How chameleons core dwarfs with cusps
  The presence of a scalar field that couples nonminimally and universally to
matter can enhance gravitational forces on cosmological scales while restoring
general relativity in the Solar neighborhood. In the intermediate regime,
kinematically inferred masses experience an additional radial dependence with
respect to the underlying distribution of matter, which is caused by the
increment of gravitational forces with increasing distance from the Milky Way
center. The same effect can influence the internal kinematics of subhalos and
cause cuspy matter distributions to appear core-like. Specializing to the
chameleon model as a worked example, we demonstrate this effect by tracing the
scalar field from the outskirts of the Milky Way halo to its interior,
simultaneously fitting observed velocity dispersions of chemo-dynamically
discriminated red giant populations in the Fornax and Sculptor dwarf
spheroidals. Whereas in standard gravity these observations suggest that the
matter distribution of the dwarfs is cored, we find that in the presence of a
chameleon field the assumption of a cuspy Navarro-Frenk-White profile becomes
perfectly compatible with the data. Importantly, chameleon models also predict
the existence of slopes between two stellar subcomponents that in Newtonian
gravity would be interpreted as a depletion of matter in the dwarf center.
Hence, an observation of such an apparently pathological scenario may serve as
a smoking gun for the presence of a chameleon field or a similar modification
of gravity, independent of baryonic feedback effects. In general, measuring the
dynamic mass profiles of the Milky Way dwarfs provides stronger constraints
than those inferred from the screening scale of the Solar System since these
are located at greater distances from the halo center.
