Stability of metastable vacua in gauge mediated SUSY breaking models with ultra light gravitino

Recently Murayama and Nomura proposed a simple scheme to construct the gauge mediation models, using metastable supersymmetry breaking vacua. It has a possibility to predict the ultra light gravitino mass m3/2≲16eV, while such a light gravitino may destabilize the metastable vacua. We investigate stability of the metastable vacuum of their model. The transition rate from the false vacuum to true ones is evaluated by numerical calculation, including the Coleman-Weinberg potential destabilizing the metastable vacuum. It is found that when the messenger sector is minimal, stability of the metastable vacuum imposes an upperbound on squark mass Mq˜ for the ultra light gravitino as Mq˜≲1800GeV at most. Squarks with this mass may be found in the LHC experiments.