Antiquark nuggets as dark matter: New constraints and detection prospects

Current evidence for dark matter in the universe does not exclude heavy composite nuclear-density objects consisting of bound quarks or antiquarks over a significant range of masses. Here we analyze one such proposed scenario, which hypothesizes antiquark nuggets with a range of log10(B) = 24-30 with specific predictions for spectral emissivity via interactions with normal matter. We find that, if these objects make up the majority of the dark matter density in the solar neighborhood, their radiation efficiency in solids is marginally constrained, due to limits from the total geothermal energy budget of the Earth. At allowed radiation efficiencies, the number density of such objects can be constrained to be well below dark matter densities by existing radio data over a mass range currently not restricted by other methods.Comment: 6 pages, 3 figures, revised references; submitted to PR

Crustal heat production in the Superior Province, Canadian Shield, and in North America inferred from heat flow data

International audienceMeasurements of heat flow and U, Th, K concentrations are used to determine the amount of heat generated in various belts of the Superior Province, the largest Archean craton on Earth. These data allow estimates of the average crustal heat production and indicate compositional differences between upper and lower crustal assemblages. The bulk average heat production of the Superior Province crust is 0.64 µW m-3 and is almost the same in different belts of slightly different ages, illustrating the remarkable uniformity of crust-building mechanisms. In the wider context of the North American continent, the bulk crustal heat production decreases from 1.0 µW m-3 in the oldest Slave Province to a minimum of 0.55 µW m-3 in the Paleo-Proterozoic Trans-Hudson Orogen. It increases in younger provinces, culminating with a high value of 1.05 µW m-3 in the Phanerozoic Appalachian Province. In all provinces, U and Th enrichment is systematically associated with sedimentary accumulations. A crustal differentiation index is obtained by calculating the ratio between the average values of heat production at the surface and in the bulk crust. The differentiation index is correlated with the bulk average heat production, which suggests that crustal differentiation processes are largely driven by internal radiogenic heat

Combined analysis of KamLAND and Borexino neutrino signals from Th and U decays in the Earth's interior

The KamLAND and Borexino experiments have detected electron antineutrinos produced in the decay chains of natural thorium and uranium (Th and U geoneutrinos). We analyze the energy spectra of current geoneutrino data in combination with solar and long-baseline reactor neutrino data, with marginalized three-neutrino oscillation parameters. We consider the case with unconstrained Th and U event rates in KamLAND and Borexino, as well as cases with fewer degrees of freedom, as obtained by successively assuming for both experiments a common Th/U ratio, a common scaling of Th+U event rates, and a chondritic Th/U value. In combination, KamLAND and Borexino can reject the null hypothesis (no geoneutrino signal) at 5 sigma. Interesting bounds or indications emerge on the Th+U geoneutrino rates and on the Th/U ratio, in broad agreement with typical Earth model expectations. Conversely, the results disfavor the hypothesis of a georeactor in the Earth's core, if its power exceeds a few TW. The interplay of KamLAND and Borexino geoneutrino data is highlighted.Comment: 12 pages, including 6 figure

The seismic signature of Upper‐Mantle Plumes: application to the Northern East African Rift

Several seismic and numerical studies proposed that below, some hotspots upper‐mantle plumelets rise from a thermal boundary layer below 660 km depth, fed by a deeper plume source. We recently found tomographic evidence of multiple upper‐mantle upwellings, spaced by several 100 km, rising through the transition zone below the northern East African Rift. To better test this interpretation, we run 3‐D numerical simulations of mantle convection for Newtonian and non‐Newtonian rheologies, for both thermal instabilities rising from a lower boundary layer, and the destabilization of a thermal anomaly placed at the base of the box (700–800 km depth). The thermal structures are converted to seismic velocities using a thermodynamic approach. Resolution tests are then conducted for the same P and S data distribution and inversion parameters as our traveltime tomography. The Rayleigh Taylor models predict simultaneous plumelets in different stages of evolution rising from a hot layer located below the transition zone, resulting in seismic structure that looks more complex than the simple vertical cylinders that are often anticipated. From the wide selection of models tested, we find that the destabilization of a 200 °C, 100 km thick thermal anomaly with a non‐Newtonian rheology, most closely matches the magnitude and the spatial and temporal distribution of the anomalies below the rift. Finally, we find that for reasonable upper‐mantle viscosities, the synthetic plume structures are similar in scale and shape to the actual low‐velocity anomalies, providing further support for the existence of upper‐mantle plumelets below the northern East African Rift

Geo-neutrinos: A systematic approach to uncertainties and correlations

Geo-neutrinos emitted by heat-producing elements (U, Th and K) represent a unique probe of the Earth interior. The characterization of their fluxes is subject, however, to rather large and highly correlated uncertainties. The geochemical covariance of the U, Th and K abundances in various Earth reservoirs induces positive correlations among the associated geo-neutrino fluxes, and between these and the radiogenic heat. Mass-balance constraints in the Bulk Silicate Earth (BSE) tend instead to anti-correlate the radiogenic element abundances in complementary reservoirs. Experimental geo-neutrino observables may be further (anti)correlated by instrumental effects. In this context, we propose a systematic approach to covariance matrices, based on the fact that all the relevant geo-neutrino observables and constraints can be expressed as linear functions of the U, Th and K abundances in the Earth's reservoirs (with relatively well-known coefficients). We briefly discuss here the construction of a tentative "geo-neutrino source model" (GNSM) for the U, Th, and K abundances in the main Earth reservoirs, based on selected geophysical and geochemical data and models (when available), on plausible hypotheses (when possible), and admittedly on arbitrary assumptions (when unavoidable). We use then the GNSM to make predictions about several experiments ("forward approach"), and to show how future data can constrain - a posteriori - the error matrix of the model itself ("backward approach"). The method may provide a useful statistical framework for evaluating the impact and the global consistency of prospective geo-neutrino measurements and Earth models.Comment: 17 pages, including 4 figures. To appear on "Earth, Moon, and Planets," Special Issue on "Neutrino Geophysics," Proceedings of Neutrino Science 2005 (Honolulu, Hawaii, Dec. 2005

Upper mantle velocity-temperature conversion and composition determined from seismic refraction and heat flow

International audience[1] We compile upper mantle P n velocities from seismic refraction/wide-angle reflection surveys in the southern Superior Province of the Canadian Shield and compare them with temperatures at the Moho deduced from heat flow data. Calculated Moho temperatures and P n velocities correlate well, showing that in this area, P n depends primarily on temperature. The obtained values of @V(P n)/@T depend weakly on the assumed value of Moho heat flow and are on the order of À6.0 Â 10 À4 ± 10% km s À1 K À1 , within the range of temperature derivatives obtained in laboratory studies of ultramafic rocks. Comparison between observed P n velocities and predicted values for several mineralogical models at Moho temperatures allows constraints on both the Moho heat flow and the shallow mantle composition. For all Moho heat flows, undepleted (clinopyroxene-rich) mantle compositions do not allow a good fit to the data. For depleted mantle compositions, temperatures consistent with the observed P n velocities correspond to values of Moho heat flow larger than 12 mW m À2. For our preferred Moho heat flow of 15 mW m À2 , the best fit mantle composition is slightly less depleted than models for average Archean subcontinental lithospheric mantle. This may be due to rejuvenation by melt-related metasomatism during the Keweenawan rifting event. The similarity in P n À T conversion factors estimated from this empirical large-scale geophysical study and those from laboratory data provides confidence in the absolute temperature values deduced from heat flow measurements and seismic studies. Citation: Perry, H. K. C., C. Jaupart, J.-C. Mareschal, and N. M. Shapiro (2006), Upper mantle velocity-temperature conversion and composition determined from seismic refraction and heat flow

The Newberry Deep Drilling Project (NDDP) workshop

The important scientific questions that will form the basis of a full proposal to drill a deep well to the ductile–brittle transition zone (T&gt;400&thinsp;°C) at Newberry Volcano, central Oregon state, USA, were discussed during an International Continental Drilling Program (ICDP) sponsored workshop held at the Oregon State University-Cascades campus in Bend, Oregon, from 10 to 13 September 2017. Newberry Volcano is one of the largest geothermal heat reservoirs in the USA and has been extensively studied for the last 40 years. The Newberry Deep Drilling Project (NDDP) will be located at an idle geothermal exploration well, NWG 46-16, drilled in 2008, 3500&thinsp;m deep and 340–374&thinsp;°C at bottom, which will be deepened another 1000 to 1300&thinsp;m to reach 500&thinsp;°C. The workshop concluded by setting ambitious goals for the NDDP: (1) test the enhanced geothermal system (EGS) above the critical point of water, (2) collect samples of rocks within the brittle–ductile transition, (3) investigate volcanic hazards, (4) study magmatic geomechanics, (5) calibrate geophysical imaging techniques, and (6) test technology for drilling, well completion, and geophysical monitoring in a very high-temperature environment. Based on these recommendations, a full drilling proposal was submitted in January 2018 to the ICDP for deepening an existing well. The next steps will be to continue building a team with project, technology, and investment partners to make the NDDP a reality.</p

Using dissolved H₂O in rhyolitic glasses to estimate palaeo-ice thickness during a subglacial eruption at Bláhnúkur(Torfajökull, Iceland)

The last decade has seen the refinement of a technique for reconstructing palaeo-ice thicknesses based on using the retained H2O and CO2 content in glassy eruptive deposits to infer quenching pressures and therefore ice thicknesses. The method is here applied to Bláhnúkur, a subglacially erupted rhyolitic edifice in Iceland. A decrease in water content from ~0.7 wt.% at the base to ~0.3 wt.% at the top of the edifice suggests that the ice was 400 m thick at the time of the eruption. As Bláhnúkur rises 350 m above the surrounding terrain, this implies that the eruption occurred entirely within ice, which corroborates evidence obtained from earlier lithofacies studies. This paper presents the largest data set (40 samples) so far obtained for the retained volatile contents of deposits from a subglacial eruption. An important consequence is that it enables subtle but significant variations in water content to become evident. In particular, there are anomalous samples which are either water-rich (up to 1 wt.%) or water-poor (~0.2 wt.%), with the former being interpreted as forming intrusively within hyaloclastite and the latter representing batches of magma that were volatile-poor prior to eruption. The large data set also provides further insights into the strengths and weaknesses of using volatiles to infer palaeo-ice thicknesses and highlights many of the uncertainties involved. By using examples from Bláhnúkur, the quantitative use of this technique is evaluated. However, the relative pressure conditions which have shed light on Bláhnúkur’s eruption mechanisms and syn-eruptive glacier response show that, despite uncertainties in absolute values, the volatile approach can provide useful insight into the mechanisms of subglacial rhyolitic eruptions, which have never been observed