Behind Horndeski: Structurally Robust Higher Derivative EFTs

Understand

Higher derivative scalar interactions can give rise to interesting cosmological scenarios.

• We present a complete classification of such operators that can yield sizeable effects without introducing ghosts and, at the same time, define an effective field theory robust under the inclusion of quantum corrections.
• A set of rules to power count consistently the coefficients of the resulting Lagrangian is provided by the presence of an approximate global symmetry.
• The interactions that we derive in this way contain a subset of the so-called Horndeski and beyond Horndeski theories.