7,369 research outputs found
CompHEP 4.4 - Automatic Computations from Lagrangians to Events
We present a new version of the CompHEP program (version 4.4). We describe
shortly new issues implemented in this version, namely, simplification of quark
flavor combinatorics for the evaluation of hadronic processes, Les Houches
Accord based CompHEP-PYTHIA interface, processing the color configurations of
events, implementation of MSSM, symbolical and numerical batch modes, etc. We
discuss how the CompHEP program is used for preparing event generators for
various physical processes. We mention a few concrete physics examples for
CompHEP based generators prepared for the LHC and Tevatron.Comment: The paper has been presented on IX International Workshop on Advanced
Computing and Analysis Techniques in Physics Research December 1-5, 2003.
KEK, Japan. 10 pages, 2 figure
Hidden Grassmann structure in the XXZ model V: sine-Gordon model
We study one-point functions of the sine-Gordon model on a cylinder. Our
approach is based on a fermionic description of the space of descendent fields,
developed in our previous works for conformal field theory and the sine-Gordon
model on the plane. In the present paper we make an essential addition by
giving a connection between various primary fields in terms of yet another kind
of fermions. The one-point functions of primary fields and descendants are
expressed in terms of a single function defined via the data from the
thermodynamic Bethe Ansatz equations.Comment: 36 pages. Some corrections are done in latest version, especially in
the subsection 10.
Modified Tetrahedron Equations and Related 3D Integrable Models
Using a modified version of the tetrahedron equations we construct a new
family of -state three-dimensional integrable models with commuting
two-layer transfer-matrices. We investigate a particular class of solutions to
these equations and parameterize them in terms of elliptic functions. The
corresponding models contain one free parameter -- an elliptic modulus.Comment: 26 pages, LaTeX fil
Hidden Grassmann Structure in the XXZ Model IV: CFT limit
The Grassmann structure of the critical XXZ spin chain is studied in the
limit to conformal field theory. A new description of Virasoro Verma modules is
proposed in terms of Zamolodchikov's integrals of motion and two families of
fermionic creation operators. The exact relation to the usual Virasoro
description is found up to level 6.Comment: 44 pages, 1 figure. Version 3: some corrections are don
Prospects of mass measurements for neutral MSSM Higgs bosons in the intense-coupling regime at a Linear Collider
We analyze the prospects for detecting the three neutral Higgs bosons of the
Minimal Supersymmetric extension of the Standard Model in the intense-coupling
regime at e+e- colliders. Due to the small mass differences between the Higgs
states in this regime and their relative large total decay widths, the
discrimination between the particles is challenging at the LHC and in some
cases even impossible. We propose to use the missing mass technique in the
Higgs-strahlung process in e+e- collisions to distinguish between the two
CP-even Higgs eigenstates h and H, relying on their b b-bar decay in the
b,b-bar,l+,l- event sample. Ah and AH associated production is then studied in
the 4b-jet event sample to probe the CP-odd A boson. At collider energies
sqrt(s) = 300 GeV and an integrated luminosity of 500 fb-1, accuracies in the
mass measurement of the CP-even Higgs bosons are expected to range from 100 to
300 MeV, while for the CP-odd A boson, accuracies of less than 500 MeV can be
obtained.Comment: 12 pages, 15 Postscript figure
Connecting lattice and relativistic models via conformal field theory
We consider the quantum group invariant XXZ-model. In infrared limit it
describes Conformal Field Theory with modified energy-momentum tensor. The
correlation functions are related to solutions of level -4 of qKZ equations. We
describe these solutions relating them to level 0 solutions. We further
consider general matrix elements (form factors) containing local operators and
asymptotic states. We explain that the formulae for solutions of qKZ equations
suggest a decomposition of these matrix elements with respect to states of
corresponding Conformal Field Theory .Comment: 22 pages, 1 figur
Simplification of Flavour Combinatorics in the Evaluation of Hadronic Processes
A serious computational problem in the evaluation of hadronic collision
processes is connected with the large number of partonic subprocesses included
in the calculation. These are from the quark and gluon content of the initial
hadrons, and from CKM quark mixing. For example, there are 180 subprocesses
which contribute to the +2jets process, and 292 subprocesses in +3jets
production at the LHC, even when quarks from only the first two generations are
taken into account.
We propose a simple modification of the rules for evaluation of cross
sections and distributions, which avoids multiplication of channels from the
mixture of quark states. The method is based on a unitary rotation of down
quarks, thus, transporting the mixing matrix elements from vertices of Feynman
diagrams to the parton distribution functions (PDF). As a result, one can
calculate cross sections with significantly fewer subprocesses. For the example
mentioned above, with the new rules, one need evaluate only 21 and 33
subprocesses respectively. The matrix elements of the subprocesses are
calculated without quark mixing but with a modified PDF convolution which
depends on the quark mixing angle, and on the topologies of gauge invariant
classes of diagrams. The proposed method has been incorporated into the CompHEP
program and checked with various examples.Comment: 10 pages (standard LaTeX code), 3 figures, 2 table
- …