Beyond general relativity: Gravitational waves in nonminimally coupled theories
Phys. Rev. D 114, 024005 – Published 1 July, 2026
DOI: https://doi.org/10.1103/d8rf-d2wf
Abstract
Nonminimal couplings between matter and curvature tensors arise in many different contexts. Such couplings modify solutions of general relativity (GR) and therefore can be probed in various astrophysical systems. A particularly interesting scenario arises if dark matter experiences nonminimal couplings, as dark matter densities are expected to spike in the vicinity of binary black hole mergers. This gives a novel setting for simultaneously studying dark matter and (beyond) GR physics via observations of gravitational waves (GWs). In this work, we explore effects of various nonminimal couplings on GWs by working with a model-independent parametrization for left- and right-handed GW strains. We extend the parametrization proposed in Jenks et al. [Phys. Rev. D 108, 044023 (2023)] and Daniel et al. [Phys. Rev. D 109, 124012 (2024)] to include early-universe effects, and we write down the generic solution assuming slowly varying matter fields. We then systematically apply our results to three models: Kalb-Ramond dark matter with dimension-four operators, axion-dilaton-Chern-Simons-Gauss-Bonnet dimension-five operators, and dimension-six couplings to a (dark) vector field.
