Escape from the swamp with spectator
  In the context of string theory, several conjectural conditions have been
proposed for low energy effective field theories not to be in swampland, the
UV-incomplete class. The recent ones represented by the de Sitter and
trans-Planckian censorship conjectures in particular seem to conflict with the
inflation paradigm of the early universe. We first point out that scenarios
where inflation is repeated several times (multi-phase inflation) can be easily
compatible with these conjectures. In other words, we relax the constraint on
the single inflation for the large scale perturbations to only continue at
least around 10 e-folds. In this context, we then investigate if a spectator
field can be a source of the almost scale-invariant primordial perturbations on
the large scale. As a consequence of such an isocurvature contribution, the
resultant perturbations exhibit the non-vanishing non-Gaussianity in general.
Also the perturbation amplitude on smaller scales can be completely different
from that on the large scale due to the multiplicity of inflationary phases.
These signatures will be a smoking gun of this scenario by the future
observations.
