  Accretion discs properties should deviate from standard theory when magnetic
pressure exceeds the thermal pressure. To quantify these deviations, we present
a systematic study of the dynamical properties of magnetically arrested discs
(MADs), the most magnetized type of accretion disc. Using an artificial cooling
function to regulate the gas temperature, we study MADs of three different
thermal thicknesses, $h_\mathrm{th}/r=0.3, 0.1$ and $0.03$. We find that the
radial structure of the disc is never mostly supported by the magnetic field.
In fact, thin MADs are very near Keplerian. However, as discs gets colder, they
become more magnetized and the largest deviations from standard theory appear
in our thinnest disc with $h_\mathrm{th}/r=0.03$. In this case, the disc is
much more extended vertically and much less dense than in standard theory
because of vertical support from the turbulent magnetic pressure and
wind-driven angular momentum transport that enhances the inflow speed. The thin
disc also dissipates a lot of thermal energy outside of $z/r = \pm 0.03$ and a
significant fraction of this dissipation happens in mildly relativistic winds.
The enhanced dissipation in low-density regions could possibly feed coronae in
X-ray binaries (XRBs) and active galactic nuclei (AGN). Wind-driven accretion
will also impact the dynamical evolution of accretion discs and could provide a
mechanism to explain the rapid evolution of changing-look AGN and the secular
evolution of XRBs. Finally, our MAD winds have terminal velocities and mass
loss rates in good agreement with the properties of ultra-fast outflows
observed in AGN.
