  The interplay between cellular growth and cell-cell signaling is essential
for the aggregation and proliferation of bacterial colonies, as well as for the
self-organization of cell tissues. To investigate this interplay, we focus here
on the collective properties of dividing chemotactic cell colonies by studying
their long-time and large-scale dynamics through a renormalization group (RG)
approach. The RG analysis reveals that a relevant but unconventional
chemotactic interaction -- corresponding to a polarity-induced mechanism -- is
generated by fluctuations at macroscopic scales, even when an underlying
mechanism is absent at the microscopic level. This emerges from the interplay
of the well-known Keller--Segel (KS) chemotactic nonlinearity and cell birth
and death processes. At one-loop order, we find no stable fixed point of the RG
flow equations. We discuss a connection between the dynamics investigated here
and the celebrated Kardar--Parisi--Zhang (KPZ) equation with long-range
correlated noise, which points at the existence of a strong-coupling,
nonperturbative fixed point.
