We extend the method of Flow Equations to the Effective Field Theory framework of inflation , in order to investigate the observable predictions of a very broad class of inflationary models .
Focusing our attention on the gravitational-wave sector , we derive a general expression for the consistency relation for effective models and provide a numerical implementation which allows to study how the generated models populate the ( r,n _ { t } ) plane .
We analyse 5 \times 10 ^ { 4 } realizations of inflationary scenarios that respect the Null-Energy Condition ( \epsilon > 0 ) and 5 \times 10 ^ { 4 } realizations that violate it ( \epsilon < 0 ) .
In both cases , 90 \% of the viable models are below the most recent upper bound on the tensor-to-scalar ratio from Planck and BICEP2/Keck Array BK15 data : r _ { 0.002 } < 0.056 at 95 \% CL .
We find that general EFT inflationary models with \epsilon > 0 are typically characterized by n _ { t } < 0 , whereas the vast majority of NEC-violating models presents a blue-tilted spectrum ( n _ { t } > 0 ) .
Since a blue tensor spectral index implies more power on small scales , this result is of considerable interest in view of a possible direct detection of the primordial gravitational-wave background .