Dieter Schildknecht

Generalized vector dominance and inelastic electron - proton scattering

Abstract We propose a model of inelastic electron-proton scattering which takes into account the coupling of the photon to higher-mass vector states. Both the virtual photon-proton cross section σT (predicted with essentially no adjustable parameters) and the q2 dependence of R are in exceedingly good agreement with the SLAC-MIT data in the diffraction region.

Trilinear couplings among the electroweak vector bosons and their determination at LEP2

Abstract We present a detailed investigation of the potential of LEP2 to measure the (trilinear) couplings of the vector bosons, Z 0 W + W − and γW + W − among one another. The restrictions imposed on non-standard trilinear couplings by symmetry requirements, thus excluding violent boson-loop divergences and a violent growth of tree amplitudes for vector-boson scattering, are discussed in detail. We elaborate on how to extract the W ± spin-density matrix and the W + , W − spin correlations from future data. Various theoretically motivated fits to artificial “data” on e + e − →W + W − are carried out in order to evaluate the potential of LEP2 for the measurement of trilinear vector boson couplings. We stress that a direct measurement of the couplings of the vector bosons with one another is indispensable for a verification of the basic SU(2) L ×U(1) Y structure of the present electroweak theory. Such measurements at LEP2 improve indirect LEP1 bounds by factors which occasionally reach a full order of magnitude.

Weak current algebra, composite W bosons and universality of the weak interactions

Abstract We postulate a local current algebra for the weak isovector currents of the subconstituents forming leptons, quarks and intermediate bosons. Dominating these currents by the lowest lying boson yields universality of weak interactions as well as the standard mass formulas for the lowest charged and neutral bosons.

Direct one-loop renormalization of SU(2)L × U(1)Y four-fermion processes and running coupling constants☆

Abstract Within the SU(2)L × U(1) electroweak theory, by combining (bosonic) vacuum polarization with vertex and box contributions, we derive gauge-invariant (one-loop) dressed propagators for the W±-boson and the γW3 system in a straightforward manner. By introducing running couplings and masses, the corresponding four-fermion amplitudes are cast into a Born term form. The subsequent “direct renormalization” expresses the running quantities in terms of their values at a chosen scale. Among other things, the value of Δr is rederived, and a comparison of our procedure and results with the results in the literature is carried out. Care is taken to give a transparent presentation of all physically relevant steps.

PHENOMENOLOGY OF WEAK ISOSCALAR VECTOR BOSONS

Motivated by the hypothesis of compositeness of leptons, quarks and vector bosons the effects of a weak isoscalar vector boson Y coupled to the weak hypercharge current, and, alternatively, the effects of an isoscalar vector boson YL coupled to the left-handed part of the weak hypercharge current only, are investigated within the framework of an effective electroweak lagrangian theory incorporating W(Y) dominance. We discuss experimental implications for the neutral current phenomenology at presently available as well as at LEP and SLC energies. From the experimental data in neutrino scattering we deduce that the Y(YL) can hardly have a mass below 250 GeV. An enhanced forward-backward asymmetry AFBin e+e− → μ+ μ− is expected at PETRA and TRISTAN energies. In fact, the one standard deviation effect seen at PETRA in AFB (e+e− → μ+ μ−) can naturally be explained through the existence of such an isoscalar boson.

Off-diagonal generalized vector dominance and inelastic ep scattering

Abstract By also taking into account off-diagonal contributions to the virtual forward Compton amplitude, scaling in ep scattering is obtained from scaling of the total cross section for e+e− annihilation into hadrons. The parameter which sets the scale for the q2 dependence in ep scattering is calculated to be m 2 ⋍ 0.61 m ϱ 2 ⋍ 0.36 GeV 2 .

A UNIQUE LAGRANGIAN FOR W+/-, Z0 SELF-INTERACTIONS CONTAINING QUADRUPOLE TERMS - TESTS IN E+E- -] W+W-

Abstract In a framework where massive vector bosons satisfy global SU(2) symmetry and electromagnetic interactions are introduced via W dominance we obtain severe restrictions on the possible W ± , Z 0 self-interaction terms namely standard anomalous magnetic moments κ γ = κ Z = 1 but quadrupole terms ϱ γ = ϱ Z . The overall consistency of the scheme is explicitly shown. A discussion of the magnitude of the quadrupole parameter is given together with consequences for cross sections and angular distributions in e + e − → W + W − at LEP 200.

VECTOR-MESON DOMINANCE AND DIFFRACTIVE ELECTROPRODUCTION OF VECTOR MESONS

Abstract A vector-meson dominance model of diffractive electroproduction of vector mesons at high energies is presented. The assumption that the invariant amplitudes are slowly varying as a function of the vector-meson mass, when extrapolating to the spacelike region, is shown to lead to serious difficulties when combined with helicity independence, i.e. equality of transverse and longitudinal on-mass-shell vector-meson forward-scattering helicity amplitudes at high energies. The assumption is adopted, therefore, that the helicity amplitudes are slowly varying, apart from the factors which guarantee the vanishing of the longitudinal amplitudes in the limit of zero mass. Assuming, in addition, helicity non-flip and helicity independence for vector-meson scattering, we derive expressions for the cross section for electroproduction of vector mesons and for the vector-meson spin-density matrix elements. We also present our conclusions on the total electroproduction cross section.

Non-standard self-interactions of the weak vector bosons and their phenomenological implications

Abstract Based upon the parts of the standard electroweak model which have been verified by experiment so far, a generalization into the sector of the weak vector boson self-interactions is undertaken. The guiding principles are dimensionless couplings, electromagnetic gauge invariance and a global SU(2) WI symmetry. The consequences of this general approach for the phenomenology at the future colliders of high center of mass energy (LEP, Tevatron, SSC) are discussed in detail. The general approach encompasses the standard model as a special case and therefore our discussion is useful as well for a synoptic view of the tests of the self-interaction part of the standard model.

Test of Higgs boson nature in e+e−→HHZ

Abstract The process e + e − →HHZ is strongly dependent on the Higgs boson couplings HZZ, HHZZ and HHH, and provides therefore a test of the Higgs assignment to gauge group representations. The cross section varies between 5 × 10 −38 and 10 −39 cm 2 for Higgs masses between 5GeV and 40 GeV in the Weinberg-Salam model.