Azimuthal instability of spinning spatiotemporal solitons

We find one-parameter families of three-dimensional spatiotemporal bright v ortex solitons (doughnuts, or spinning light bullets), in dispersive quadra tically nonlinear media. We show that they are subject to a strong instabil ity against azimuthal perturbations, similarly to the previously studied (2 + 1)-dimensional bright spatial vortex solitons. The instability breaks th e spinning soliton into several fragments, each being a stable nonspinning light bullet.