Several recent studies have demonstrated the importance of crustal corrections when inverting surface wave data to model lateral variations in mantle radial anisotropy. It has also been shown that the choice of the prior crustal model to correct the data can strongly influence the anisotropy model and potentially lead to different geodynamic interpretations. In comparing tomographic models of radial anisotropy obtained from different crustal corrections, these studies did not, however, determine quantitative model uncertainties. Nevertheless, mantle models resulting from different prior crustal corrections are statistically different only if the posterior model errors stemming from the non-uniqueness of the inverse problem are smaller than the effect of the crustal correction itself. Here, we applied a model space search approach to global fundamental and higher mode Rayleigh and Love wave phase velocity maps to determine reliable, quantitative model uncertainties on seismic velocities and radial anisotropy. The technique employed enabled us to describe the model space with a posterior probability density function, and therefore to test whether models obtained from different crustal corrections are statistically different. We thus assessed the significance of the choice of the crustal model by comparing the posterior model errors to the differences in mantle structure resulting from different crustal corrections. We tested prior crustal models CRUST2.0, CRUST1.0, and 3SMAC. Our study shows that the use of prior crustal corrections from different crustal models yields significant discrepancies in mantle velocities around 50 km depth and in radial anisotropy down to 100 km. The impact of the crustal correction on radial anisotropy can extend down to 250 km in some locations.We found that choosing 3SMAC instead of the other crustal models has a stronger influence on the mantle model, but that CRUST1.0 and CRUST2.0 yield statistically identical anisotropy models at all depths, except at a few grid cells. Importantly, the effect of the crustal model is most significant in continental regions and not so much beneath oceans, which has important consequences for determining the depth of continental roots. Our results therefore suggest that improving constraints on crustal structure in continents is essential for our understanding of continent formation. Our work also demonstrates that the prior crustal model does not significantly affect radial anisotropy and velocities at depths greater than 100 km. This implies that if geodynamic interpretations of radial anisotropy below 100 km depth were to account for tomographic model uncertainties, they would not depend on the choice of the prior crustal model. It is therefore important for geodynamicists and seismologists to work in concert and to put effort into determining quantitative tomographic model uncertainties before interpreting the results. Our results also caution against the use of 3SMAC to correct surface wave data for studies of the continental lithosphere, and suggest that the solid Earth community would benefit from putting some efforts toward building a revised 3SMAC. The discrepancies between mantle models built based on 3SMAC crustal corrections and those based on CRUST1.0 or CRUST2.0 should also help shed light on the validity of the geodynamical assumptions made in the construction of models like 3SMAC.

© The Authors 2015. Several recent studies have demonstrated the importance of crustal corrections when inverting surface wave data tomodel lateral variations in mantle radial anisotropy. It has also been shown that the choice of the prior crustal model to correct the data can strongly influence the anisotropy model and potentially lead to different geodynamic interpretations. In comparing tomographic models of radial anisotropy obtained from different crustal corrections, these studies did not, however, determine quantitative model uncertainties. Nevertheless, mantle models resulting from different prior crustal corrections are statistically different only if the posterior model errors stemming from the non-uniqueness of the inverse problem are smaller than the effect of the crustal correction itself. Here, we applied a model space search approach to global fundamental and higher mode Rayleigh and Love wave phase velocity maps to determine reliable, quantitative model uncertainties on seismic velocities and radial anisotropy. The technique employed enabled us to describe the model space with a posterior probability density function, and therefore to test whether models obtained from different crustal corrections are statistically different. We thus assessed the significance of the choice of the crustal model by comparing the posterior model errors to the differences in mantle structure resulting from different crustal corrections. We tested prior crustal models CRUST2.0, CRUST1.0 and 3SMAC. Our study shows that the use of prior crustal corrections from different crustal models yields significant discrepancies in mantle velocities around 50 km depth and in radial anisotropy down to 100 km. The impact of the crustal correction on radial anisotropy can extend down to 250 km in some locations.We found that choosing 3SMAC instead of the other crustal models has a stronger influence on the mantle model, but that CRUST1.0 and CRUST2.0 yield statistically identical anisotropy models at all depths, except at a few grid cells. Importantly, the effect of the crustal model is most significant in continental regions and not so much beneath oceans, which has important consequences for determining the depth of continental roots. Our results therefore suggest that improving constraints on crustal structure in continents is essential for our understanding of continent formation. Our work also demonstrates that the prior crustal model does not significantly affect radial anisotropy and velocities at depths greater than 100 km. This implies that if geodynamic interpretations of radial anisotropy below 100 km depth were to account for tomographic model uncertainties, they would not depend on the choice of the prior crustal model. It is therefore important for geodynamicists and seismologists to work in concert and to put effort into determining quantitative tomographic model uncertainties before interpreting the results. Our results also caution against the use of 3SMAC to correct surface wave data for studies of the continental lithosphere and suggest that the solid Earth community would benefit from putting some efforts towards building a revised 3SMAC. The discrepancies between mantle models built based on 3SMAC crustal corrections and those based on CRUST1.0 or CRUST2.0 should also help shed light on the validity of the geodynamical assumptions made in the construction of models like 3SMAC.

The boundary between the lithosphere and asthenosphere is associated with a platewide high-seismic velocity "lid" overlying lowered velocities, consistent with thermal models. Seismic body waves also intermittently detect a sharp velocity reduction at similar depths, the Gutenberg (G) discontinuity, which cannot be explained by temperature alone. We compared an anisotropic tomography model with detections of the G to evaluate their context and relation to the lithosphere-asthenosphere boundary (LAB). We find that the G is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled LAB, implying that the two are not equivalent interfaces. The origin of the G is a result of frozen-in lithospheric structures, regional compositional variations of the mantle, or dynamically perturbed LAB.

© 2017 IOP Publishing Ltd and Sissa Medialab srl. We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos.

A search for the rare decay D0→μ+μ- is performed using a data sample, corresponding to an integrated luminosity of 0.9fb-1, of pp collisions collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The observed number of events is consistent with the background expectations and corresponds to an upper limit of B(D0→μ+μ-)<6.2(7.6)×10-9 at 90% (95%) confidence level. This result represents an improvement of more than a factor twenty with respect to previous measurements. © 2013 CERN.