  In this paper we develop a field-theoretic description for run and tumble
chemotaxis, based on a density functional description of crystalline materials
modified to capture orientational ordering. We show that this framework, with
its in-built multi-particle interactions, soft-core repulsion and elasticity is
ideal for describing continuum collective phases with particle resolution, but
on diffusive timescales. We show that our model exhibits particle aggregation
in an externally imposed constant attractant field, as is observed for
phototactic or thermotactic agents. We also show that this model captures
particle aggregation through self-chemotaxis, an important mechanism that aids
quorum dependent cellular interactions.
