11,367 research outputs found
The contribution of O(alpha) radiative corrections to the renormalised anisotropy and application to general tadpole improvement schemes: addendum to "One loop calculation of the renormalised anisotropy for improved anisotropic gluon actions on a lattice" [hep-lat/0208010]
General O(alpha) radiative corrections to lattice actions may be interpreted
as counterterms that give additive contributions to the one-loop
renormalisation of the anisotropy. The effect of changing the radiative
coefficients is thus easily calculable. In particular, the results obtained in
a previous paper for Landau mean link improved actions apply in any tadpole
improvement scheme. We explain how this method can be exploited when tuning
radiatively improved actions. Efficient methods for self-consistently tuning
tadpole improvement factors are also discussed.Comment: 3 pages of revte
Contingent plan structures for spacecraft
Most current AI planners build partially ordered plan structures which delay decisions on action ordering. Such structures cannot easily represent contingent actions. A representation which can is presented. The representation has some other useful features: it provides a good account of the causal structure of a plan, can be used to describe disjunctive actions, and it offers a planner the opportunity of even less commitment than the classical partial order on actions. The use of this representation is demonstrated in an on-board spacecraft activity sequencing problem. Contingent plan execution in a spacecraft context highlights the requirements for a fully disjunctive representation, since communication delays often prohibit extensive ground-based accounting for remotely sensed information and replanning on execution failure
Tree-Level Amplitudes in N=8 Supergravity
We present an algorithm for writing down explicit formulas for all tree
amplitudes in N=8 supergravity, obtained from solving the supersymmetric
on-shell recursion relations. The formula is patterned after one recently
obtained for all tree amplitudes in N=4 super Yang-Mills which involves nested
sums of dual superconformal invariants. We find that all graviton amplitudes
can be written in terms of exactly the same structure of nested sums with two
modifications: the dual superconformal invariants are promoted from N=4 to N=8
superspace in the simplest manner possible--by squaring them--and certain
additional non-dual conformal gravity dressing factors (independent of the
superspace coordinates) are inserted into the nested sums. To illustrate the
procedure we give explicit closed-form formulas for all NMHV, NNMHV and NNNMV
gravity superamplitudes.Comment: 27 pages, 5 figures, v2: typos correcte
Kappa-symmetric deformations of M5-brane dynamics
We calculate the first supersymmetric and kappa-symmetric derivative
deformation of the M5-brane worldvolume theory in a flat eleven-dimensional
background. By applying cohomological techniques we obtain a deformation of the
standard constraint of the superembedding formalism. The first possible
deformation of the constraint and hence the equations of motion arises at cubic
order in fields and fourth order in a fundamental length scale . The
deformation is unique up to this order. In particular this rules out any
induced Einstein-Hilbert terms on the worldvolume. We explicitly calculate
corrections to the equations of motion for the tensor gauge supermultiplet.Comment: 17 pages. Additional comments in section
Spectral methods for modeling supersonic chemically reacting flow fields
A numerical algorithm was developed for solving the equations describing chemically reacting supersonic flows. The algorithm employs a two-stage Runge-Kutta method for integrating the equations in time and a Chebyshev spectral method for integrating the equations in space. The accuracy and efficiency of the technique were assessed by comparison with an existing implicit finite-difference procedure for modeling chemically reacting flows. The comparison showed that the procedure presented yields equivalent accuracy on much coarser grids as compared to the finite-difference procedure with resultant significant gains in computational efficiency
The one-loop six-dimensional hexagon integral and its relation to MHV amplitudes in N=4 SYM
We provide an analytic formula for the (rescaled) one-loop scalar hexagon
integral with all external legs massless, in terms of classical
polylogarithms. We show that this integral is closely connected to two
integrals appearing in one- and two-loop amplitudes in planar
super-Yang-Mills theory, and . The derivative of
with respect to one of the conformal invariants yields
, while another first-order differential operator applied to
yields . We also introduce some kinematic
variables that rationalize the arguments of the polylogarithms, making it easy
to verify the latter differential equation. We also give a further example of a
six-dimensional integral relevant for amplitudes in
super-Yang-Mills.Comment: 18 pages, 2 figure
Kappa-symmetric Derivative Corrections to D-brane Dynamics
We show how the superembedding formalism can be applied to construct
manifestly kappa-symmetric higher derivative corrections for the D9-brane. We
also show that all correction terms appear at even powers of the fundamental
length scale . We explicitly construct the first potential correction, which
corresponds to the kappa-symmetric version of the , which one
finds from the four-point amplitude of the open superstring.Comment: 20 pages. Minor changes, added reference
A new dawn? The Roman Catholic Church and environmental issues
This is a PDF version of an article published in New Blackfriars© 1997. The definitive version is available at www.blackwell-synergy.com.This article discusses the stance of the Roman Catholic Church on environmental issues and argues that the Church tends to stay on the fringe rather than get involved. Some of the ways in which Roman Catholic theologians have incorporated environmental issues into theological reflection is discussed, as are environmental challenges facing the Church in Britain (conservation, resources, biodiversity, animal welfare, biotechnology, cooperate/individual ethics, environmental justice, economics/policy development, and global issues)
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