Effects of Chameleon Scalar Field on Rotation Curves of the Galaxies

TL;DR

This paper explores how chameleon scalar fields influence galaxy rotation curves, suggesting they can cause steeper cusps and providing observational constraints on the matter-chameleon coupling strength.

Contribution

It introduces the impact of chameleon scalar fields on dark matter halos and derives observational upper limits on their coupling strength from galaxy data.

Findings

Chameleon fields can significantly modify galaxy rotation curves.

Steeper cusps in rotation curves can be caused by chameleon fifth forces.

Upper limit on coupling constant is approximately 10^{-3}.

Abstract

We investigate the effects of chameleon scalar field to the effective density and pressure of a dark matter halo. The pressure is generated from the chameleonic fifth force on the matter. We demonstrate that the thick-shell non-singular boundary condition which forbids singular point leads to extremely stringent constraint on the matter-chameleon coupling when applied to galaxy. We argue that chameleon profile with central singularity is more likely to develop in general physical situation. The chameleonic fifth force from the chameleon profile with central singularity experienced by the dark matter could significantly modify the rotation curve of galaxies. The chameleonic fifth force could generate steeper cusp to the rotation curves in any dark matter profiles starting from the Navarro-Frenk-White (NFW) to the pseudo-isothermal (ISO) profile. Upper limits on the coupling constant between the chameleon and the dark matter are estimated from observational data of the late-type Low-Surface-Brightness galaxies (LSB). It is in the order of $\beta < 10^{-3}$.