Non-trivial gravitational waves and structure formation phenomenology from dark energy

Understand

The detection of the GW170817/GRB170817A event improved the constraints on the propagation speed of gravitational waves, thus placing possible variations caused by dark energy under restraint.

• For models based on scalar fields belonging to the family of Horndeski Lagrangians, non-minimal derivative couplings are now severely constrained, entailing a substantially limited phenomenology.
• In this work we want to stress that there is still a plethora of dark energy models that get around this obstacle while still providing interesting phenomenologies able to distinguish them from the standard cosmology.
• We focus on a class involving vector fields as a proxy, but our discussion is extensible to a broader class of models.