Primordial beryllium as a big bang calorimeter

Many models of new physics including variants of supersymmetry predict metastable long-lived particles that can decay during or after primordial nucleosynthesis, releasing significant amounts of nonthermal energy. The hadronic energy injection in these decays leads to the formation of ?Be via the chain of nonequilibrium transformations: Energy(h)→T, 3He→?He, ?Li→?Be. We calculate the efficiency of this transformation and show that if the injection happens at cosmic times of a few hours the release of O(10 MeV) per baryon can be sufficient for obtaining a sizable ?Be abundance. The absence of a plateau structure in the ?Be/H abundance down to a O(10?1?) level allows one to use beryllium as a robust constraint on new physics models with decaying or annihilating particles.