Aberration of gravitational waveforms by peculiar velocity

Camille Bonvin*, Giulia Cusin, Cyril Pitrou, Simone Mastrogiovanni, Giuseppe Congedo, Jonathan Gair

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

One key prediction of General Relativity is that gravitational waves are emitted with two independent polarizations. Any observation of extra polarization mode, spin-1 or spin-0, is consequently considered a smoking gun for deviations from General Relativity. In this paper, we show that the velocity of merging binaries with respect to the observer gives rise to spin-1 polarization in the observer frame even in the context of General Relativity. These are pure projection effects, proportional to the plus and cross polarizations in the source frame, hence they do not correspond to new degrees of freedom. We demonstrate that the spin-1 modes can always be rewritten as pure spin-2 modes coming from an aberrated direction. Since gravitational waves are not isotropically emitted around binary systems, this aberration modifies the apparent orientation of the binary system with respect to the observer: the system appears slightly rotated due to the source velocity. Fortunately, this bias does not propagate to other parameters of the system (and therefore does not spoil tests of General Relativity), since the impact of the velocity can be fully reabsorbed into new orientation angles.

Original languageEnglish
Pages (from-to)476-488
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Volume525
Issue number1
Early online date27 Jun 2023
DOIs
Publication statusPublished - 1 Oct 2023

Keywords / Materials (for Non-textual outputs)

  • cosmology: theory
  • gravitational waves

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