61,296 research outputs found
Reconstructing the geometric structure of a Riemannian symmetric space from its Satake diagram
The local geometry of a Riemannian symmetric space is described completely by
the Riemannian metric and the Riemannian curvature tensor of the space. In the
present article I describe how to compute these tensors for any Riemannian
symmetric space from the Satake diagram, in a way that is suited for the use
with computer algebra systems. As an example application, the totally geodesic
submanifolds of the Riemannian symmetric space SU(3)/SO(3) are classified.
The submission also contains an example implementation of the algorithms and
formulas of the paper as a package for Maple 10, the technical documentation
for this implementation, and a worksheet carrying out the computations for the
space SU(3)/SO(3) used in the proof of Proposition 6.1 of the paper.Comment: 23 pages, also contains two Maple worksheets and technical
documentatio
Threshold expansion of massive coloured particle cross sections
Pair production of massive coloured particles in hadron collisions is
accompanied by potentially large radiative corrections related to the
suppression of soft gluon emission and enhanced Coulomb exchange near the
production threshold. We recently developed a framework to sum both series of
corrections for the partonic cross section using soft-collinear and
non-relativistic effective theory. If it can be argued that the resummed cross
section approximates the complete result over a significant kinematic range, an
improvement of the hadronic cross section results, even when the production is
not kinematically constrained to the threshold. This is discussed here for the
case of top quark production.Comment: 5 pages, to appear in: Proceedings of the 10th DESY Workshop on
Elementary Particle Theory: Loops and Legs in Quantum Field Theory 2010,
W\"orlitz, Germany, 25-30 Apr 201
An assessment and validation study of nuclear reactors for low power space applications
The feasibility and safety of six conceptual small, low power nuclear reactor designs was evaluated. Feasibility evaluations included the determination of sufficient reactivity margins for seven years of full power operation and safe shutdown as well as handling during pre-launch assembly phases. Safety evaluations were concerned with the potential for maintaining subcritical conditions in the event of launch or transportation accidents. These included water immersion accident scenarios both with and without water flooding the core. Results show that most of the concepts can potentially meet the feasibility and safety requirements; however, due to the preliminary nature of the designs considered, more detailed designs will be necessary to enable these concepts to fully meet the safety requirements
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