Improved expressions for the energy-momentum current of matter

We consider a material system in special relativity. Its Noether identities for the canonical energy-momentum and angular momentum currents are invariant under a transformation which is induced by superpotentials. This relocalization invariance alone is used for the derivation of a symmetric and divergence-free energy-momentum current. If the system admits and additional dilation or scale invariance, the energy-momentum current can also be made traceless by the same method. The whole procedure is extended to general relativity thereby yielding a nice derivation, inter alia, of the Mathisson-Papapetrou force acting on spinning matter. (author)