Phenomenological explorations of a quasi-degenerate $Z^{\prime }$ boson

Abstract

We do a general model-independent phenomenological analysis of the curious case of a $Z^{\prime }$ boson with mass close to that of the Standard Model (SM) $Z$ boson. From tree-level calculation alone we show that presence of such a quasi-degenerate or `practically' degenerate $Z^{\prime }$ boson affects both the cross-section and forward-backward asymmetry of the process $e^{+}{e}^{-}\to f\bar{f}$ where $f$ (with $f\ne e^{-}$) can be a lepton or quark. Most importantly the effect on forward-backward asymmetry is found to be more prominent away from the $Z$-pole. We provide constraints on such a $Z^{\prime }$ from the measurement of $N_{\nu }$, the number of light neutrino species.

arXiv comment16 pages, 6 figures