Big Bang Nucleosynthesis and Particle Dark Matter

TL;DR

This work surveys how Big Bang Nucleosynthesis constrains particle dark matter by examining (i) standard BBN theory and its sensitivity to early-Universe conditions, (ii) observed light-element abundances and their agreement or tension with predictions, and (iii) non-standard DM effects including cascade nucleosynthesis from energy injection, residual DM annihilation, catalyzed BBN (CBBN), and DM production during BBN via NLSP decays. The authors detail the mechanisms by which DM-related processes can alter $^4$He, D, $^3$He/$^{2}$H, $^7$Li, $^6$Li, and $^9$Be yields, derive constraints on relic abundances and lifetimes, and illustrate scenarios (e.g., gravitino LSP with stau NLSP) where Li-7 destruction and Li-6 production may align with observations while yielding testable DM densities and cosmological signatures. A central unresolved issue is the $^7$Li discrepancy, which may hint at either stellar depletion or new physics linked to dark matter; ongoing improvements in elemental abundance measurements and collider tests will be essential to distinguish between explanations. Overall, BBN remains a critical crossroad for particle cosmology, linking early-Universe expansion, non-thermal processes, and the particle properties of dark matter.

Abstract

We review how our current understanding of the light element synthesis during the Big Bang Nucleosynthesis era may help shed light on the identity of particle dark matter.

Figures (6)

• Figure 1: Constraints on the abundance $\Omega_Xh^2$ of relic particles decaying at $\tau_X$ assuming $M_X = 100\,$GeV for the particle mass. The most stringent limits are given, from early to late times, by $^{4}$He, D, $^{6}$Li, and $^{3}$He/D overproduction, respectively. The various lines are for different ${\rm log_{10}}B_h$, as labeled, where $B_h$ is the hadronic branching ratio. >From Ref. Jedamzik:2006xz.
• Figure 2: Upper bound on the annihilation cross section of particle dark matter of mass $M_{\chi}$ from BBN. Here the upper line assumes annihilation into only electromagnetically interacting particles, whereas the two lower lines assume annihilation into a light quark-anti-quark pair. Adopted limits on the light element abundances are as indicated in the figure.
• Figure 3: Dark matter annihilation rate versus dark matter mass. The blue band shows parameters where $^{6}$Li due to residual dark matter annihilation may account for the $^{6}$Li abundance as inferred in HD84937 ($^{6}$Li/$^{7}$Li$\approx 0.014-0.09$ at 2-$\sigma$), whereas the orange-red-green-yellow region shows where $^{7}$Li is efficiently destroyed i.e. $^{7}$Li/H$<1.5,2,3,$ and $4\times 10^{-10}$, respectively. Above the lower (upper) dashed line D/H exceeds $4\times 10^{-5}$ ($5.3\times 10^{-5}$), such that parameter space above the upper dashed line is ruled out by D overproduction. Scenarios between this line and the upper edge of the blue band are problematic since severely overproducing $^{6}$Li. Dark matter annihilation into light quarks has been assumed.
• Figure 4: Left panel shows CBBN constraints on the abundance vs lifetime of $X^-$. The red cross corresponds to a point in the parameter space, for which the temporal development of $^6$Li and $^9$Be is shown in the right panel, following Ref. Pospelov:2008ta.
• Figure 5: Parameter space in the relic decaying particle abundance times hadronic branching ratio $B_h$, i.e. $\Omega_Xh^2B_h$, and life time $\tau_X$ plane, where $^{7}$Li is significantly reduced (red and blue) and $^{6}$Li is efficiently produced (green and blue). See text for further details. From Ref. Bailly:2008yy.