The Delta-isobar masquerade: intrahadronic phase transitions and their quark-mimicking signatures in neutron stars
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2026
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| author | Canullan-Pascual, Martin O. Lugones, Germán Ranea-Sandoval, Ignacio F. Orsaria, Milva G. |
| author_facet | Canullan-Pascual, Martin O. Lugones, Germán Ranea-Sandoval, Ignacio F. Orsaria, Milva G. |
| contents | We investigate the conditions under which $Δ(1232)$ isobars trigger a first-order phase transition within purely hadronic neutron-star matter, using the SW4L relativistic mean-field parametrization. For scalar-vector coupling differences $0.15 \lesssim x_{σΔ} - x_{ωΔ} \lesssim 0.2$ and $x_{σΔ} \gtrsim 1.3$, the onset of $Δ^-$ resonances produces a van der Waals-like instability driven by a self-amplifying feedback in the scalar meson sector, in which the $Δ^-$ particle fraction acts as the order parameter of a Landau-type transition. A Maxwell construction yields a sharp density discontinuity at baryon densities $n_b \sim (1.3$-$2)\,n_0$, separating a $Δ$-free outer core from a $Δ$-rich inner core. The resulting neutron-star sequences satisfy all current multimessenger constraints: maximum masses $M_{\rm max} \approx 2.15$-$2.25\,M_\odot$, radii $R_{1.4} \approx 11$-$12$ km, and tidal deformabilities $Λ_{1.4} \approx 190$-$480$, compatible with NICER observations and GW170817. We compute, for the first time for a $Δ$-induced interface, the $\ell = 2$ composition $g$-mode eigenfrequencies, obtaining $ν_g \sim 400$-$1100$ Hz with gravitational-wave damping times $τ_g \sim 10^3$-$10^9$ s. These frequencies overlap quantitatively with those predicted for hadron-quark phase-transition interfaces, demonstrating that the mass-radius ``knee'', reduced tidal deformability, and $g$-mode spectrum conventionally regarded as signatures of quark deconfinement can be reproduced by a purely intrahadronic mechanism. This extends the masquerade problem from static observables to the domain of gravitational-wave asteroseismology, implying that a future detection of a discontinuity $g$-mode alone would not suffice to identify quark matter in neutron-star cores. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2602_22969 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The Delta-isobar masquerade: intrahadronic phase transitions and their quark-mimicking signatures in neutron stars Canullan-Pascual, Martin O. Lugones, Germán Ranea-Sandoval, Ignacio F. Orsaria, Milva G. Nuclear Theory High Energy Astrophysical Phenomena We investigate the conditions under which $Δ(1232)$ isobars trigger a first-order phase transition within purely hadronic neutron-star matter, using the SW4L relativistic mean-field parametrization. For scalar-vector coupling differences $0.15 \lesssim x_{σΔ} - x_{ωΔ} \lesssim 0.2$ and $x_{σΔ} \gtrsim 1.3$, the onset of $Δ^-$ resonances produces a van der Waals-like instability driven by a self-amplifying feedback in the scalar meson sector, in which the $Δ^-$ particle fraction acts as the order parameter of a Landau-type transition. A Maxwell construction yields a sharp density discontinuity at baryon densities $n_b \sim (1.3$-$2)\,n_0$, separating a $Δ$-free outer core from a $Δ$-rich inner core. The resulting neutron-star sequences satisfy all current multimessenger constraints: maximum masses $M_{\rm max} \approx 2.15$-$2.25\,M_\odot$, radii $R_{1.4} \approx 11$-$12$ km, and tidal deformabilities $Λ_{1.4} \approx 190$-$480$, compatible with NICER observations and GW170817. We compute, for the first time for a $Δ$-induced interface, the $\ell = 2$ composition $g$-mode eigenfrequencies, obtaining $ν_g \sim 400$-$1100$ Hz with gravitational-wave damping times $τ_g \sim 10^3$-$10^9$ s. These frequencies overlap quantitatively with those predicted for hadron-quark phase-transition interfaces, demonstrating that the mass-radius ``knee'', reduced tidal deformability, and $g$-mode spectrum conventionally regarded as signatures of quark deconfinement can be reproduced by a purely intrahadronic mechanism. This extends the masquerade problem from static observables to the domain of gravitational-wave asteroseismology, implying that a future detection of a discontinuity $g$-mode alone would not suffice to identify quark matter in neutron-star cores. |
| title | The Delta-isobar masquerade: intrahadronic phase transitions and their quark-mimicking signatures in neutron stars |
| topic | Nuclear Theory High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2602.22969 |