Can Stop be Light Enough for TRISTAN ?

Abstract

\def\nle{{\stackrel{<}{\sim}}} We examine a possibility for existence of a light supersymmetric partner of the top quark (stop) with mass 15 $\sim$ 16 GeV in the framework of the minimal supergravity GUT model. Such light stop could explain the slight excess of the high $p_{T}$ cross section of the $D^{*\pm}$-meson production in two-photon process at TRISTAN. We point out that the existence of such stop could change the dominant decay mode of gluino and could weaken substantially present experimental bounds on the mass of gluino. It seems that there is a finite parameter region allowing existence of such light stop even if we consider the present experimental data. Inversely, if such light stop was discovered at TRISTAN, masses and mixing parameters of the other SUSY partners as well as masses of the Higgs and the top will be severely constrained, for example, $m_{\tilde{g}}\simeq$85GeV, $m_{\tilde{W_{1}}}\nle$50GeV, 110GeV$\nle m_{\tilde{\ell}}\nle$140GeV, 120GeV$\nle m_{\tilde{q}}\nle$160GeV, $\theta_{t}\simeq0.9$, $m_{h}\nle$ 65GeV and 130GeV$\nle m_{t}\nle$140GeV. We also discuss briefly the proton decay and the dark matter constraints.