Gravity in mimetic scalar-tensor theories after GW170817

Understand

We derive the most general mimetic scalar-tensor theory assuming a healthy "seed" action and accounting for the constraints on the speed of gravitational-wave propagation arising from the GW170817 event.

• By analysing linear perturbations around a flat FLRW background in this model, we obtain a suitable form of the Poisson equation, which allows us to calculate the effective gravitational constant felt by "ordinary" matter.
• By restricting to a minimally coupled model, such an effective gravitational constant is equivalent to that obtained within General Relativity, with cold dark matter plus a perfect fluid dark energy component, with vanishing sound speed.
• Assuming, further, a $\Lambda$CDM background, the effective gravitational constant cannot be distinguished from that of the standard $\Lambda$CDM model, at linear order.