3,002 research outputs found
Subtraction method of computing QCD jet cross sections at NNLO accuracy
We present a general subtraction method for computing radiative corrections
to QCD jet cross sections at next-to-next-to-leading order accuracy. The steps
needed to set up this subtraction scheme are the same as those used in
next-to-leading order computations. However, all steps need non-trivial
modifications, which we implement such that that those can be defined at any
order in perturbation theory. We give a status report of the implementation of
the method to computing jet cross sections in electron-positron annihilation at
the next-to-next-to-leading order accuracy.Comment: 6 pages, talk given at the conference "Loops and Legs in Quantum
Field Theory", Sondershausen, April 200
Antenna Factorization in Strongly-Ordered Limits
When energies or angles of gluons emitted in a gauge-theory process are small
and strongly ordered, the emission factorizes in a simple way to all orders in
perturbation theory. I show how to unify the various strongly-ordered soft,
mixed soft-collinear, and collinear limits using antenna factorization
amplitudes, which are generalizations of the Catani--Seymour dipole
factorization function.Comment: 21 pages, 8 figures; final Phys Rev version, corrected definition of
multiple-emission recosnstruction functions for strongly-ordered limit, added
appendix with new form of double-emission antenna function valid in
strongly-ordered limi
The triple collinear limit of one-loop QCD amplitudes
We consider the singular behaviour of one-loop QCD matrix elements when
several external partons become simultaneously parallel. We present a new
factorization formula that describes the singular collinear behaviour directly
in colour space. The collinear singularities are embodied in
process-independent splitting matrices that depend on the momenta, flavours,
spins and colours of the collinear partons. We give the general structure of
the infrared and ultraviolet divergences of the one-loop splitting matrices. We
also present explicit one-loop results for the triple collinear splitting, , of a quark and a quark--antiquark pair of different
flavours. The one-loop triple collinear splitting is one of the ingredients
that can be used to compute the evolution of parton distributions at the
next-to-next-to-leading order in QCD perturbation theory.Comment: 11 pages, 1 figure, uses axodraw. Final version to appear in
Phys.Lett.B. One reference adde
Infrared finite cross sections at NNLO
I discuss methods for the cancellation of infrared divergences at NNLO.Comment: 5 pages, talk given at Loops and Legs 2004, Zinnowitz, German
All-Multiplicity One-Loop Corrections to MHV Amplitudes in QCD
We compute the complete one-loop corrections to the simplest class of QCD
gluon amplitudes, those with two color-adjacent opposite-helicity external
particles. We present results for an arbitrary number of external legs. The
computation uses the recently-developed on-shell recursion relations for the
rational parts, along with older unitarity-based results for the cut-containing
terms.Comment: 5 pages; corrected typos, minor text addition; final Phys Rev versio
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