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arXiv:2506.19194 · Physical review. D/Physical review. D.

Quantum vs semiclassical description of in-QGP quarkonia in the quantum Brownian regime

Aoumeur Daddi Hammou, Stéphane Delorme, Jean-Paul Blaizot, Pol-Bernard Gossiaux, Thierry Gousset

Published Nov 26, 2025• 3 citations
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Abstract

In this work, we explore the range of validity of the semiclassical approximation of a quantum master equation designed to describe the c c ¯ dynamics in a quark-gluon plasma at various temperatures, in the quantum Brownian regime. We perform a comparative study of various properties, e.g., the charmonia yield, of the Wigner density obtained both with the Lindblad equation and with the associated semiclassical Fokker-Planck equation. The semiclassical description is found to reproduce with a remarkable accuracy the results obtained through the full quantum description. We show that, to a large extent, this can be attributed to the nonunitary components of the dynamics that result from the contact of the c c ¯ subsystem with the thermal quark-gluon bath, leading to a rapid classicalization of the subsystem.

DOI
10.1103/kyc5-mrj3

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Physical Review A•Feb 1, 1989•8 citations
In this work, we explore the range of validity of the semiclassical approximation of a quantum master equation designed to describe the c c ¯ dynamics in a quark-gluon plasma at various temperatures, in the quantum Brownian regime. We perform a comparative study of various properties, e.g., the charmonia yield, of the Wigner density obtained both with the Lindblad equation and with the associated semiclassical Fokker-Planck equation. The semiclassical description is found to reproduce with a remarkable accuracy the results obtained through the full quantum description. We show that, to a large extent, this can be attributed to the nonunitary components of the dynamics that result from the contact of the c c ¯ subsystem with the thermal quark-gluon bath, leading to a rapid classicalization of the subsystem.
Traitement amélioré de la description théorique de la dynamique des quarkonia dans le plasma quarks-gluons : de l'approximation semi-classique aux équations maîtresses quantiques unifiées entre le régime brownien quantique et le régime optique quantique Les quarkonia lourds sont l'une des sondes du plasma de quarks et de gluons (QGP) formé dans les collisions ultrarelativistes d'ions lourds. Au cours de la dernière décennie, l'utilisation du formalisme des systèmes quantiques ouverts (SQO) dans l'étude de la dynamique des quarkonia dans le QGP a suscité un intérêt croissant. En particulier, il a été montré que l'équation de Lindblad peut donner lieu à des équations semi-classiques, qui ont été précédemment utilisées par plusieurs modèles phénoménologiques. Dans une première partie de cette thèse, nous étudions la validité de l'approximation semi-classique, et sa capacité à décrire certains effets quantiques non triviaux et à atteindre la limite thermique appropriée. La deuxième partie de la thèse a pour but de relever certains défis théoriques associés à l'utilisation du formalisme SQO dans l'étude de la dynamique des quarkonia dans le QGP. En particulier, en raison de l'aspect dynamique du QGP et de sa température dépendant du temps, la dynamique des quarkonia dans le QGP couvre deux régimes différents du formalisme SQO qui sont décrits par deux équations maîtresses différentes, à savoir le régime brownien quantique et le régime optique quantique. Nous explorons tout d'abord la transition entre les deux régimes et élucidons le lien entre leurs équations maîtresses respectives. Ensuite, afin de décrire l'évolution temporelle complète du quarkonia dans le QGP avec une seule équation maîtresse, nous appliquons l'équation universelle de Lindblad au système QGPquarkonia et dérivons un ensemble d'équations universelles couplées des états singlet et octet.
Accurate modelling and understanding of quarkonium production in ultrarelativistic heavy ion collisions requires a formalism that preserves the quantum properties of microscopic QˉQ\bar{Q}QQˉ​Q systems while treating the interaction of such pairs with the quark-gluon plasma (QGP). The open quantum system approach has recently emerged as one of the most fruitful schemes to meet such requirements. However, the quantum master equations obtained so far in this context are derived assuming a strict ordering between the QGP temperature TTT and the QˉQ\bar{Q}QQˉ​Q energy gaps (ΔEΔEΔE) of the quarkonia bound states. This limits their predictive power since, as the QGP expands and cools down, the system traverse all regimes between the quantum Brownian motion (QBM) regime for T≳ΔET\gtrsim ΔET≳ΔE to the quantum optical (QO) regime for ΔE≳TΔE\gtrsim TΔE≳T. In this paper, we derive and present a more general non-abelian quantum master equation of the Lindblad type, which does not suffer from these limitations and thus allows to faithfully describe the quantum evolution of the QQˉQ\bar{Q}QQˉ​ pairs during the whole QGP-evolution. We also provide some illustration of the key quantities governing this equation.
In recent years, a significant theoretical effort has been made towards a dynamical description of quarkonia inside the Quark-Gluon Plasma (QGP), using the open quantum systems formalism. In this framework, one can get a real-time description of a quantum system (here the quarkonium) in interaction with a thermal bath (the QGP) by integrating out the bath degrees of freedom and studying the system reduced density matrix. We investigate the real-time dynamics of a correlated heavy quark-antiquark pair inside the QGP using a quantum master equation previously derived from first QCD principles in [4]. The full equation is directly resolved in 1D to lessen computing costs and is used for the first time to gain insight on the dynamics in both a static and evolving medium following a Björken-like temperature evolution.
Recently, a set of coupled singlet-octet universal Lindblad equations (ULEs) was derived within the framework of non-relativistic QCD (NRQCD) to describe quarkonium dynamics in the quark-gluon plasma (QGP). These equations provide a unified quantum description spanning the quantum Brownian and quantum optical regimes. In this work, we further develop this framework and establish its connection with semiclassical transport. We first derive the universal Lindblad equations within the potential non-relativistic QCD (pNRQCD) effective field theory and show that they coincide with the small-dipole limit of the NRQCD ULEs. We then derive the semiclassical limit of the NRQCD ULEs, obtaining a set of coupled singlet-octet Boltzmann equations. To our knowledge, this is the first derivation of Boltzmann transport equations directly from the universal Lindblad framework. The resulting equations are valid beyond the small-dipole approximation, allowing the evolution of heavy-quark pairs from compact to widely separated configurations. Taking their small-dipole limit allows a direct comparison with the Boltzmann equations of Yao et al. [Phys. Rev. D 99, 096028 (2019)], which were derived within pNRQCD from the Davies secular equation, relying on the rotating-wave approximation (RWA). While the singlet equations are found to be in near-complete agreement, the octet equation contains an additional collision term describing transitions within the continuum of octet scattering states, which is absent from the RWA-based derivation. Finally, we derive the leading quantum correction to the singlet Boltzmann equation. Our results establish a more general and systematic theoretical foundation for the semiclassical transport description of quarkonium in the QGP.
\nIn recent years, a significant theoretical effort has been made towards a dynamical description of quarkonia inside the Quark-Gluon Plasma (QGP), using the open quantum systems formalism. In this framework, one can get a real-time description of a quantum system (here the quarkonium) in interaction with a thermal bath (the QGP) by integrating out the bath degrees of freedom and studying the system reduced density matrix. We investigate the real-time dynamics of a correlated heavy quark-antiquark pair inside the QGP using a quantum master equation previously derived from first QCD principles in [4]. The full equation is directly resolved in 1D to lessen computing costs and is used for the first time to gain insight on the dynamics in both a static and evolving medium following a Björken-like temperature evolution.\n