Speaker
Description
We present a unified Bayesian analysis of the dense-matter equation of state (EOS) of neutron stars by incorporating exotic hadronic degrees of freedom, namely antikaon condensation and Δ-resonances, within a density-dependent relativistic hadron framework. The model is constrained using nuclear saturation properties, chiral effective field theory ($\chi$EFT) calculations for symmetric and pure neutron matter up to $\sim 2\rho_0$, and multi-messenger astrophysical observations, including NICER mass–radius measurements of PSR J0030+0451 and PSR J0740+6620, tidal deformability constraints from GW170817, and the existence of $\sim 2~M_\odot$ neutron stars. For the antikaon sector, Bayesian inference yields an optical potential depth at nuclear saturation density of $U_{\bar{K}}(\rho_0)=-129.4_{-3.8}^{+12.5}$MeV ($68\%$ credible interval), indicating moderately strong attraction. We find that $K^⁻$ condensation is absent in canonical $1.4~M_\odot$ neutron stars but becomes energetically favourable in massive stars with $M\geq 2~M_\odot$, leading to significant EOS softening and a reduction of the squared speed of sound to $c_s^2\leq 0.3$ in the condensed phase. In parallel, the inclusion of Δ-resonances softens the EOS at intermediate densities $(\sim 1 - 3\rho_0)$ while preserving sufficient stiffness at higher densities to support maximum masses above $2~M_\odot$. Δ baryons are found to populate the outer core, contributing up to $\sim 20\%$ of the baryon fraction in the most massive configurations, and yielding radii $R_{1.4}\sim 12 - 13$ km and tidal deformabilities $\Lambda_{1.4}\sim 300 - 600$, consistent with GW170817. Furthermore, Δ-admixed EOSs predict fundamental f-mode frequencies $f_{1.4}=1.97_{-0.22}^{+0.17}$ kHz with damping times $τ_f\sim0.19_{-0.03}^{+0.05}$ s, highlighting strong correlations between compactness, tidal deformability, and asteroseismic observables. Our results demonstrate that antikaon condensation and Δ-resonances play complementary yet competing roles in neutron star interiors and establish a statistically consistent framework for probing dense QCD matter through current and future multi-messenger observations.