  We study properties of classical reparametrization-invariant matter systems,
mainly the relativistic particle and its d-brane generalization. The
corresponding matter Lagrangian naturally contains background interaction
fields, such as a 1-form field, analogous to the electromagnetic vector
potential, and a metric tensor. In order to make the theory free of background
fields and prepare for quantum theory of fields, we discuss the field
Lagrangians consistent with the gauge symmetries presented in the equations of
motion for the matter.
