Standard sirens with a running Planck mass
Abstract
We consider the effect of a timevarying Planck mass on the propagation of gravitational waves (GWs). A running Planck mass arises naturally in several modifiedgravity theories, and here we focus on those that carry an additional dark energy field responsible for the latetime accelerated expansion of the Universe, yet—like general relativity (GR)—propagate only two GW polarizations, both traveling at the speed of light. Because a timevarying 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 timevarying Planck mass, where c_{M}=0 corresponds to GR with a constant Planck mass. The effect of nonzero c_{M} will have a noticeable impact on GWs emitted by binary neutron stars (BNSs) at the sensitivities and distances observable by groundbased 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 cold dark matter 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 (e.g., from the cosmic microwave background), then 100 BNS events detected by Advanced LIGO can constrain c_{M} to within ±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 ±0.5 . When analyzing joint H_{0} and c_{M} constraints we find that ̃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 σ to 4 σ too low if we incorrectly assume c_{M}=0 .
 Publication:

Physical Review D
 Pub Date:
 April 2019
 DOI:
 10.1103/PhysRevD.99.083504
 arXiv:
 arXiv:1901.03321
 Bibcode:
 2019PhRvD..99h3504L
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Minor changes and new references