arXiv subjects

Najmul Haque

Publications and source records attributed to Najmul Haque.

At least 19 recordsLinked to original sources

arXiv2026

Electrical conductivity of QGP with quasiparticle quarks and Gribov gluon

We investigate the electrical conductivity of the quark-gluon plasma (QGP) using a non-perturbative resummation scheme incorporating the Gribov-modified gluon propagator. The electrical conductivity is evaluated by solving the relativistic Boltzmann transport equation within the relaxation-time approximation, where the relaxation times are obtained from microscopic two-body scattering amplitudes. A quasiparticle description is employed for quarks, providing a unified framework for studying transport properties across both weakly and strongly coupled regimes. Above the deconfinement transition temperature, we estimate the electrical conductivity of the QGP and compare our results with available lattice QCD data and various phenomenological models, finding good agreement with the lattice results.

hep-ph↗

arXiv2025

Shear and bulk viscosity for a pure glue theory using an effective matrix model

At nonzero temperatures, the deconfining phase transition can be analyzed using an effective matrix model to characterize the change in holonomy. The model includes gluons and two-dimensional ghost fields in the adjoint representation, or ``teens''. As ghosts, the teen fields are responsible for the decrease of the pressure as $T \rightarrow T_d$, with $T_d$ the transition temperature for deconfinement. Using the solution of this matrix model for a large number of colors, the parameters of the teen fields are adjusted so that the expectation value of the Polyakov loop is close to the values from the lattice. The shear, $η$, and bulk, $ζ$, viscosities are computed in weak coupling but nonzero holonomy. In the pure glue theory, the value of the Polyakov loop is relatively large in the deconfined phase, $\approx 1/2$ at $T_d$. Consequently, if $s$ is the entropy density, while $η/s$ decreases as $T\rightarrow T_d$, it is still well above the conformal bound. In contrast, $ζ/s$ is largest at $T_d$, comparable to $η/s$, then falls off rapidly with increasing temperature and is negligible by $\sim 2 T_d$.

hep-ph↗

arXiv2025

Anisotropy effects on heavy quark dynamics in Gribov modified gluon plasma

In the early stages of relativistic heavy-ion collisions, the quark-gluon plasma momentum distribution is anisotropic, leading to instabilities driven by chromomagnetic plasma modes. In this work, we consider the anisotropic momentum distribution of the medium constituents to investigate its effects on charm and bottom quark dynamics using the nonperturbative Gribov resummation approach within the Fokker-Planck equation framework. Specifically, we investigate the impact of nonperturbative effects and weak anisotropies on the heavy-quark transport coefficients, accounting for the angular dependence of the anisotropy vector relative to the heavy-quark motion direction. Furthermore, the calculated drag and diffusion coefficients are used to estimate heavy-quark energy loss and the nuclear modification factor, accounting for both elastic and inelastic collisions. Our findings indicate that momentum anisotropy, angular dependence, and nonperturbative effects-captured through the scattering amplitudes-play a significant role in determining the transport properties of heavy quarks.

hep-ph↗

arXiv2025

Complex heavy-quarkonium potential in an anisotropic collisional quark-gluon plasma

We compute the complex heavy-quark potential in an anisotropic quark-gluon plasma (QGP) using kinetic theory with a Bhatnagar-Gross-Krook collision kernel. By incorporating momentum anisotropy and a finite collision rate into the medium dielectric response, we derive both the real and the imaginary parts of the in-medium potential. The real part of the inverse dielectric function is obtained from the retarded/advanced gluon propagator, while the imaginary part is determined from the Feynman (symmetric) propagator. We find that collisions have only a minimal impact on the real part of the potential, suggesting a similarly weak effect on the binding energy. In an anisotropic plasma, the Weibel instability induces a pinch singularity that can render the imaginary part of the potential ill-defined; we show that sufficiently large collision rates regularize this singularity, yielding a well-defined imaginary potential in the corresponding region of parameter space. In this well-defined regime, collisions significantly enhance the magnitude of the imaginary part and modify the effect of anisotropy. This enhancement leads to larger quarkonium thermal widths and dissociation rates in a nonequilibrium QGP, providing further insight into quarkonium suppression mechanisms.

hep-ph↗

arXiv2024

Shear and bulk viscosity of quark-gluon plasma with Gribov gluons and quasiparticle quarks

In this study, we analyze the transport properties of the Quark-Gluon Plasma, focusing on bulk ($ζ$) and shear ($η$) viscosities at vanishing chemical potential. To describe the QGP, we employ a quasiparticle model for quarks along with Gribov's prescription for gluons, which effectively captures non-perturbative dynamics. The Gribov parameter $γ_G$ and the dynamical mass $m_g$ are obtained by solving the one-loop gap equation in the $\overline{\text{MS}}$ renormalization scheme and further using lattice QCD data for the equation of state (EoS) of pure gluonic matter. The interaction between quarks and gluons is reflected in the quark quasi-mass $m_q$, again obtained using lattice EoS data for (2+1)-flavor QCD. Our primary goal is to invertigate the influence of quasi-quarks on the transport coefficients of QGP. Interestingly, we find a substantial decrease in the scaled transport coefficients with rising temperatures within the range ($1 \le T/T_c \le 3.5$).

hep-ph↗

arXiv2024

Hard Thermal Loop -- theory and applications

In this review, we present the key aspects of modern thermal perturbation theory based on the hard thermal loop (HTL) approximation, including its theoretical foundations and applications within quantum electrodynamics (QED) and quantum chromodynamics (QCD) plasmas. To maintain conciseness, we focus on scenarios in thermal equilibrium, examining a variety of physical quantities and settings. Specifically, we explore both bulk thermodynamic properties and real-time observables in high-temperature domains relevant to heavy-ion physics.

hep-ph↗

arXiv2024

Heavy quark dynamics via Gribov-Zwanziger approach

In this work, we investigate the momentum-dependent drag and diffusion coefficient of heavy quarks (HQs) moving in the quark-gluon plasma (QGP) background. The leading order scattering amplitudes required for this purpose have been obtained using the Gribov-Zwanziger propagator for the mediator gluons to incorporate the non-perturbative effects relevant to the phenomenologically accessible temperature regime. The drag and diffusion coefficients so obtained have been implemented to estimate the temperature and momentum dependence of the energy loss of the HQ as well as the temperature dependence of the specific shear viscosity ($η/s$) of the background medium. Our results suggest a higher energy loss of the propagating HQ compared to the perturbative estimates, whereas the $η/s$ is observed to comply with the AdS/CFT estimation over a significantly wider temperature range compared to the perturbative expectation.

hep-ph↗

arXiv2024

The complex heavy-quark potential with the Gribov-Zwanziger action

Gribov-Zwanziger prescription in Yang-Mills theory improves the infrared dynamics. In this work, we study the static potential of a heavy quark-antiquark pair with the HTL resummed perturbation method within the Gribov-Zwanziger approach at finite temperature. The real and imaginary parts of the heavy quark complex potential are obtained from the one-loop effective static gluon propagator. The one-loop effective gluon propagator is obtained by calculating the one-loop gluon self-energies containing the quark, gluon, and ghost loop. The gluon and ghost loops are modified in the presence of the Gribov parameter. We also calculate the decay width from the imaginary part of the potential. We also discuss the medium effect of heavy quark potential with the localized action via auxiliary fields.

hep-ph↗

arXiv2023

Heavy quarkonia in QGP medium in an arbitrary magnetic field

We compute the heavy quarkonium complex potential in an arbitrary magnetic field strength generated in the relativistic heavy-ion collision. First, the one-loop gluon polarization tensor is obtained in the presence of an external, constant, and homogeneous magnetic field using the Schwinger proper time formalism in Euclidean space. The gluon propagator is computed from the gluon polarization tensor, and it is used to calculate the dielectric permittivity in the presence of the magnetic field in the static limit. The modified dielectric permittivity is then used to compute the heavy quarkonium complex potential. We find that the heavy quarkonium complex potential is anisotropic in nature, which depends on the angle between the quark-antiquark ($Q\bar{Q}$) dipole axis and the direction of the magnetic field. We discuss the effect of the magnetic field strength and the angular orientation of the dipole on the heavy quarkonium potential. We discuss how the magnetic field influences the thermal widths of quarkonium states. Further, we also discuss the limitation of the strong-field approximation as done in literature in the light of heavy-ion observables, as the effect of the magnetic field is very nominal to the quarkonium potential.

hep-ph↗

arXiv2023

QCD mesonic screening masses using Gribov quantization

The screening masses of mesons provide a gauge invariant and definite order parameter of chiral symmetry restoration. Different mesonic correlation lengths for flavor non-singlets, at least up to NLO, are well-defined gauge invariant physical quantities calculated earlier using the perturbative resummation techniques. The NLO perturbative results match the available non-perturbative lattice QCD results at the high-temperature regime. We have studied the spatial correlation lengths of various mesonic observables using the non-perturbative Gribov resummation, both for quenched QCD and (2 + 1) flavor QCD. The study follows the analogies with the NRQCD effective theory, a well-known theory for studying heavy quarkonia at zero temperature.

hep-ph↗

arXiv2023

NLO quark self-energy and dispersion relation using the hard thermal loop resummation

Using the hard-thermal-loop (HTL) resummation in real-time formalism, we study the next-to-leading order (NLO) quark self-energy and corresponding NLO dispersion laws. In NLO, we have replaced all the propagators and vertices with the HTL-effective ones in the usual quark self-energy diagram. Additionally, a four-point vertex diagram also contributes to the quark NLO self-energy. We calculate the usual quark self-energy diagram and the four-point vertex diagram separately. Using those, we express the NLO quark self-energy in terms of the three- and four-point HTL-effective vertex functions. Using the Feynman parametrization, we express the integrals containing the three- and four-point HTL effective vertex functions in terms of the solid angles. After completing the solid angle integrals, we numerically calculate the momentum integrals in the NLO quark self-energy and plot them as a function of the ratio of momentum and energy. Using the NLO quark self-energy, we plot the NLO correction to dispersion laws.

hep-ph↗

arXiv2023

Liénard-Wiechert potential of a heavy quark moving in QGP medium

We investigate the nature of the complex retarded potential of a heavy quarkonium moving in a hot and dense static deconfined nuclear medium. The well-known concept of the retarded potential in electrodynamics is extended to the context of the heavy-quark by modifying the static vacuum Cornell potential through Lorentz transformation to the static frame of the medium. The resulting potential in the vacuum is further corrected to incorporate the screening effect offered by the thermal medium. To do so, the retarded Cornell potential is modified by the dielectric function of the static quark-gluon plasma (QGP) medium. We present the numerical results for the real and imaginary parts of the potential along with the analytical expression of the potential approximated by a small velocity limit. Finally, we present the thermal width of quarkonia in the QGP medium derived using the imaginary part of the potential and study its dependence on velocity and temperature.

hep-ph↗

arXiv2023

Estimation of the diffusion coefficient of Heavy Quarks in light of Gribov-Zwanziger action

The heavy quark momentum diffusion coefficient ($κ$) is one of the most essential ingredients for the Langevin description of heavy quark dynamics. In the temperature regime relevant to the heavy ion collision phenomenology, a substantial difference exists between the lattice estimations of $κ$ and the corresponding leading order (LO) result from the hard thermal loop (HTL) perturbation theory. Moreover, the indication of poor convergence in the next-to-leading order (NLO) perturbative analysis has motivated the development of several approaches to incorporate the non-perturbative effects in the heavy quark phenomenology. In this work, we estimate the heavy quark diffusion coefficient based on the Gribov-Zwanziger prescription. In this framework, the gluon propagator depends on the temperature-dependent Gribov mass parameter, which has been obtained self-consistently from the one-loop gap equation. Incorporating this modified gluon propagator in the analysis, we find a reasonable agreement with the existing lattice estimations of $κ$ within the model uncertainties.

hep-ph↗

arXiv2022

Neutral pion mass in warm magnetized medium within Linear Sigma Model coupled to Quarks $\left(\text{LSM}_q\right)$ framework

We study the neutral pion mass in the presence of an external arbitrary magnetic field in the framework of the linear sigma model coupled to quark (LSMq) at finite temperature. In doing so, we have calculated the pion self-energy, constructed the dispersion equation via re-summation, and solved the dispersion relation at zero three momentum limit. In calculating the pion mass, we have included meson self-coupling's thermal and magnetic contribution and approximate chiral order parameter $v_0$. We report that the $π^0$ mass decreases with the magnetic field and increases with temperature.

hep-ph↗

arXiv2022

Dynamics of Hot QCD Matter -- Current Status and Developments

The discovery and characterization of hot and dense QCD matter, known as Quark Gluon Plasma (QGP), remains the most international collaborative effort and synergy between theorists and experimentalists in modern nuclear physics to date. The experimentalists around the world not only collect an unprecedented amount of data in heavy-ion collisions, at Relativistic Heavy Ion Collider (RHIC), at Brookhaven National Laboratory (BNL) in New York, USA, and the Large Hadron Collider (LHC), at CERN in Geneva, Switzerland but also analyze these data to unravel the mystery of this new phase of matter that filled a few microseconds old universe, just after the Big Bang. In the meantime, advancements in theoretical works and computing capability extend our wisdom about the hot-dense QCD matter and its dynamics through mathematical equations. The exchange of ideas between experimentalists and theoreticians is crucial for the progress of our knowledge. The motivation of this first conference named "HOT QCD Matter 2022" is to bring the community together to have a discourse on this topic. In this article, there are 36 sections discussing various topics in the field of relativistic heavy-ion collisions and related phenomena that cover a snapshot of the current experimental observations and theoretical progress. This article begins with the theoretical overview of relativistic spin-hydrodynamics in the presence of the external magnetic field, followed by the Lattice QCD results on heavy quarks in QGP, and finally, it ends with an overview of experiment results.

nucl-th↗

arXiv2022

Quarkonium in a bulk viscous QGP medium

The non-equilibrium properties of quark-gluon plasma (QGP) have been a topic of intensive research. In this contribution, we explore the nature of heavy quarkonia immersed in a QGP with bulk viscosity. We incorporate the bulk viscous effect through the deformation of the distribution functions of thermal quarks and gluons, with which the color dielectric permittivity can be computed. We use the color dielectric permittivity to compute the heavy quark potential inside a bulk viscous plasma and solve the Schrödinger equation using the potential to obtain the physical properties such as binding energies and decay widths. We discuss the effect of the bulk viscous correction on the quarkonium properties and the melting temperatures.

hep-ph↗

arXiv2022

Shear Viscosity of hadronic matter at finite temperature and magnetic field

We calculate the transport coefficient of hadronic matter in the presence of temperature and magnetic field using the linear sigma model. In the relaxation time approximation, we estimate the shear viscosity over entropy density $η/s$. The point-like interaction rates of hadrons are evaluated through the $S$-matrix approach in the presence of a magnetic field to obtain the temperature and magnetic field-dependent relaxation time. We observe that the transport coefficients are anisotropic in the presence of the magnetic field. We calculate the temperature and magnetic field-dependent anisotropic shear viscosity coefficients by incorporating the estimated relaxation time. The value of viscosity over entropy density is lower in the presence of a magnetic field than the value of it in a thermal medium. The behavior of the perpendicular components of the shear-viscous coefficient is also discussed. We consider the temperature-dependent hadron masses from mean-field effects in this work.

hep-ph↗

arXiv2021

Anisotropic pressure and quark number susceptibility of strongly magnetized QCD medium

In this work, we compute the hard thermal loop pressure of quark-gluon plasma within strong magnetic field approximation at one-loop order. Magnetic field breaks the rotational symmetry of the system. As a result, the pressure of QGP becomes anisotropic and one finds two different pressures along the longitudinal (along the magnetic field direction) and transverse direction. Similarly, the second-order quark number susceptibility, which represents the fluctuation of the net quark number density, also becomes anisotropic. We compute the second order QNS of deconfined QCD matter in strong field approximation considering same chemical potential for two quark flavors.

hep-ph↗