Standard sirens with a running Planck mass

Macarena Lagos; Maya Fishbach; Philippe Landry; Daniel E. Holz

doi:10.1103/PhysRevD.99.083504

paper

Standard sirens with a running Planck mass

arXiv:1901.03321 · doi:10.1103/PhysRevD.99.083504

Abstract

We consider the effect of a time-varying Planck mass on the propagation of gravitational waves (GWs). A running Planck mass arises naturally in several modified gravity theories, and here we focus on those that carry an additional dark energy field responsible for the late-time accelerated expansion of the universe, yet--like general relativity (GR)--propagate only two GW polarizations, both traveling at the speed of light. Because a time-varying Planck mass affects the amplitude of the GWs and therefore the inferred distance to the source, standard siren measurements of $H_{0}$ are degenerate with the parameter $c_{M}$ characterizing the time-varying Planck mass, where $c_{M} = 0$ corresponds to GR with a constant Planck mass. The effect of non-zero $c_{M}$ will have a noticeable impact on GWs emitted by binary neutron stars (BNSs) at the sensitivities and distances observable by ground-based GW detectors such as advanced LIGO and A+, implying that standard siren measurements can provide joint constraints on $H_{0}$ and $c_{M}$ . Assuming a $Λ$ CDM evolution of the universe and taking Planck's measurement of $H_{0}$ as a prior, we find that GW170817 constrains $c_{M} = - 9_{- 28}^{+ 21}$ ( $68.3%$ credibility). We also discuss forecasts, finding that if we assume $H_{0}$ is known independently, then 100 BNS events detected by advanced LIGO can constrain $c_{M}$ to within $\pm 0.9$ . This is comparable to the current best constraints from cosmology. Similarly, for 100 LIGO A+ BNS detections, it is possible to constrain $c_{M}$ to $\pm 0.5$ . When analyzing joint $H_{0}$ and $c_{M}$ constraints we find that $\sim 400$ LIGO A+ events are needed to constrain $H_{0}$ to $1%$ accuracy. Finally, we discuss the possibility of a nonzero value of $c_{M}$ biasing standard siren $H_{0}$ measurements from 100 LIGO A+ detections, and find that $c_{M} = + 1.35$ could bias $H_{0}$ by 3-4 $σ$ too low if we incorrectly assume $c_{M} = 0$ .

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Standard sirens with a running Planck mass

Abstract

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