Geometric Structure of Multi-Form-Field Isotropic Inflation and
  Primordial Fluctuations
  An inflationary scenario is expected to be embedded into an ultraviolet (UV)
complete theory such as string theory. Quasi-heavy fields are ubiquitous in UV
complete theory. The effect of these heavy fields may appear as nontrivial
kinetic terms in the low energy effective field theory, which provides a
nontrivial geometry in field space. In this paper, we study the effect of the
geometry of multi-form-field space on an inflationary scenario. In particular,
we focus on the geometric destabilization mechanism which induces the phase
transition from the conventional slow-roll inflation to a novel inflationary
scenario. Anisotropic inflation is a typical example of the new phase. To
conform to observations, we restrict us to isotropic configuration of form
fields. We clarify the conditions for the onset of the destabilization and
reveal the geometric structure of attractors after the destabilization. We
classify the viable models from the observational point of view. We also
investigate the features of the primordial fluctuations and find the similarity
to hyperbolic inflation. By calculating the power spectrum, we make several
phenomenological predictions which are useful to discriminate our models from
others inflation models.
