Higher Spins and Current Exchanges

The simplest higher-spin interactions involve classical external currents and symmetric ten- sors μ1...μs , and convey three instructive lessons. The first is a general form of the van Dam- Veltman-Zakharov discontinuity in flat space for this class of fields. The second is the rationale for its disappearance in (A)dS spaces. Finally, the third is a glimpse into an option which is commonly overlooked in Field Theory, and which both higher spins and String Theory are con- fronting us with: one can well allow in the Lagrangians non-local terms that do not spoil the local nature of physical quantities.