Observations Of Light Elements Research Articles

Probing physics beyond the standard model: limits from BBN and the CMB independently and combined

We present new Big Bang Nucleosynthesis (BBN) limits on the cosmic expansion rate or relativistic energy density, quantified via the number Nν of equivalent neutrino species. We use the latest light element observations, neutron mean lifetime, and update our evaluation for the nuclear rates d + d ⟶ 3He + n and d + d ⟶ 3H+ p. Combining this result with the independent constraints from the cosmic microwave background (CMB) yields tight limits on new physics that perturbs Nν and η prior to cosmic nucleosynthesis: a joint BBN+CMB analysis gives Nν = 2.898 ± 0.141, resulting in Nν < 3.180 at 2σ. We apply these limits to a wide variety of new physics scenarios including right-handed neutrinos, dark radiation, and a stochastic gravitational wave background. The strength of the independent BBN and CMB constraints now opens a new window: we can search for limits on potential changes in Nν and/or the baryon-to-photon ratio η between the two epochs. The present data place strong constraints on the allowed changes in Nν between BBN and CMB decoupling; for example, we find -0.708 < Nν CMB - Nν BBN < 0.328 in the case where η and the primordial helium mass fraction Yp are unchanged between the two epochs; we also give limits on the allowed variations in η or in (η, Nν ) jointly. We discuss scenarios in which such changes could occur, and show that BBN+CMB results combine to place important constraints on some early dark energy models to explain the H0 tension. Looking to the future, we forecast the tightened precision for Nν arising from both CMB Stage 4 measurements as well as improvements in astronomical 4He measurements. We find that CMB-S4 combined with present BBN and light element observation precision can give σ(Nν ) ≃ 0.03. Such future precision would reveal the expected effect of neutrino heating (Neff -3 = 0.044) of the CMB during BBN, and would be near the level to reveal any particle species ever in thermal equilibrium with the standard model. Improved Yp measurements can push this precision even further.

Using Single-Crystal Graphene to Form Arrays of Nanocapsules Enabling the Observation of Light Elements in Liquid Cell Transmission Electron Microscopy.

We have designed and fabricated a TEM (transmission electron microscopy) liquid cell with hundreds of graphene nanocapsules arranged in a stack of two Si3N4-x membranes. These graphene nanocapsules are formed on arrays of nanoholes patterned on the Si3N4-x membrane by focused ion beam milling, allowing for better resolution than for the conventional graphene liquid cells, which enables the observation of light elements, such as atomic structures of silicon. We suggest that multiple nanocapsules provide opportunities for consecutive imaging under the same conditions in a single liquid cell. The use of single-crystal graphene windows offers an excellent signal-to-noise ratio and high spatial resolution. The motion of silicon nanoparticles (a low atomic number (Z) material) interacting with nanobubbles was observed, and analyzed, in detail. Our approach will help advance liquid-phase TEM observations by providing a straightforward method to encapsulate liquid between monolayers of various 2-dimensional materials.

Novel spectro-electrochemical cell for in situ/operando observation of common composite electrode with liquid electrolyte by X-ray absorption spectroscopy in the tender X-ray region

A novel spectro-electochemical cell for X-ray absorption spectroscopy in the tender X-ray region (TX-XAS) was designed and fabricated to investigate the electrochemical behavior of common battery materials with liquid electrolytes under in situ/operando conditions. The cell has several unique features, such as high X-ray transmittance, high signal to noise ratio, and high vacuum tightness. These features enable us quick and reliable XAS measurements. Operando P K-edge XAS measurements of an olivine-type LiFePO4 composite positive electrode were carried out to clarify its phosphorus environment during the electrochemical charging process. Results of spectral analysis show that there is no significant change in the oxidation state of phosphorus and in the coordination of the phosphate anions in the charging process, but a closer look of the consecutive XAS spectra suggests the shrinkage of the PO4 cage during the charging process, and the structural changes in a biphasic manner. These results demonstrate the usefulness of the cell for in situ/operando TX-XAS observations of light elements in practical batteries.

METAL-RICH ACCRETION AND THERMOHALINE INSTABILITIES IN EXOPLANET-HOST STARS: CONSEQUENCES ON THE LIGHT ELEMENTS ABUNDANCES

The early evolution of planetary systems is expected to depend on various periods of disk matter accretion onto the central star, which may include the accretion of metal-rich matter after the star settles on the main sequence. When this happens, the accreted material is rapidly mixed within the surface convective zone and induces an inverse mean-molecular-weight gradient, unstable for thermohaline convection. The induced mixing, which dilutes the metal excess, may also have important consequences on the light elements abundances. We model and analyze this process, and present the results according to various possible accretion scenarios. We give a detailed discussion of the different ways of treating thermohaline mixing, as proposed by previous authors, and we converge on a consistent view, including the most recent numerical simulations. We show how the observations of light elements in stars can be used as tracers of such events.

Oxygen‐Vacancy Ordering at Surfaces of Lithium Manganese(III,IV) Oxide Spinel Nanoparticles

Direct observation of light elements (Li and O) in oxygen-deficient lithium manganese spinel by spherical aberration-corrected scanning transmission electron microscopy is reported. A previously unknown ordered structure was revealed by annular dark-field (ADF) imaging of oxygen columns, while Li ions are visualized successfully by annular bright-field (ABF) imaging (see picture).

Observations of light elements in massive stars

AbstractObservations of light elements in hot massive stars are limited to few transitions of boron in the satellite-ultraviolet; lithium and beryllium are not observable at all. But because of its high sensitivity to the effects of rotational mixing, boron abundance determinations in massive stars have excelled as the definite test for evolutionary models with rotation. In this paper the observational evidence for rotational mixing in massive stars is reviewed and alternative interpretations are discussed.

Reply to “Comment on ‘Heavy element production in inhomogeneous big bang nucleosynthesis’”

This is a reply to Rauscher [Phys. Rev. D 75, 068301 (2007)]. We studied heavy element production in the high baryon density region in the early universe [Phys. Rev. D 72, 123505 (2005)]. However, it is claimed by Rauscher [Phys. Rev. D 75, 068301 (2007)] that a small scale but high baryon density region contradicts observations for the light element abundance or, in order not to contradict the observations, the high density region must be so small that it cannot affect the present heavy element abundance. In this paper, we study big bang nucleosynthesis in the high baryon density region and show that in certain parameter spaces it is possible to produce enough of the heavy element without contradiction to cosmic microwave background and light element observations.

What's Next for Big Bang Nucleosynthesis?

Big bang nucleosynthesis (BBN) plays an important role in the standard hot big bang cosmology. BBN theory is used to predict the primordial abundances of the lightest elements, hydrogen, helium and lithium. Comparison between the predicted and observationally determined light element abundances provides a general test of concordance and can be used to fix the baryon content in the universe. Measurements of the cosmic microwave background (CMB) anisotropies now supplant BBN as the premier baryometer, especially with the latest results from the WMAP satellite. With the WMAP baryon density, the test of concordance can be made even more precise. Any disagreement between theory predictions and observations requires careful discussion. Several possibilities exist to explain discrepancies; (1) observational systematics (either physical or technical) may not be properly treated in determining primordial light element abundances, (2) nuclear inputs that determine the BBN predictions may have unknown systematics or may be incomplete, and (3) physics beyond that included in the standard BBN scenario may need to be included in the theory calculation. Before we can be absolutely sure new physics is warranted, points (1) and (2) must be addressed and ruled out. All of these scenarios rely on experimental or observational data to make definitive statements of their applicability and range of validity, which currently is not at the level necessary to discern between these possibilities with high confidence. Thus, new light element abundance observations and nuclear experiments are needed to probe these further. Assuming concordance is established, one can use the light element observations to explore the evolution from their primordial values. This can provide useful information on stellar evolution, cosmic rays and other nuclear astrophysics. When combined with detailed models, BBN, the CMB anisotropy and nuclear astrophysics can provide us with information about the populations or environments in which the light elements are observed. Precision cosmology becomes precision astrophysics.

Precision primordial4Hemeasurement from the CMB

Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are two major pillars of cosmology. Standard BBN accurately predicts the primordial light element abundances ${(}^{4}\mathrm{He},$ D, ${}^{3}\mathrm{He}$ and ${}^{7}\mathrm{Li}),$ depending on one parameter, the baryon density. Light element observations are used as a baryometer. The CMB anisotropies also contain information about the content of the Universe which allows an important consistency check on the big bang model. In addition CMB observations now have sufficient accuracy to not only determine the total baryon density, but also resolve its principal constituents H and ${}^{4}\mathrm{He}.$ We present a global analysis of all recent CMB data, with special emphasis on the concordance with BBN theory and light element observations. We find ${\ensuremath{\Omega}}_{B}{h}^{2}{=0.0250}_{\ensuremath{-}0.0026}^{+0.0019}$ and ${Y}_{p}{=0.250}_{\ensuremath{-}0.014}^{+0.010}$ (fraction of baryon mass as ${}^{4}\mathrm{He})$ using CMB data alone, in agreement with ${}^{4}\mathrm{He}$ abundance observations. The determination of ${Y}_{p}$ allows us to constrain the relativistic degrees of freedom during BBN, measured through the effective number of light neutrino species, ${N}_{\ensuremath{\nu},eff}{=3.02}_{\ensuremath{-}0.79}^{+0.85},$ in accord with the standard model of particle physics. With this concordance established we show that the inclusion of standard, ${N}_{\ensuremath{\nu},eff}\ensuremath{\equiv}3,$ BBN theory priors significantly reduces the volume of parameter space. In this case, we find ${\ensuremath{\Omega}}_{B}{h}^{2}{=0.0245}_{\ensuremath{-}0.0028}^{+0.0015}$ and ${Y}_{p}{=0.2493}_{\ensuremath{-}0.0010}^{+0.0007}.$ We also find that the inclusion of deuterium abundance observations reduces the ${Y}_{p}$ and ${\ensuremath{\Omega}}_{B}{h}^{2}$ ranges by a factor of $\ensuremath{\sim}2.$ Further light element observations and CMB anisotropy experiments will refine this concordance and sharpen BBN and the CMB as tools for precision cosmology.

Primordial nucleosynthesis in light of WMAP

Big bang nucleosynthesis has long provided the primary determination of the cosmic baryon density ΩBh2, or equivalently the baryon-to-photon ratio, η. Recently, data on CMB anisotropies have become increasingly sensitive to η. The comparison of these two independent measures provides a key test for big bang cosmology. The first release of results from the Wilkinson Microwave Anisotropy Probe (WMAP) marks a milestone in this test. With the precision of WMAP, the CMB now offers a significantly stronger constraint on η. We discuss the current state of BBN theory and light element observations (including their possible lingering systematic errors). The resulting BBN baryon density prediction is in overall agreement with the WMAP prediction, an important and non-trivial confirmation of hot big bang cosmology. Going beyond this, the powerful CMB baryometer can be used as an input to BBN and one can accurately predict the primordial light element abundances. By comparing these with observations one can obtain new insight into post-BBN nucleosynthesis processes and associated astrophysics. Finally, one can test the possibility of nonstandard physics at the time of BBN, now with all light elements available as probes. Indeed, with the WMAP precision η, deuterium is already beginning to rival 4He's sensitivity to nonstandard physics, and additional D/H measurements can improve this further.

The NACRE thermonuclear reaction compilation and big bang nucleosynthesis

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 1 σ 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.

Decaying neutrino and a high cosmological baryon density

The low second acoustic peak in the recent Boomerang data may indicate a cosmological baryon density which is larger than allowed by standard big bang nucleosynthesis. We show that the decay of the tau-neutrino: ν τ → ν e + φ, where ν e is the electron neutrino and φ is a scalar, essentially can assure agreement between BBN calculations and light element observations for a large baryon density.

Transport Phenomena and Light Element Abundances in the Sun and Solar Type Stars

The observations of light elements in the Sun and Solar type stars give special clues for understanding the hydrodynamical processes at work in stellar interiors. In the Sun 7Li is depleted by 140 while 3He has not increased by more than ≅ 10% in 3 Gyrs. Meanwhile the inversion of helioseismic modes lead to a precision on the sound velocity of about 1%. The mixing processes below the solar convection zone are constrained by these observations. Lithium is depleted in most Pop I solar type stars. In halo stars however, the lithium abundance seems constant in the “spite plateau” with no observed dispersion, which is difficult to reconcile with the theory of diffusion processes. In the present paper, the various relevant observations will be discussed. It will be shown that the μ-gradients induced by element settling may help solving the ‘lithium paradox’.

Primordial nucleosynthesis in an inhomogeneous universe

From recent studies of nucleosynthesis in inhomogeneous universe, it has been pointed out that (1) ΩB = 1 model becomes consistent with light element observations, (2) heavy elements including r-process elements are abundantly synthesized, and (3) 9Be plays a role of the indicator of inhomogeneity since 9Be is also abundantly synthesized. These suggestions were, however, based on a simple two-zone model in which back diffusion of neutrons are neglected during the nucleosynthesis. In this short review, it is shown that (1) the upper limit of ΩB which is consistent with light element observations is almost the same as that of homogeneous case, (2) the 9Be abundance in the simple two-zone model is overestimated at least two orders of magnitude in plausible parameter space and (3) the abundances of CNO elements are very small in the proper range of baryon/photon ratio consistent with the abundances of light elements.

Small-scale anisotropies in the microwave background in a baryon-dominated open universe

The anisotropies of the cosmic microwave background (CMB) radiation in a baryon-dominated universe (BDU) are calculated using a gauge-invariant method. The theoretical predictions on a 4.5-arcmin angular scale are compared with the observational data of Uson and Wilkinson (1984). Both adiabatic and isocurvature scenarios predict roughly the same amplitudes of the anisotropies on this scale, in spite of the difference of the physical mechanism of the anisotropy generation. As a result, CMB isotropy requires that the density parameter of a BDU must be larger than 0.8 even in an isocurvature scenario. This conclusion is compatible with the observation of light elements only if the universe were fairly inhomogeneous at the epoch of primordial nucleosynthesis. In turn, to the extent that standard primordial nucleosynthesis predictions are assumed, the idea of a BDU based on either adiabatic or isocurvature models can be ruled out. 22 references.