  Extreme active matter, an assembly of self-propelled particles with large
persistence time $\tau_p$ and high P\'eclet number, exhibits remarkable
behaviour at high densities. As $\tau_p\to 0$, the assembly undergoes a gradual
slowing down of density relaxations, as one reduces the active propulsion force
$f$, until at the glass transition, the relaxation times diverge. In the other
limit, $\tau_p \to \infty$, the fluid jams on lowering $f$, at a critical
threshold $f^*(\infty)$, with stresses concentrated along force-chains. As one
moves away from this jamming threshold, the force-chains dynamically remodel,
and the lifetime of the force-balanced configurations diverges as one
approaches $f^*(\infty)$, by tuning $\tau_p$. In between these limits, the
approach to dynamical arrest at low $f$, goes through a phase characterised by
intermittency in the kinetic energy. This intermittency is a consequence of
long periods of jamming followed by bursts of plastic yielding associated with
Eshelby deformations, akin to the response of dense amorphous solids to an
externally imposed shear. The frequency of these plastic bursts increases as
one moves towards the intermittent phase-fluid boundary, where the correlated
plastic events result in large scale vorticity and turbulence. Dense extreme
active matter brings together the physics of glass, jamming, plasticity and
turbulence, in a new state of driven classical matter.
