ANOMALOUS GAUGE BOSON INTERACTIONS

We discuss the direct measurement of the trilinear vector boson couplings in present and future collider experiments. The major goals of such experiments will be the confirmation of the Standard Model (SM) predictions and the search for signals of new physics. We review our current theoretical understanding of anomalous trilinear gauge boson self-interactions. If the energy scale of the new physics is $\sim 1$ TeV, these low energy anomalous couplings are expected to be no larger than ${\cal O}(10^{-2})$. Constraints from high precision measurements at LEP and low energy charged and neutral current processes are critically reviewed.Comment: 53 pages with 17 embedded figures, LaTeX, uses axodraw.sty, figures available on request. The complete paper, is available at ftp://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z or http://phenom.physics.wisc.edu/pub/preprints/1995/madph-95-871.ps.Z Summary of the DPF Working Subgroup on Anomalous Gauge Boson Interactions of the DPF Long Range Planning Stud

Sum rules for e+e−→W+W−e^+e^- \to W^+W^- helicity amplitudes from BRS invariance

The BRS invariance of the electroweak gauge theory leads to relationships between amplitudes with external massive gauge bosons and amplitudes where some of these gauge bosons are replaced with their corresponding Nambu-Goldstone bosons. Unlike the equivalence theorem, these identities are exact at all energies. In this paper we discuss such identities which relate the process $e^+e^- \to W^+W^-$ to $W^\pm\chi^\mp$ and $\chi^+\chi^-$ production. By using a general form-factor decomposition for $e^+e^- \to W^+W^-$, $e^+e^- \to W^\pm \chi^\mp$ and $e^+e^- \to \chi^+\chi^-$ amplitudes, these identities are expressed as sum rules among scalar form factors. Because these sum rules may be applied order by order in perturbation theory, they provide a powerful test of higher order calculations. By using additional Ward-Takahashi identities we find that the various contributions are divided into separately gauge-invariant subsets, the sum rules applying independently to each subset. After a general discussion of the application of the sum rules we consider the one-loop contributions of scalar-fermions in the Minimal Supersymmetric Standard Model as an illustration.Comment: 37 pages, including 16 figure

Constraints on New Physics in the Electroweak Bosonic Sector from Current Data and Future Experiments

Extensions of the Standard Model which involve a new scale, $\Lambda$, may, for energies sufficiently small compared to this new scale, be expressed in terms of operators with energy dimension greater than four. The coefficients of just four SU(2)$\times$U(1)-gauge-invariant energy-dimension-six operators are sufficient to parameterize the contributions of new physics in the electroweak bosonic sector to electroweak precision measurements. In this letter we update constraints on the coefficients of these four operators due to recent precision measurements of electroweak observables. We further demonstrate how such constraints may be improved by experiments at TRISTAN, LEP2 and at a future linear $e^+e^-$ collider. The relationship of these operators to the oblique parameters $S$, $T$ and $U$ is examined. Two of the operators contribute to a non-standard running of the electroweak charge form-factors $\overline{\alpha}(q^2)$, $\overline{s}^2(q^2)$, $\overline{g}_Z^2(q^2)$ and $\overline{g}_W^2(q^2)$; in the special case where the coefficients of these two vanish the operator analysis reduces to an analysis in terms of $S$, $T$ and $U$ with $U = 0$.Comment: documentstyle[preprint,aps,floats,cite,psfig,subeqn]{revtex}, one figure compressed and encoded using uufiles, .ps version available via anonymous ftp from ftp://ftp.kek.jp/kek/preprints/TH/TH-44

Low-Energy Constraints on New Physics Revisited

It is possible to place constraints on non-Standard-Model gauge-boson self-couplings and other new physics by studying their one-loop contributions to precisely measured observables. We extend previous analyses which constrain such nonstandard couplings, and we present the results in a compact and transparent form. Particular attention is given to comparing results for the light-Higgs scenario, where nonstandard effects are parameterized by an effective Lagrangian with a linear realization of the electroweak symmetry breaking sector, and the heavy-Higgs/strongly interacting scenario, described by the electroweak chiral Lagrangian. The constraints on nonstandard gauge-boson self-couplings which are obtained from a global analysis of low-energy data and LEP/SLC measurements on the Z pole are updated and improved from previous studies. Replaced version: tables and figures of Section VIb recalculated. There were roundoff problems, especially in Fig. 8. Text unchanged.Comment: \documentstyle[preprint,aps,floats,psfig]{revtex}, 10 figures, postscript version available from ftp://ftp.kek.jp/kek/preprints/TH/TH-51

Probing color-singlet exchange in Z+2Z+2-jet events at the LHC

The purely electroweak process $qq\to qqZ$ (via $t$-channel $\gamma/Z$ or $W$ exchange) provides a copious and fairly clean source of color-singlet exchange events in $pp$ collisions at the LHC. A judicious choice of phase-space region allows the suppression of QCD backgrounds to the level of the signal. The color-singlet-exchange signal can be distinguished from QCD backgrounds by the radiation patterns of additional minijets in individual events. A rapidity-gap trigger at the minijet level substantially enhances the signal versus the background. Analogous features of weak boson scattering events make $Z+2$-jet events at the LHC an ideal laboratory for investigation of the soft-jet activity expected in weak-boson scattering events.Comment: 24 pages (with 7 embedded figures), Revtex, uses epsf.sty. Z-compressed postscript version also available at http://phenom.physics.wisc.edu/pub/preprints/1996/madph-96-943.ps.Z or at ftp://phenom.physics.wisc.edu/pub/preprints/1996/madph-96-943.ps.

Contributions of LEP1.5, LEP2 and linear-collider data to indirect constraints on non-Abelian gauge-boson couplings

It is possible to place direct constraints on WW-photon and WWZ couplings by studying their tree-level contributions to the process e^+e^- ---> W^+W^-. However, these couplings also contribute at the loop level to e^+e^- ---> f fbar processes where `f' is any Standard-Model fermion. In this paper the available LEP1.5 and LEP2 data, the anticipated LEP2 data and possible linear collider data for these latter processes is combined with low-energy and Z-pole data to place indirect constraints on nonstandard WW-photon and WWZ couplings. The direct and indirect constraints are then compared. An effective Lagrangian is used to describe the new physics. In order that the implications of this analysis are as broad as possible, both the light-Higgs scenario, described by an effective Lagrangian with a linear realization of the symmetry-breaking sector, and the strongly interacting scenario, described by the electroweak chiral Lagrangian, are considered.Comment: \documentstyle[preprint,aps,floats,psfig]{revtex}, 4 figures, postscript version available from ftp://ftp.kek.jp/kek/preprints/TH/TH-53