63 research outputs found
Counting tree diagrams: asymptotic results for QCD-like theories
We discuss the enumeration of Feynman diagrams at tree order for processes
with external lines of different types. We show how this can be done by
iterating algebraic Schwinger-Dyson equations. Asymptotic estimates for very
many external lines are derived. Applications include QED, QCD and scalar QED,
and the asymptotic estimates are numerically confronted with the exact results.Comment: 16 page
Multi-jet Production in Hadron Collisions
The advent of high-energy hadron colliders necessitates efficient and
accurate computation of multi-jet production processes, both as QCD processes
in their own right and as backgrounds for other physics. The algorithm that
performs these tasks and a brief numerical study of multi-jet processes are
presented.Comment: 21 pages, 9 figure
Recursive actions for scalar theories
We introduce a class of self-interacting scalar theories in which the various
coupling contants obey a recursive relation. These imply a particularly simple
form for the generating function of the Feynman amplitudes with vanishing
external momenta, as well as for the effective potential. In addition we
discuss an interesting duality inherent in these models. Specializing to the
case of zero spacetime dimensions we find intriguing nullification properties
for the amplitudes.Comment: 28 pages, 2 figures Replaced contract numbe
Black hole gas in the early universe
We consider the early universe at temperatures close to the fundamental scale
of gravity (M_D << M_Planck) in models with extra dimensions. At such
temperatures a small fraction of particles will experience transplanckian
collisions that may result in microscopic black holes (BHs). BHs colder than
the environment will gain mass, and as they grow their temperature drops
further. We study the dynamics of a system (a black hole gas) defined by
radiation at a given temperature coupled to a distribution of BHs of different
mass. Our analysis includes the production of BHs in photon-photon collisions,
BH evaporation, the absorption of radiation, collisions of two BHs to give a
larger one, and the effects of the expansion. We show that the system may
follow two different generic paths depending on the initial temperature of the
plasma.Comment: 17 pages, version to appear in JCA
Thread-Scalable Evaluation of Multi-Jet Observables
A leading-order, leading-color parton-level event generator is developed for
use on a multi-threaded GPU. Speed-up factors between 150 and 300 are obtained
compared to an unoptimized CPU-based implementation of the event generator. In
this first paper we study the feasibility of a GPU-based event generator with
an emphasis on the constraints imposed by the hardware. Some studies of Monte
Carlo convergence and accuracy are presented for PP -> 2,...,10 jet observables
using of the order of 1e11 events.Comment: 16 pages, 5 figures, 3 table
Color-flow decomposition of QCD amplitudes
We introduce a new color decomposition for multi-parton amplitudes in QCD,
free of fundamental-representation matrices and structure constants. This
decomposition has a physical interpretation in terms of the flow of color,
which makes it ideal for merging with shower Monte-Carlo programs. The
color-flow decomposition allows for very efficient evaluation of amplitudes
with many quarks and gluons, many times faster than the standard color
decomposition based on fundamental-representation matrices. This will increase
the speed of event generators for multi-jet processes, which are the principal
backgrounds to signals of new physics at colliders.Comment: 23 pages, 11 figures, version to appear on Phys. Rev.
Improved Phase Space Treatment of Massive Multi-Particle Final States
In this paper the revised Kajantie-Byckling approach and improved phase space
sampling techniques for the massive multi-particle final states are presented.
The application of the developed procedures to the processes representative for
LHC physics indicates the possibility of a substantial simplification of
multi-particle phase space sampling while retaining a respectable weight
variance reduction and unweighing efficiencies in the event generation process.Comment: Minor stilistic changes, submitted to EPJ
A Tree-Loop Duality Relation at Two Loops and Beyond
The duality relation between one-loop integrals and phase-space integrals,
developed in a previous work, is extended to higher-order loops. The duality
relation is realized by a modification of the customary +i0 prescription of the
Feynman propagators, which compensates for the absence of the multiple-cut
contributions that appear in the Feynman tree theorem. We rederive the duality
theorem at one-loop order in a form that is more suitable for its iterative
extension to higher-loop orders. We explicitly show its application to two- and
three-loop scalar master integrals, and we discuss the structure of the
occurring cuts and the ensuing results in detail.Comment: 20 pages. Few typos corrected, some additional comments included,
Appendix B and one reference added. Final version as published in JHE
A note on the boundary contribution with bad deformation in gauge theory
Motivated by recently progresses in the study of BCFW recursion relation with
nonzero boundary contributions for theories with scalars and
fermions\cite{Bofeng}, in this short note we continue the study of boundary
contributions of gauge theory with the bad deformation. Unlike cases with
scalars or fermions, it is hard to use Feynman diagrams directly to obtain
boundary contributions, thus we propose another method based on the SYM theory. Using this method, we are able to write down a useful
on-shell recursion relation to calculate boundary contributions from related
theories. Our result shows the cut-constructibility of gauge theory even with
the bad deformation in some generalized sense.Comment: 16 pages, 7 figure
SUSY Ward identities for multi-gluon helicity amplitudes with massive quarks
We use supersymmetric Ward identities to relate multi-gluon helicity
amplitudes involving a pair of massive quarks to amplitudes with massive
scalars. This allows to use the recent results for scalar amplitudes with an
arbitrary number of gluons obtained by on-shell recursion relations to obtain
scattering amplitudes involving top quarks.Comment: 22 pages, references adde
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