Non-Associative Geometry and the Spectral Action Principle

Chamseddine and Connes have argued that the action for Einstein gravity, coupled to the SU(3)\times SU(2)\times U(1) standard model of particle physics, may be elegantly recast as the "spectral action" on a certain "non-commutative geometry." In this paper, we show how this formalism may be extended to "non-associative geometries," and explain the motivations for doing so. As a guiding illustration, we present the simplest non-associative geometry (based on the octonions) and evaluate its spectral action: it describes Einstein gravity coupled to a G_2 gauge theory, with 8 Dirac fermions (which transform as a singlet and a septuplet under G_2). This is just the simplest example: in a forthcoming paper we show how to construct more realistic models that include Higgs fields, spontaneous symmetry breaking and fermion masses.Comment: 24 pages, no figures, matches JHEP versio

A new algebraic structure in the standard model of particle physics

We introduce a new formulation of the real-spectral-triple formalism in non-commutative geometry (NCG): we explain its mathematical advantages and its success in capturing the structure of the standard model of particle physics. The idea, in brief, is to represent $A$ (the algebra of differential forms on some possibly-noncommutative space) on $H$ (the Hilbert space of spinors on that space), and to reinterpret this representation as a simple super-algebra $B=A\oplus H$ with even part $A$ and odd part $H$. $B$ is the fundamental object in our approach: we show that (nearly) all of the basic axioms and assumptions of the traditional real-spectral-triple formalism of NCG are elegantly recovered from the simple requirement that $B$ should be a differential graded $\ast$-algebra (or "$\ast$-DGA"). Moreover, this requirement also yields other, new, geometrical constraints. When we apply our formalism to the NCG traditionally used to describe the standard model of particle physics, we find that these new constraints are physically meaningful and phenomenologically correct. In particular, these new constraints provide a novel interpretation of electroweak symmetry breaking that is geometric rather than dynamical. This formalism is more restrictive than effective field theory, and so explains more about the observed structure of the standard model, and offers more guidance about physics beyond the standard model.Comment: 30 pages, no figures, matches JHEP versio

Scaling Evalutation of the Lattice Solid Model on the SGI Altix 3700

The Lattice Solid Model is a particle based method which has been successfully employed for simulating the fracturing of rocks, the dynamics of faults, earthquakes and gouge processes. However, results from initial simulations demonstrate that models consisting of only thousands of particles are inadequate to accurately reproduce the micro-physics of seismic phenomenon. Instead, models with millions or tens of millions of particles are required to produce realistic simulations. Parallel computing architectures, such as the SGI Altix 3700, provide the opportunity to solve much larger computational problems than traditional single processor systems. In order to take advantage of high performance systems, a Message Passing Interface version of the Lattice Solid Model has been implemented. Benchmarks, presented in this paper, demonstrate an 80% parallel efficiency for the parallel Lattice Solid Model on 128 processors of the SGI Altix 3700. These results, for a two--dimensional wave propagation problem, indicate the potential for the Lattice Solid Model to simulate more computationally challenging three-dimensional geophysical processes

Techniques in helical scanning, dynamic imaging and image segmentation for improved quantitative analysis with X-ray micro-CT

This paper reports on recent advances at the micro-computed tomography facility at the Australian National University. Since 2000 this facility has been a significant centre for developments in imaging hardware and associated software for image reconstruction, image analysis and image-based modelling. In 2010 a new instrument was constructed that utilises theoretically-exact image reconstruction based on helical scanning trajectories, allowing higher cone angles and thus better utilisation of the available X-ray flux. We discuss the technical hurdles that needed to be overcome to allow imaging with cone angles in excess of 60°. We also present dynamic tomography algorithms that enable the changes between one moment and the next to be reconstructed from a sparse set of projections, allowing higher speed imaging of time-varying samples. Researchers at the facility have also created a sizeable distributed-memory image analysis toolkit with capabilities ranging from tomographic image reconstruction to 3D shape characterisation. We show results from image registration and present some of the new imaging and experimental techniques that it enables. Finally, we discuss the crucial question of image segmentation and evaluate some recently proposed techniques for automated segmentation

X-ray attenuation models to account for beam hardening in computed tomography

We introduce a beam-hardening correction method for lab-based X-ray computed tomography (CT) by modifying existing iterative tomographic reconstruction algorithms. Our method simplifies the standard Alvarez-Macovski X-ray attenuation model [Phys. Med. Biol. 21, 733 (1976)] and is compatible with conventional (i.e., singlespectrum) CT scans. The sole modification involves a polychromatic projection operation, which is equivalent to applying a weighting that more closely matches the attenuation of polychromatic X-rays. Practicality is a priority, so we only require information about the X-ray spectrum and some constants relating to material properties. No other changes to the experimental setup or the iterative algorithms are necessary. Using reconstructions of simulations and several large experimental datasets, we show that this method is able to remove or reduce cupping, streaking, and other artefacts from X-ray beam hardening and improve the self-consistency of projected attenuation in CT. When the assumptions made in the simplifications are valid, the reconstructed tomogram can even be quantitative.Australian Research Council (LP150101040); partner company FEI (now Thermo-Fisher) through Linkage (Project LP150101040)

IMAGING OF PORE SCALE DISTRIBUTION OF FLUIDS AND WETTABILITY

ABSTRACT Wettability has a profound effect on reservoir recovery and productivity. It determines the microscopic distribution of fluids in the pore-space which, in turn, determine important global multiphase properties such as capillary pressure, relative permeability, residual saturation and resistivity index. Complexities in pore-space geometry, rock-fluid and fluidfluid interactions have limited descriptions of wettability to highly simplified model systems and wettability in real porous systems remains a poorly understood phenomenon. This paper utilizes two new techniques which have the potential to greatly improve our understanding of wettability in real porous systems. The first is a technique to reproducibly clean and modify the surface energy of clastic and carbonate cores to produce well defined wettability states. The second is a technique for directly imaging the pore-scale distribution of fluids in reservoir cores using high resolution tomography and a newly developed 3D registration technique which allows voxel perfect alignment of a set of images of the same core. We present results for a preliminary study of drainage and imbibition in Fontainebleau sandstone, sucrosic dolomite and oomoldic grainstone cores at well defined wettability states using air and water to demonstrate the applicability of the techniques. The imaged fluid distributions show that gas is preferentially located in larger pores with water occupying smaller pores. The gas saturations measured compare well with those calculated from the imaged fluid distributions. The imaged pore-scale fluid distributions are also compared with predictions based on computations made directly on dry images of the pore-space and in equivalent network models. The computations use simple percolation concepts to model the pore-scale distributions. Drainage saturations and fluid distributions compare well with invasion percolation. Imbibition fluid distributions compare well with ordinary percolation. The comparisons show, for the first time, the feasibility of testing the validity of network models for multi-phase flow by directly comparing model fluid saturations with imaged saturations in real systems on a pore-to-pore basis

TOI-2119: A transiting brown dwarf orbiting an active M-dwarf from NASA’s TESS mission

We report the discovery of TOI-2119b, a transiting brown dwarf (BD) that orbits and is completely eclipsed by an active M-dwarf star. Using light curve data from the Transiting Exoplanet Survey Satellite mission and follow-up high-resolution Doppler spectroscopic observations, we find the BD has a radius of $R_b = 1.08 \pm 0.03{\rm R_J}$, a mass of $M_b = 64.4 \pm 2.3{\rm M_J}$, an orbital period of $P = 7.200865 \pm 0.00002$ days, and an eccentricity of $e=0.337\pm 0.002$. The host star has a mass of $M_\star = 0.53 \pm 0.02{\rm M_\odot}$, a radius of $R_\star= 0.50 \pm 0.01{\rm R_\odot}$, an effective temperature of $T_{\rm eff} = 3621 \pm 48$K, and a metallicity of $\rm [Fe/H]=+0.06\pm 0.08$. TOI-2119b joins an emerging population of transiting BDs around M-dwarf host stars, with TOI-2119 being the ninth such system. These M-dwarf--brown dwarf systems typically occupy mass ratios near $q = M_b/M_\star \approx 0.1-0.2$, which separates them from the typical mass ratios for systems with transiting substellar objects and giant exoplanets that orbit more massive stars. The nature of the secondary eclipse of the BD by the star enables us to estimate the effective temperature of the substellar object to be $2030\pm 84$K, which is consistent with predictions by substellar evolutionary models.Comment: 14 pages, 13 figures, 4 tables, accepted in MNRA