Quintessence–Chameleon transitions in anisotropic Kiselev model of neutron stars

We investigate a chameleon scalar field dynamically interacting with a Kiselev-type metric, where the static anisotropic fluid part of the metric is replaced by a density-dependent scalar field nonminimally coupled to curvature. This construction enables a transition from screened behavior in high-density regions — where the scalar acquires an effective mass [Formula: see text] — to unscreened quintessence dynamics at large scales, characterized by a critical screening radius [Formula: see text]. By solving the modified Tolman–Oppenheimer–Volkoff equations under spherical symmetry, we show that radial scalar gradients [Formula: see text] induce pressure anisotropies [Formula: see text] in neutron star envelopes, while deviations from general relativity (GR) are suppressed deep in the core [Formula: see text] without destabilizing it. We further demonstrate that increasing the scalar coupling [Formula: see text] enhances scalar energy density, which counteracts anisotropic pressure support and slightly reduces the maximum mass. The resulting (stable) configurations yield maximum mass [Formula: see text] and radii [Formula: see text], consistent with conservative upper and lower bounds from multimessenger observations. Scalar contributions induce a modest suppression in the dimensionless tidal deformability [Formula: see text] at [Formula: see text], i.e. 86% suppression compared to typical GR star, falling well within the LIGO/Virgo range [Formula: see text]. These results demonstrate that environmentally screened scalar fields can dynamically generate anisotropies and modify neutron star structure without violating current astrophysical bounds. In particular, percent-level deviations in compactness and tidal response provide falsifiable signatures of short-range scalar forces, offering a novel target for next-generation gravitational wave and multimessenger surveys.