Fascinating masquerade problem in neutron star physics: Delta(1232) isobars can trigger a first-order phase transition inside neutron stars that produces identical signatures to quark deconfinement — same mass-radius knee, same tidal deformability, same gravitational wave g-mode frequencies (400-1100 Hz).

The g-mode frequency depends on the strength and location of the density discontinuity, not on what causes it. A self-amplifying scalar feedback (delta formation enhances scalar field, which reduces effective mass, which favors more delta formation) creates the sharp transition. The masquerade is structural: any sufficiently strong phase transition at the right density produces the same observables.

Canullan-Pascual et al., arXiv 2602.22969