Neutron stars in minimal dilatonic gravity

Abstract We study the structure of neutron stars within the framework of minimal dilatonic gravity (MDG), a scalar–tensor theory related to Brans–Dicke gravity with $$ \omega = 0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ω</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> </mml:mrow> </mml:math> . Using three realistic unified equations of state (EOSs), LOCV1804, LOCV1811, and LOCV1815, enabling us to investigate the sensitivity of MDG predictions to the stiffness of dense matter, we analyze stellar configurations for different values of the dilaton field mass $$ m_{\Phi } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:mi>Φ</mml:mi> </mml:msub> </mml:math> . Our results show that a dilaton halo forms around the neutron star, contributing significantly to the total mass. The halo mass fraction reaches 20–30% in neutron stars with masses greater than $$ 2M_{\odot } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2</mml:mn> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:mrow> </mml:math> , leading to total masses that exceed those predicted by General Relativity. These results are consistent with mass measurements from recent gravitational wave and NICER (Neutron Star Interior Composition Explorer) observations. We also find that smaller dilaton field masses yield more massive neutron star–halo systems. For high-density stars, the dilaton pressure becomes negative at the center and behaves like dark energy, modifying the radial profile of the dilaton field.