arXiv subjects

Fabrizio Murgana

Publications and source records attributed to Fabrizio Murgana.

8 recordsLinked to original sources

arXiv2026

Elliptic flow of charm quarks produced in the early stage of pA collisions

We investigate the build-up of elliptic flow of charm quarks produced in the early pre-equilibrium stage of high-energy proton--nucleus collisions. The initial stage is modeled within the Color Glass Condensate framework as an evolving glasma, initialized through the McLerran--Venugopalan model. Subnucleonic fluctuations have been implemented as constituent-quark hotspots for both the proton and the nuclear participants. Charm quarks are propagated in the evolving non-Abelian background by solving the relativistic Wong equations for their coordinates, momenta, and color charges. First, we compute the nuclear modification factor of charm quarks, finding a slight migration towards higher $p_T$ states in agreement with previous results in the literature. Then, we focus on the azimuthal anisotropies acquired through the interaction with glasma fields. We find that glasma-induced momentum anisotropies are efficiently transmitted to heavy quarks within $τ\sim 0.4~\mathrm{fm/c}$, leading to a sizeable charm-quark $v_2$, with a magnitude that increases with the strength of the initial fields and with the number of nuclear participants. Remarkably, we show that the early-stage contribution alone can account for a significant fraction of the experimentally observed $J/ψ$ elliptic flow in p-Pb collisions, indicating that pre-hydrodynamic dynamics can play a non-negligible role in the final-state heavy-flavor collectivity, especially in small systems.

hep-ph↗

arXiv2026

Analysis of regulator and cutoff artifacts in the phase diagram of the quark-meson model

We study regulator and cutoff artifacts in the quark-meson model at finite temperature and quark chemical potential within the functional renormalization-group approach using the local potential approximation. To this end, we discuss the concept of renormalization-group consistency in effective models, which necessitates a nontrivial parameter-fixing procedure to enable a meaningful comparison of results obtained with different regulators and cutoffs. We employ a standard range of cutoff values used in phenomenological studies and regulators that differ significantly in their analytic properties as well as in their classification according to the principle of strongest singularity. We find that regulator and cutoff dependences are small at low temperatures and quark chemical potentials. At high temperatures and low quark chemical potentials, significant cutoff artifacts arise, whereas the properties of the regulator affect the dynamics in the regime governed by a chiral phase transition of first order at low temperatures and high quark chemical potentials.

hep-ph↗

arXiv2025

Assessing the Reconstruction of the Critical Line in the QCD Phase Diagram from Imaginary to Real Chemical Potential

We test a technique adopted in the lattice simulations framework, to reconstruct the chiral-phase boundary at real chemical potential, $μ$, via extrapolation from imaginary $μ$. We use a low-energy effective model, the Quark-Meson model, both in the mean-field approximation and within the Functional Renormalization Group, the latter in the Local Potential Approximation. The model provides results both for real and imaginary values of $μ$, thus a direct comparison can be performed between the prediction of the model for real values of $μ$ and the ones obtained via extrapolation from the results at imaginary $μ$. We compute an effective convergence radius for the reconstruction technique, $μ_\mathrm{conv}$, and find $μ_\mathrm{conv}\approx146$ MeV. This value sustains the validity of the reconstruction technique also for finite and moderate values of the chemical potential. On the other hand, within our model, $μ_\mathrm{conv}$ is quite smaller then the value of $μ$ where we find the actual critical endpoint. Near this point of the phase diagram, we find a discrepancy between the actual phase boundary and the one pbtained via extrapolatin of $\approx150\%$. Therefore, our results show that the location of the critical endpoint obtained via reconstruction from imaginary $μ$ should be considered with due caution

hep-ph↗

arXiv2025

Topological Susceptibility in the Superconductive Phases of Quantum Chromodynamics: a Dyson-Schwinger Perspective

We test non-perturbative gluon propagators recently studied in the literature, by computing the topological susceptibility, $χ$, of the superconductive phases of Quantum Chromodynamics at high density. We formulate the problem within the High-Density Effective Theory, and use the 2-particle irreducible formalism to compute the effective potential of the dense phases. We focus on superconductive phases with two and three massless flavors. Within this formalism, we write a Dyson-Schwinger equation in the rainbow approximation for the anomalous part of the quark propagator in the superconductive phases, in which the non-perturbative gluon propagator plays its role. We complete the model by adding a $U(1)_A$-breaking term whose coupling is fixed perturbatively at large quark chemical potential. We then use the effective potential to compute $χ$ in the superconductive phases. We finally discuss implications of the results for the axion mass in superdense phases of Quantum Chromodynamics.

hep-ph↗

arXiv2024

Functional Renormalization Group analysis of the quark-condensation pattern on the Fermi surface: A simple effective-model approach

A simple effective model for the intermediate-density regime is constructed from the high-density effective theory of quantum chromodynamics (QCD). In the effective model, under a renormalization-group (RG) scaling towards low momenta, the original QCD interactions lead to four-quark contact interactions for the relevant quark and hole modes around the Fermi surface. The contact interaction in the scalar channel can be traced back to zero-sound-type collinear quark scattering near the Fermi surface in an instanton background. The quark and hole states in opposite directions of a given Fermi velocity form the collective scalar bosonic mode $σ$. The magnitude of $σ$ is investigated via the non-perturbative Functional Renormalization Group (FRG) evolution of the effective average action from the ultraviolet (UV) to the infrared (IR). In the mean background-field approximation for $σ$, nontrivial minima ($\barσ \neq 0$) are found in the IR limit of the effective average action. A nonvanishing $\barσ$ corresponds to condensation of quark and hole states in opposite directions of a given Fermi velocity, in a thin shell-like structure in momentum space around the Fermi surface. This looks similar to the shell-like baryon distribution in momentum space assumed in the quarkyonic-matter concept. However, when including a dynamic bosonic $σ$-mode in the RG flow, we find that its diffusive nature destroys the quark-hole condensate, i.e., the IR potential does not show any minima beyond the trivial one.

nucl-th↗

arXiv2024

Topological susceptibility and axion potential in two-flavor superconductive quark matter

We study the potential of the axion, $a$, of Quantum Chromodynamics, in the two-flavor color superconducting phase of cold and dense quark matter. We adopt a Nambu-Jona-Lasinio-like model. Our interaction contains two terms, one preserving and one breaking the $U(1)_A$ symmetry: the latter is responsible of the coupling of axions to quarks. We introduce two quark condensates, $h_L$ and $h_R$, describing condensation for left-handed and right-handed quarks respectively; we then study the loci of the minima of the thermodynamic potential, $Ω$, in the $(h_L,h_R)$ plane, noticing how the instanton-induced interaction favors condensation in the scalar channel when the $θ-$angle, $θ=a/f_a$, vanishes. Increasing $θ$ we find a phase transition where the scalar condensate rotates into a pseudo-scalar one. We present an analytical result for the topological susceptibility, $χ$, in the superconductive phase, which stands both at zero and at finite temperature. Finally, we compute the axion mass and its self-coupling. In particular, the axion mass $m_a$ is related to the full topological susceptibility via $χ=m_a^2 f_a^2$, hence our result for $χ$ gives an analytical result for $m_a$ in the superconductive phase of high-density Quantum Chromodynamics.

hep-ph↗

arXiv2023

Functional Renormalization Group Study of Thermodynamic Geometry Around the Phase Transition of Quantum Chromodynamic

We investigate the thermodynamic geometry of the quark-meson model at finite temperature, $T$, and quark number chemical potential, $μ$. We extend previous works by the inclusion of fluctuations exploiting the functional renormalization group approach. We use recent developments to recast the flow equation into the form of an advection-diffusion equation. We adopt the local potential approximation for the effective average action. We focus on the thermodynamic curvature, $R$, in the $(μ,T)$ plane, in proximity of the chiral crossover, up to the critical point of the phase diagram. We find that the inclusion of fluctuations results in a smoother behavior of $R$ near the chiral crossover. Moreover, for small $μ$, $R$ remains negative, signaling the fact that bosonic fluctuations reduce the capability of the system to completely overcome the fermionic statistical repulsion of the quarks. We investigate in more detail the small $μ$ region by analyzing a system in which we artificially lower the pion mass, thus approaching the chiral limit in which the crossover is actually a second order phase transition. On the other hand, as $μ$ is increased and the critical point is approached, we find that $R$ is enhanced and a sign change occurs, in agreement with mean field studies. Hence, we completely support the picture that $R$ is sensitive to a crossover and a phase transition, and provides information about the effective behavior of the system at the phase transition.

hep-ph↗

arXiv2023

Reanalysis of critical exponents for the O(N) model via a hydrodynamic approach to the Functional Renormalization Group

We compute the critical exponents of the O(N) model within the Functional Renormalization Group (FRG) approach. We use recent advances which are based on the observation that the FRG flow equation can be put into the form of an advection-diffusion equation. This allows to employ well-tested hydrodynamical algorithms for its solution. In this study we work in the local potential approximation (LPA) for the effective average action and put special emphasis on estimating the various sources of errors. Our results complement previous results for the critical exponents obtained within the FRG approach in LPA. Despite the limitations imposed by restricting the discussion to the LPA, the results compare favorably with those obtained via other methods.

hep-th↗