Universal Non-Equilibrium Cascade in QGP Light-Nuclei Formation and Cosmological Bose-Einstein Condensation

TL;DR

This work argues that the apparent thermal yields of light nuclei in heavy-ion collisions arise from a universal non-equilibrium cascade, where high-energy degrees of freedom funnel through short-lived intermediate excitations (like $\Delta$ resonances) before forming fragile bound states as the system cools. It draws a deep analogy to cosmological Bose-Einstein condensation of scalar-field dark matter, where collapse-induced density spikes act as transient reservoirs that drive the system from an incoherent excited fraction to a macroscopic condensate core. The authors formalize both processes with minimal rate equations and establish a three-stage mapping between the two domains, revealing a shared dynamical attractor governing structure formation across extreme conditions. The findings suggest a broader applicability of non-equilibrium cascade concepts beyond their original contexts, with potential cross-disciplinary modeling approaches for non-equilibrium many-body systems.

Abstract

Recent ALICE results demonstrate that over 90\% of light nuclei and anti-nuclei ($d$, $\bar d$) observed in heavy-ion collisions originate from a non-equilibrium, multi-stage process: $Δ$-resonance production, decay into correlated nucleons, and their subsequent coalescence in a cooler hadronic environment. Although the final particle yields appear thermal, the underlying dynamics is strongly time-ordered and highly non-equilibrium. We show that this mechanism exhibits a striking universality with the formation of Bose-Einstein condensates (BEC) and associated density spikes in cosmological scalar-field dark-matter scenarios. In both systems -- the quark-gluon plasma near hadronization and the early universe approaching the BEC critical temperature -- the relevant degrees of freedom reorganize through a hierarchical cascade: high-energy modes first convert into intermediate excitations, which then seed low-energy coherent structures once the temperature crosses a threshold. This work highlights an unexpected theoretical bridge between heavy-ion physics and cosmology, suggesting a common class of emergent non-equilibrium phenomena behind structure formation in both extremes.

Figures (3)

• Figure 1: Schematic time-ordered cascade in heavy-ion collisions.
• Figure 2: Schematic non-equilibrium dynamics of cosmological Bose--Einstein condensation. The excited fraction $n_{\rm ex}$ dominates at early times. As the system cools toward the critical temperature $T_c$, nonlinear gravitational and self-interaction effects generate short-lived collapse-induced density spikes ("lumps"). These unstable intermediate excitations redistribute particles and correlations, feeding the coherent condensate fraction $n_0$. The repeated appearance of such spikes leads to the gradual growth of a macroscopic condensate core.
• Figure 3: Correspondence between the three-stage non-equilibrium cascade in ALICE light-nuclei production and in cosmological BEC dynamics. In heavy-ion collisions, free nucleons ($p,n$) are supplied through short-lived $\Delta$ resonances, enabling the formation of deuterons $d$ in a cooler hadronic environment. In the cosmological BEC scenario, incoherent excited modes ($n_{\rm ex}$) evolve through unstable collapse-induced nonlinear lumps, which act as intermediate reservoirs feeding the final coherent condensate core ($n_0$). In both systems, the apparent thermal-like final state emerges from a time-ordered, strongly non-equilibrium cascade mediated by unstable intermediate excitations.