Positivity in the effective field theory of cosmological perturbations

Understand

Requiring the existence of a unitary, causal and local UV-completion places a set of positivity bounds on the corresponding effective field theories (EFTs).

• We discuss the obstructions and possibility in applying the positivity bound to cosmology, in particular the EFT of cosmological perturbations.
• Taking a $c_T=1$ beyond-Horndeski EFT as an illustrative example, we derive such bounds, which incorporate the cosmological correction of order $H^2/\Lambda^2$, $\Lambda$ being the cutoff scale.
• The derived bounds are applied to slow-roll inflation with beyond Horndeski operators.