Light Particles with Spin in Inflation

Understand

The existence of light particles with spin during inflation is prohibited by the Higuchi bound.

• This conclusion can be evaded if one considers states with a sizeable coupling with the inflaton foliation, since this breaks the de Sitter isometries.
• The action for these states can be constructed within the Effective Field Theory of Inflation, or using a CCWZ procedure.
• Light particles with spin have prescribed couplings with soft inflaton perturbations, which are encoded in consistency relations.