Aggregation processes with an arbitrary number of conserved quantities are
investigated. On the mean-field level, an exact solution for the size
distribution is obtained. The asymptotic form of this solution exhibits
nontrivial ``double'' scaling. While processes with one conserved quantity are
governed by a single scale, processes with multiple conservation laws exhibit
an additional diffusion-like scale. The theory is applied to ballistic
aggregation with mass and momentum conserving collisions and to diffusive
aggregation with multiple species.Comment: 18 pages, te