Do Electroweak Precision Data and Higgs-Mass Constraints Rule Out a Scalar Bottom Quark with Mass of Order 5 GeV?

We study the implications of a scalar bottom quark, with a mass of $O\left(5\mathrm{GeV}\right)$, within the minimal supersymmetric standard model. Light sbottoms may naturally appear for large $\tan \beta$ and, depending on the decay modes, may have escaped experimental detection. We show that a light sbottom cannot be ruled out by electroweak precision data and the bound on the lightest $\mathrm{CP}$-even Higgs-boson mass. We infer that a light $\tilde{b}$ scenario requires a relatively light scalar top quark whose mass is typically about the top-quark mass. In this scenario the lightest Higgs boson decays predominantly into $\tilde{b}$ pairs and obeys the mass bound $m_h\lesssim 123\mathrm{GeV}$.