Gluon saturation and the glasma fields
Relativistic heavy-ion collisions at the LHC and RHIC briefly create the quark-gluon plasma, the primordial soup of quarks and gluons that filled the early universe. Before the collision, a high-energy nucleus is dominated by gluons. The gluon density grows until non-linear effects saturate it, a regime described by the Color Glass Condensate effective theory of Quantum Chromodynamics. When two such gluon-dense nuclei pass through each other, they produce the glasma: strong classical gluon fields organized into longitudinal color-electric and color-magnetic flux tubes. These fields quickly thermalize into the quark-gluon plasma, from which all final particles are formed.
Hard probes as messengers of the early stages
Jets and heavy quarks are produced at the moment of impact and experience the entire evolution of the collision. This makes them sensitive tools to characterize the quark-gluon plasma. Their transport coefficients are extracted by comparing measurements with models of how the probes interact with the medium. Such models usually begin with the plasma and neglect the glasma altogether.
This dissertation studies hard probes in the glasma by solving the classical gluon field equations on a real-time lattice and propagating classical probes through the resulting fields. The main finding is that the transport coefficients are substantially larger than in the plasma, and highly anisotropic rather than isotropic. On the phenomenology side, the azimuthal decorrelation of back-to-back heavy quark pairs in the glasma is comparable to that from the entire plasma phase, making angular correlations a potentially measurable signature of the earliest stage.
From classical particles to quantum evolution
Treating the probes as classical colored particles is only an approximation. In this thesis their real-time quantum evolution in the glasma is computed for the first time, using light-front quantization. The two descriptions agree, establishing a framework in which energy loss in the glasma can be addressed: how much radiation takes place there compared to the later plasma, and what that implies for phenomenology.
The public examination of M.Sc. Dana Avramescu's doctoral dissertation "Transport of hard probes in the glasma" will be held on Friday, 18 September 2026 at 12 o'clock in the lecture hall FYS1 on Ylistönrinne. The Opponent is Senior Researcher Dr. François Gelis (Institut de Physique Théorique, Université Paris-Saclay, CEA/Saclay) and the Custos is Professor Tuomas Lappi (University of Jyväskylä). The defense will be held in English.
The dissertation "Transport of hard probes in the glasma" is available in the JYX digital archive.
You can also follow the dissertation event online here.
