Effects of Chameleon Scalar Field on Rotation Curves of the Galaxies
  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 $\beta < 10^{-3}$.
