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 ${}^9\mathrm{Be}$ via the chain of nonequilibrium transformations: ${\mathrm{\text{Energy}}}_h\to \mathrm{T}$, ${}^3\mathrm{He}\to {}^6\mathrm{He}$, ${}^6\mathrm{Li}\to {}^9\mathrm{Be}$. We calculate the efficiency of this transformation and show that if the injection happens at cosmic times of a few hours the release of $\mathcal{O}(10\mathrm{MeV})$ per baryon can be sufficient for obtaining a sizable ${}^9\mathrm{Be}$ abundance. The absence of a plateau structure in the ${}^9\mathrm{Be}/\mathrm{H}$ abundance down to a $\mathcal{O}({10}^{-14})$ level allows one to use beryllium as a robust constraint on new physics models with decaying or annihilating particles.

Figure 1

Beryllium detections (squares) and fit of their Be-Fe trend taken from 17. The triangle shows the upper limit from 18; $A(X)\equiv {log}_{10}(X/\mathrm{H})+12$.

Figure 2

Conversion probabilities $P_{\mathrm{Be}}$ as a function of photon temperature $T$ for the various channels depicted; thermal destruction of ${}^9\mathrm{Be}$ is not included.

Figure 3

Contours of constant ${}^9\mathrm{Be}$ (solid lines) and ${}^6\mathrm{Li}$ (dashed lines) as a function of ${\tau }_X$ and ${ϵ}_{\mathrm{had}}{Y}_X$; $B_h=1$ and $m_X=1\mathrm{TeV}$ is assumed.