  We introduce and develop the theory of metaparticles. At the classical level,
this is a world-line theory with the usual reparameterization invariance and
two additional features. The theory is motivated by string theory on compact
targets, and can be thought of, at least at the non-interacting level, as a
theory of particles at a given string level, or as a particle model for Born
geometries. The first additional feature of the model is the presence of an
additional local symmetry, which from the string point of view corresponds to
the completion of worldsheet diffeomorphism invariance. From the particle
world-line point of view, this symmetry is associated with an additional local
constraint. The second feature is the presence of a non-trivial symplectic form
on the metaparticle phase space, also motivated by string theory [1, 2].
Because of its interpretation as a particle model on Born geometry, the
space-time on which the metaparticle propagates is ambiguous, with different
choices related by what in string theory we would call T-duality. In this
paper, we define the model, and explore some of its principle classical and
quantum properties, including causality and unitarity.
