Gravitational-wave emission in shift-symmetric Horndeski theories

TL;DR

This paper demonstrates that in shift-symmetric Horndeski theories, stellar sensitivities and dipolar gravitational radiation vanish under certain conditions, aligning predictions with binary pulsar observations and extending understanding of gravitational wave emission beyond General Relativity.

Contribution

The authors develop a formalism to compute sensitivities in scalar-tensor theories and show their vanishing in shift-symmetric Horndeski models under perturbative conditions.

Findings

Stellar sensitivities vanish in shift-symmetric Horndeski theories.

Dipolar gravitational radiation is suppressed under the studied conditions.

Results align with observed binary pulsar orbital decay.

Abstract

Gravity theories beyond General Relativity typically predict dipolar gravitational emission by compact-star binaries. This emission is sourced by "sensitivity" parameters depending on the stellar compactness. We introduce a general formalism to calculate these parameters, and show that in shift-symmetric Horndeski theories stellar sensitivities and dipolar radiation vanish, provided that the binary's dynamics is perturbative (i.e. the post-Newtonian formalism is applicable) and cosmological-expansion effects can be neglected. This allows reproducing the binary-pulsar observed orbital decay.