Off-Shell Scattering Amplitudes for WW Scattering and the Role of the Photon Pole

We derive analytic expressions for high energy $2 \to 2$ off-shell scattering amplitudes of weak vector bosons. They are obtained from six fermion final states in processes of the type $e^+ e^- \to \bar\nu_e + (WW) + \nu_e \to \bar\nu_e + (l\nu)(l\nu) + \nu_e$. As an application we reconsider the unitarity bounds on the Higgs mass. Particular attention is given to the role of the photon exchange which has not been considered in earlier investigations; we find that the photon weakens the bound of the Higgs mass.Comment: 16 pages, 8 figure

Geometric Scaling in Inclusive Charm Production

We show that the cross section for inclusive charm production exhibits geometric scaling in a large range of photon virtualities. In the HERA kinematic domain the saturation momentum $Q_{sat}^2(x)$ stays below the hard scale $\mu_c^2=4m_c^2$, implying charm production probing mostly the color transparency regime and unitarization effects being almost negligible. We derive our results considering two saturation models which are able to describe the DESY ep collider HERA data for the proton structure function at small values of the Bjorken variable $x$. A striking feature is the scaling on $\tau=Q_2^2/Q_{sat}^2(x)$ above saturation limit, corroborating recent theoretical studies.Comment: 4 pages, 2 figures. Version to be published in Physical Review Letter

Pore Stabilization in Cohesive Granular Systems

Cohesive powders tend to form porous aggregates which can be compacted by applying an external pressure. This process is modelled using the Contact Dynamics method supplemented with a cohesion law and rolling friction. Starting with ballistic deposits of varying density, we investigate how the porosity of the compacted sample depends on the cohesion strength and the friction coefficients. This allows to explain different pore stabilization mechanisms. The final porosity depends on the cohesion force scaled by the external pressure and on the lateral distance between branches of the ballistic deposit r_capt. Even if cohesion is switched off, pores can be stabilized by Coulomb friction alone. This effect is weak for round particles, as long as the friction coefficient is smaller than 1. However, for nonspherical particles the effect is much stronger.Comment: 10 pages, 15 figure

Colored Spin Systems, BKP Evolution and finite N_c effects

Even within the framework of the leading logarithmic approximation the eigenvalues of the BKP kernel for states of more than three reggeized gluons are unknown in general, contrary to the planar limit case where the problem becomes integrable. We consider a 4-gluon kernel for a finite number of colors and define some simple toy models for the configuration space dynamics, which are directly solvable with group theoretical methods. Then we study the dependence of the spectrum of these models with respect to the number of colors and make comparisons with the large limit case.Comment: 17 pages, 4 figures, references update, to appear on EPJ

Saturation Effects in Deep Inelastic Scattering at low Q2Q^2 and its Implications on Diffraction

We present a model based on the concept of saturation for small $Q^2$ and small $x$. With only three parameters we achieve a good description of all Deep Inelastic Scattering data below $x=0.01$. This includes a consistent treatment of charm and a successful extrapolation into the photoproduction regime. The same model leads to a roughly constant ratio of diffractive and inclusive cross section.Comment: 24 pages, 12 figures, Latex-fil

QCD evolution and skewedness effects in color dipole description of DVCS

We show the role played by QCD evolution and skewedness effects in the DVCS cross section at large $Q^2$ within the color dipole description of the process at photon level. The dipole cross section is given by the saturation model, which can be improved by DGLAP evolution at high photon virtualities. We investigate both possibilities as well as the off-forward effect through a simple phenomenological parametrisation. The results are compared to the recent ZEUS DVCS data.Comment: LaTeX, 6 pages, 5 Figs. Vers 2: Minor modifications. Accepted by EPJ

Effective action for the Regge processes in gravity

It is shown, that the effective action for the reggeized graviton interactions can be formulated in terms of the reggeon fields $A^{++}$ and $A^{--}$ and the metric tensor $g_{\mu \nu}$ in such a way, that it is local in the rapidity space and has the property of general covariance. The corresponding effective currents $j^{-}$ and $j^{+}$ satisfy the Hamilton-Jacobi equation for a massless particle moving in the gravitational field. These currents are calculated explicitly for the shock wave-like fields and a variation principle for them is formulated. As an application, we reproduce the effective lagrangian for the multi-regge processes in gravity together with the graviton Regge trajectory in the leading logarithmic approximation with taking into account supersymmetric contributions.Comment: 39 page

Frictional coupling between sliding and spinning motion

We show that the friction force and torque, acting at a dry contact of two objects moving and rotating relative to each other, are inherently coupled. As a simple test system, a sliding and spinning disk on a horizontal flat surface is considered. We calculate, and also measure, how the disk is slowing down, and find that it always stops its sliding and spinning motion at the same moment. We discuss the impact of this coupling between friction force and torque on the physics of granular materials.Comment: 4 pages, 5 figures; submitte

Strategien zur Reduzierung der Kupferaufwandmengen im ökologischen Kartoffelanbau – Projekt “ÖKO-SIMPHYT“

Potato late blight (Phytophthora infestans) is still an unsolved problem in organic farming. Up to now the disease can only be controlled by copper fungicides. Our project is aiming to reduce the application of copper-containing fungicides by introduc-tion of the new blight forecasting system “ÖKO-SIMPHYT” based on meteorological parameters. Primary stem infections should be reduced by seed treatment with copper fungicides thus to postpone the beginning of the blight epidemic as well as the start of spraying. To control secondary infections on the foliage, fungicide strategies should be elaborated to achieve best efficacy with reduced amounts of copper. Therefore copper amounts and spraying intervals should be adjusted to the infection pressure. Based on the biological and epidemiological conditions for primary and secondary infections the new developed potato blight forecast system ÖKO-SIMPHYT should be optimized

QCD analysis of the diffractive structure function F_2^{D(3)}

The proton diffractive structure function $F_2^{D(3)}$ measured in the H1 and ZEUS experiments at HERA is analyzed in terms of both Regge phenomenology and perturbative QCD evolution. A new method determines the values of the Regge intercepts in ``hard'' diffraction, confirming a higher value of the Pomeron intercept than for soft physics. The data are well described by a QCD analysis in which point-like parton distributions, evolving according to the DGLAP equations, are assigned to the leading and sub-leading Regge exchanges. The gluon distributions are found to be quite different for H1 and ZEUS. A {\it global fit} analysis, where a higher twist component is taken from models, allows us to use data in the whole available range in diffractive mass and gives a stable answer for the leading twist contribution. We give sets of quark and gluon parton distributions for the Pomeron, and predictions for the charm and the longitudinal proton diffractive structure function from the QCD fit. An extrapolation to the Tevatron range is compared with CDF data on single diffraction. Conclusions on factorization breaking depend critically whether H1 (strong violation) or ZEUS (compatibility at low $\beta$) fits are taken into account.Comment: 24 page