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Adiabatic perturbations in GW170817-compatible Einstein-Gauss-Bonnet inflation

S. D. Odintsov1,2,* and V. K. Oikonomou3,4,†

  • *Contact author: odintsov@ieec.cat
  • †Contact author: voikonomou@gapps.auth.gr
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Phys. Rev. D 114, 084026 – Published 7 October, 2026

DOI: https://doi.org/10.1103/hndp-kq49

Abstract

We study the adiabaticity of the cosmological perturbations in the context of inflationary Einstein-Gauss-Bonnet theories. We focus on viable inflationary Einstein-Gauss-Bonnet theories which are compatible with the current cosmic microwave background radiation experiments and also are compatible with the GW170817 observations. We derive the effects of the adiabaticity requirement on the Einstein-Gauss-Bonnet physical parameters and we show that the sound speed of the scalar perturbations and the propagation speed of the tensor perturbations are constrained. We consider two classes of inflationary viable and GW170817-compatible theories, and in the first class the adiabaticity is not violated during inflation, while in the second class the adiabaticity is violated only at the end of inflation. We discuss the effects of the adiabaticity violation in the second class of models. From our analysis, it seems that only one class of viable EGB inflationary theories, which is also compatible with the GW170817 event, is free from adiabaticity pathologies.

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Phys. Rev. D 114, 084026– Published 7 October, 2026
  • Received 10 August 2026
  • Accepted 22 September 2026
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