Lorentz invariant dark-spinor and inflation
  We investigate the possibility of the inflation driven by a Lorentz invariant
non-standard spinor field. As these spinors are having dominant interaction via
gravitational field only, they are considered as \emph{Dark Spinors}. We study
how these dark-spinors can drive the inflation and investigate the cosmological
(scalar) perturbations generated by them. Though the dark-spinors obey a
Klein-Gordon like equation, the underlying theory of the cosmological
perturbations is far more complex than the theories which are using a canonical
scalar field. For example the sound speed of the perturbations is not a
constant but varies with time. We find that in order to explain the observed
value of the spectral-index $n_s$ one must have upper bound on the values of
the background NSS-field. The tensor to scalar ratio remains as small as that
in the case of canonical scalar field driven inflation because the correction
to tensor spectrum due to NSS is required to be very small. In addition we
discuss the relationship of results with previous results obtained by using the
Lorentz invariance violating theories.
