A geometric basis for the standard-model gauge group

A geometric approach to the standard model in terms of the Clifford algebra Cl_7 is advanced. A key feature of the model is its use of an algebraic spinor for one generation of leptons and quarks. Spinor transformations separate into left-sided ("exterior") and right-sided ("interior") types. By definition, Poincare transformations are exterior ones. We consider all rotations in the seven-dimensional space that (1) conserve the spacetime components of the particle and antiparticle currents and (2) do not couple the right-chiral neutrino. These rotations comprise additional exterior transformations that commute with the Poincare group and form the group SU(2)_L, interior ones that constitute SU(3)_C, and a unique group of coupled double-sided rotations with U(1)_Y symmetry. The spinor mediates a physical coupling of Poincare and isotopic symmetries within the restrictions of the Coleman--Mandula theorem. The four extra spacelike dimensions in the model form a basis for the Higgs isodoublet field, whose symmetry requires the chirality of SU(2). The charge assignments of both the fundamental fermions and the Higgs boson are produced exactly.Comment: 17 pages, LaTeX requires iopart. Accepted for publication in J. Phys. A: Math. Gen. 9 Mar 2001. Typos correcte

Do galaxies that leak ionizing photons have extreme outflows?

To reionize the early universe, high-energy photons must escape the galaxies that produce them. It has been suggested that stellar feedback drives galactic outflows out of star-forming regions, creating low density channels through which ionizing photons escape into the inter-galactic medium. We compare the galactic outflow properties of confirmed Lyman continuum (LyC) leaking galaxies to a control sample of nearby star-forming galaxies to explore whether the outflows from leakers are extreme as compared to the control sample. We use data from the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure the equivalent widths and velocities of Si II and Si III absorption lines, tracing neutral and ionized galactic outflows. We find that the Si II and Si III equivalent widths of the LyC leakers reside on the low-end of the trend established by the control sample. The leakers' velocities are not statistically different than the control sample, but their absorption line profiles have a different asymmetry: their central velocities are closer to their maximum velocities. The outflow kinematics and equivalent widths are consistent with the scaling relations between outflow properties and host galaxy properties -- most notably metallicity -- defined by the control sample. Additionally, we use the Ly\alpha\ profiles to show that the Si II equivalent width scales with the Ly\alpha\ peak velocity separation. We determine that the low equivalent widths of the leakers are likely driven by low metallicities and low H I column densities, consistent with a density-bounded ionization region, although we cannot rule out significant variations in covering fraction. While we do not find that the LyC leakers have extreme outflow velocities, the low maximum-to-central velocity ratios demonstrate the importance of the acceleration and density profiles for LyC and Ly\alpha\ escape. [abridged]Comment: 17 pages, 8 Figures. Accepted for publication in Astronomy & Astrophysic

Provenance response to evolving palaeogeography recorded by Carboniferous sandstones in the northern Pennine Basin, UK

We are grateful to BGS for financial support with collection of Coal Measures samples while JIC was an Honorary Research Associate, to Alison & Barry Tymon for help with collection of many other samples, to Lee Clark for sample preparation, and John Still for help and advice with microprobe analyses. The manuscript was improved following insightful comments by Professor Christopher Fielding and an anonymous reviewer, and we are especially grateful to Professor Fielding for supplying additional palaeocurrent data supporting sediment transport from the west during the late Langsettian.Peer reviewe

A preliminary phylogenetic analysis of the Capsalidae (Platyhelminthes : Monogenea : Monopisthocotylea) inferred from large subunit rDNA sequences

Phylogenetic relationships within the Capsalidae (Monogenea) were examined using large subunit ribosomal DNA sequences from 17 capsalid species (representing 7 genera, 5 subfamilies), 2 outgroup taxa (Monocotylidae) plus Udonella caligorum (Udonellidae). Trees were constructed using maximum likelihood, minimum evolution and maximum parsimony algorithms. An initial tree, generated from sequences 315 bases long, suggests that Capsalinae, Encotyllabinae, Entobdellinae and Trochopodinae are monophyletic, but that Benedeniinae is paraphyletic. Analyses indicate that Neobenedenia, currently in the Benedeniinae, should perhaps be placed in a separate subfamily. An additional analysis was made which omitted 3 capsalid taxa (for which only short sequences were available) and all outgroup taxa because of alignment difficulties. Sequence length increased to 693 bases and good branch support was achieved. The Benedeniinae was again paraphyletic. Higher-level classification of the Capsalidae, evolution of the Entobdellinae and issues of species identity in Neobenedenia are discussed.I. D. Whittington, M. R. Deveney, J. A. T. Morgan, L. A. Chisholm and R. D. Adlar

Older and Younger Driver Performance at Complex Intersections: Implications for Using Perception-Response Time and Driving Simulation

Older drivers are at increased accident risk at intersections for a variety of maneuvers. To examine why, a study was conducted to assess older driver performance at complex intersections in a driving simulator. The University of Calgary Driving Simulator was used to test healthy older drivers (65-83, M = 71.4) and younger drivers (19-22, M = 20.7). Critical scenarios included the sudden appearance of a pedestrian in an intersection, a lastsecond yellow light, an unexpected change during a left, and a vehicle violating a stoplight. Older drivers had significantly higher perception response times (PRT) than younger drivers for the latter three of the four intersection scenarios. Analysis of specific maneuvers also revealed qualitative response differences between young and old groups. In contradiction to expectation, more older drivers ran the yellow light than younger drivers. The capability of older drivers to respond under time constraints is implicated. The utility of driving simulators to assess older driver performance at intersections was limited by the prevalence of simulator sickness

Older and Younger Driver Performance at Complex Intersections: Implications for Using Perception-Response Time and Driving Simulation

Older drivers are at increased accident risk at intersections for a variety of maneuvers. To examine why, a study was conducted to assess older driver performance at complex intersections in a driving simulator. The University of Calgary Driving Simulator was used to test healthy older drivers (65-83, M = 71.4) and younger drivers (19-22, M = 20.7). Critical scenarios included the sudden appearance of a pedestrian in an intersection, a lastsecond yellow light, an unexpected change during a left, and a vehicle violating a stoplight. Older drivers had significantly higher perception response times (PRT) than younger drivers for the latter three of the four intersection scenarios. Analysis of specific maneuvers also revealed qualitative response differences between young and old groups. In contradiction to expectation, more older drivers ran the yellow light than younger drivers. The capability of older drivers to respond under time constraints is implicated. The utility of driving simulators to assess older driver performance at intersections was limited by the prevalence of simulator sickness

Adiabatic transfer of light in a double cavity and the optical Landau-Zener problem

We analyze the evolution of an electromagnetic field inside a double cavity when the difference in length between the two cavities is changed, e.g. by translating the common mirror. We find that this allows photons to be moved deterministically from one cavity to the other. We are able to obtain the conditions for adiabatic transfer by first mapping the Maxwell wave equation for the electric field onto a Schroedinger-like wave equation, and then using the Landau-Zener result for the transition probability at an avoided crossing. Our analysis reveals that this mapping only rigorously holds when the two cavities are weakly coupled (i.e. in the regime of a highly reflective common mirror), and that, generally speaking, care is required when attempting a hamiltonian description of cavity electrodynamics with time-dependent boundary conditions.Comment: 24 pages, 18 figures. Version 2 includes a new section (Sec. VIII) on the regimes of validity of the Schroedinger-like equations and also of the adiabatic approximation, together with a new figure (Fig. 10). The discussion section (Sec. XI) has also been enhance

Once again on the equivalence theorem

We present the proof of the equivalence theorem in quantum field theory which is based on a formulation of this problem in the field-antifield formalism. As an example, we consider a model in which a different choices of natural finite counterterms is possible, leading to physically non-equivalent quantum theories while the equivalent theorem remains valid.Comment: 12 pages, LATEX, report number was correcte