Scalar Domain Wall as the Universe
  We develop a formulation where for an arbitrarily given warp factor, we
construct a scalar field action which reproduces the warp factor as a solution
of the Einstein equation and field equation corresponding to the action. This
formulation could be called as the reconstruction. By using the formulation of
the reconstruction, we construct models which have an exact solution describing
the domain wall. The shape of the domain wall can be flat, de Sitter
space-time, or anti-de Sitter space-time. In the constructed domain wall
solutions, there often appears ghost with negative kinetic energy. We give,
however, an example of the de Sitter domain wall solution without ghost, which
could be a toy model of inflation. We also investigate the localization of
gravity as in the Randall-Sundrum model. It is demonstrated that the four
dimensional Newton law could be reproduced even in the de Sitter space-time
domain wall solution. We show that we can construct a space-time, where the
domain wall is the general Friedmann-Robertson-Walker (FRW) universe and the
warp factor can be arbitrary. For such a construction, we use two scalar
fields. It is also illustrated that the scalar field equations are equivalent
to the Bianchi identities: $\nabla^\mu (R_{\mu\nu} - \frac{1}{2}R
g_{\mu\nu})=0$.
