More about stable wormholes in beyond Horndeski theory

Understand

It is known that Horndeski theories, like many other scalar-tensor gravities, do not support static, spherically symmetric wormholes: they always have either ghosts or gradient instabilities among parity-even linearized perturbations.

• Here we address the issue of whether or not this no-go theorem is valid in "beyond Horndeski" theories.
• We derive, in the latter class of theories, the conditions for the absence of ghost and gradient instabilities for non-spherical parity even perturbations propagating in the radial direction.
• We find, in agreement with existing arguments, that the proof of the above no-go theorem does not go through beyond Horndeski.