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Scalar emission from binary neutron stars in scalar-tensor theories with kinetic screening

Ramiro Cayuso1,2,*, Adrien Kuntz3,†, Thiago Assumpção4,‡, Miguel Bezares5,6,§, and Enrico Barausse1,2,∥

  • *Contact author: rcayuso@sissa.it
  • †Contact author: adrien.kuntz@tecnico.ulisboa.pt
  • ‡Contact author: tassumpo@uwm.edu
  • §Contact author: miguel.bezaresfigueroa@nottingham.ac.uk
  • ∥Contact author: barausse@sissa.it
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Phys. Rev. D 114, 024073 – Published 27 July, 2026

DOI: https://doi.org/10.1103/tvym-y49r

Abstract

We investigate the scalar emission from binary neutron stars in shift-symmetric scalar-tensor theories with kinetic screening (K-essence), using 3+1 numerical simulations in the decoupling limit. To construct static binary initial data in the regime where the screening radius r* greatly exceeds the orbital separation, we introduce a hyperbolization of the static field equations that bypasses the Keldysh-type breakdown affecting direct time evolutions. For equal-mass binaries, where the scalar emission is dominated by the ℓ=m=2 mode, kinetic screening acts nonmonotonically on the scalar radiation, suppressing or enhancing the quadrupolar amplitude depending on the relative size of r* and λ22 (with λ22 the wavelength): for λ22≪r* it is suppressed relative to the Fierz-Jordan-Brans-Dicke (FJBD) case, while for λ22≳r* it is amplified above FJBD. For unequal-mass binaries a scalar dipole reemerges, growing linearly with the mass asymmetry, while the quadrupolar screening remains close to the equal-mass case down to mass ratios ∼0.6. The nonmonotonic behavior of kinetic screening that we uncover has potential implications for gravitational-wave-based tests of gravity. The relativistic double pulsar, in particular, requires r*≫109  km to efficiently suppress the scalar quadrupole; for cosmologically-motivated Λ, r*∼1011  km (for a solar-mass source), giving only moderate suppression.

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Phys. Rev. D 114, 024073– Published 27 July, 2026
  • Received 4 May 2026
  • Accepted 13 July 2026
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