  Conformal higher spin (CHS) fields, despite being non unitary, provide a
remarkable example of a consistent interacting higher spin theory in flat space
background, that is local to all orders. The non-linear action is defined as
the logarithmically UV divergent part of a one-loop scalar effective action. In
this paper we take a particle model, that describes the interaction of a scalar
particle to the CHS background, and compute its path integral on the circle. We
thus provide a worldline representation for the CHS action, and rederive its
quadratic part. We plan to come back to the subject, to compute cubic and
higher vertices, in a future work.
