arXiv subjects
Publications and source records attributed to D. Schildknecht.
Application of a Stueckelberg transformation allows one to connect various Lagrangians which have been independently proposed for non-standard couplings. We discuss the reduction of the number of independent parameters in the Lagrangian and compare symmetry arguments with dimensional arguments.
The $Z^0 \to b\bar b$ width, $Γ_b$, is analysed in conjunction with the total and hadronic $Z^0$ widths, $Γ_T$ and $Γ_h$. Assuming, tentatively, that the present 2$σ$ discrepancy in $Γ_b$ will substantiate as time goes on, for large values of $m_H$ it will be sufficient to modify the $Z^0 b \bar b$ vertex only. In contrast, for small values of $m_H$, the theoretical predictions for both the $Z^0$ width into light quarks and leptons as well as the $Z^0 \to b\bar b$ vertex will have to be modified.
We refine our recent analysis of the electroweak precision data at the \PZO\ pole by including the hadronic decay modes of the \PZO. Within the framework of an effective Lagrangian we parametrize $SU(2)$ violation by the additional process-specific parameters $\De y_ν$, $\De\yh$, and $\De\yb$ (for the $\PZOν\barν$, $\PZO\Pq\bar\Pq$, and $\PZO\Pb\bar\Pb$ vertices) together with the previously introduced parameters $\De x$, $\De y$, and $\eps$. We find that a six-parameter analysis of the experimental data is indeed feasible, and it is carried out in addition to a four-parameter fit for $\De x$, $\De y$, $\eps$, and $\De\yb$ only. We reemphasize that the experimental data have become sensitive to the (combined) magnitude of the vertex corrections at the $\PWp\Pl\barν$ ($\PWmν\bar\Pl$) and $\PZO\Pl\bar\Pl$ vertices, $\De y$, which is insensitive to the notion of the Higgs mechanism but dependent on the non-Abelian, trilinear vector-boson coupling. Full explicit analytical results for the standard one-loop predictions for the above-mentioned parameters are given, and the leading two-loop top-quark effects are included. The analytic formluae for the analysis of the experimental data in terms of the parameters $\De x$, $\De y$ etc.\ are presented in order to encourage experimentalists to persue such an analysis by themselves with future data.
Invited Talk presented at the First Arctic Workshop on Particle Physics, Saariselkae, August 1994 and at the Workshop on Elementary Particles and Quantum Field Theory, Moscow, September 1994
Based on the observables $\MW$, $Γ_l$, $\bar\sw^2(\MZ^2)$, we evaluate the parameters $Δx, Δy$ and $\varepsilon$ at one-loop level within an electroweak massive vector-boson theory, which does not employ the Higgs mechanism. The theoretical results are consistent with the experimental ones on $Δx$, $Δy$, $\varepsilon$. The theoretical prediction for $Δy$ coincides with the standard-model one (apart from numerically irrelevant terms which vanish for $\MH\to\infty$). Non-renormalizability only affects $Δx$ and $\varepsilon$, which differ from the standard-model results by the replacement $\log\MH\to\logΛ$ for a heavy Higgs mass, $\MH$ (where $Λ$ denotes an effective UV cut-off).
We elaborate on a recently suggested effective Lagrangian for charged-current and neutral-current electroweak interactions which in comparison with the standard electroweak theory contains three free parameters $Δx, Δy$, $\varepsilon$ which quantify different sources for violations of $SU(2)$ symmetry. Within the standard $SU(2)_I \times U(1)_Y$ electroweak theory, we present both exact and very much refined approximate analytical one-loop expressions for these parameters in terms of the canonical input, $G_μ, \MZ$, $\alpz$, the top-quark mass, $\Mt$, and the Higgs-boson mass, $\MH$. We reemphase the importance of discriminating between the {\it empirically well-known purely fermionic} (vacuum polarization) contributions to $Δx, Δy$, $\varepsilon$ and the {\it empirically unknown bosonic} ones with respect to present and future electroweak precision tests. The parameters $Δx$ and $\varepsilon$ are hardly affected by standard bosonic corrections, while the full one-loop results for $Δy$ differ appreciably from the ones obtained by taking into account fermion loops only. A detailed comparison with the experimental data on $\MWpm/\MZ$, $\bar\sw^2$, $Γ_l$ shows that these data start to become accurate enough to be sensitive to standard (bosonic) contributions to $Δy$ beyond fermion loops.
The recent precision electroweak data on $Γ^l, \bar s^2_W$ and $M_W/M_Z$ are compared with the tree-level and the dominant-fermion-loop as well as the full one-loop standard-model predictions. While the tree-level predictions are ruled out, the dominant-fermion-loop predictions, defined by using $α(M^2_Z)\cong 1/128.9$ in the tree-level formulae, as well as the full one-loop predictions are consistent with the experimental data. Deviations from the dominant-fermion-loop predictions are quantified in terms of an effective Lagrangian containing three additional parameters which have a simple meaning in terms of $SU(2)$ symmetry violation. The effective Lagrangian yields the standard one-loop predictions for specific values of these parameters, which are determined by $m_t$ and $m_H$.
We study the accuracy to be obtained in measuring trilinear $Z^0W^+W^-$ and $γW^+W^-$ couplings in the reaction $e^+e^- \to W^+W^-$ at "New Linear Collider" energies of $500GeV$ to $1000GeV$. We derive simple scaling laws for the sensitivity in the measurement of these couplings. For most couplings the sensitivity increases as $\sqrt{L\cdot s}$, where $L$ denotes the integrated luminosity and $\sqrt s$ denotes the $e^+e^-$ center-of-mass energy. Detailed investigations based on various fits confirm these scaling laws and show that an accuracy of the order of the standard radiative corrections can be reached at the NLC for the design values of the luminosity.
We study the vector-boson production processes e+e- --> WWZ and e+e- -->WWgamma which are directly affected by the trilinear and quadrilinear self couplings of the W, Z and gamma. Our analysis is based upon a single-parameter effective-Lagrangian model for these self interactions which contains the standard model as a special case. Consequences for the phenomenology at an e+e- collider of 500 GeV (NLC) are discussed, and fits of the free parameter around its standard model value are carried out.