Gravitational Waves in Metastable Supersymmetry Breaking
  If supersymmetry is broken in metastable vacua, it is not clear why we are
now in there rather than supersymmetric vacua. Moreover, it is natural to
expect that we were in supersymmetric vacua, which have higher symmetry than
metastable vacua, in the early universe. In this paper, we reexamine and
improve the previous analysis on the cosmological evolution of the vacuum
structure in the ISS model of metastable supersymmetry breaking by taking into
account constraints on the reheating temperature, which is needed to avoid the
overproduction of gravitinos. It turns out that the desired phase transition
from a supersymmetric vacuum to a metastable vacuum is allowed only in the
light gravitino mass region $m_{3/2} < 4.7$\,eV. This is achieved by either
rolling down a potential or tunneling processes depending on the reheating
temperature. We show that when the tunneling processes are realized, abundant
gravitational waves could be produced from collisions of runaway bubbles. The
resulting gravitational waves are detectable with the future gravitational wave
interferometers like LISA and DECIGO.
