Dark matter and string T-duality density

Abstract Understanding the nature of dark matter remains one of the most enigmatic and unresolved issues in astrophysics. Certain theoretical models address this by introducing a novel component to account for dark matter. In this study, we propose a new scalar field derived from string T-duality, where its associated density represents the density of the surrounding matter field, in the spherically symmetric and static medium. Our exploration reveals that this scalar field behaves as the baryonic fluid, characterized by a positive effective state equation, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ω</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">e</mml:mi> </mml:mrow> </mml:msub> <mml:mo>&gt;</mml:mo> <mml:mn>0</mml:mn> </mml:math> . Furthermore, a detailed investigation demonstrates that this model satisfies all energy conditions beyond the event horizon of a central black hole. Considering the light deflection and radar echo delay suggests that in this scalar field, the dark matter grows up in the halo and surrounding regions of galaxy systems. This indicates that dark matter accumulates as an effective field outside the observable regions of galaxies.