arXiv subjects

Ashutosh Dwibedi

Publications and source records attributed to Ashutosh Dwibedi.

18 recordsLinked to original sources

arXiv2026

Towards compressed baryonic matter densities: thermodynamics and transport coefficients

We study the thermodynamic and transport properties of hot and dense quantum chromodynamic matter expected to be produced in low-energy heavy-ion collisions, using three different effective quantum chromodynamic frameworks: the Nambu--Jona-Lasinio model, the chiral effective model, and the hadron resonance gas model. We briefly outline the theoretical formulation of thermodynamic quantities and transport coefficients within these approaches, where quarks are treated with effective masses in the Nambu--Jona-Lasinio and chiral effective models, and hadronic degrees of freedom are employed in the hadron resonance gas model. The transport coefficients are evaluated using the Boltzmann transport equation in the relaxation-time approximation. Following the theoretical overview, we present a comprehensive analysis of the behavior of these quantities as functions of the baryon chemical potential or net baryon density. The Lorenz ratio $κ/(σT)$ is found to increase rapidly-indicating a strong violation of the Wiedemann-Franz law in the low-$μ_{B}$ regime--while approaching the universal value at higher baryon chemical potentials or densities. The shear-viscosity-to-entropy-density ratio $η/s$ remains nearly constant at low $μ_{B}$ but exhibits a gradual increase as $μ_{B}$ grows. We also discuss the qualitative similarities of these trends with those observed in the electron-hole plasma of graphene, an emergent quasi-relativistic system characterized by massless energy-momentum dispersion.

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arXiv2026

Electron-Ion Collision Environment: Distribution of Quark Spin and Orbital Angular Momentum

The future Electron-Ion Collider (EIC) will enable measurements of the same partonic distributions inside both the proton and the nucleus through electron-proton (eP) and electron-ion (eA) collisions. This capability motivates the present theoretical study of the distributions of quark spin and orbital angular momentum within the proton and the nucleus. To map the eP and eA collision environments, we employ the Nambu--Jona-Lasinio (NJL) model at finite nuclear density to determine the constituent quark masses at zero nuclear density and near the nuclear saturation density. Using these quark mass inputs, we calculate the generalized transverse momentum-dependent parton distributions (GTMDs) associated with quark orbital angular momentum (OAM), spin, and spin-orbit correlations within the light-front dressed quark model. Furthermore, inspired by the nuclear suppression factor widely used in heavy-ion collision experiments, we introduce a set of GTMD ratios between eP and eA collisions. Any deviation of these ratios from unity provides an indirect measure of many-body nuclear density effects arising from non-perturbative quantum chromodynamics (QCD).

hep-ph↗

arXiv2026

An expanding spherical fireball model for light hadron production at RHIC ($\sqrt{s_{\rm NN}}=7.7$--$39$ GeV)

We investigate the transverse momentum ($p_T$) spectra and rapidity distributions of the light hadrons $π^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ produced in Au+Au collisions at RHIC for $\sqrt{s_{\rm NN}} = 7.7$--39 GeV and different collision centralities. The produced medium is modeled as an expanding spherical fireball, with the radial expansion velocity determined from the rate of increase of the fireball radius. The particle spectra are calculated using the Cooper--Frye freeze-out prescription with a local equilibrium distribution function and a blast-wave-like flow profile. The model parameters are fixed from the midrapidity $p_T$ spectra of pions at kinetic freeze-out for different centralities. The same parameters are then used for the other hadron species, with the kinetic freeze-out chemical potential as the only additional free parameter. The model provides a good description of the STAR collaboration data for the $p_{T}$ spectra of light hadrons and predicts Gaussian-like rapidity distributions over the considered energy range across different centralities.

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arXiv2026

Mechanical distribution of the pseudoscalar charmonium and bottomonium on the light-front

We investigate the energy-momentum tensor of pseudoscalar charmonium and bottomonium within the framework of the light-front quark model. The gravitational form factors (GFFs), namely the $A$ and $D$-terms, are evaluated in terms of the light-front wave functions. The corresponding spatial mechanical distributions in the transverse plane are obtained through the Fourier transform of these GFFs. To examine the sensitivity of the results to the internal quark-antiquark distribution inside the meson, two distinct Gaussian forms are employed for the spatial part of the wave function. We analyze several mechanical properties in the transverse plane, including the momentum density, pressure distribution, shear stress, force density, and internal energy density. The pressure distribution exhibits a node where it changes sign from positive (repulsive) to negative (attractive) with increasing transverse distance. The force distribution remains positive throughout the transverse plane, supporting the stability condition proposed in earlier studies. Most of the spatial distributions, except for the shear stress, are found to be sensitive to the choice of the spatial wave function near the center of the meson, while they become nearly insensitive toward the periphery. In contrast, the shear stress distribution exhibits noticeable sensitivity to the choice of wave function in the intermediate transverse region.

hep-ph↗

arXiv2026

Spectra and elliptic flow of light hadrons in an expanding fire-cylinder model for the RHIC Beam Energy Scan

We investigate the transverse momentum spectra ($p_T$) and elliptic flow ($v_2$) of $π^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$ produced in peripheral Au+Au collisions at $\sqrt{s_{\rm NN}} = 7.7$, 11.5, 19.6, 27, and 39 GeV in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). The analysis is carried out within an expanding elliptic fire-cylinder model that incorporates longitudinal expansion and anisotropic transverse flow. Particle production at kinetic freeze-out is obtained using a local equilibrium distribution function with a blast-wave-like fluid velocity profile derived from the expansion dynamics of the elliptic fire-cylinder. The model parameters governing the collective expansion are first constrained by fitting the midrapidity $p_T$ spectra of $π^{\pm}$ and are then applied, without further adjustment, to $K^{\pm}$, $p$, and $\bar{p}$. The model provides a consistent description of the $p_T$ spectra and reproduces the qualitative behavior of the elliptic flow for all considered particle species.

nucl-th↗

arXiv2026

Valence quark distribution of the pion inside a medium with finite baryon density: A Nambu--Jona-Lasinio model approach

We calculate the in-medium valence quark distribution of the pion immersed in a finite baryon density using the light-cone quark model. The medium-modified pion properties are obtained by using the constituent quark mass-dependent light cone wave functions. To obtain the constituent quark masses at finite baryon density, we employ the two-flavor Nambu--Jona-Lasinio model. We primarily focus on the in-medium electromagnetic form factor, distribution amplitude, and the parton distribution function of the pion. The parton distribution functions are also evolved from the model scale to a perturbative scale using next to leading order Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations. Furthermore, our calculated form factors are compared with available experimental measurements and lattice quantum chromodynamics studies. We also examine the Mellin moments derived from our parton distribution functions in comparison with existing extractions and theoretical model predictions.

hep-ph↗

arXiv2026

Shear Viscosity and Electrical Conductivity of Rotating Nuclear Medium in Hadron Resonance Gas and Nambu-Jona Lasinio Models

Motivated by recent observations of spin polarization and alignment in heavy-ion collisions, we study the impact of rotation on the transport properties of strongly interacting matter within kinetic theory in the relaxation time approximation. Our analysis focuses on the anisotropic shear viscosity--parallel ($η_{\parallel}$), perpendicular ($η_{\perp}$), and Hall ($η_{\times}$)--and electrical conductivity--$σ_{\parallel}$, $σ_{\perp}$, and $σ_{\times}$--induced by the Coriolis force in a rotating medium. We employ two approaches: a combined quark-gluon plasma--hadron resonance gas (QGP--HRG) framework and a two-flavor Nambu--Jona-Lasinio (NJL) model. In the QGP--HRG description, noninteracting HRG (massless partonic) degrees of freedom are used below (above) the transition temperature. In the NJL model, rotation enters through spinorial connections in the Lagrangian, and the constituent quark masses are obtained over the full temperature range. Rotation suppresses the chiral condensate and slightly enhances the transport coefficients for phenomenologically relevant angular velocities. Assuming a temperature-dependent angular velocity consistent with standard cooling, we find that $η_{||,\perp,\times}/s$ and $σ_{\perp,\times}/T$ exhibit a valley-like temperature dependence, with reduced magnitudes compared to the isotropic $η/s$ and $σ/T$ obtained without rotation. At zero net baryon density, rotation generates a sizable nondissipative Hall-like conductivity, unlike the case with magnetic fields where baryon and antibaryon contributions cancel.

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arXiv2026

Distribution Functions of Radially Excited Pion using the Light-Front Quark Model

We investigate the internal structure of the ground ($1S$) and the first two radially excited ($2S,3S$) states of the pion within the light-front quark model. The valence Fock sector is described using pure harmonic-oscillator eigenstates and mixed states formed as orthogonal linear combinations of these eigenfunctions. The optimal wavefunction parameters are determined through a variational procedure based on a QCD-motivated effective Hamiltonian. Using the resulting light-front wavefunctions, we study the pion distribution amplitude, parton distribution function, and electromagnetic form factor. After QCD evolution, the ground state distribution amplitude and parton distribution function are found to be in good agreement with available experimental data. At the model scale, the parton distribution functions of the $1S$ and $2S$ states show clear sensitivity to state mixing, while the distribution amplitudes and electromagnetic form factors are weakly sensitive. In contrast, for the $3S$ state, all three observables exhibit a pronounced sensitivity to mixing. The decay constants of the mixed states are also found to decrease sequentially with increasing radial excitation.

hep-ph↗

arXiv2025

Electron Hydrodynamics in Graphene : Experimental and Theoretical Status

The present work comprehensively reviews electron hydrodynamics in graphene, highlighting both experimental observations and theoretical developments. Key experimental signatures such as negative vicinity resistance, Poiseuille flow, and significant violation of the Wiedemann-Franz (WF) law have been discussed, with special emphasis on Lorenz ratio measurements. In the theoretical direction, recent efforts have focused on developing hydrodynamic frameworks for calculating the thermodynamic and transport coefficients of electrons in graphene. The present work has briefly addressed the theoretical framework adopted by our group.

cond-mat.mes-hall↗

arXiv2025

Probing Dynamical Electrical Conductivity via Dilepton Emission: A Kinetic theory approach

Dileptons serve as a clean and penetrating probe of the Quark--Gluon Plasma created in high-energy heavy-ion collisions. In this work, we investigate thermal dilepton spectra and their elliptic flow through the dynamical conductivity that governs the production rate. The conductivity is obtained from the trace of the spectral function within relativistic kinetic theory using the Relaxation Time Approximation. This allows us to derive for the first time an analytical expression for the dilepton rate with explicit dependence on the relaxation time of quark-antiquark interactions. We find a non-monotonic dependence of the dilepton rate on the relaxation time and compare the resulting transverse momentum, invariant mass spectra and elliptic flow with previous quantum field theory results. The spectra and elliptic flow are obtained by integrating the rate over the full spacetime volume of the evolving medium, using temperature and flow profiles from realistic MUSIC hydrodynamic simulations without considering the effect of magnetic fields in the profiles itself. However, we study the role of an external space-time dependent magnetic field by making the conductivity anisotropic. At small relaxation times, magnetic fields have negligible impact, while for larger relaxation times and stronger initial fields, modifications of up to $\sim$20\% appear in both spectra and elliptic flow. Assuming instead a constant magnetic field of $\sim 1\,m_π^2$ at large relaxation times yields more modest effects, with changes of about 10\% in spectra and 5\% in elliptic flow.

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arXiv2025

Possibility of quantum Hall effect in dense quark matter environments: A chiral model approach

A high baryon density and strong magnetic fields are expected in peripheral collisions in heavy ion collision experiments, such as the upcoming CBM experiment at FAIR in Germany and NICA in Russia. Such densities are also likely in the core of massive neutron stars, possibly with mixed quark-hadron phases. We employed the chiral effective model to obtain the constituent quark mass in this non-perturbative QCD regime. A quantized version of conductivity and resistivity is found reliable in the quantum domain of low density and high magnetic fields. Landau quantization gives rise to phenomena similar to SdH oscillations and quantum Hall effect in this regime. We have used a density-dependent magnetic field to observe SdH-type oscillations and the possibility of the quantum Hall effect in the interior of neutron stars where the magnetic field varies as a function of the baryon density. Our results indicate the possibility of observing the quantum Hall effect in a neutron star environment.

nucl-th↗

arXiv2025

On the Wiedemann-Franz law violation in Graphene and quark-gluon plasma systems

A comparative study of the thermodynamic and transport properties of the ultra-relativistic quark-gluon plasma produced in heavy ion collisions with the "quasi-relativistic" massless electron-hole plasma in graphene sample has been performed. We observe that the enthalpy per net charge carriers emerges as a useful physical quantity determining the transport variables in hydrodynamic domain. Lorenz ratio is defined as thermal to electrical conductivity ratio, normalized by temperature and Lorenz number $L_{0}=\frac{π^{2}}{3}\left(\frac{k_{B}}{e}\right)^{2}$. The validity of the Wiedemann-Franz law can be checked by evaluating the Lorenz ratio, which is expected to be unity. We investigate the validity of the Wiedemann-Franz law by examining whether the Lorenz ratio equals unity or deviates from it. Our findings indicate that, within the fluid-based framework, the Lorenz ratio consistently leads to a violation of the Wiedemann-Franz law. This is attributed to the proportional relation between Lorenz ratio and enthalpy per net charge carriers in the fluid. Based on the experimental observation, graphene and quark-gluon plasma, both systems at a low net carrier density, violate the Wiedemann-Franz law due to their fluidic nature. However, graphene at a relatively high net carrier density obeys the Wiedemann-Franz law, followed by metals with high Fermi energy or electron density. It indicates a fluid to the non-fluid transition of the graphene system from low to high carrier density. In this regard, the fluid or non-fluid aspect of quark-gluon plasma at high density is yet to be explored by future facilities like Compressed Baryonic Matter and Nuclotron-based Ion Collider fAcility experiments.

cond-mat.str-el↗

arXiv2025

Effect of Coriolis Force on Diffusion of D Meson

We have attempted to calculate and estimate the spatial diffusion coefficients of D meson through rotating hadron resonance gas, which can be produced in the late stage of peripheral heavy ion collisions. Employing the framework of kinetic theory in relaxation time approximation, and using Einstein's diffusion relation, one can express the spatial diffusion coefficients of D meson as a ratio of its conductivity to its susceptibility. Here, we have tuned D meson relaxation time from the knowledge of earlier works on its spatial diffusion estimations, and then we have extended the framework for the finite rotation picture of hadronic matter, where only the effect of Coriolis force is considered. Our study also revealed the anisotropic nature of diffusion in the presence of rotation with future possibilities of phenomenological signature.

hep-ph↗

arXiv2024

Dynamics of Hot QCD Matter 2024 -- Bulk Properties

The second Hot QCD Matter 2024 conference at IIT Mandi focused on various ongoing topics in high-energy heavy-ion collisions, encompassing theoretical and experimental perspectives. This proceedings volume includes 19 contributions that collectively explore diverse aspects of the bulk properties of hot QCD matter. The topics encompass the dynamics of electromagnetic fields, transport properties, hadronic matter, spin hydrodynamics, and the role of conserved charges in high-energy environments. These studies significantly enhance our understanding of the complex dynamics of hot QCD matter, the quark-gluon plasma (QGP) formed in high-energy nuclear collisions. Advances in theoretical frameworks, including hydrodynamics, spin dynamics, and fluctuation studies, aim to improve theoretical calculations and refine our knowledge of the thermodynamic properties of strongly interacting matter. Experimental efforts, such as those conducted by the ALICE and STAR collaborations, play a vital role in validating these theoretical predictions and deepening our insight into the QCD phase diagram, collectivity in small systems, and the early-stage behavior of strongly interacting matter. Combining theoretical models with experimental observations offers a comprehensive understanding of the extreme conditions encountered in relativistic heavy-ion and proton-proton collisions.

nucl-th↗

arXiv2024

Effect of Coriolis Force on Electrical Conductivity Tensor for Rotating Hadron Resonance Gas

We have investigated the influence of the Coriolis force on the electrical conductivity of hadronic matter formed in relativistic nuclear collisions, employing the Hadron Resonance Gas (HRG) model. A rotating matter in the peripheral heavy ion collisions can be expected from the initial stage of quark matter to late-stage hadronic matter. Present work is focused on rotating hadronic matter, whose medium constituents - hadron resonances can face a non-zero Coriolis force, which can influence the hadronic flow or conductivity. We estimate this conductivity tensor by using the relativistic Boltzmann transport equation. In the absence of Coriolis force, an isotropic conductivity tensor for hadronic matter is expected. However, our study finds that the presence of Coriolis force can generate an anisotropic conductivity tensor with three main conductivity components - parallel, perpendicular, and Hall, similar to the effect of Lorentz force at a finite magnetic field. Our study has indicated that a noticeable anisotropy of conductivity tensor can be found within the phenomenological range of angular velocity $Ω= 0.001-0.02$ GeV and hadronic scattering radius $a=0.2-2$ fm.

hep-ph↗

arXiv2024

Effect of the Coriolis force on the electrical conductivity of quark matter: A nonrelativistic description

Rotating quarks and hadronic systems, produced in peripheral heavy ion collisions, can experience Coriolis force and other forces due to rotational motion. Considering only the effect of Coriolis force, we have calculated the electrical conductivity for non-relativistic rotating matter using the Relaxation Time Approximation based Boltzmann transport equation. A similarity in mathematical calculations of electrical conductivity at finite rotation and finite magnetic fields is exposed, where an equivalence role between Coriolis force on massive particle's motion and Lorentz force on charged particle's motion is noticed. As the beginning level step, we consider only the Coriolis force in the non-relativistic formalism, which will be extended in the future towards the relativistic case, and to adopt other forces for a more realistic description of the rotating quark and hadronic system.

nucl-th↗

arXiv2024

Transport Coefficients of relativistic matter: A detailed formalism with a gross knowledge of their magnitude

The present review article has attempted a compact formalism description of transport coefficient calculations for relativistic fluid, which is expected in heavy ion collision experiments. Here, we first address the macroscopic description of relativistic fluid dynamics and then its microscopic description based on the kinetic theory framework. We also address different relaxation time approximation-based models in Boltzmann transport equations, which make a sandwich between Macro and Micro frameworks of relativistic fluid dynamics and finally provide different microscopic expressions of transport coefficients like the fluid's shear viscosity and bulk viscosity. In the numeric part of this review article, we put stress on the two gross components of transport coefficient expressions: relaxation time and thermodynamic phase-space part. Then, we try to tune the relaxation time component to cover earlier theoretical estimations and experimental data-driven estimations for RHIC and LHC matter. By this way of numerical understanding, we provide the final comments on the values of transport coefficients and relaxation time in the context of the (nearly) perfect fluid nature of the RHIC or LHC matter.

nucl-th↗

arXiv2024

Effect of Coriolis force on the shear viscosity of quark matter: A nonrelativistic description

Shear viscosity becomes anisotropic in a rotating medium. It is discovered here that for rotating thermalized quantum systems such as those created in relativistic heavy-ion collisions, the coeffficient of shear viscosity breaks up into five independent components. Similar phenomena were also discovered for quark-gluon plasma in the presence of the magnetic field. Like the Lorentz force at a finite magnetic field, the Coriolis force also creates anisotropic viscosity at nonzero rotation. As a first approach, for simplicity, the calculations are done in the nonrelativistic prescription, with a future proposal to extend it toward a relativistic description. Introducing the Coriolis force term in relaxation time approximated Boltzmann transport equation, we have found different effective relaxation times along the parallel, perpendicular, and Hall directions in terms of actual relaxation time and rotating time period. Comparing the present formalism with the finite magnetic field picture, we have shown the equivalence of roles between the rotating and cyclotron time periods, where the rotating time period is inverse of twice the angular velocity.

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