On constraining the speed of gravitational waves following GW150914 (1602.04188v2)

Abstract: We point out that the observed time delay between the detection of the signal at the Hanford and Livingston LIGO sites from the gravitational wave event GW150914 places an upper bound on the speed of propagation of gravitational waves, $c_{gw}\lesssim 1.7$ in the units of speed of light. Combined with the lower bound from the absence of gravitational Cherenkov losses by cosmic rays that rules out most of subluminal velocities, this gives a model-independent double-sided constraint $1\lesssim c_{gw}\lesssim 1.7$. We compare this result to model-specific constraints from pulsar timing and cosmology.

• The paper provides a model-independent bound on gravitational wave speed using GW150914 time-delay data from LIGO detectors.
• It establishes an upper limit of about 1.7 times the speed of light while the lower limit remains near c, ruling out significant subluminal speeds.
• These constraints support tests of Lorentz violation and quantum gravity models, paving the way for more refined astrophysical studies.

Constraining the Speed of Gravitational Waves Following GW150914

The paper titled "On constraining the speed of gravitational waves following GW150914" by Blas et al. focuses on deriving constraints on the speed of gravitational waves (GW) using observational data from the GW150914 event detected by the LIGO experiment. This analysis is grounded in employing a model-independent approach to establish a double-sided constraint on the gravitational wave speed relative to the speed of light.

Summary of Findings

The authors present an upper bound for the speed of GWs derived from the time delay observed between the signal arrivals at two separate LIGO sites, namely Hanford and Livingston. Their estimation places the upper limit of the GW speed to be $c_{gw} \lesssim 1.7$ times the speed of light. This constraints gravitational wave propagation in the regime of faster-than-light speeds. Complementary to this, the absence of gravitational Cherenkov radiation from cosmic rays provides a lower bound, eliminating most possibilities of subluminal GW velocities. As a result, the paper proposes a model-independent range of $1 \lesssim c_{gw} \lesssim 1.7$.

Technical Implications

The approach used by the authors leverages the dispersion relation of gravitational waves, parameterized with the speed of gravity $c_{gw}$, while considering higher-order terms in the wave's momentum. By examining the detectable impact of different $c_{gw}$ in cosmological and astrophysical contexts, this paper makes a significant contribution towards understanding how deviations in GW speed can serve as an observational probe for new physics, including Lorentz-violating theories or models of quantum gravity.

Existing Theoretical Context

It is essential to highlight that while alternative bounds on GW speed exist in astrophysical and cosmological literature, these often derive from specific theoretical frameworks. Examples include radiation damping constraints in binary systems and scalar-tensor theories that also incorporate tests of Lorentz invariance. However, such bounds are not universally applicable across potential gravity theories.

Discussion and Future Work

This analysis opens up further possibilities for using gravitational wave observations as a tool to investigate fundamental aspects of gravity. The constraints deduced are conservative in nature, with potential enhancements feasible through additional factors like precise detector orientation and waveform amplitude analysis. The authors also suggest extending this work through detailed numerical simulations of binaries or employing data-driven methods to differentiate time delay measurements from gravitational wave emission modeling.

The implications of these findings are broad, ranging from testing the foundations of relativity under extreme conditions to exploring gravitational interactions beyond the classical regime. As observational capabilities improve and more events are recorded, future studies are expected to refine these constraints and explore the connection between gravitational wave speed and underlying theories of quantum gravity.