Spin-orbit effects for compact binaries in scalar-tensor gravity
Publication Date
2021-10Journal Title
Journal of Cosmology and Astroparticle Physics
ISSN
1475-7516
Publisher
IOP Publishing
Volume
2021
Issue
10
Language
en
Type
Article
This Version
VoR
Metadata
Show full item recordCitation
Brax, P., Davis, A., Melville, S., & Wong, L. (2021). Spin-orbit effects for compact binaries in scalar-tensor gravity. Journal of Cosmology and Astroparticle Physics, 2021 (10) https://doi.org/10.1088/1475-7516/2021/10/075
Abstract
Gravitational waves provide us with a new window into our Universe, and have
already been used to place strong constrains on the existence of light scalar
fields, which are a common feature in many alternative theories of gravity.
However, spin effects are still relatively unexplored in this context. In this
work, we construct an effective point-particle action for a generic spinning
body that can couple both conformally and disformally to a real scalar field,
and we show that requiring the existence of a self-consistent solution
automatically implies that if a scalar couples to the mass of a body, then it
must also couple to its spin. We then use well-established effective field
theory techniques to conduct a comprehensive study of spin-orbit effects in
binary systems to leading order in the post-Newtonian (PN) expansion. Focusing
on quasicircular nonprecessing binaries for simplicity, we systematically
compute all key quantities, including the conservative potential, the orbital
binding energy, the radiated power, and the gravitational-wave phase. We show
that depending on how strongly each member of the binary couples to the scalar,
the spin-orbit effects that are due to a conformal coupling first enter into
the phase at either 0.5PN or 1.5PN order, while those that arise from a
disformal coupling start at either 3.5PN or 4.5PN order. This suppression by
additional PN orders notwithstanding, we find that the disformal spin-orbit
terms can actually dominate over their conformal counterparts due to an
enhancement by a large prefactor. Accordingly, our results suggest that
upcoming gravitational-wave detectors could be sensitive to disformal
spin-orbit effects in double neutron star binaries if at least one of the two
bodies is sufficiently scalarised.
Keywords
paper, Gravitational waves in GR and beyond : theory, dark energy theory, modified gravity
Identifiers
jcap_108p_0721, jcap_108p_0721
External DOI: https://doi.org/10.1088/1475-7516/2021/10/075
This record's URL: https://www.repository.cam.ac.uk/handle/1810/329903
Rights
Licence:
http://creativecommons.org/licenses/by/4.0/
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