29,038 research outputs found
Two-loop soft anomalous dimensions and NNLL resummation for heavy quark production
I present results for two-loop soft anomalous dimensions for heavy quark
production which control soft-gluon resummation at
next-to-next-to-leading-logarithm (NNLL) accuracy. I derive an explicit
expression for the exact result and study it numerically for top quark
production via e+ e- -> t tbar, and I construct a surprisingly simple but very
accurate approximation. I show that the two-loop soft anomalous dimensions with
massive quarks display a simple proportionality relation to the one-loop result
only in the limit of vanishing quark mass. I also discuss the extension of the
calculation to single top and top pair production in hadron colliders.Comment: 10 pages, 6 figures; improved form of the analytical result; equation
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A new N = 8 nonlinear supermultiplet
We construct a new off-shell , nonlinear
supermultiplet proceeding from the nonlinear realization of
the , superconformal group in its
supercoset . The irreducibility constraints for the
superfields automatically follow from appropriate covariant conditions on the
-valued Cartan superforms. We present the most general
sigma-model type action for supermultiplet. The relations
between linear and nonlinear supermultiplets and linear
vector supermultiplet are discussed.Comment: 15 pages, LaTeX file, PACS numbers: 11.30.Pb, 03.65.-
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