Residual New Physics Effects in $e^+e^-$ and $γγ$ Collisions

Abstract

We present a set of studies concerning the description of New Physics (NP) effects caracterized by a scale much higher than the electroweak scale. We show that both present experimental results and several types of theretical considerations about the Standard Model (SM) and NP suggest a hierarchy among the sectors in which NP manifestations should appear. We concentrate on residual effects described by effective lagrangians involving bosonic and/or heavy quark fields. For each operator we propose an unambiguous definition of the NP scale given by the energy at which unitarity is saturated. We also consider the possible existence of Higher Vector Bosons. We then study the tests realizable at present and future colliders. We start from the analysis of the high precision tests at Z peak, discussing separately the constraints obtained from the light fermionic sector and those due to the $b\bar b$ sector. We then consider the process $e^+e^-\to f\bar f$ at higher energies (LEP2 and NLC) and we propose the "Z peak subtracted representation" which allows to automatically take into account Z peak constraints and to describe several types of NP effects at any other energy. Applications to various NP effects (Higher Vector Bosons, Technicolour resonances, Anomalous Gauge Boson couplings) are given. We then concentrate on several bosonic processes, $e^+e^-\to W^+W^-$, $HZ$, $Hγ$, and $γγ$ collisions producing boson pairs or a single Higgs. We study the sensitivities to the various operators involved in the effective lagrangian and we propose ways to disentangle them. The NP scales which can be felt vary from a few TeV at LEP2 up to 200 TeV in single H production at NLC.