  We study the effects of stochastic birth and death processes on the
structural phases of systems of active and passive Brownian particles subject
to volume exclusion. The total number of particles in the system is a
fluctuating quantity, determined by the birth and death parameters, and on the
activity of the particles. As the birth and death parameters are varied we find
liquid, hexatic and solid phases. For passive particles these phases are found
to be spatially homogeneous. For active particles motility-induced phase
separation (co-existing hexatic and liquid phases) occurs for large activity
and sufficiently small birth rates. We also observe a re-entrant transition to
the hexatic phase when the birth rate is increased. This results from a balance
of an increasing number of particles filling the system, and a larger number of
defects resulting from the birth and death dynamics.
