Electromagnetic corrections to deep inelastic scattering at HERA

The dominant electromagnetic radiative corrections to neutral current deep inelastic scattering at HERA energies have been calculated analytically in collinear approximation for unpolarized beams. The results may be used for the construction of an event generator and are applied to discuss the influence of cuts on the magnitude of the correction. For final state collinear photon emission the measurement of the resulting electromagnetic jet (electron plus collinear photon) reducesx-andy-dependence of the correction factor. Electromagnetic corrections to charged current interactions are discussed in leading logarithmic approximation.     

Perturbative contributions to the electroweak interface tension

The main perturbative contribution to the free energy of an electroweak interface is due to the effective potential and the tree level kinetic term. The derivative corrections are investigated with one-loop perturbation theory. The action is treated in derivative, in heat kernel, and in a multi local expansion. The massive contributions turn out to be well described by the Z-factor. The massless mode, plagued by infrared problems, is numerically less important. Its perturbatively reliable part can by calculated in derivative expansion as well. A self consistent way to include the Z-factor in the formula for the interface tension is presented.     

Hadron production at large transverse momentum and QCD

The predictions of a QCD-based hardscattering model for large p_T hadronic processes are investigated. Not only quark-quark scattering but all contributions in lowest order are considered. At low x_T, gluon-gluon and quark-gluon scattering are found to dominate the quark-quark term. At present energies the QCD predictions lie below the data but already come very close at the highest ISR energy. Predictions for higher p_T values and higher energies are made.     

Lepton pair production in two-dimensional QCD

Large q² lepton pair production is calculated in leading order in 1/N_c in two-dimensional quantum chromodynamics (QCD). From this confinement model the (Drell-Yan) parton model result is recovered.     

Higher order QCD contributions to electron structure functions

We study deep inelastice ⁺ e ^? scattering with untagged throughgoing target electrons. The corresponding electron structure functions are not trivially related to photon structure functions. Both can be calculated in QCD perturbation theory but the first ones can be measured more easily. In studying next-to-leading log contributions to electron structure functions we find that the leading logQ ² approximation completely fails at present energies. This is due to different scales λ andm _e . A modified leading-log approximation is introduced. Higher order corrections to this approximation are small away fromx=0 or 1.     

Higher order leading logarithmic QED corrections to deep inelasticep scattering at very high energies

Higher order electromagnetic radiative corrections to neutral current deep inelastic electron proton scattering are studied in collinear approximation. Second order corrections show qualitatively new features compared to the first order ones and are non-negligible for largey and smallx. We also show how kinematical cuts on the recoil quark jet, in particular the jet angle, will allow a strong reduction of the contribution from radiative events for smallx and largey.     

Inpolygons of minimal diameter

The present paper deals with an application of a distributional version of Pontryagin's maximum principle to the following geometrical problem: Find to a given convex polygon an inpolygon of minimal diameter. This geometrical problem is formulated as a problem of optimal control. For some special cases optimal inpolygons are determined.     

Baryon asymmetry from a two stage electroweak phase transition?

We investigate an extension of the Standard Model with a second Higgs doublet, showing a two stage phase transition. Wash-out of a baryon asymmetry after the phase transition can be easily avoided in this class of models.B+L transitions are more strongly suppressed in the intermediate phase than in the high temperature symmetric phase, however. Therefore, it becomes more difficult if not impossible to generate a sufficient baryon asymmetry during the phase transition.supported by Landes Graduierten Förderungs Gesetz     

Remark on the production cross section of J particles in hadron-hadron collisions according to the statistical bootstrap model

Heavy J particles decaying into e⁺e^? were recently found in p-Be collisions [1] as well as in e⁺e^? annihilations [2, 3], where also the decay into hadrons with a branching ratio of about $\text{σ(}\text{J}\text{→}\text{h}\text{)}\text{σ(}\text{J}\text{→}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{) = 15}$ was observed.     

Electroweak baryon number violation at finite temperature

We consider baryon and lepton number violating processes in the electroweak theory induced by gauge and Higgs fields passing the sphaleron solution at finite temperature. We show that for temperatures larger than 19 GeV the anomalous baryon and lepton number violating processes are suppressed by the Boltzmann factor exp (?βE _sp), whereE _sp is the sphaleron energy, rather than by the instanton tunneling factor exp (?8π²/g ²). We caculate the rate of baryon and lepton number violating processes at finite temperature and determine the freezing temperature of the anomalous processes in the early universe as a function of the Higgs mass. We compare the freezing temperature with the critical temperature of the electroweak phase transition infered from the one-loop finite-temperature effective potential. We obtain a critical Higgs mass of the order of 100 GeV, slightly depending on the top mass and the magnitude of the pre-exponential factor in the rate of theB non-conservation, above which the anomalous processes are certainly in equilibrium after the electroweak phase transition. Assuming that the temperature-dependence of the sphaleron energy is given by that found from the one-loop finitetemperature effective potential, this critical Higgs mass is lowered to a value of the order of 50 GeV.