Quintessence-Chameleon transitions in anisotropic Kiselev model of neutron stars

TL;DR

This paper explores how a chameleon scalar field interacting with an anisotropic neutron star model can cause observable effects like pressure anisotropies and modifications in star mass, radius, and tidal deformability, consistent with current observations.

Contribution

It introduces a novel model where a scalar field causes anisotropies in neutron stars, bridging screening mechanisms with astrophysical observations.

Findings

Scalar field induces pressure anisotropies in neutron star envelopes.

Maximum neutron star mass is around 1.75 solar masses, consistent with observations.

Scalar effects suppress tidal deformability, providing testable signatures.

Abstract

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 non-minimally coupled to curvature. This construction enables a transition from screened behavior in high-density regions-where the scalar acquires an effective mass m_\phi\propto\rho^1/2-to unscreened quintessence dynamics at large scales, characterized by a critical screening radius r_\rm crit\propto m_\phi^-1. By solving the modified TOV equations under spherical symmetry, we show that radial scalar gradients \partial_r\phi induce pressure anisotropies \Delta p\propto r^-1 in neutron star envelopes, while deviations from general relativity are suppressed deep in the core r<r_\rm crit\sim 0.03\,\mathrm{km} without destabilizing it. We further demonstrate that increasing the scalar coupling \beta enhances scalar energy density, which counteracts anisotropic pressure support and slightly reduces the maximum mass. The resulting (stable) configurations yield maximum mass M_max\approx 1.75\pm0.280\,M_\odot and radii R\approx11.35\pm1.11\,\mathrm{km}, consistent with conservative upper and lower bounds from multimessenger observations. Scalar contributions induce a modest suppression in the dimensionless tidal deformability \Lambda_\rm ST\Lambda_\rm GR\sim0.137 at 1.4\,M_\odot i.e, 86% suppression compared to typical GR star, falling well within the LIGO/Virgo range 70\lesssim\Lambda_1.4\lesssim 580. 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 GW and multimessenger surveys.