Oblique radiative corrections from Majorana neutrinos

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Abstract
We analyze in (S,T,U) space one-loop oblique (vacuum-polarization) corrections, assuming the scenario for a naturally heavy fourth-generation neutrino proposed by Hill and Paschos. Since this model suggests that the Majorana mass be of the order of the weak scale, it is crucial to employ a formulation of oblique corrections that correctly accommodates also the standard-model physics at that energy scale. We confront our results with precise data from CERN LEP and other experiments, and search the mass parameter space of the novel particles for allowed regions. We also investigate the implications for the upper bound on the top-quark mass coming from measurements of the W-boson mass. A heavy Majorana neutrino in the third generation decouples from electroweak physics and cannot be excluded experimentally.