Galilean Creation of the Inflationary Universe
  It has been pointed out that the null energy condition can be violated stably
in some non-canonical scalar-field theories. This allows us to consider the
Galilean Genesis scenario in which the universe starts expanding from Minkowski
spacetime and hence is free from the initial singularity. We use this scenario
to study the early-time completion of inflation, pushing forward the recent
idea of Pirtskhalava et al. We present a generic form of the Lagrangian
governing the background and perturbation dynamics in the Genesis phase, the
subsequent inflationary phase, and the graceful exit from inflation, as opposed
to employing the effective field theory approach. Our Lagrangian belongs to a
more general class of scalar-tensor theories than the Horndeski theory and
Gleyzes-Langlois-Piazza-Vernizzi generalization, but still has the same number
of the propagating degrees of freedom, and thus can avoid Ostrogradski
instabilities. We investigate the generation and evolution of primordial
perturbations in this scenario and show that one can indeed construct a stable
model of inflation preceded by (generalized) Galilean Genesis.
