74 research outputs found
Symmetry of Anomalous Dimension Matrices for Colour Evolution of Hard Scattering Processes
In a recent paper, Dokshitzer and Marchesini rederived the anomalous
dimension matrix for colour evolution of scattering, first derived
by Kidonakis, Oderda and Sterman. They noted a weird symmetry that it possesses
under interchange of internal (colour group) and external (scattering angle)
degrees of freedom and speculated that this may be related to an embedding into
a context that correlates internal and external variables such as string
theory.
In this short note, I point out another symmetry possessed by all the colour
evolution anomalous dimension matrices calculated to date. It is more prosaic,
but equally unexpected, and may also point to the fact that colour evolution
might be understood in some deeper theoretical framework. To my knowledge it
has not been pointed out elsewhere, or anticipated by any of the authors
calculating these matrices. It is simply that, in a suitably chosen colour
basis, they are complex symmetric matrices.Comment: 3 page
Color evolution of 2 -> 3 processes
The color structure needed for resummation of all colored 2 -> 3 processes is
calculated using multiplet inspired s-channel bases. In this way the resulting
matrices, describing the color structure, are guaranteed to obey simplifying
symmetries.Comment: 25 page
Symmetry of anomalous dimension matrices explained
In a previous paper, one of us pointed out that the anomalous dimension
matrices for all physical processes that have been calculated to date are
complex symmetric, if stated in an orthonormal basis. In this paper we prove
this fact and show that it is only true in a subset of all possible orthonormal
bases, but that this subset is the natural one to use for physical
calculations.Comment: 4 page
Circular embeddings of planar graphs in nonspherical surfaces
AbstractWe show that every 3-connected planar graph has a circular embedding in some nonspherical surface. More generally, we characterize those planar graphs that have a 2-representative embedding in some nonspherical surface
Gaps between Jets in the High Energy Limit
We use perturbative QCD to calculate the parton level cross section for the
production of two jets that are far apart in rapidity, subject to a limitation
on the total transverse momentum Q0 in the interjet region. We specifically
address the question of how to combine the approach which sums all leading
logarithms in Q/Q0 (where Q is the jet transverse momentum) with the BFKL
approach, in which leading logarithms of the scattering energy are summed. This
paper constitutes progress towards the simultaneous summation of all important
logarithms. Using an "all orders" matching, we are able to obtain results for
the cross section which correctly reproduce the two approaches in the
appropriate limits.Comment: 29 pages, 9 figures, minor corrections to text and improved figure
Color structure for soft gluon resummation - a general recipe
A strategy for calculating the color structure needed for soft gluon
resummation for processes with any number of colored partons is introduced
using a N_c --> infinity inspired basis. In this basis a general formalism can
be found at the same time as the calculations are simplified.
The advantages are illustrated by recalculating the soft anomalous dimension
matrix for the processes gg --> gg, q\qbar --> q \qbar g and q\qbar --> ggg.Comment: 16 page
Soft gluons in Higgs plus two jet production
We investigate the effects of an all order QCD resummation of soft gluon
emissions for Higgs boson production in association with two hard jets. We
consider both the gluon-gluon fusion and weak boson fusion processes and show
how to resum a large part of the leading logarithms in the jet veto scale. Our
resummation improves on previous analyses which also aim to include the effects
of multiple soft gluon radiation. In addition we calculate the interference
between weak boson fusion and gluon-gluon fusion and find that it is small.Comment: 15 pages and 5 figure
The resummation of inter-jet energy flow for gaps-between-jets processes at HERA
We calculate resummed perturbative predictions for gaps-between-jets
processes and compare to HERA data. Our calculation of this non-global
observable needs to include the effects of primary gluon emission (global
logarithms) and secondary gluon emission (non-global logarithms) to be correct
at the leading logarithm (LL) level. We include primary emission by calculating
anomalous dimension matrices for the geometry of the specific event definitions
and estimate the effect of non-global logarithms in the large limit. The
resulting predictions for energy flow observables are consistent with
experimental data.Comment: 31 pages, 4 figures, 2 table
Jet vetoing at the LHC
We study the effect of a veto on additional jets in the rapidity region
between a pair of high transverse momentum jets at the LHC. We aim to sum the
most important logarithms in the ratio of the jet transverse momentum to the
veto scale and to that end we attempt to assess the significance of the
super-leading logarithms that appear at high orders in the perturbative
expansion. We also compare our results to those of HERWIG++, in an attempt to
ascertain the accuracy of the angular ordered parton shower. We find that there
are large corrections that arise for large enough jet transverse momenta as a
consequence of Coulomb gluon exchanges.Comment: 25 page
Towards Jetography
As the LHC prepares to start taking data, this review is intended to provide
a QCD theorist's understanding and views on jet finding at hadron colliders,
including recent developments. My hope is that it will serve both as a primer
for the newcomer to jets and as a quick reference for those with some
experience of the subject. It is devoted to the questions of how one defines
jets, how jets relate to partons, and to the emerging subject of how best to
use jets at the LHC.Comment: 95 pages, 28 figures, an extended version of lectures given at the
CTEQ/MCNET school, Debrecen, Hungary, August 2008; v2 includes additional
discussion in several places, as well as other clarifications and additional
references
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