Piercing the Vainshtein screen with anomalous gravitational wave speed: Constraints on modified gravity from binary pulsars

TL;DR

Using binary pulsar observations, the paper constrains the speed of gravitational waves to test modified gravity theories, particularly scalar-tensor models with anomalous GW propagation, revealing that certain effects persist despite screening mechanisms.

Contribution

The study applies pulsar data to limit GW speed in scalar-tensor theories, challenging assumptions about screening effects in modified gravity models.

Findings

GW speed constrained to 1% level from pulsar data

Scalar field gradients can bypass Vainshtein screening

Constraints placed on dark energy effective field theory

Abstract

By using observations of the Hulse-Taylor pulsar we constrain the gravitational wave (GW) speed to the level of $10^{-2}$. We apply this result to scalar-tensor theories that generalize Galileon 4 and 5 models, which display anomalous propagation speed and coupling to matter for GWs. We argue that this effect survives conventional screening due to the persistence of a scalar field gradient inside virialized overdensities, which effectively "pierces" the Vainshtein screening. In specific branches of solutions, our result allows to directly constrain the cosmological couplings in the effective field theory of dark energy formalism.