7,967 research outputs found

### Gauge Invariant Classes of Feynman Diagrams and Applications for Calculations

In theories like SM or MSSM with a complex gauge group structure the complete
set of Feynman diagrams contributed to a particular physics process can be
splited to exact gauge invariant subsets. Arguments and examples given in the
review demonstrate that in many cases computations and analysis of the gauge
invariant subsets are important.Comment: To appear in the Proceedings of the Seventh International Workshop on
Advanced Computing and Analysis Technics in Physics Research (ACAT2000,
Fermilab, October 16-20, 2000); 3 page

### Modified tetrahedron equation and related 3D integrable models,II

This work is a continuation of paper (hep-th/9407146) where the Boltzmann
weights for the N-state integrable spin model on the cubic lattice has been
obtained only numerically. In this paper we present the analytical formulae for
this model in a particular case. Here the Boltzmann weights depend on six free
parameters including the elliptic modulus. The obtained solution allows to
construct a two-parametric family of the commuting two-layer transfer matrices.
Presented model is expected to be simpler for a further investigation in
comparison with a more general model mentioned above.Comment: 17 pages,LaTeX fil

### Optimized Neural Networks to Search for Higgs Boson Production at the Tevatron

An optimal choice of proper kinematical variables is one of the main steps in
using neural networks (NN) in high energy physics. Our method of the variable
selection is based on the analysis of a structure of Feynman diagrams
(singularities and spin correlations) contributing to the signal and background
processes. An application of this method to the Higgs boson search at the
Tevatron leads to an improvement in the NN efficiency by a factor of 1.5-2 in
comparison to previous NN studies.Comment: 4 pages, 4 figures, partially presented in proceedings of ACAT'02
conferenc

### Factorization of the finite temperature correlation functions of the XXZ chain in a magnetic field

We present a conjecture for the density matrix of a finite segment of the XXZ
chain coupled to a heat bath and to a constant longitudinal magnetic field. It
states that the inhomogeneous density matrix, conceived as a map which
associates with every local operator its thermal expectation value, can be
written as the trace of the exponential of an operator constructed from
weighted traces of the elements of certain monodromy matrices related to $U_q
(\hat{\mathfrak{sl}}_2)$ and only two transcendental functions pertaining to
the one-point function and the neighbour correlators, respectively. Our
conjecture implies that all static correlation functions of the XXZ chain are
polynomials in these two functions and their derivatives with coefficients of
purely algebraic origin.Comment: 35 page

### Infrared singularities in Landau gauge Yang-Mills theory

We present a more detailed picture of the infrared regime of Landau gauge
Yang-Mills theory. This is done within a novel framework that allows one to
take into account the influence of finite scales within an infrared power
counting analysis. We find that there are two qualitatively different infrared
fixed points of the full system of Dyson-Schwinger equations. The first extends
the known scaling solution, where the ghost dynamics is dominant and gluon
propagation is strongly suppressed. It features in addition to the strong
divergences of gluonic vertex functions in the previously considered uniform
scaling limit, when all external momenta tend to zero, also weaker kinematic
divergences, when only some of the external momenta vanish. The second solution
represents the recently proposed decoupling scenario where the gluons become
massive and the ghosts remain bare. In this case we find that none of the
vertex functions is enhanced, so that the infrared dynamics is entirely
suppressed. Our analysis also provides a strict argument why the Landau gauge
gluon dressing function cannot be infrared divergent.Comment: 29 pages, 25 figures; published versio

### Minimal Gauge Invariant Classes of Tree Diagrams in Gauge Theories

We describe the explicit construction of groves, the smallest gauge invariant
classes of tree Feynman diagrams in gauge theories. The construction is valid
for gauge theories with any number of group factors which may be mixed. It
requires no summation over a complete gauge group multiplet of external matter
fields. The method is therefore suitable for defining gauge invariant classes
of Feynman diagrams for processes with many observed final state particles in
the standard model and its extensions.Comment: 13 pages, RevTeX (EPS figures

### Quantum model of interacting ``strings'' on the square lattice

The model which is the generalization of the one-dimensional XY-spin chain
for the case of the two-dimensional square lattice is considered. The subspace
of the ``string'' states is studied. The solution to the eigenvalue problem is
obtained for the single ``string'' in cases of the ``string'' with fixed ends
and ``string'' of types (1,1) and (1,2) living on the torus. The latter case
has the features of a self-interacting system and looks not to be integrable
while the previous two cases are equivalent to the free-fermion model.Comment: LaTeX, 33 pages, 16 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

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