to zero, with | ΩK | < 0.005. Adding a tensor component as a single-parameter extension to base ΛCDM we find an upper limit on the tensor-to-scalar ratio of r0.002< 0.11, consistent with the Planck 2013 results and consistent with the B-mode polarization constraints from a joint analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP B-mode data to our analysis leads to a tighter constraint of r0.002 < 0.09 and disfavours inflationarymodels with a V(φ) ∝ φ2 potential. The addition of Planck polarization data leads to strong constraints on deviations from a purely adiabatic spectrum of fluctuations. We find no evidence for any contribution from isocurvature perturbations or from cosmic defects. Combining Planck data with other astrophysical data, including Type Ia supernovae, the equation of state of dark energy is constrained to w = −1.006 ± 0.045, consistent with the expected value for a cosmological constant. The standard big bang nucleosynthesis predictions for the helium and deuterium abundances for the best-fit Planck base ΛCDM cosmology are in excellent agreement with observations. We also constraints on annihilating dark matter and on possible deviations from the standard recombination history. In neither case do we find no evidence for new physics. The Planck results for base ΛCDM are in good agreement with baryon acoustic oscillation data and with the JLA sample of Type Ia supernovae. However, as in the 2013 analysis, the amplitude of the fluctuation spectrum is found to be higher than inferred from some analyses of rich cluster counts and weak gravitational lensing. We show that these tensions cannot easily be resolved with simple modifications of the base ΛCDM cosmology. Apart from these tensions, the base ΛCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.

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Planck 2015 results - XIII. Cosmological parameters

We present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. From the Planck temperature and lensing data, for this cosmology we find a Hubble constant, H0= (67.8 +/- 0.9) km/s/Mpc, a matter density parameter Omega_m = 0.308 +/- 0.012 and a scalar spectral index with n_s = 0.968 +/- 0.006. (We quote 68% errors on measured parameters and 95% limits on other parameters.) Combined with Planck temperature and lensing data, Planck LFI polarization measurements lead to a reionization optical depth of tau = 0.066 +/- 0.016. Combining Planck with other astrophysical data we find N_ eff = 3.15 +/- 0.23 for the effective number of relativistic degrees of freedom and the sum of neutrino masses is constrained to < 0.23 eV. Spatial curvature is found to be |Omega_K| < 0.005. For LCDM we find a limit on the tensor-to-scalar ratio of r <0.11 consistent with the B-mode constraints from an analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP data leads to a tighter constraint of r < 0.09. We find no evidence for isocurvature perturbations or cosmic defects. The equation of state of dark energy is constrained to w = -1.006 +/- 0.045. Standard big bang nucleosynthesis predictions for the Planck LCDM cosmology are in excellent agreement with observations. We investigate annihilating dark matter and deviations from standard recombination, finding no evidence for new physics. The Planck results for base LCDM are in agreement with BAO data and with the JLA SNe sample. However the amplitude of the fluctuations is found to be higher than inferred from rich cluster counts and weak gravitational lensing. Apart from these tensions, the base LCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.

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Planck 2015 results. XIII. Cosmological parameters

Graphs.- Groups.- Transitive Graphs.- Arc-Transitive Graphs.- Generalized Polygons and Moore Graphs.- Homomorphisms.- Kneser Graphs.- Matrix Theory.- Interlacing.- Strongly Regular Graphs.- Two-Graphs.- Line Graphs and Eigenvalues.- The Laplacian of a Graph.- Cuts and Flows.- The Rank Polynomial.- Knots.- Knots and Eulerian Cycles.- Glossary of Symbols.- Index.

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Algebraic Graph Theory

We review the Galactic chemical evolution of Li6 and compare these results with recent observational determinations of the lithium isotopic ratio. In particular, we concentrate on so-called standard Galactic cosmic-ray nucleosynthesis in which Li, Be, and B are produced (predominantly) by the inelastic scattering of accelerated protons and \alpha's off of CNO nuclei in the ambient interstellar medium. If O/Fe is constant at low metallicities, then the Li6 vs Fe/H evolution-as well as Be and B vs Fe/H-has difficulty in matching the observations. However, recent determinations of Population II oxygen abundances, as measured via OH lines, indicate that O/Fe increases at lower metallicity; if this trend is confirmed, then the Li6 evolution in a standard model of cosmic-ray nucleosynthesis is consistent with the data. We also show that another key indicator of Li6BeB origin is the Li6/Be ratio which also fits the available data if O/Fe is not constant at low metallicity. Finally we note that Li6 evolution in this scenario can strongly constrain the degree to which Li6 and Li7 are depleted in halo stars.

The Evolution of Li6 in Standard Cosmic-Ray Nucleosynthesis

Recent observations by Bania et al. measure 3He versus oxygen in Galactic H II regions, finding that 3He/H is within a factor of 2 of the solar abundance for [O/H] -0.6. These results are consistent with a flat behavior in this metallicity range, tempting one to deduce from these observations a primordial value for the 3He abundance, which could join D and 7Li as an indicator of the cosmic baryon density. However, using the same data, we show that it is not possible to obtain a strong constraint on the baryon density range. This is due to (1) the intrinsically weak sensitivity of the primordial 3He abundance to the baryon density, (2) the limited range in metallicity of the sample, (3) the intrinsic scatter in the data, and (4) our limited understanding of the chemical and stellar evolution of this isotope. Consequently, the 3He observations correspond to an extended range of baryon-to-photon ratio, η = (2.2-6.5) × 10-10, which diminishes the role of 3He as a precision baryometer. On the other hand, once the baryon-to-photon ratio is determined by the cosmic microwave background, D/H, or 7Li/H, the primordial value of 3He/H can be inferred. Henceforth, new observations of Galactic 3He can in principle greatly improve our understanding of stellar and/or chemical evolution and reconcile the observations of the H II regions and those of the planetary nebulae.

http://iopscience.iop.org/article/10.1086/346232/pdf

On the Baryometric Status of 3He

Because of the roughly linear correlation between Be/H and Fe/H in low metallicity halo stars, it has been argued that a ``primary'' component in the nucleosynthesis of Be must be present in addition to the ``secondary'' component from standard Galactic cosmic ray nucleosynthesis. In this paper we critically re-evaluate the evidence for the primary versus secondary character of Li, Be, and B evolution, analyzing both in the observations and in Galactic chemical evolution models. While it appears that [Be/H] versus [Fe/H] has a logarithmic slope near 1, it is rather the Be-O trend that directly arises from the physics of spallation production. Using new abundances for oxygen in halo stars based on UV OH lines, we find that the Be-O slope has a large uncertainty due to systematic effects, rendering it difficult to distinguish from the data between the secondary slope of 2 and the primary slope of 1. The possible difference between the Be-Fe and Be-O slopes is a consequence of the variation in O/Fe versus Fe: recent data suggests a negative slope rather than zero (i.e., Fe $\propto$ O) as is often assumed. In addition to a phenomenological analysis of Be and B evolution, we have also examined the predicted LiBeB, O, and Fe trends in Galactic chemical evolution models which include outflow. Based on our results, it is possible that a good fit to the LiBeB evolution requires only traditional the Galactic cosmic ray spallation, and the (primary) neutrino-process contribution to B11. We thus suggest that these two processes might be sufficient to explain Li6, Be, and B evolution in the Galaxy, without the need for an additional primary source of Be and B.

The Revival of Galactic Cosmic Ray Nucleosynthesis

The abundance of interstellar 7Li in the low-metallicity gas of the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun’s metallicity, is nearly equal to the Big Bang nucleosynthesis predictions. The predicted primordial abundance of the lithium-7 isotope in the primordial Universe is four times greater than that measured in the atmospheres of Galactic halo stars, but it is hard to trace this isotope in the Milky Way because it has most probably been burnt up. This paper reports the detection of interstellar lithium beyond the Milky Way, in the low-metallicity gas of the nearby Small Magellanic Cloud galaxy. Present-day lithium-7 abundance in this galaxy is nearly equal to the predictions of the standard theory of Big Bang nucleosynthesis — although the data can also be reconciled with non-standard models. The primordial abundances of light elements produced in the standard theory of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to photons, a quantity inferred from observations of the microwave background1. The predicted2,3,4 primordial 7Li abundance is four times that measured in the atmospheres of Galactic halo stars5,6,7. This discrepancy could be caused by modification of surface lithium abundances during the stars’ lifetimes8 or by physics beyond the Standard Model that affects early nucleosynthesis9,10. The lithium abundance of low-metallicity gas provides an alternative constraint on the primordial abundance and cosmic evolution of lithium11 that is not susceptible to the in situ modifications that may affect stellar atmospheres. Here we report observations of interstellar 7Li in the low-metallicity gas of the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun’s metallicity. The present-day 7Li abundance of the Small Magellanic Cloud is nearly equal to the BBN predictions, severely constraining the amount of possible subsequent enrichment of the gas by stellar and cosmic-ray nucleosynthesis. Our measurements can be reconciled with standard BBN with an extremely fine-tuned depletion of stellar Li with metallicity. They are also consistent with non-standard BBN.

Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud

We explore a nuclear physics resolution to the discrepancy between the predicted standard big-bang nucleosynthesis (BBN) abundance of $^{7}\mathrm{Li}$ and its observational determination in metal-poor stars. The theoretical $^{7}\mathrm{Li}$ abundance is 3--4 times greater than the observational values, assuming the baryon-to-photon ratio, ${\ensuremath{\eta}}_{\mathrm{wmap}}$, determined by WMAP. The $^{7}\mathrm{Li}$ problem could be resolved within the standard BBN picture if additional destruction of $A=7$ isotopes occurs due to new nuclear reaction channels or upward corrections to existing channels. This could be achieved via missed resonant nuclear reactions, which is the possibility we consider here. We find some potential candidate resonances which can solve the lithium problem and specify their required resonant energies and widths. For example, a ${1}^{\ensuremath{-}}$ or ${2}^{\ensuremath{-}}$ excited state of $^{10}\mathrm{C}$ sitting at approximately 15.0 MeV above its ground state with an effective width of order 10 keV could resolve the $^{7}\mathrm{Li}$ problem; the existence of this excited state needs experimental verification. Other examples using known states include $^{7}\mathrm{Be}+t\ensuremath{\rightarrow}^{10}\mathrm{B}(18.80\text{ }\text{ }\mathrm{MeV})$, and $^{7}\mathrm{Be}+d\ensuremath{\rightarrow}^{9}\mathrm{B}(16.71\text{ }\text{ }\mathrm{MeV})$. For all of these states, a large channel radius ($ag10\text{ }\text{ }\mathrm{fm}$) is needed to give sufficiently large widths. Experimental determination of these reaction strengths is needed to rule out or confirm these nuclear physics solutions to the lithium problem.

Brian D. Fields

Papers

The Evolution of Li6 in Standard Cosmic-Ray Nucleosynthesis

On the Baryometric Status of 3He

The Revival of Galactic Cosmic Ray Nucleosynthesis

Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud

Resonant destruction as a possible solution to the cosmological lithium problem