The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum?

An inflationary gravitational wave background consistent with BICEP2 is difficult to reconcile with a simple power-law spectrum of primordial scalar perturbations. Tensor modes contribute to the temperature anisotropies at multipoles with $l\lesssim 100$, and this effect --- together with a prior on the form of the scalar perturbations --- was the source of previous bounds on the tensor-to-scalar ratio. We compute Bayesian evidence for combined fits to BICEP2 and Planck for three nontrivial primordial spectra: a) a running spectral index, b) a cutoff at fixed wavenumber, and c) a spectrum described by a linear spline with a single internal knot. We find no evidence for a cutoff, weak evidence for a running index, and significant evidence for a "broken" spectrum. Taken at face-value, the BICEP2 results require two new inflationary parameters in order to describe both the broken scale invariance in the perturbation spectrum and the observed tensor-to-scalar ratio. Alternatively, this tension may be resolved by additional data and more detailed analyses.Comment: 14 pages, 5 figures, 4 tables; v2: references added, discussion updated, matches published versio

The Knotted Sky I: Planck constraints on the primordial power spectrum

Using the temperature data from Planck we search for departures from a power-law primordial power spectrum, employing Bayesian model-selection and posterior probabilities. We parametrize the spectrum with $n$ knots located at arbitrary values of $\log{k}$, with both linear and cubic splines. This formulation recovers both slow modulations and sharp transitions in the primordial spectrum. The power spectrum is well-fit by a featureless, power-law at wavenumbers $k>10^{-3} \, \mathrm{Mpc}^{-1}$. A modulated primordial spectrum yields a better fit relative to $\Lambda$CDM at large scales, but there is no strong evidence for a departure from a power-law spectrum. Moreover, using simulated maps we show that a local feature at $k \sim 10^{-3} \, \mathrm{Mpc}^{-1}$ can mimic the suppression of large-scale power. With multi-knot spectra we see only small changes in the posterior distributions for the other free parameters in the standard $\Lambda$CDM universe. Lastly, we investigate whether the hemispherical power asymmetry is explained by independent features in the primordial power spectrum in each ecliptic hemisphere, but find no significant differences between them.Comment: 24 pages, 9 figures, 4 tables, 1 appendix; v2: references added, discussion updated, matches published versio

Testing for New Physics: Neutrinos and the Primordial Power Spectrum

We test the sensitivity of neutrino parameter constraints from combinations of CMB and LSS data sets to the assumed form of the primordial power spectrum (PPS) using Bayesian model selection. Significantly, none of the tested combinations, including recent high-precision local measurements of $\mathrm{H}_0$ and cluster abundances, indicate a signal for massive neutrinos or extra relativistic degrees of freedom. For PPS models with a large, but fixed number of degrees of freedom, neutrino parameter constraints do not change significantly if the location of any features in the PPS are allowed to vary, although neutrino constraints are more sensitive to PPS features if they are known a priori to exist at fixed intervals in $\log k$. Although there is no support for a non-standard neutrino sector from constraints on both neutrino mass and relativistic energy density, we see surprisingly strong evidence for features in the PPS when it is constrained with data from Planck 2015, SZ cluster counts, and recent high-precision local measurements of $\mathrm{H}_0$. Conversely combining Planck with matter power spectrum and BAO measurements yields a much weaker constraint. Given that this result is sensitive to the choice of data this tension between SZ cluster counts, Planck and $\mathrm{H}_0$ measurements is likely an indication of unmodeled systematic bias that mimics PPS features, rather than new physics in the PPS or neutrino sector.Comment: 23 pages, 9 figures, 8 tables; matches version published in JCA

Mechanisms of degassing at Nevado del Ruiz volcano, Colombia

Author Posting. © Geological Society, 2003. This article is posted here by permission of Geological Society for personal use, not for redistribution. The definitive version was published in Journal of the Geological Society 160 (2003): 507-521, doi:10.1144/0016-764902-028.Nevado del Ruiz volcano is an andesite stratovolcano located in the northern Andes of Colombia. The volcano erupted on 11 September 1985, 13 November 1985, and 1 September 1989. The last two eruptions emitted juvenile solid material. This paper examines the volatile and light lithophile trace element contents of melt inclusions and matrix glasses from this juvenile material, and proposes a model for degassing within the volcano. Major element distributions in the glasses show two evolutionary trends, with subsidiary points that lie between the two trends. The data suggest the existence of two separate magmas, which have interacted, mingled, and mixed during their ascent and eruption. Water contents in melt inclusions, as determined by secondary ionization mass spectrometric analysis, are generally low, averaging between 1.6 and 3.3 wt.%. Halogen concentrations in the glasses range from 400 to 1200 ppm for fluorine and from 1100 to 1500 ppm for chlorine. Sulphur contents are low, not exceeding 500 ppm, with most glasses containing <200 ppm. Lithium concentrations range from 20 to 40 ppm, beryllium from 1.5 to 2 ppm, and boron exhibits high variability from 30 to 100 ppm. The only significant difference between melt inclusions and matrix glasses is for water, with matrix glasses having significantly lower concentrations (<0.5 wt.%) than the melt inclusions. The generally elevated concentrations of boron in the magma may be a consequence of enrichment in the source region of the magma, i.e. by subduction of altered oceanic crust and/or sediments. Yet the large degree of boron heterogeneity in both melt inclusions and matrix glasses necessitates subsequent addition of boron at shallower depths as well, by the assimilation of crustal sedimentary rocks or by interaction with hydrothermal fluids. Evidence for pre-eruptive magma emplacement at shallow levels is provided by (1) anhydrous mineral assemblages of plagioclase and pyroxene, (2) high silica contents of glasses, and (3) low water contents in melt inclusions. When combined, these observations suggest a period of magma residence at shallow depths, probably <3 km beneath the summit of the volcano. A multistage model of magma transport and degassing involves alternating periods of magma ascent and magma ponding. Initially, volatile-bearing magma ascends from depths of 9–15 km, driven by buoyancy. During decompression, the magma loses gas, particularly CO2 and sulphur. The magma eventually ponds at its neutral buoyancy level. At this point, the gas-saturated magma cools and crystallizes, thereby liberating gas under isobaric conditions. As a result, CO2 is depleted from the magma whereas H2O and SiO2 are enriched. The H2O enrichment is caused by its increased solubility in the magma as CO2 is degassed, whereas SiO2 is enriched by fractional crystallization. The density of the magma decreases as the level of dissolved H2O increases, eventually causing the magma to become buoyant once more and to continue its ascent, either to erupt or to freeze at shallow depths.This work was funded with grants to J.S. by the Natural Sciences and Engineering Research Council of Canada and by the Fonds pour la formation de chercheurs et l’aide a` la recherche (Que´bec)

Community Perceptions Concerning Key Ecological Resources at Risk in Baringo District, Kenya

Key ecological resources in arid and semi-arid lands are often characterized by small patches of seasonal grazing and important water points that lend critical support to entire production systems. When key resources are degraded or lost, production systems can be badly compromised. The Baringo District of north-central Kenya is well known for enduring decades of environmental degradation and food relief. As an initial part of an effort to map and characterize key ecological resources at risk in Baringo, we interviewed 136 resident leaders from pastoral and agro-pastoral areas. We asked them to identify and rank their most vulnerable ecological resources, clarify why these resources have become compromised, and propose ideas for resource rehabilitation. Overall, pastoralists and agro-pastoralists ranked vulnerable resources differently. Climate and human factors were mentioned as being responsible for resource-related problems. When solutions to problems were discussed, respondents noted that government must play the critical role in resource rehabilitation. In contrast, they rarely proposed solutions based on their own initiative, and we interpreted this to suggest that the population in general has become overly dependent on outside forces to affect change. Resource rehabilitation efforts would require strong partnerships between government and resource users to be sustainable. How to forge and sustain such partnerships should be a focus of future research and development efforts

Degree of Sedentarization Affects Risks and Conflicts for the Waso Boran in Northern Kenya

The Waso Borana have lived for over a century in northern Kenya. In the last few decades, however, their ability to maintain their traditions has been severely challenged. Here we report survey results from 540 households in Isiolo District, stratified among three groups differing in terms of lifestyle: sedentary, semi-sedentary, and mobile. In some cases these groups vary with respect to important perceived risks, causes of natural-resource related conflict, and possible solutions to conflict. For example, sedentary respondents often noted concerns over land tenure problems, human diseases, and political incitement. Mobile respondents, in contrast, often noted primary concerns over drought, shortages of human food, and inappropriate water developments. Semi-sedentary households could reportedly evade some risks and conflicts better than the other groups by using short, opportunistic movements of people or livestock. Despite variation among groups in their perceptions of problems, it was generally agreed that control of weapons proliferation, promotion of appropriate resource-use policies, control over political incitement, and (in some cases) reduction of livestock numbers are important partial solutions. In conclusion, we feel that government has failed the Waso Boran in several respects. These include failures to provide external livelihood options to reduce local population pressure, a safe and secure production environment, and an appropriate and enforceable land use policy for the area. International coordination is also needed to address local problems that originate outside of Kenya

Collective Action Among Agro-pastoralists in Baringo District, Kenya: Identifying and Nurturing the Entrepreneurs

The rural population of Baringo District in the Rift Valley of north-central Kenya faces numerous challenges including widespread environmental degradation and poverty. The region has endured decades of failed development projects, proliferation of food aid, and has been studied extensively. We have recently undertaken a different approach focused on bottom-up participatory action research and outreach among the Il Chamus and Tugen ethnic communities. The objective is to explore new ways to empower local people via provision of information, novel experiences, and initial access to resources to allow them to envision an alternative future and implement their own activities to better-manage risks. Here we report on the first phase of this activity. Twelve potential entrepreneurs (six from each of the two ethnic groups) were carefully selected and sent on an extensive training and educational tour to Mwingi District in eastern Kenya. There they visited a variety of successful, community-led development projects. The tour helped convince the entrepreneurs of neglected opportunities in Baringo. They have since taken a lead in assisting their communities to form collective-action groups. The groups are now registered with the Kenya government and pursuing work plans aimed at improving their circumstances

Pb isotopic variability in melt inclusions from the EMI–EMII–HIMU mantle end-members and the role of the oceanic lithosphere

Melt inclusions from four individual lava samples representing the HIMU (Mangaia Island), EMI (Pitcairn Island) and EMII (Tahaa Island) end member components, have heterogeneous Pb isotopic composition larger than that defined by the erupted lavas in each island. The broad linear trend in ^(207)Pb/^(206)Pb–^(208)Pb/^(206)Pb space produced by the melt inclusions from Mangaia, Tahaa and fPitcairn samples reproduces the entire trend defined by the Austral chain, the Society islands and the Pitcairn island and seamount groups. The inclusions preserve a record of melt composition of far greater isotopic diversity than that sampled in whole rock basalts. These results can be explained by mixing of a common depleted component with the HIMU, EMI and EMII lavas, respectively. We favor a model that considers the oceanic lithosphere to be that common component. We suggest that the Pb isotopic compositions of the melt inclusions reflect wall rock reaction of HIMU, EMI and EMII melts during their percolation through the oceanic lithosphere. Under these conditions, the localized rapid crystallization of olivine from primitive basalt near the reaction zone would allow the entrapment of melt inclusions with different isotopic composition