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

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

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

Higgs-radion similarity in production processes involving off-shell fermions

The appearance of the radion field, which is associated with the spin-0 metric fluctuations combined in some manner with the scalar stabilizing field, and of the radion, the corresponding lowest Kaluza-Klein (KK) mode, is a generic prediction of stabilized brane world models. In such models the radion plays the role of the dilaton, and its mass may be somewhat smaller than that of all the KK modes of other particles propagating in the multidimensional bulk. Due to its origin, the radion couples to the trace of the energy-momentum tensor of the Standard Model, the interaction Lagrangian of the radion and the Standard Model fermions being similar to that of the SM Higgs-fermion interactions except for additional terms, which come into play only in the case of off-shell fermions. In the present paper it is shown that all the contributions to perturbative amplitudes of physical processes due to these additional terms are canceled out for both massless and massive off-shell fermions. Thus the additional fermion-radion terms in the interaction Lagrangian do not alter any production and decay properties of the radion compared to those of the Higgs boson.Comment: 13 pages, 3 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

Single top quarks at the Fermilab Tevatron

We present a calculation of the single top quark cross section for proton-antiproton interactions with sqrt(s) = 1.8 TeV at the Fermilab Tevatron collider. We examine the effects of top mass, parton distribution functions, QCD scale, and collision energy, on each of the component production mechanisms, and study the kinematic distributions for standard model electroweak production. At the upgraded Tevatron with sqrt(s) = 2.0 TeV and high luminosity, it will be possible to test the nature of the Wtb coupling using single top production. We estimate the sensitivity to measure the single top cross section, and thus to directly measure V_tb and the top quark partial width. We show what happens to the V_tb measurement when an anomalous (V+A) component is added to the Wtb coupling, and how the top quark polarization affects the kinematic distributions.Comment: 31 pages including 11 figure

Invisible Higgs in weak bosons associative production with heavy quarks at LHC: probing mass and width

New physics coupled to the Higgs boson may hide it in the standard decay channels to be investigated at LHC. We consider the models where new invisible dominant decay modes of the Higgs boson are responsible for this hiding. We propose to study at LHC the weak boson production associated with heavy quarks: our analysis revealed that boson pair invariant mass distribution is sensitive to both mass and width of the invisible Higgs boson, if it is not too far from the weak boson pair threshold. We present tree-level results for the most relevant cases of top quarks and of bottom quarks in Standard Model extensions with large $b$-quark Yukawa coupling. We argue that QCD corrections do not spoil these results allowing for unambiguous extraction of the Higgs boson mass and width from the analysis of large enough amount of data.Comment: 26 pages, 14 figures, references adde

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 $W$+2jets process, and 292 subprocesses in $W$+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

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