I study nonequilibrium cascades in which fragile bound or coherent structures are formed through intermediate states rather than by direct equilibration. Motivated by light-nuclei production in relativistic heavy-ion collisions and by Bose-Einstein condensation in cosmological settings, I analyze such processes within the Schwinger-Keldysh real-time formalism. I show that commonly used rate equations can be understood as a controlled Markovian approximation obtained by integrating out intermediate reservoirs in an underlying multicomponent nonequilibrium dynamics. When the finite lifetime of these reservoirs is retained, non-Markovian memory effects naturally appear, leading to delayed and history-dependent formation dynamics. The associated memory time provides a quantitative criterion for the validity of reduced, rate-based descriptions far from equilibrium. Applying this framework to light-nuclei formation mediated by $\mathrm{\Delta }$ resonances and to condensate formation with localized intermediate structures, I show that equilibrium-like final yields arise as a consequence of finite-lifetime intermediate reservoirs and memory effects, rather than from genuine thermal equilibration.

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• Models & methods for nuclear reactions
• Particle & resonance production
• Relativistic heavy-ion collisions