0000000000204369
AUTHOR
Kostas Philippides
Gauge-invariant 3-boson vertices and their ward identities in the standard model
In the context of the Standard Model we extend the S--matrix pinch technique for non--conserved currents to the case of three boson vertices. We outline in detail how effective gauge invariant three boson vertices can be constructed, with all three incoming momenta {\it off--shell}. Explicit closed expressions for the vertices γW−W+, ZW−W+, and χW−W+ are reported. The three boson vertices so constructed satisfy naive QED--like Ward identities which relate them to the gauge invariant gauge boson self--energies previously constructed by the same method. The derivation of the aforementioned Ward identities relies on the sole requirement of complete gauge invariance of the S--matrix element con…
Two-loop electroweak corrections to the ρ parameter beyond the leading approximation
We show that in the framework of the pinch technique the universal part of the $\rho$ parameter can be meaningfully defined, beyond one loop. The universal part so obtained satisfies the crucial requirements of gauge-independence, finiteness, and process-independence, even when subleading contributions of the top quark are included. The mechanism which enforces the aforementioned properties is explained in detail, and several subtle field theoretical issues are discussed. Explicit calculations of the sub-leading two-loop corrections of order $O(G_{\mu}^{2}m^{2}_{t}M_{Z}^{2})$ are carried out in the context of an $SU(2)$ model, with $M_{W}=M_{Z}$, and various intermediate and final results a…
Heavy quark decomposition of the S matrix and its relation to the pinch technique.
We propose a decomposition of the S-matrix into individually gauge invariant sub-amplitudes, which are kinematically akin to propagators, vertices, boxes, etc. This decompsition is obtained by considering limits of the S-matrix when some or all of the external particles have masses larger than any other physical scale. We show at the one-loop level that the effective gluon self-energy so defined is physically equivalent to the corresponding gauge independent self-energy obtained in the framework of the pinch technique. The generalization of this procedure to arbitrary gluonic $n$-point functions is briefly discussed.
Set of sum rules for anomalous gauge boson couplings
The dependence of the differential cross-section for on-shell W-pair production on the anomalous trilinear gauge couplings invariant under C and P is examined. It is shown that the contributions of the anomalous magnetic moments of the W boson due to the photon and the Z can be individually projected out by means of two appropriately constructed polynomials. The remaining four anomalous couplings are shown to satisfy a set of model-independent sum rules. Specific models which predict special relations among the anomalous couplings are then studied; in particular, the composite model of Brodsky and Hiller, and the linear and non-linear effective Lagrangian approaches. The relations predicted…
Dual gauge-fixing property of the S matrix.
The {ital S} matrix is known to be independent of the gauge-fixing parameter to all orders in perturbation theory. In this paper by employing the pinch technique we prove at one loop a stronger version of this independence. In particular, we show that one can use a gauge-fixing parameter for the gauge bosons inside quantum loops which is different from that used for the bosons outside loops, and the {ital S} matrix is independent of both. Possible phenomenological applications of this result are briefly discussed. {copyright} {ital 1996 The American Physical Society.}