Scale-Invariant Dynamics of Galaxies, MOND, Dark Matter, and the Dwarf
  Spheroidals
  The Scale-Invariant Vacuum (SIV) theory is based on Weyl's Integrable
Geometry, endowed with a gauge scalar field. The main difference between MOND
and the SIV theory is that the first considers a global dilatation invariance
of space and time, where the scale factor $\lambda$ is a constant, while the
second opens the likely possibility that $\lambda$ is a function of time. The
key equations of the SIV framework are used here to study the relationship
between the Newtonian gravitational acceleration due to baryonic matter
$g_{\mathrm{bar}}$ and the observed kinematical acceleration
$g_{\mathrm{obs}}$. The relationship is applied to galactic systems of the same
age where the Radial Acceleration Relation (RAR), between the
$g_{\mathrm{obs}}$ and $g_{\mathrm{bar}}$ accelerations, can be compared with
observational data. The SIV theory shows an excellent agreement with
observations and with MOND for baryonic gravities $g_{\mathrm{bar}}>10^{-11.5}$
m s$^{-2}$. Below this value, SIV still fully agrees with the observations, as
well as with the horizontal asymptote of the RAR for dwarf spheroidals, while
this is not the case for MOND. These results support the view that there is no
need for dark matter and that the RAR and related dynamical properties of
galaxies can be interpreted by a modification of gravitation.
