On the Experimental Effects of the Off-shell Structure in Anomalous Neutral Triple Gauge Vertices

Abstract

We discuss differences between on-shell and off-shell treatments in the search for anomalous neutral triple gauge couplings in $\mathrm{e^+ e^-}$ collisions. We find that the usual on-shell framework represents an optimal starting point, covering all scenarios in which a reasonable experimental sensitivity is expected. We show that off-shell effects lead to negligible deviations at the experimental level, provided that $\mathrm{e^+ e^-}\to\mathrm{f}\bar{\mathrm{f}}\gamma$ and $\mathrm{e^+ e^-}\to\mathr performed in regions where $\mathrm{Z}^*\to\mathrm{f}\bar{\mathrm{f}},\mathrm{f^\prime}\math production is dominant. For consistency reasons, we advocate the use of a natural extension of the on-shell definitions, which takes into account the correct off-shell dependences. Contrary to what has been recently suggested in the literature, we find that no $SU(2)_L\times U(1)_Y$ constraints among neutral triple gauge couplings can be imposed in a general case.