  Supersymmetric theories, including the minimal supersymmetric standard model,
usually contain many scalar fields whose potentials are absent in the exact
supersymmetric limit and within the renormalizable level. Since their
potentials are vulnerable to the finite energy density of the Universe through
supergravity effects, these flat directions have nontrivial dynamics in the
early Universe. Recently, we have pointed out that a flat direction may have a
positive Hubble induced mass term during inflation whereas a negative one after
inflation. In this case, the flat direction stays at the origin of the
potential during inflation and then obtain a large vacuum expectation value
after inflation. After that, when the Hubble parameter decreases down to the
mass of the flat direction, it starts to oscillate around the origin of the
potential. In this paper, we investigate the dynamics of the flat direction
with and without higher dimensional superpotentials and show that topological
defects, such as cosmic strings and domain walls, form at the end of inflation
and disappear at the beginning of oscillation of the flat direction. We
numerically calculate their gravitational signals and find that the observation
of gravitational signals would give us information of supersymmetric scale, the
reheating temperature of the Universe, and higher dimensional operators.
