Big-Bang Nucleosynthesis and Hadronic Decay of Long-Lived Massive Particles

TL;DR

Kawasaki, Kohri, and Moroi study Big-Bang Nucleosynthesis with a long-lived particle X, focusing on hadronic decays that create non-thermal reactions affecting light-element abundances. The authors couple hadronization spectra (via JETSET 7.4) with detailed energy-loss, inter-conversion, and hadrodissociation processes, updating photodissociation channels and employing Monte Carlo methods to quantify uncertainties. They derive conservative upper bounds on the primordial abundance of X, showing that constraints tighten as the hadronic branching ratio B_h increases, with distinct timing regimes (inter-conversion at τ_X ≲ 10^2–10^3 s, hadrodissociation at 10^2–10^7 s, and photodissociation at τ_X ≳ 10^7 s). As a key application, they translate these bounds into limits on the reheating temperature after inflation in unstable gravitino scenarios, linking particle physics to early-universe cosmology and providing guidance for SUSY-breaking models and baryogenesis constraints.

Abstract

We study the big-bang nucleosynthesis (BBN) with the long-lived exotic particle, called X. If the lifetime of X is longer than \sim 0.1 sec, its decay may cause non-thermal nuclear reactions during or after the BBN, altering the predictions of the standard BBN scenario. We pay particular attention to its hadronic decay modes and calculate the primordial abundances of the light elements. Using the result, we derive constraints on the primordial abundance of X. Compared to the previous studies, we have improved the following points in our analysis: The JETSET 7.4 Monte Carlo event generator is used to calculate the spectrum of hadrons produced by the decay of X; The evolution of the hadronic shower is studied taking account of the details of the energy-loss processes of the nuclei in the thermal bath; We have used the most recent observational constraints on the primordial abundances of the light elements; In order to estimate the uncertainties, we have performed the Monte Carlo simulation which includes the experimental errors of the cross sections and transfered energies. We will see that the non-thermal productions of D, He3, He4 and Li6 provide stringent upper bounds on the primordial abundance of late-decaying particle, in particular when the hadronic branching ratio of X is sizable. We apply our results to the gravitino problem, and obtain upper bound on the reheating temperature after inflation.

Figures (49)

• Figure 1: Abundances of the light elements as functions of $\eta$. The solid lines are the center value while the dotted lines show the theoretical uncertainties. Observational constraints are also shown.
• Figure 2: $\chi^2$ variable as a function of $\eta$ for SBBN with three degrees of freedom. For the constraint on $Y$, we used Fields and Olive's result (solid) and Izotov and Thuan's (dashed), which are given in Eqs. (\ref{['FieOLi']}) and (\ref{['highY']}), respectively. The shaded band (vertical solid lines) shows the baryon-to-photon ratio suggested by the WMAP at the 1$\sigma$ (2$\sigma$) level.
• Figure 3: Flow-chart of the hadronic decay of massive particles.
• Figure 4: Feynman diagrams for the decay processes $\psi_\mu\rightarrow g+\tilde{g}$ and $\psi_\mu\rightarrow q+\tilde{q}$, where $\psi_\mu$, $g$, $\tilde{g}$, $q$, and $\tilde{q}$ are the gravitino, gluon, gluino, quark, and squark, respectively. Here, the black blob represents the vertex originating from the gravitino-supercurrent interaction.
• Figure 5: Same as Fig. \ref{['fig:feyngravhad']}, but for the radiative decay modes. (Here, $\gamma$ is the photon while $\tilde{\chi}^0$ is the neutralino.)