A spherical scalar-tensor galaxy model
  We build a spherical halo model for galaxies using a general scalar-tensor
theory of gravity in its Newtonian limit. The scalar field is described by a
time-independent Klein-Gordon equation with a source that is coupled to the
standard Poisson equation of Newtonian gravity. Our model, by construction,
fits both the observed rotation velocities of stars in spirals and a typical
luminosity profile. As a result, the form of the new Newtonian potential, the
scalar field, and dark matter distribution in a galaxy are determined. Taking
into account the constraints for the fundamental parameters of the theory
(lambda,alpha), we analyze the influence of the scalar field in the dark matter
distribution, resulting in shallow density profiles in galactic centers.
