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 $m_{3\mathrm{/}2}$ smaller than 1 keV as required from the standard cosmology. If all Yukawa coupling constants are of order one,the SUSY-breaking scale $m_{SUSY}$ transmitted into the standard-model sector is given by $m_{SUSY} \simeq 0.1 \alpha_i/(4\pi) \Lambda$where$\Lambda$ is the original dynamical SUSY-breaking scale. Imposing $m_{SUSY}\simeq ({10}^2-{10}^3)$ GeV, we get $\mathrm{\Lambda }\simeq ({10}^5-{10}^6)$ GeV, which yields the gravitino mass $m_{3\mathrm{/}2}\simeq ({10}^{-2}-1)$ keV.