5,905 research outputs found
GR@PPA 2.7 event generator for / collisions
The GR@PPA event generator has been updated to version 2.7. This distribution
provides event generators for ( or ) + jets ( 4 jets), +
jets ( 2 jets) and QCD multi-jet ( 4 jets) production processes at
and collisions, in addition to the four bottom quark
productions implemented in our previous work (GR@PPA\_4b). Also included are
the top-pair and top-pair + jet production processes, where the correlation
between the decay products are fully reproduced at the tree level. Namely,
processes up to seven-body productions can be simulated, based on ordinary
Feynman diagram calculations at the tree level. In this version, the GR@PPA
framework and the process dependent matrix-element routines are separately
provided. This makes it easier to add further new processes, and allows users
to make a choice of processes to implement. This version also has several new
features to handle complicated multi-body production processes. A systematic
way to combine many subprocesses to a single base-subprocess has been
introduced, and a new method has been adopted to calculate the color factors of
complicated QCD processes. They speed up the calculation significantly.Comment: 21 pages, no figur
A Q-operator for the twisted XXX model
Taking the isotropic limit in a recent representation theoretic construction
of Baxter's Q-operators for the XXZ model with quasi-periodic boundary
conditions we obtain new results for the XXX model. We show that quasi-periodic
boundary conditions are needed to ensure convergence of the Q-operator
construction and derive a quantum Wronskian relation which implies two
different sets of Bethe ansatz equations, one above the other below the
"equator" of total spin zero. We discuss the limit to periodic boundary
conditions at the end and explain how this construction might be useful in the
context of correlation functions on the infinite lattice. We also identify a
special subclass of solutions to the quantum Wronskian for chains up to a
length of 10 sites and possibly higher.Comment: 19 page
Correcting the Colour-Dipole Cascade Model with Fixed Order Matrix Elements
An algorithm is presented in which the Colour-Dipole Cascade Model as
implemented in the Ariadne program is corrected to match the fixed order
tree-level matrix elements for e+e- -> n jets. The result is a full parton
level generator for e+e- annihilation where the generated states are correct on
tree-level to fixed order in alpha_S and to all orders with modified leading
logarithmic (MLLA) accuracy. In this paper, matrix elements are used up to
second order in alpha_S, but the scheme is applicable also for higher orders.
An improvement to also include exact virtual corrections to fixed order is
suggested and the possibility to extend the scheme to hadronic collisions is
discussed
Two-loop corrections to the correlator of tensor currents in gluodynamics
Results of evaluating the leading order corrections to the
correlator of tensor currents in pure gluodynamics are presented. These
corrections to the parton result for the correlator are not large numerically
that allows one to use perturbation theory for the analysis of the resonance
spectrum within the sum rules method.Comment: 10 pages, latex, no figure
Three Numerical Puzzles and the Top Quark's Chiral Weak-Moment
Versus the standard model's t --> W b decay helicity amplitudes, three
numerical puzzles occur at the 0.1 % level when one considers the amplitudes in
the case of an additional (f_M + f_E) coupling of relative strength 53 GeV. The
puzzles are theoretical ones which involve the t --> W b decay helicity
amplitudes in the two cases, the relative strength of this additional coupling,
and the observed masses of these three particles. A deeper analytic realization
is obtained for two of them. Equivalent realizations are given for the
remaining one. An empirical consequence of these analytic realizations is that
it is important to search for effects of a large chiral weak-moment of the
top-quark, the effective mass-scale is about 53 GeV. A full theoretical
resolution would include relating the origin of such a chiral weak-moment and
the mass generation of the top-quark, the W-boson, and probably the b-quark.Comment: 18 pages, 1 postscript table (revised to better explain notation,
model #1, add a little material...
Identifying the Higgs Boson in Electron--Photon Collisions
We analyze the production and detection of the Higgs boson in the next
generation of linear colliders operating in the mode. In
particular, we study the production mechanism , where one photon is generated via the laser
backscattering mechanism, while the other is radiated via the usual
bremsstrahlung process. We show that this is the most important mechanism for
Higgs boson production in a GeV collider for
M_H\raisebox{-.4ex}{\rlap{\sim}} \raisebox{.4ex}{>}140 GeV. We also study
the signals and backgrounds for detection of the Higgs in the different decay
channels, , , and , and suggest kinematical cuts to
improve the signature of an intermediate mass Higgs boson.Comment: (REVTEX 2.0, 12 pages and 9 figures available upon request, Preprint
MAD/PH/753
Report of the QCD Tools Working Group
We report on the activities of the ``QCD Tools for heavy flavors and new
physics searches'' working group of the Run II Workshop on QCD and Weak Bosons.
The contributions cover the topics of improved parton showering and comparisons
of Monte Carlo programs and resummation calculations, recent developments in
Pythia, the methodology of measuring backgrounds to new physics searches,
variable flavor number schemes for heavy quark electro-production, the
underlying event in hard scattering processes, and the Monte Carlo MCFM for NLO
processes.Comment: LaTeX, 47 pages, 41 figures, 10 tables, uses run2col.sty, to appear
in the Proceedings of the Workshop on "QCD and Weak Boson Physics in Run II",
Fermilab, March - November 199
Holonomy of the Ising model form factors
We study the Ising model two-point diagonal correlation function by
presenting an exponential and form factor expansion in an integral
representation which differs from the known expansion of Wu, McCoy, Tracy and
Barouch. We extend this expansion, weighting, by powers of a variable
, the -particle contributions, . The corresponding
extension of the two-point diagonal correlation function, , is shown, for arbitrary , to be a solution of the sigma
form of the Painlev{\'e} VI equation introduced by Jimbo and Miwa. Linear
differential equations for the form factors are obtained and
shown to have both a ``Russian doll'' nesting, and a decomposition of the
differential operators as a direct sum of operators equivalent to symmetric
powers of the differential operator of the elliptic integral . Each is expressed polynomially in terms of the elliptic integrals and . The scaling limit of these differential operators breaks the
direct sum structure but not the ``Russian doll'' structure. The previous -extensions, are, for singled-out values ( integers), also solutions of linear differential
equations. These solutions of Painlev\'e VI are actually algebraic functions,
being associated with modular curves.Comment: 39 page
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