@article{TEXTUAL,
      recid = {12184},
      author = {Motohashi, Hayato and Hu, Wayne},
      title = {Effective field theory of degenerate higher-order  inflation},
      journal = {Physical Review D},
      address = {2020-04-23},
      number = {TEXTUAL},
      abstract = {We extend the effective field theory of inflation to a  general Lagrangian constructed from Arnowitt-Deser-Misner  variables that encompasses the most general interactions  with up to second derivatives of the scalar field whose  background breaks temporal diffeomorphism invariance.  Degeneracy conditions, corresponding to 8 distinct  types-only one of which corresponds to known degenerate  higher-order scalar-tensor models-provide necessary  conditions for eliminating the Ostrogradsky ghost in a  covariant theory at the level of the quadratic action in  unitary gauge. Novel implications of the degenerate  higher-order system for the Cauchy problem are illustrated  with the phase space portrait of an explicit inflationary  example: Not all field configurations lead to physical  solutions for the metric even for positive potentials;  solutions are unique for a given configuration only up to a  branch choice; solutions on one branch can apparently end  at nonsingular points of the metric and their continuation  on alternate branches lead to nonsingular bouncing  solutions; unitary gauge perturbations can go unstable even  when degenerate terms in the Lagrangian are infinitesimal.  The attractor solution leads to an inflationary scenario  where slow-roll parameters vary and running of the tilt can  be large even with no explicit features in the potential  far from the end of inflation, requiring the optimized  slow-roll approach for predicting observables.},
      url = {http://knowledge.uchicago.edu/record/12184},
}