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Dynamical hair growth in black hole binaries in Einstein-scalar-Gauss-Bonnet gravity

Lodovico Capuano1,2,3,*, Llibert Aresté Saló4,5,†, Daniela D. Doneva6,7,‡, Stoytcho S. Yazadjiev8,9,§, and Enrico Barausse1,2,∥

  • *Contact author: lcapuano@sissa.it, lodovico.capuano@uniroma1.it
  • †Contact author: llibert.arestesalo@kuleuven.be
  • ‡Contact author: daniela.doneva@uni-tuebingen.de
  • §Contact author: yazad@phys.uni-sofia.bg
  • ∥Contact author: barausse@sissa.it
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Phys. Rev. D 113, 124038 – Published 12 June, 2026

DOI: https://doi.org/10.1103/hgfh-rwrw

Abstract

Within the framework of scalar-tensor theories of gravity, certain models can evade classical black hole no-hair theorems. A well-known example is Einstein-scalar-Gauss-Bonnet gravity, where black holes carrying a scalar charge can exist. We find that, within this theory, binary black holes initially described by general relativity can acquire scalar charges once they reach a critical orbital separation (“dynamical scalarization”). We develop a simple semianalytic model, based on the adiabatic conservation of the total Wald entropy, to estimate the scalar charge evolution during the binary inspiral. We also run fully nonlinear numerical-relativity simulations for different configurations, finding consistent results. The gravitational-wave phase difference between Einstein-scalar-Gauss-Bonnet and general relativity waveforms, which we use to assess detectability, is also computed. We find that dynamical scalarization might be observable in nearly equal-mass binary black hole mergers with third-generation ground-based gravitational-wave detectors, in a narrow range of the dimensional coupling of the theory.

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Phys. Rev. D 113, 124038– Published 12 June, 2026
  • Received 25 February 2026
  • Accepted 4 May 2026
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