Jet Quenching in Holographic QCD as an Indicator of Phase Transitions in Anisotropic Regimes

TL;DR

We study jet quenching in a holographic QCD framework built from Einstein-Maxwell-dilaton gravity at finite $T$ and $\mu$, using anisotropic backgrounds with a magnetic field $c_B$ to compute the jet-quenching parameter $\hat{q}$ via the IJQ construction. By scanning $(T,\mu,c_B)$ and varying the anisotropy $\nu$, we identify discontinuities in $\log a$ (and thus in $\hat{q}$) at first-order phase transitions and track how phase boundaries move with $\nu$ and $c_B$, including orientation-dependent effects $\hat{q}_2$ and $\hat{q}_3$. The results are contrasted with prior running-coupling analyses to map critical regions in the holographic QCD phase diagram and to illuminate the nonperturbative dynamics governing phase structure. The work provides theoretical insights into how nonperturbative jet-quenching observables encode QCD phase transitions in strongly coupled, anisotropic media relevant for heavy-ion phenomenology.

Abstract

In this paper, we employ the gauge/gravity duality to study jet quenching (JQ) phenomena in the quark-gluon plasma. For this purpose, we implement holographic QCD models constructed from an Einstein-Maxwell-dilaton gravity at finite temperature and finite chemical potential for light and heavy quarks. The models capture both the confinement and deconfinement phases of QCD and the first-order phase transitions. We calculate the JQ parameter in different models and compare them with the experimental data obtained in heavy-ions studies. In particular, we investigate how JQ, as a function of temperature $T$, chemical potential $μ$, and magnetic field $c_B$, serves as a probe for identifying first-order phase transitions within the $(T,μ,c_B)$ parameter space of holographic QCD. Particular attention is paid to the dependence of JQ on the parameter $ν$, which characterizes longitudinal versus transverse anisotropy relative to the heavy-ion collision axis. By analyzing the dependence of the JQ parameters on these thermodynamic variables, we map critical regions associated with phase boundaries. We compare our findings to earlier studies of the running coupling constant's behavior within the gauge-gravity duality framework. This approach provides new insights into the interplay between non-perturbative dynamics and phase structure in strongly coupled systems.

Figures (54)

• Figure 1: (A) We calculate the JQ parameter for the LQ model, with $\nu=1$ and $c_B=0$, along vertical lines (constant $\mu$) in the $(\mu,T)$-planeat $\mu = 0.04$, $0.3$, and $0.7$ (GeV). Segments of these lines are colored blue (QGP), brown (hadronic), and green (quarkyonic) according to the phase traversed. The resulting plots of $\log a$ versus temperature are displayed in the bottom panels (B, C, D), using the same color scheme.
• Figure 2: The dependence of $\log a T^3$ on $T$ for the isotropic LQ model, with $\nu=1$ and $c_B=0$, at fixed chemical potentials: (A) $\mu=0.04$ GeV, (B) $\mu=0.3$ GeV, (C) $\mu=0.7$ GeV.
• Figure 3: (A) Density plots of $\log a$ for the LQ model, with $c_B=0$ and $\nu = 1$. (B) The same with phase transition lines: i) the magenta line shows the first-order transition line that starts at CEP with coordinates ($\mu_{CEP}$,$T_{CEP}$)$\simeq$(0.046 GeV, 0.158 GeV) shown by magenta star; ii) the blue line shows the second-order phase transition line between hadron and QGP phases (for $0<\mu<0.095$ GeV) and between quarkyonic and QGP phases ($\mu>$0.095 GeV). (C) The light quark phase diagram, showing the hadronic phase below the magenta line, the quarkyonic phase between the magenta and blue lines, and the QGP phase above the blue line.
• Figure 4: (A) We calculate the JQ parameter for the LQ model, with $\nu=1.5$ and $c_B=0$, along vertical lines (constant $\mu$) in the $(\mu,T)$-plane at $\mu = 0.04$, $0.3$, $0.7$ and $\mu=1$ (GeV), shown in this panel. Segments of these lines are colored blue (QGP), brown (hadronic), and green (quarkyonic) according to the phase traversed. The resulting plots of $\log a$ versus temperature are displayed in the bottom panels (B, C, D, E), using the same color scheme.
• Figure 5: (A) We calculate the JQ parameter for the LQ model, with $\nu=3$ and $c_B=0$, along vertical lines at fixed $\mu = 0.04$, $0.3$, $1$, and $\mu =1.4$ (GeV) presented at the panel. Segments of these lines are colored blue, brown, and green corresponding to the QGP, hadronic, and quarkyonic phases they traverse, respectively. The resulting plots for log of the JQ parameter verse temperature are presented on two bottom panels (B, C, D, E) are colored using the same scheme.