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Kostas Philippides

Publications and source records attributed to Kostas Philippides.

9 recordsLinked to original sources
arXiv2000

A method for determining anomalous gauge boson couplings from e^{+}e^{-} experiments

We present a model-independent method for determining anomalous gauge boson couplings from ongoing and future e^{+}e^{-} -> W^{+} W^{-} experiments. First we generalize an already existing method, which relies on the study of four observables constructed through appropriate projections of the unpolarized differential cross-section. In particular, we retain both linear and quadratic terms in the unknown couplings, and compute contributions to these observables originating from anomalous couplings which do not separately conserve the discrete C, P, and T symmetries. Second, we combine the above set of observables with three additional ones, which can be experimentally obtained from the total cross-sections for polarized final state W bosons. The resulting set of seven observables may provide useful information for constraining, and in some cases for fully determining, various of the possible anomalous gauge boson couplings.

hep-ph↗
arXiv1998

A 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 by these models, when combined with the aforementioned sum rules, give rise to definite predictions, particular to each model. These predictions can be used, at least in principle, in order to exclude or constrain such models.

hep-ph↗
arXiv1996

The dual gauge fixing property of the S matrix

The $S$-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 $S$-matrix is independent from both. Possible phenomenological applications of this result are briefly discussed.

hep-ph↗
arXiv1995

Application of the Pinch Technique to Neutral Current Amplitudes and the Concept of the Z Mass

The pinch technique (PT) is applied to neutral current amplitudes, focusing on the mixing problem. Extending recent arguments due to Papavassiliou and Pilaftsis, it is shown that the use of the PT self-energies does not shift the complex-valued position of the pole through order {\cal O}($g^4$). This leads (to the same accuracy) to a simple interpretation of $M_Z$, the mass measured at LEP, in terms of the PT self-energies. It is pointed out that the PT approach provides a convenient and rather elegant formalism to discuss important neutral current amplitudes, such as those relevant to four-fermion processes and LEP2.

hep-ph↗
arXiv1995

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 $ρ$ 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 $O(G_μ^{2}m^{2}_{t}M_{Z}^{2})$ are carried out in the context of an $SU(2)$ model, with $M_{W}=M_{Z}$, and various intermediate and final results are reported.

hep-ph↗
arXiv1995

The Ward Identities of the Gauge Invariant Three Boson Vertices

We outline the pinch technique for constructing gauge invariant Green's functions in gauge theories and derive the Ward identities that must be satisfied by the gauge invariant three boson vertices of the standard model. They are generalizations of their tree level Ward identities and are shown to be crucial for the delicate gauge cancellations of the S-matrix.

hep-ph↗
arXiv1994

The 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.

hep-th↗
arXiv1993

Gauge Invariant Three-Boson Vertices in the Standard Model and the Static Properties of the W

We use the S-matrix pinch technique to derive to one loop-order gauge independent $γW^{+} W^{-} $ and Z $W^{+} W^{-}$ vertices in the context of the Standard Model,with all three incoming momenta off-shell. We show that the $γW^{+} W^{-}$ vertex so constructed is related to the gauge-independent W self-energy,derived by Degrassi and Sirlin,by a very simple QED-like Ward identity.The same results are obtained by the pinch technique applied directly to the process $e^{+}e^{-} \rightarrow W^{+}W^{-}$. Explicit calculations give rise to expressions for the static properties of the W gauge bosons like magnetic dipole and electric quadruple moments which being gauge independent satisfy such crucial properties as infrared finiteness and perturbative unitarity.

hep-ph↗