  We study self-propelled particles with velocity reversal interacting by
uniaxial (nematic) alignment within a coarse-grained hydrodynamic theory.
Combining analytical and numerical continuation techniques, we show that the
physics of this active system is essentially controlled by the reversal
frequency. In particular, we find that elongated, high-density, ordered
patterns, called bands, emerge via subcritical bifurcations from spatially
homogeneous states. Our analysis reveals further that the interaction of bands
is weakly attractive and, consequently, bands fuse upon collision in analogy
with nonequilibrium nucleation processes. Moreover, we demonstrate that a
renormalized positive line tension can be assigned to stable bands below a
critical reversal rate, beyond which they are transversally unstable. In
addition, we discuss the kinetic roughening of bands as well as their nonlinear
dynamics close to the threshold of transversal instability. Altogether, the
reduction of the multi-particle system onto the dynamics of bands provides a
framework to understand the impact of the reversal frequency on the emerging
nonequilibrium patterns in self-propelled particle systems. In this regard, our
results constitute a proof-of-principle in favor of the hypothesis in
microbiology that reversal of gliding rod-shaped bacteria regulates the
occurrence of various self-organized pattens observed during life-cycle phases.
