12,904 research outputs found
Codimension zero superembeddings
Superembeddings which have bosonic codimension zero are studied in 3,4 and 6
dimensions. The worldvolume multiplets of these branes are off-shell vector
multiplets in these dimensions, and their self-interactions include a
Born-Infeld term. It is shown how they can be written in terms of standard
vector multiplets in flat superspace by working in the static gauge. The action
formula is used to determine both Green-Schwarz type actions and superfield
actions.Comment: Improved spelling, one reference adde
Gaussian quantum Monte Carlo methods for fermions
We introduce a new class of quantum Monte Carlo methods, based on a Gaussian
quantum operator representation of fermionic states. The methods enable
first-principles dynamical or equilibrium calculations in many-body Fermi
systems, and, combined with the existing Gaussian representation for bosons,
provide a unified method of simulating Bose-Fermi systems. As an application,
we calculate finite-temperature properties of the two dimensional Hubbard
model.Comment: 4 pages, 3 figures, Revised version has expanded discussion,
simplified mathematical presentation, and application to 2D Hubbard mode
Superpropagator and superconformal invariants
We construct a superpropagator in maximally supersymmetric Yang-Mills theory
which is invariant off-shell under a chiral half of supersymmetries. Motivated
by the duality with scattering amplitudes in this theory, we apply this
superpropagator to supersymmeytric Wilson loop on polygonal contours. By
performing explicit one-loop calculations we confirm the absence of anomalies
and verify the duality between the object under study and NMHV amplitudes.Comment: 8 pages, 3 figure
Modeling of supersonic reacting flow fields
A detailed understanding of the scramjet combustor flow field is critical to the achievement of a successful design. Even though the combustor flow field is quite complex, it can be realistically viewed as a collection of spatially developing and reacting supersonic mixing layers that are initially discrete, but that ultimately merge into larger more complex zones. These mixing layers begin downstream of a set of fuel injectors that introduce gaseous hydrogen in both a parallel and transverse direction into a supersonic air stream entering from the engine inlet. The behavior of the initial portion of the combustor flow, in the mixing layers near the fuel injectors, appears to be most critical, since this is where the mechanism for efficient high speed mixing must be established to achieve the required degree of combustion downstream. Because of the structure of the flow field in this initial portion of the combustor, a single supersonic, spatially developing and reacting mixing layer serves as an excellent physical model for the overall flow field. Even though this reacting mixing layer flow is geometrically simple, it can still be made to retain all of the fluid mechanical and chemical complexities present in the actual combustor flow field
A modeling technique for STOVL ejector and volume dynamics
New models for thrust augmenting ejector performance prediction and feeder duct dynamic analysis are presented and applied to a proposed Short Take Off and Vertical Landing (STOVL) aircraft configuration. Central to the analysis is the nontraditional treatment of the time-dependent volume integrals in the otherwise conventional control-volume approach. In the case of the thrust augmenting ejector, the analysis required a new relationship for transfer of kinetic energy from the primary flow to the secondary flow. Extraction of the required empirical corrections from current steady-state experimental data is discussed; a possible approach for modeling insight through Computational Fluid Dynamics (CFD) is presented
Differential equations for multi-loop integrals and two-dimensional kinematics
In this paper we consider multi-loop integrals appearing in MHV scattering
amplitudes of planar N=4 SYM. Through particular differential operators which
reduce the loop order by one, we present explicit equations for the two-loop
eight-point finite diagrams which relate them to massive hexagons. After the
reduction to two-dimensional kinematics, we solve them using symbol technology.
The terms invisible to the symbols are found through boundary conditions coming
from double soft limits. These equations are valid at all-loop order for double
pentaladders and allow to solve iteratively loop integrals given lower-loop
information. Comments are made about multi-leg and multi-loop integrals which
can appear in this special kinematics. The main motivation of this
investigation is to get a deeper understanding of these tools in this
configuration, as well as for their application in general four-dimensional
kinematics and to less supersymmetric theories.Comment: 25 pages, 7 figure
The role of leading twist operators in the Regge and Lorentzian OPE limits
We study two kinematical limits, the Regge limit and the Lorentzian OPE
limit, of the four-point function of the stress-tensor multiplet in Super
Yang-Mills at weak coupling. We explain how both kinematical limits are
controlled by the leading twist operators. We use the known expression of the
four-point function up to three loops, to extract the pomeron residue at
next-to-leading order. Using this data and the known form of pomeron spin up to
next-to-leading order, we predict the behaviour of the four-point function in
the Regge limit at higher loops. Specifically, we determine the leading log
behaviour at any loop order and the next-to-leading log at four loops. Finally,
we check the consistency of our results with conformal Regge theory. This leads
us to predict the behaviour around of the OPE coefficient of the spin
leading twist operator in the OPE of two chiral primary operators.Comment: 22+14 page
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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