ALBERT

Description: A large data set of surface-wave phase anomalies, body-wave travel times, normal-mode splitting functions and long-period waveforms is used to investigate the scaling between shear velocity, density and compressional velocity in the Earth's mantle. We introduce a methodology that allows construction of joint models with various levels of scaling complexity ( , ), in order to detect seismological signatures of chemical heterogeneity. We demonstrate that the datasets considered cannot be fit concurrently with a uniform ν or a positive and uniform ϱ throughout the mantle. The variance reductions to P-wave travel times and v P -sensitive modes are up to 40 percent higher with our preferred model of anisotropic shear and compressional velocity than the recent anisotropic shear-velocity model S362ANI+M, which was constructed assuming a uniform ν throughout the mantle. Several features reported in earlier tomographic studies persist after the inclusion of new and larger data sets; anti-correlation between bulk-sound and shear velocities in the lowermost mantle as well as an increase in ν with depth in the lower mantle are largely independent of the regularization scheme. When correlations between density and shear-velocity variations are imposed in the lowermost mantle, variance reductions of several spheroidal and toroidal modes deteriorate by as much as 40 percent. Recent measurements of the splitting of 0 S 2 , in particular, are largely incompatible with perfectly correlated shear-velocity and density heterogeneity throughout the mantle. A way to significantly improve the fits to various data sets is by allowing independent density perturbations in the lowermost mantle. Our preferred joint model consists of denser-than-average anomalies (∼1 % peak-to-peak) at the base of the mantle roughly coincident with the low-velocity superplumes. The relative variation of shear velocity, density and compressional velocity in our study disfavors a purely thermal contribution to heterogeneity in the lowermost mantle, with implications for the long-term stability and evolution of superplumes.

Description: Author(s): A. Ekström, G. R. Jansen, K. A. Wendt, G. Hagen, T. Papenbrock, B. D. Carlsson, C. Forssén, M. Hjorth-Jensen, P. Navrátil, and W. Nazarewicz With the goal of developing predictive ab initio capability for light and medium-mass nuclei, two-nucleon and three-nucleon forces from chiral effective field theory are optimized simultaneously to low-energy nucleon-nucleon scattering data, as well as binding energies and radii of few-nucleon syste... [Phys. Rev. C 91, 051301] Published Fri May 01, 2015

Description: Author(s): S. Binder, A. Ekström, G. Hagen, T. Papenbrock, and K. A. Wendt We develop interactions from chiral effective field theory (EFT) that are tailored to the harmonic oscillator basis. As a consequence, ultraviolet convergence with respect to the model space is implemented by construction and infrared convergence can be achieved by enlarging the model space for the … [Phys. Rev. C 93, 044332] Published Mon Apr 25, 2016

Description: Author(s): A. Bansal, S. Binder, A. Ekström, G. Hagen, G. R. Jansen, and T. Papenbrock We compute the medium-mass nuclei O 16 and Ca 40 using pion-less effective field theory (EFT) at next-to-leading order (NLO). The low-energy coefficients of the EFT Hamiltonian are adjusted to experimental data for nuclei with mass numbers A = 2 and 3, or alternatively to results from lattice quantum ch... [Phys. Rev. C 98, 054301] Published Thu Nov 01, 2018

Description: Author(s): A. Ekström, G. Hagen, T. D. Morris, T. Papenbrock, and P. D. Schwartz We construct a nuclear interaction in chiral effective field theory with explicit inclusion of the Δ -isobar Δ ( 1232 ) degree of freedom at all orders up to next-to-next-to-leading order (NNLO). We use pion-nucleon ( π N ) low-energy constants (LECs) from a Roy-Steiner analysis of π N scattering data, opti... [Phys. Rev. C 97, 024332] Published Mon Feb 26, 2018