Precision Electroweak Tests of the Minimal and Flipped SU(5) Supergravity Models

Abstract

We explore the one-loop electroweak radiative corrections in the minimal $SU(5)$ and the no-scale flipped $SU(5)$ supergravity models via explicit calculation of vacuum polarization contributions to the ${ϵ}_{1,2,3}$ parameters. Experimentally, ${ϵ}_{1,2,3}$ are obtained from a global fit to the LEP observables, and $M_W/M_Z$ measurements. We include $q^2$-dependent effects which have been neglected in most previous ``model-independent" analyses of this type. These effects induce a large systematic negative shift on ${ϵ}_{1,2,3}$ for light chargino masses ($m_{{\chi }_1^{\pm }}\text{lsim}70\text{GeV}$). In agreement with previous general arguments, we find that for increasingly large sparticle masses, the heavy sector of both models rapidly decouples, \ie, the values for ${ϵ}_{1,2,3}$ quickly asymptote to the Standard Model values with a {\it light} Higgs ($m_{H_{SM}}\sim 100\text{GeV}$). Specifically, at present the $90\%$ CL upper limit on the top-quark mass is $m_t\text{lsim}175\text{GeV}$ in the no-scale flipped $SU(5)$ supergravity model. These bounds can be strengthened for increasing chargino masses in the $50-100\text{GeV}$ interval. In particular, for $m_t\text{gsim}160\text{GeV}$, the Tevatron may be able to probe through gluino($\tilde{g}$) and squark($\tilde{q}$) production up to $m_{\tilde{g}}\approx m_{\tilde{q}}\approx 250\text{GeV}$, exploring at least half of the parameter space in this model.

Comments: 15 pages,(6 ps figures available upon request), TeX(harvmac), CTP-TAMU-19/93, ACT-07/93