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Chowdhury Aminul Islam

Publications and source records attributed to Chowdhury Aminul Islam.

At least 19 recordsLinked to original sources
arXiv2026

Effective QCD model with consistent quasi-gluon treatment : formulation and application

The Polyakov loop enhanced Nambu-Jona-Lasinio model is reformulated in terms of the gluon quasi-particles in addition to the already existing quark quasi-particles. The formulation goes beyond the saddle point approximation for the gluon sector. The framework provides a physically consistent quasiparticle model for QCD thermodynamics. The ensuing advantages of this formulation is discussed using transport coefficients in the light quark sector.

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arXiv2026

Electromagnetic spectral properties and Debye screening of a strongly magnetized hot medium

We have evaluated the electromagnetic spectral function and its spectral properties by computing the one-loop photon polarization tensor in presence of magnetic field, particularly in a strong field approximation compared to the thermal scale. When the magnetic scale is higher than the thermal scale the lowest Landau level (LLL) becomes effectively (1+1) dimensional strongly correlated system that provides a kinematical threshold based on the mass scale. Beyond this threshold the photon strikes the LLL and the spectral strength starts with a high value due to the dimensional reduction and then falls off with increase of the photon energy due to LLL dynamics in a strong field approximation. This strongly enhances the dilepton rate over the thermal perturbative leading order (Born) rate at very low invariant mass. We have also investigated the electromagnetic screening by computing the Debye screening mass and it depends distinctively on three different scales (mass of the quasiquark, temperature and the magnetic field strength) of a hot magnetized system. The mass dependence of the Debye screening supports the occurrence of a magnetic catalysis effect in the strong field approximation.

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arXiv2026

Dilepton Production as a Probe of Pion Condensation in Hot and Dense QCD Matter

We investigate dilepton production from an isospin-asymmetric hot and dense medium in order to explore the role of isospin imbalance in electromagnetic spectral properties. We focus in particular on modifications of the dilepton production rate associated with the onset of pion condensation, which can occur in the presence of a finite isospin chemical potential. We employ the Nambu--Jona-Lasinio model with isoscalar--vector interaction. We examine the phase structure in the $T-μ_I$ plane and estimate the vector current correlator--resummed dilepton rate for an effective quark chemical potential. We find that the interplay between isospin asymmetry, pion condensation, and vector interactions leads to nontrivial modifications of the dilepton yield. In particular, we observe two key features of the pion condensed phase: an enhancement at lower invariant mass and a prominent plateau-like structure which also help clearly identify the pion condensed phase from a chirally broken/restored phase. These results highlight the potential sensitivity of dilepton observables to pion-condensed phase of QCD matter, with possible implications for future low-energy heavy-ion collision experiments as well as isospin-rich environments such as neutron star matter.

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arXiv2026

Thermal Field Theory in the Presence of a Background Magnetic Field and its Application to QCD

This review has explored the fundamental principles of thermal field theory in the context of a background magnetic field, highlighting its theoretical framework and some of its applications to the thermo-magnetic QCD plasma generated in heavy-ion collisions. Our discussion has been limited to equilibrium systems for clarity and conciseness. We analysed bulk thermodynamic characteristics, including the phase diagram as well as real-time observables, shedding light on the behaviour and dynamics of the thermo-magnetic QCD medium relevant to heavy-ion physics.

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arXiv2025

Vector interaction bounds in NJL-like models from LQCD estimated curvature of the chiral crossover line

We obtain improved bounds on both the flavor-independent and -dependent vector interactions in a $2+1$-flavor Nambu\textendash Jona-Lasinio (NJL) model using the latest precise LQCD results of the curvature coefficients of the chiral crossover line. We find that these lattice estimated curvature coefficients allow for both attractive and repulsive types of interactions in both the cases. With this constrained ranges of vector interactions, we further predict the behavior of the second $(κ_2^B)$ and fourth $(κ_4^B)$ order curvature coefficients as a function of the strangeness chemical potential $(μ_S)$. We observe that the flavor mixing effects, arising from the flavor-independent vector interaction as well as from the 't Hooft interaction, play an important role in $k_2^B$. We propose that the mixing effects due to the vector interaction can be separated from those arising from the 't Hooft interaction by analyzing the behavior of $k_2^B$ as a function of $μ_S$. Finally, we locate the critical endpoint in the $T-μ_B$ plane using the model-estimated ranges of vector interactions and find the model's predictions to be consistent with the latest LQCD bounds.

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arXiv2025

Dilepton Spectra and Even Flow Harmonics in a Magnetized QGP: An Ideal Hydrodynamic Study

We present the first comprehensive study of dilepton production from a hot, magnetized quark-gluon plasma in heavy-ion collisions (HIC), incorporating realistic, time-dependent, and spatially inhomogeneous magnetic field profiles within an analytically solvable Gubser flow background. This framework provides a significant improvement over previous static calculations with homogeneous fields and moves toward the long-term goal of full $3+1$D magnetohydrodynamic simulations. We explore the effects of impact parameter, electrical conductivity, and invariant mass on the dilepton spectra and anisotropic even flow coefficients. It is found that transverse momentum spectra increase with impact parameter, dominated by annihilation processes, while decay contributions remain sub-leading. Strikingly, the elliptic flow $v_2$ from decay channels is nonzero even in nearly central collisions, exhibiting a characteristic shape--positive at low $p_T$ and negative at high $p_T$--that is largely independent of impact parameter and conductivity. In contrast, $v_2$ from annihilation processes is smaller in magnitude but dominates the total flow in magnitude due to its larger yield. Higher harmonics, such as $v_4$, are an order of magnitude smaller as compared to $v_2$ along with distinctive zero-crossing patterns. Conductivity enhances both spectra and flow but leaves no unambiguous signature for its extraction. Varying the invariant mass reveals the strongest enhancements at low mass, with harmonic coefficients suppressed at higher masses. Overall, our results suggest that central and semi-central collisions can carry imprints of the background magnetic field, and that characteristic correlations in even flow harmonics may provide a robust probe of electromagnetic effects in HICs.

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arXiv2025

The role of the pion mass on the QCD phase diagram in the $T-eB$ plane

We investigated the role of the pion mass on the QCD phase diagram in the $T-eB$ plane using an effective model treatment. Such treatments are able to capture the main features predicted by first-principles calculations. We also employed the model to estimate the pion mass beyond which the inverse magnetic catalysis (IMC) effect disappears. The value is found to be independent of the strength of the magnetic field.

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arXiv2024

Strongly interacting matter in extreme magnetic fields

Magnetic fields are ubiquitous across different physical systems of current interest; from the early Universe, compact astrophysical objects and heavy-ion collisions to condensed matter systems. A proper treatment of the effects produced by magnetic fields during the dynamical evolution of these systems, can help to understand observables that otherwise show a puzzling behavior. Furthermore, when these fields are comparable to or stronger than Λ_QCD, they serve as excellent probes to help elucidate the physics of strongly interacting matter under extreme conditions of temperature and density. In this work we provide a comprehensive review of recent developments on the description of QED and QCD systems where magnetic field driven effects are important. These include the modification of meson static properties such as masses and form factors, the chiral magnetic effect, the description of anomalous transport coefficients, superconductivity in extreme magnetic fields, the properties of neutron stars, the evolution of heavy-ion collisions, as well as effects on the QCD phase diagram. We describe recent theory and phenomenological developments using effective models as well as LQCD methods. The work represents a state-of-the-art review of the field, motivated by presentations and discussions during the "Workshop on Strongly Interacting Matter in Strong Electromagnetic Fields" that took place in the European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) in the city of Trento, Italy, September 25-29, 2023.

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arXiv2024

QCD phase diagram in the $T-eB$ plane for varying pion mass

We study the effect of a varying pion mass on the quantum chromodynamics (QCD) phase diagram in the presence of an external magnetic field, aiming to understand it, for the first time, using Nambu\textendash Jona-Lasinio like effective models. We compare results from both its local and nonlocal versions. In both cases, we find that the inverse magnetic catalysis (IMC) near the crossover is eliminated with increasing pion mass, while the decreasing trend of crossover temperature with increasing magnetic field persists for pion mass values at least up to $440$ MeV. Thus, the models are capable of capturing qualitatively the results found by lattice QCD (LQCD) for heavy (unphysical) pions. The key feature in the models is the incorporation of the effect of a reduction in the coupling constant with increasing energy. Along with reproducing the IMC effect, it enables models to describe the effects of heavier current quark masses without introducing additional parameters. For the local NJL model, this agreement depends on how the parameters of the model are fit at the physical point. In this respect, the nonlocal version, which, due to its formulation, automatically exhibits the IMC effect around the crossover region, captures the physics more naturally. We further use the nonlocal framework to determine the pion mass beyond which the IMC effect around the transition region does not exist anymore.

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arXiv2024

An NJL model analysis of a magnetised nonextensive QCD medium

We investigate the effect of a background magnetic field when applied to a nonextensive QCD medium in a $2+1$ flavour Nambu\textemdash Jona-Lasinio model. The effect of a constant as well as an $eB$-dependent coupling is considered. For the constant coupling, the well-known magnetic catalysis effect is observed with reduced strength in both the condensates and the transition temperatures compared to the standard extensive medium. In the case of a field-dependent coupling, we observe a competition between the nonextensive parameter, $q$ and $eB$. With sufficiently high $q$-values, the phenomenon of inverse magnetic catalysis \textemdash\, a well-known trait in effective models featuring $eB$-dependent coupling, appears to be eliminated within the range of magnetic fields examined in our present study.

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arXiv2023

The role of $U(1)_A$ symmetry breaking in the QCD corrections to the pion mass difference

The charged and neutral pion mass difference can be attributed to both the QED and QCD contributions. The current quark mass difference ($Δm$) is the source of the QCD contribution. Here, in a two-flavour non-local NJL model, we try to estimate the QCD contribution. Interestingly, we find that the strength of the $U(1)_A$ symmetry-breaking parameter $c$ plays a crucial role in obtaining the pion mass difference while intertwined with the current quark mass difference. To obtain the QCD contribution for the pion mass difference, we scan the parameter space in $\{Δm,\; c\}$, and by comparing this with the existing results, we constrained the parameter space. Further, using a fitted value of $c$, we determine the allowed range for the $Δm$ in the model. The model estimated $Δm$ ranges enable us to extract the chiral perturbation theory low-energy constant, $l_7$ and verify the dependence of the pion mass difference on $Δm$. We also find out its dependence on $c$ \textemdash\, it increases with the decreasing value of $c$, i.e., toward an axial anomaly restored phase.

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arXiv2023

Consistent approach to study gluon quasi-particles

We discuss a novel approach to estimate the partition function in effective model frameworks when the effective potentials have multiple extrema, so that ascertaining a mean field becomes difficult. Using this approach we present a consistent model to study the thermodynamic properties of gluon quasi-particles as a function of temperature, both in the color confined and the color deconfined phases.

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arXiv2023

Deciding on the anomalous magnetic moment of quarks in a framework of nonlocal NJL model

Anomalous magnetic moment (AMM) of quarks in presence of an external magnetic field has been explored using a nonlocal Nambu\textemdash Jona-Lasinio (NJL) model. Various strengths of AMM differing in orders of magnitude are used in the literature. We explore them in our nonlocal framework to decide on their strength. We checked the validity of using constant AMM of quarks and investigate two different temperature and magnetic field dependent forms. The forms are taken as the AMM being proportional to the i) meanfield and the ii) square of the meanfield. On comparison with the lattice data for both the condensate averages and differences, it turns out that the second choice is the most suitable one, in such an effective model scenario. In the process, we also keep track of the phase diagram in the $T-eB$ plane arising from our model calculation. The outcome is reasonable as far as the lattice QCD result is concerned.

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arXiv2022

Lepton pair production from a hot and dense QCD medium in the presence of an arbitrary magnetic field

In this article, we have explored the very important quantity of lepton pair production from a hot and dense QCD medium in presence of an arbitrary external magnetic field for simultaneous nonzero values of both the parallel (along the direction of the external field) and perpendicular (lying on the transverse plane to the external field) components of the dilepton momentum. As opposed to the zero magnetic field case (the so-called Born rate) or the lowest Landau level approximated rate, where only the annihilation process contributes, here we observe contributions also arising out of the quark and antiquark decay processes. We found the encouraging result of considerable enhancement of lepton pair production in presence of an arbitrary magnetic field. We decompose the total rate into different physical processes and discuss their behaviors for both zero and nonzero baryon density. The whole analysis is then subjected to an effective model treatment, where we have incorporated the magnetic field induced novel effects of magnetic catalysis (MC) and inverse MC (IMC) through a medium dependent scalar coupling, which leads to some further interesting observations.

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arXiv2022

Production rate and ellipticity of lepton pairs from a rotating hot and dense QCD medium

Using a current-current correlation function (CF), the photon polarization tensor is calculated for a rotating hot and dense QCD medium. The spectral function (SF) and the dilepton rate (DR) are estimated therefrom. Numerical results show that both SF and DR are enhanced in a rotating medium, especially in a low invariant mass region. SF and DR are also explored in the consequences of the interplay among the angular velocity, temperature and chemical potential. We also estimated the electromagnetic screening by calculating the Debye mass and it shows a suppression for a rotating QCD medium. The most interesting observation is the azimuthal anisotropy of the dilepton production, i.e, the elliptic flow $v_{2}$ of the lepton pair induced by the rotation as an external field. The competition between the centrifugal effect and the spin polarization effect due to rotation results in a convex down behaviour of the elliptic flow as a function of the transverse momentum in a relatively large magnitude of angular velocity. It is noticed that quark spin polarization induces a negative $v_2$ in the case of large angular velocity.

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arXiv2021

Studying explicit $U(1)_A$ symmetry breaking in hot and magnetised two flavour non-local NJL model constrained using lattice results

We study the two flavour non-local Nambu\textemdash Jona-Lasinio (NJL) model in the presence of a magnetic field and explore the chiral crossover in presence of a non-local form of the 't Hooft determinant term. Its coupling is governed by a dimensionless parameter $c$. This term is responsible for the explicit breaking of $U(1)_A$ symmetry. We have attempted a systematic analysis of the model parameters by fitting to self-consistent lattice QCD calculations. Three parameters of the model are fixed by $eB=0$ results from published lattice QCD on the chiral condensate, the pion decay constant ($F_π$), and the pion mass ($m_π$). The difference of the $u$ and $d$ quark condensates in the presence of a magnetic field ($eB$) is quite sensitive to $c$ and we fix $c$ using published lattice QCD results for this observable. We see no evidence that $c$ depends on $eB$. The crossover temperature decreases with increasing $eB$ only for condensate values at the lower end of the allowed values (as already seen in~\cite{Pagura:2016pwr}) and $F_π$ at the upper end of the allowed values. We further check our model predictions by calculating the topological susceptibility with the fitted $c$ values and comparing it with lattice results. Since the topological susceptibility is related to the extent of the $U(1)_A$ symmetry breaking, we find that it is sensitive to the value of $c$.

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arXiv2021

A Beyond Mean Field Approach to Yang-Mills Thermodynamics

We propose a beyond mean field approach to evaluate Yang-Mills thermodynamics from the partition function with n-body gluon contribution, in the presence of a uniform background Polyakov field. Using a path integral based formalism, we obtain, unlike the previous mean field studies within this model framework, physically consistent results with good agreement to the lattice data throughout the temperature range.

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