Inflatonary model of a single scalar field with primordial potential
V(\phi)=\frac{1}{2}m^2\phi^2+\frac{\lambda}{4}\phi^4 (m^2 >0) non-minimally
coupled to gravity is studied in two-measures theory (TMT) in the Palatini
formalism. In the equations of motion presented in the Einstein frame and
rewritten in terms of the canonically normalized scalar field \varphi, there
arises a TMT effective potential, which differs from the potential of the
T-model in that it has a plateau of finite length: for \varphi greater a
certain value varphi_0 the TMT effective potential becomes exponentially steep.
The length of the plateau, and hence the duration of a quasi-de Sitter
inflation, is controlled by a model parameter. The appearance of this
parameter, as well as the form of the TMT effective potential, are a direct
consequence of the features inherent only in TMT. A detailed analysis shows
that there is a rather narrow interval of initial values of \varphi, bounded
from above by \varphi_0, in which the initial kinetic \rho_{kin,in} and
gradient \rho_{grad,in} energy densities turn out to be less than the potential
energy density; this requires the only additional condition, which is that
\rho_{kin,in}>\rho_{grad,in}. Therefore, in the space-time domain where these
restrictions are satisfied, the initial conditions necessary for inflation are
guaranteed.
