Direct-transmission models of dynamical supersymmetry breaking

We systematically construct gauge-mediated supersymmetry- (SUSY-)breaking models with direct transmission of SUSY-breaking effects to the standard-model sector. We obtain a natural model with the gravitino mass $m_{3/2}$ smaller than $1\hspace{0.5em}\mathrm{keV}$ as required from the standard cosmology. If all Yukawa coupling constants are of order one, the SUSY-breaking scale $m_{\mathrm{SUSY}}$ transmitted into the standard-model sector is given by $m_{\mathrm{SUSY}}\simeq 0.1({\alpha }_i/4\mathrm{}\pi )\Lambda$ where $\Lambda$ is the original dynamical SUSY-breaking scale. Imposing $m_{\mathrm{SUSY}}\simeq {(10\mathrm{}}^2$–${10}^3)$ GeV, we get $\Lambda \simeq {(10\mathrm{}}^5–{10}^6)$ GeV, which yields the gravitino mass $m_{3/2}\simeq {(10\mathrm{}}^{-2}$–1) keV.