Exploring gravitational waveforms beyond general relativity

Key experts gather for the workshop “Connecting the dots” at the Max Planck Institute for Gravitational Physics in Potsdam, June 14th-16th, 2023.

June 08, 2023

Einstein’s general theory of relativity has proven to be an extremely successful tool for exploring the universe. Coalescing compact binaries – black holes and/or neutron stars – and their gravitational-wave signals are described and understood by solving Einstein’s equations. Even though no deviation from General Relativity has been observed so far, there are good arguments from both cosmology and quantum gravity to look for alternatives. The key focus of this workshop is to pave the way toward complete and accurate inspiral-merger-ringdown waveform templates in gravity theories beyond General Relativity. The workshop is supported by the Gravity Theory Trust.

With 90 detected gravitational waves since 2015 and many more to come during the recently launched observing run O4, gravitational-wave astronomy has become a valuable method for observing the dark side of the universe. Astronomers are no longer blind to black holes in compact binary systems, and they can extract more and more astrophysical and cosmological information from the data.

The detection and parameter estimation of these events depend crucially on providing accurate waveform templates to the LIGO-Virgo-KAGRA Collaboration, or to its successors in the next decade (such as the Einstein Telescope, the Cosmic Explorer, and LISA). To date, however, only General Relativity has libraries of such waveform templates.

Despite the success of Einstein’s theory, there are strong motivations to modify it, both from observational cosmology (e.g., dark energy and dark matter) and from theoretical puzzles in quantum gravity (e.g., non-renormalizability and the information loss paradox). But deriving gravitational waveforms in modified gravity theories is technically challenging. So far, existing works provide only partial waveforms covering either the early or late inspiral, merger, or ringdown stages of a compact binary coalescence.

The key focus of this workshop is to “connect the dots”, and pave the way toward complete and accurate inspiral-merger-ringdown waveform templates in gravity theories beyond General Relativity. This goal will be achieved by gathering key experts in the field to identify the synergy between their own activities, foster new collaborations and bring novel ideas on the following issues

  • Which modified gravity theories are best motivated?
  • What are the limitations of current tests of general relativity with gravitational-wave observations?
  • What is the state of the art in the modeling of the inspiral, merger and ringdown beyond general relativity?
  • How to fit these developments together and obtain complete inspiral-merger-ringdown waveforms beyond general relativity?
  • Can we test gravity in new ways with such waveforms, and are there new beyond- general relativity effects?
  • What are the challenges for detecting beyond-General-Relativity physics with next-generation detectors?
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