The Primordial Lithium Problem

Big-bang nucleosynthesis (BBN) theory, together with the precise WMAP cosmic baryon density, makes tight predictions for the abundances of the lightest elements. Deuterium and 4He measurements agree well with expectations, but 7Li observations lie a factor 3-4 below the BBN+WMAP prediction. This 4-5\sigma\ mismatch constitutes the cosmic "lithium problem," with disparate solutions possible. (1) Astrophysical systematics in the observations could exist but are increasingly constrained. (2) Nuclear physics experiments provide a wealth of well-measured cross-section data, but 7Be destruction could be enhanced by unknown or poorly-measured resonances, such as 7Be + 3He -> 10C^* -> p + 9B. (3) Physics beyond the Standard Model can alter the 7Li abundance, though D and 4He must remain unperturbed; we discuss such scenarios, highlighting decaying Supersymmetric particles and time-varying fundamental constants. Present and planned experiments could reveal which (if any) of these is the solution to the problem.Comment: 29 pages, 7 figures. Per Annual Reviews policy, this is the original submitted draft. Posted with permission from the Annual Review of Nuclear and Particle Science, Volume 61. Annual Reviews, http://www.annualreviews.org . Final published version at http://www.annualreviews.org/doi/abs/10.1146/annurev-nucl-102010-13044

Cosmological Cosmic Rays: Sharpening the Primordial Lithium Problem

Cosmic structure formation leads to large-scale shocked baryonic flows which are expected to produce a cosmological population of structure-formation cosmic rays (SFCRs). Interactions between SFCRs and ambient baryons will produce lithium isotopes via \alpha+\alpha \to ^{6,7}Li. This pre-Galactic (but non-primordial) lithium should contribute to the primordial 7Li measured in halo stars and must be subtracted in order to arrive to the true observed primordial lithium abundance. In this paper we point out that the recent halo star 6Li measurements can be used to place a strong constraint to the level of such contamination, because the exclusive astrophysical production of 6Li is from cosmic-ray interactions. We find that the putative 6Li plateau, if due to pre-Galactic cosmic-ray interactions, implies that SFCR-produced lithium represents Li_{SFCR}/Li_{plateau}\approx 15% of the observed elemental Li plateau. Taking the remaining plateau Li to be cosmological 7Li, we find a revised (and slightly worsened) discrepancy between the Li observations and Big Bang Nucleosynthesis predictions by a factor of ^7Li_{BBN}/^7Li_{plateau} \approx 3.7. Moreover, SFCRs would also contribute to the extragalactic gamma-ray background (EGRB) through neutral pion production. This gamma-ray production is tightly related to the amount of lithium produced by the same cosmic rays; the 6Li plateau limits the pre-Galactic (high-redshift) SFCR contribution to be at the level of I_{\pi_{\gamma}SFCR}/I_{EGRB} < 5% of the currently observed EGRB.Comment: 4 pages, accepted for publication in PR

Resonant Destruction as a Possible Solution to the Cosmological Lithium Problem

We explore a nuclear physics resolution to the discrepancy between the predicted standard big-bang nucleosynthesis (BBN) abundance of 7Li and its observational determination in metal-poor stars. The theoretical 7Li abundance is 3-4 times greater than the observational values, assuming the baryon-to-photon ratio, eta_wmap, determined by WMAP. The 7Li 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^- or 2^- excited state of 10C sitting at approximately 15.0 MeV above its ground state with an effective width of order 10 keV could resolve the 7Li problem; the existence of this excited state needs experimental verification. Other examples using known states include 7Be+t \rightarrow 10B(18.80 MeV), and 7Be+d \rightarrow 9B(16.71 MeV). For all of these states, a large channel radius (a > 10 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.Comment: 37 pages, 9 figures. Additional discussion of channel widths and radii. Matches published versio

Bell's Theorem from Moore's Theorem

It is shown that the restrictions of what can be inferred from classically-recorded observational outcomes that are imposed by the no-cloning theorem, the Kochen-Specker theorem and Bell's theorem also follow from restrictions on inferences from observations formulated within classical automata theory. Similarities between the assumptions underlying classical automata theory and those underlying universally-unitary quantum theory are discussed.Comment: 12 pages; to appear in Int. J. General System

Diffuse Gamma Rays from the Galactic Plane: Probing the "GeV Excess" and Identifying the "TeV Excess"

Pion decay gamma rays have long been recognized as a unique signature of hadronic cosmic rays and their interactions with the interstellar medium. We present a model-independent way of constraining this signal with observations of the Galactic Plane in diffuse gamma rays. We combine detections by the EGRET instrument at GeV energies and the Milagro Cherenkov detector at TeV energies with upper limits from KASCADE and CASA-MIA ground arrays at PeV energies. Such a long "lever arm", spanning at least six orders of magnitude in energy, reveals a "TeV excess" in the diffuse Galactic Plane gamma-ray spectrum. While the origin of this excess is unknown, it likely implies also enhanced TeV neutrino fluxes, significantly improving the prospects for their detection. We show that unresolved point sources are a possible source of the TeV excess. In fact, the spectra of the unidentified EGRET sources in the Milagro region must break between ~10 GeV and ~1 TeV to avoid strongly overshooting the Milagro measurement; this may have important implications for cosmic-ray acceleration. Finally, we use our approach to examine the recent suggestion that dark-matter annihilation may account for the observed excess in diffuse Galactic gamma-rays detected by EGRET at energies above 1 GeV. Within our model-independent approach, current data cannot rule this possibility in or out; however we point out how a long "lever arm" can be used to constrain the pionic gamma-ray component and in turn limit the "GeV excess" and its possible sources. Experiments such as HESS and MAGIC, and the upcoming VERITAS and GLAST, should be able to finally disentangle the main sources of the Galactic gamma rays.Comment: 26 pages, 3 figures, AASTeX. Comments welcom

Double layer charging driven carbon dioxide adsorption limits the rate of electrochemical carbon dioxide reduction on Gold.

Electrochemical CO[Formula: see text] reduction is a potential route to the sustainable production of valuable fuels and chemicals. Here, we perform CO[Formula: see text] reduction experiments on Gold at neutral to acidic pH values to elucidate the long-standing controversy surrounding the rate-limiting step. We find the CO production rate to be invariant with pH on a Standard Hydrogen Electrode scale and conclude that it is limited by the CO[Formula: see text] adsorption step. We present a new multi-scale modeling scheme that integrates ab initio reaction kinetics with mass transport simulations, explicitly considering the charged electric double layer. The model reproduces the experimental CO polarization curve and reveals the rate-limiting step to be *COOH to *CO at low&nbsp;overpotentials, CO[Formula: see text] adsorption at intermediate&nbsp;ones, and CO[Formula: see text] mass transport at high overpotentials. Finally, we show the Tafel slope to arise from the electrostatic interaction&nbsp;between the dipole of&nbsp;*CO[Formula: see text] and the interfacial field. This work highlights the importance of surface charging for electrochemical kinetics and mass transport

The Revival of Galactic Cosmic Ray Nucleosynthesis?

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.Comment: 25 pages, latex, 8 ps figures, figure 1 correcte

QCD near the Light Cone

Starting from the QCD Lagrangian, we present the QCD Hamiltonian for near light cone coordinates. We study the dynamics of the gluonic zero modes of this Hamiltonian. The strong coupling solutions serve as a basis for the complete problem. We discuss the importance of zero modes for the confinement mechanism.Comment: 32 pages, ReVTeX, 2 Encapsulated PostScript figure

Conservative upper limits on WIMP annihilation cross section from Fermi-LAT γ\gamma-rays

The spectrum of an isotropic extragalactic $\gamma$-ray background (EGB) has been measured by the Fermi-LAT telescope at high latitudes. Two new models for the EGB are derived from the subtraction of unresolved point sources and extragalactic diffuse processes, which could explain from 30% to 70% of the Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely due to the annihilation of dark matter (DM) particles in the Galactic halo, we obtain $conservative$ upper limits on their annihilation cross section \sigmav. Severe bounds on a possible Sommerfeld enhancement of the annihilation cross section are set as well. Finally, would {\sigmav} be inversely proportional to the WIMP velocity, very severe limits are derived for the velocity-independent part of the annihilation cross section.Comment: Proceedings of XII Taup Conference, Munich, September 201