Probing the speed of gravity with LVK, LISA, and joint observations

Ian Harry, Johannes Noller

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Theories of dark energy that affect the speed of gravitational waves cGW on cosmological scales naturally lead to a frequency-dependent transition of that speed close to the LIGO/Virgo/KAGRA (LVK) band. While observations such as GW170817 assure us that cGW is extremely close to the speed of light in the LVK band, a frequency-dependent transition below the LVK band is a smoking-gun signal for large classes of dynamical dark energy theories. Here we discuss (1) how the remnants of such a transition can be constrained with observations in the LVK band, (2) what signatures are associated with such a transition in the LISA band, and (3) how joint observations in the LVK and LISA bands allow us to place tight constraints on this transition and the underlying theories. We find that deviations of cGW can be constrained down to a level of ∼10−17 in the LVK and LISA bands even for mild frequency-dependence, much stronger than existing bounds for frequency-independent cGW≠c. We use the strain data from GW170817 to bound the deviation of cGW to be less than 10−17 at 100 Hz and less than 10−18 at 500 Hz. We also identify a particularly interesting type of transition in between the LVK and LISA bands and show how multi-band observations can constrain this further. Finally, we discuss what these current and forecasted constraints imply for the underlying dark energy theories.
Original languageEnglish
Article number133
Number of pages34
JournalGeneral Relativity and Gravitation
Publication statusPublished - 26 Oct 2022


  • gr-qc
  • astro-ph.CO
  • astro-ph.HE
  • hep-th
  • Gravitational waves
  • Dark Energy
  • Modified Gravity
  • UKRI
  • STFC
  • ST/S004572/1
  • ST/T000333/1
  • ST/V005715/1
  • TC_highlight


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