Description
Scalar-tensor theories of gravity play an essential role for building models of inflation and dark
energy. For a very long time the focus has been placed on those theories leading to second order
field equations, believing all the others plagued by instabilities. In this talk I will present new
degenerate theories that, despite higher order in the equations of motion, are free from such a kind
of pathology. Moreover, I will show that some higher order scalar-tensor theories are a useful tool
to study parity violating effects in the gravity sector.