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Low energy theorems and the SU(3)-flux-tube
Michael Rueter
Physics , 1996,
Abstract: The total energy and action, which is stored in the flux-tube between a static quark-antiquark pair, can be compared with the potential of the pair with the help of two low energy theorems. The flux-tube and the potential are calculated in the framework of the model of the stochastic vacuum. Using the low energy theorems we obtain consistency of the results and can predict the scale where the model describes the non-perturbative gluon dynamics of QCD.
Energy and Q^2 dependence of elastic vectormeson production and the proton structure function F_2
Michael Rueter
Physics , 1998, DOI: 10.1007/s100529801002
Abstract: In the framework of the Model of the Stochastic Vacuum elastic hadron-hadron scattering, photo- and electroproduction of vectormesons and also F_2(Q^2) can be well described at center of mass energy approximately 20 GeV. The scattering amplitude is derived by smearing the color dipole-dipole scattering, which is calculated nonperturbatively in the Model of the Stochastic Vacuum, with appropriate wavefunctions. For the considered processes the dipoles have extensions in the range of hadron sizes. We now extend this idea to small dipoles and high energies. The energy dependence is modeled in a phenomenological way: we assume that there a two pomerons, the soft- and the hard-pomeron, each being a simple pole in the complex angular plane. We couple dipoles of hadronic size to the soft-pomeron and small dipoles to the hard-pomeron. For small dipoles we take the perturbative gluon exchange into account. By that way we obtain an energy dependent dipole-dipole scattering amplitude which can be used for all the processes with the same parameters. We show that this approach can describe in addition to all the low energy results (20 GeV) also the HERA data for the considered processes in a large energy and Q^2 range. Especially the right transition from the soft to the hard behavior is observed.
Hadron structure and odderon exchange
Michael Rueter
Physics , 1996,
Abstract: We calculate the C=P=-1 contribution to high-energy scattering of hadrons in the framework of the model of the stochastic vacuum. In models, where the pomeron is generated by a two gluon exchange, this odderon contribution comes from a three gluon exchange and is much too large as compared to experimental data for pp- and $p\bar{p}$-scattering. In our model, where we have no quark-additivity, the hadron structure is very important. It is shown that a natural suppression of the odderon contribution is given by a diquark-structure of the nucleon.
Description of elastic vectormeson production and F_2 by two pomerons
Michael Rueter
Physics , 1998, DOI: 10.1016/S0920-5632(99)00145-0
Abstract: Using the Model of the Stochastic Vacuum many diffractive processes have been calculated by investigating the dipole-dipole scattering at a cm-energy of 20 GeV. In this work we extend the calculation to larger energies and small dipoles. We assume that there are two pomerons, the hard- and the soft-pomeron, which cause the different energy dependence for processes dominated by small or large dipoles. The physical processes are obtained by smearing the dipole-dipole amplitude with wavefunctions. For small dipoles the leading perturbative contribution is taken into account. By that way we can describe in addition to the already calculated low energy results (20 GeV) also the HERA data for the considered processes in nearly the whole energy and Q^2 range.
Comunidades vegetales y factores ambientales en los ca?adones costeros de Patagonia
Rueter,Bárbara; Bertolami,Miguel;
Ecolog?-a austral , 2010,
Abstract: the san jorge gulf district in patagonia has great interest for biodiversity conservation because it is subjected to intense mining and cattle raising. this paper describes the plant communities and their relation with environmental gradients in the coastal valleys of the eastern portion of the district. during three consecutive years, we measured plant composition and geographic, topographic, and soil environmental variables in 100 m2 plots. we identified eight plant communities grouped in three vegetation units: i) xerophytic scrub of nanofanerophytes, ii) xerophytic steppe of nanofanerophytes and hemicriptophytes, and iii) grassland of hydrophytes. these vegetation units were ordered across a gradient of soil and topography. two plant communities on coarsely textured soils (open and closed scrubs) were grouped at one end of the gradient, whereas one plant community on clay soils with high salinity (shrub steppes) was located at the other end. herbaceous steppes and herbaceous shrub steppes were located in an intermediate position of the gradient. the plant communities belonging to the xerophytic scrub of nanofanerophytes vegetation unit had the highest species richness and diversity. the soil (texture and salinity) and topographic gradients structured the vegetation units of these coastal valleys, as well as the distribution and diversity of plant communities.
Nucleon Structure and High Energy Scattering
Michael Rueter,H. G. Dosch
Physics , 1996, DOI: 10.1016/0370-2693(96)00490-X
Abstract: If the pomeron is generated by a two gluon exchange there is no a priori reason for a drastic suppression of three gluon exchange with negative parity and charge parity. This would lead to an unacceptably large difference between $p\,p$ and $p\, \bar{p}$ scattering. It is shown that a natural suppression of the $C$=$P$=--1 contribution to high energy scattering is given by a cluster structure of the nucleon.
SU(3) Flux Tubes in a Model of the stochastic Vacuum
M. Rueter H. G. Dosch
Physics , 1994, DOI: 10.1007/BF01496598
Abstract: We calculate the squared gluon field strengths of a heavy q-$\rm \bar{q}$-pair in the model of the stochastic vacuum. We observe that with increasing separation a chromoelectric flux tube is built. The properties of the emerging flux tube are investigated.
Diffractive color-dipole nucleon scattering
Michael Rueter,H. G. Dosch
Physics , 1997, DOI: 10.1103/PhysRevD.57.4097
Abstract: We determine the diffractive scattering amplitude of a color-dipole on a nucleon using a non-perturbative model of QCD which contains only parameters taken from low-energy physics. This allows to relate specific features of the confinement mechanisms with diffractive electro-production processes and structure functions. The agreement with phenomenological data is satisfactory.
STRING FORMATION IN THE MODEL OF THE STOCHASTIC VACUUM AND CONSISTENCY WITH LOW ENERGY THEOREMS
H. G. Dosch,O. Nachtmann,Michael Rueter
Physics , 1995,
Abstract: We re-derive and discuss two low energy theorems which relate the potential of a static quark-antiquark pair with the total energy and action stored in the flux tube between the sources. In lattice QCD these relations are known as Michael's sum-rules, but we give an essential correction to one of them. Then we relate the low energy theorems to the virial theorem for a heavy quark-antiquark bound state. Finally we compare the results for the flux tube formation, which have been calculated in the model of the stochastic vacuum, with the low energy theorems and obtain consistency. From this we conclude that the model describes the non perturbative gluon dynamics of QCD at a renormalization scale, where the strong coupling constant is given by $\al_s = 0.57$.
Two Photon Reactions at High Energies
A. Donnachie,H. G. Dosch,Michael Rueter
Physics , 1998, DOI: 10.1103/PhysRevD.59.074011
Abstract: Cross sections for the reactions gamma^(*) gamma^(*) --> hadrons and gamma^(*) gamma^(*) --> 2 vector mesons are calculated as functions of energy (sqrt(s) > 20 GeV) and photon virtualities. Good agreement with experiment is obtained for the total hadronic cross section and, after allowing for a valence-quark contribution from the hadronic part of the photon, with the photon structure function at small x. The cross section for vector meson production are shown to be experimentally accessible for moderate values of Q^2. This is sufficient to probe the nature of the hard pomeron which has recently been proposed.
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