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Reaction-constrained composition g-modes in neutron stars with antikaon condensates, hyperons, and Δ(1232) resonances

Prashant Thakur1,* and Ishfaq Ahmad Rather2,†

  • 1Department of Physics, Yonsei University, Seoul, 03722, South Korea
  • 2Institut für Theoretische Physik, Goethe Universität, Max-von-Laue-Straße 1, D-60438 Frankfurt am Main, Germany

  • *Contact author: prashant@yonsei.ac.kr
  • †Contact author: rather@astro.uni-frankfurt.de
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Phys. Rev. D 114, 083034 – Published 19 October, 2026

DOI: https://doi.org/10.1103/146c-y868

Abstract

We investigate core composition g1 modes of cold, nonrotating neutron stars containing antikaon condensates, hyperons, and Δ(1232) baryons. To our knowledge, this is the first fully general-relativistic calculation of the continuous-composition core g1-mode frequency and gravitational-wave damping time for stars with a K− condensate. Using the BigApple equation of state (EOS), we compute frequencies and damping times in full general relativity (GR) and evaluate frozen-composition tidal overlaps from full-GR eigenfunctions within a leading-order hybrid resonance prescription. A species-resolved Ledoux decomposition, cross-checked through mode-frequency sensitivities, identifies the driving channels. We compare frozen composition with a fast-K limit for n↔p+K− and a strong-equilibrium limit for the Δ quartet. Fast-K equilibration retains 36%–44% of the peak local value of cs2−ce2. At the physical maxima or EOS-validity end points, the frequencies retain 65.7%–73.4% of their frozen values and the gravitational-wave damping times increase by factors of 14.3–31.9, while the kaon-associated mode remains above the nucleonic band. Strong Δ equilibration removes most of the direct Δ-induced enhancement, returning the NΔ mode toward the nucleonic band, whereas the high-frequency NYΔ branch survives because of the frozen Λ gradient. Eigenfunction tracking confirms a continuous g1 branch, and DD-ME2 reproduces this hierarchy. For circular, equal-mass binary neutron-star inspirals, the frozen-composition phase-shift estimates satisfy |ΔΦg1|≤1.410×10−3  rad, a factor of 21 below the 0.03-rad favorable-event benchmark reported for the Einstein Telescope. An exotic species therefore produces a distinct composition mode only if its composition gradient, or a coupled slowly equilibrating gradient, survives over the oscillation period.

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Phys. Rev. D 114, 083034– Published 19 October, 2026
  • Received 1 August 2026
  • Accepted 21 September 2026
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