arXiv subjects

Jan-e Alam

Publications and source records attributed to Jan-e Alam.

At least 37 records · Page 2Linked to original sources

arXiv2020

Dispersion and suppression of sound near QCD critical point

We have used second order relativistic hydrodynamics equipped with equation of state which includes the critical point to study the propagation of perturbation in a relativistic QCD fluid. Dispersion relation for the sound wave has been derived to ascertain the fate of the perturbation in the fluid near the QCD critical end point (CEP). We observe that the threshold value of the wavelength of the sound in the fluid diverges at the CEP, implying that all the modes of the perturbations are dissipated at this point. Some consequences of the suppression of sound near the critical point have been discussed.

nucl-th↗

arXiv2020

Transmission of airborne virus through sneezed and coughed droplets

The spread of COVID19 through droplets ejected by infected individuals during sneezing and coughing has been considered as a matter of key concern. Therefore, a quantitative understanding of the propagation of droplets containing virus assumes immense importance. Here we investigate the evolution of droplets in space and time under varying external conditions of temperature, humidity and wind flow by using laws of statistical and fluid mechanics. The effects of drag, diffusion and the gravity on droplets of different sizes and ejection velocities have been considered during their motion in the air. In still air we found that bigger droplets traverse larger distance but the smaller droplets remain suspended in the air for longer time. So, in still air the horizontal distance that a healthy individual should maintain from an infected one is determined by the bigger droplets but the time interval to be maintained is determined by the smaller droplets. We show that in places with wind flow the lighter droplets travel larger distance and remain suspended in the air for longer time. Therefore, we conclude that both temporal and the geometric distance that a healthy individual should maintain from an infected one is determined by the smaller droplets under flowing air which makes the use of mask mandatory to prevent the virus. The maintenance of only stationary separation between healthy and infected individuals is not substantiated. The quantitative results obtained here will be useful to devise strategies for preventing the spread of other types of droplets also containing microorganisms.

physics.flu-dyn↗

arXiv2020

Effect of magnetic screening mass on the diffusion of heavy quarks

The drag and diffusion coefficients of heavy quarks propagating through quark gluon plasma (QGP) have been estimated by shielding both the electric and magnetic type infra-red divergences. The electric type screening in perturbative quantum chromodynamics (pQCD) has been widely studied and used in evaluating the diffusion coefficient of heavy quarks (HQs). To our knowledge the impact of magnetic screening in diffusion coefficients of HQs is not studied before. It is found that the effect of magnetic screening mass on the drag and diffusion coefficients of HQs is quite significant and its contribution should not be ignored for explaining the experimental data of heavy quark observables.

nucl-th↗

arXiv2020

HTL effective action of topologically massive gluons in 3+1 dimensions

We construct an effective action for "soft" gluons by integrating out hard thermal modes of topologically massive vector bosons at one loop order. The loop carrying hard gluons (momentum $\sim T$) are known as hard thermal loop (HTL). The gluons are massive in the non-Abelian topologically massive model (TMM) due to a quadratic coupling $B\wedge F$ where a 2-form field $B$ is coupled quadratically with the field strength $F$ of Yang-Mills (YM) field. The mass of the gluons plays an important role in the perturbative analysis of thermal field theory. Due to the presence of this infrared cut-off in the model, the color diffusion constant and conductivity can be analyzed in perturbative regime.

hep-th↗

arXiv2020

Glauber model for small system using anisotropic and inhomogeneous density profile of proton

Recent studies reveal that at high energies, collisions of small system like $p+p$ gives signatures similar to that widely observed in heavy ion collisions hinting towards a possibility of forming a medium with collective behaviour. With this motivation, we have used the Glauber model, which is traditionally applied to heavy ion collisions, in small system using anisotropic and inhomogeneous density profile of proton and found that the proposed model reproduces the charged particle multiplicity distribution of $p+p$ collisions at LHC energies very well. Collision geometric properties like mean impact parameter, mean number of binary collisions ($\langle N_{coll} \rangle$) and mean number of participants ($\langle N_{part} \rangle$) at different multiplicities are determined. Having estimated $\langle N_{coll} \rangle$, we have calculated nuclear modification-like factor ($R_{HL}$) in $p+p$ collisions. We also estimated eccentricity and elliptic flow as a function of charged particle multiplicity using the linear response to initial geometry.

hep-ph↗

arXiv2020

Thermal Field Theory of the Tsallis statistics

Classical and quantum Tsallis distributions have been widely used in many branches of natural and social sciences. But, the quantum field theory of the Tsallis distributions is relatively a less explored arena. In this article we derive the expression for the thermal two-point functions for the Tsallis statistics with the help of the corresponding statistical mechanical formulations. We show that the quantum Tsallis distributions used in the literature appear in the thermal part of the propagator much in the same way the Boltzmann-Gibbs distributions appear in the conventional thermal field theory. As an application of our findings, thermal mass of the real scalar bosons subjected to phi^4 interaction has been calculated in the Tsallis statistics.

hep-ph↗

arXiv2018

Effects of causality on the fluidity and viscous horizon of quark-gluon plasma

The second order Israel-Stewart-M$\ddot{u}$ller relativistic hydrodynamics has been applied to study the effects of causality on the acoustic oscillation in relativistic fluid. Causal dispersion relations have been derived with non-vanishing shear viscosity, bulk viscosity and thermal conductivity at non-zero temperature and chemical potential. These relations have been used to investigate the fluidity of Quark Gluon Plasma (QGP) at finite temperature ($T$). Results of the first order dissipative hydrodynamics have been obtained as limiting case of the second order theory. The effects of the causality on the fluidity near the transition point and on viscous horizon are found to be significant. We observe that the inclusion of causality reduces the fluidity of QGP. It has also been shown that the inclusion of large magnetic field in the causal hydrodynamics alters the fluidity of QGP

nucl-th↗

arXiv2018

Contribution of Kaon component in viscosity and conductivity of hadronic medium

The two-point correlation functions of kaonic viscous stress tensors and electro-magnetic currents have been calculated respectively to estimate the contributions of the strange sector in the shear viscosity and electrical conductivity of hadronic medium. In the one-loop correlators, kaon propagators contain a non-zero thermal width that leads to non-divergent values of transport coefficients. With the help of effective Lagrangian densities of strange hadrons, we have calculated in-medium self-energy of kaon for different possible mesonic loops, whose imaginary part provide the estimation of kaon thermal width. It is observed that near the quark-hadron transition temperature, the contribution of kaons to shear viscosity is larger and increases faster with temperature than pionic contribution. In case of electrical conductivity the trend due kaon component appears to be opposite in nature with respect to pion component.

nucl-th↗

arXiv2018

Effect of initial-state nucleon shadowing on the elliptic flow of thermal photons

Recently the effect of nucleon shadowing on the Monte-Carlo Glauber initial condition was studied and its role on the centrality dependence of elliptic flow ($v_2$) and fluctuations in initial eccentricity for different colliding nuclei were explored. It was found that the results with shadowing effects are closer to the QCD based dynamical model as well as to the experimental data. Inspired by this outcome, in this work we study the transverse momentum ($p_T$) spectra and elliptic flow of thermal photons for Au+Au collisions at RHIC and Pb+Pb collisions at LHC by incorporating the shadowing effects in deducing the initial energy density profile required to solve the relativistic hydrodynamical equations. We find that the thermal photon spectra remain almost unaltered, however, the elliptic flow of photon is found to be enhanced significantly due to shadowing effects.

nucl-th↗

arXiv2018

Calculation of Power Spectrum in the Little Bangs

The power spectrum of fluctuations in the momentum distributions of particles have been estimated with optical Glauber and Monte-Carlo Glauber initial conditions for relativistic heavy ion collisions. The evaluation procedure adopted in this work is analogous to the one used in the calculation of power spectrum in Cosmic Microwave Background Radiation (CMBR). The power spectrum due to perturbations in the phase space distribution of the particles has also been evaluated. The perturbation in phase space has been evolved through the Boltzmann transport equation in an expanding quark gluon plasma (QGP) background. The expansion of the QGP has been treated within the purview of (3+1) dimensional relativistic hydrodynamics. We observe that the non-equlibrium effects introduced as perturbations in the phase space distributions can be traced from the enhancement of the power spectrum as well as through its variation with temperature which is distinctly different from the case of vanishing perturbation. A relation has been derived between the power spectrum and the flow harmonics.

nucl-th↗

arXiv2018

Kinetic evolution and correlation of fluctuations in an expanding quark gluon plasma

Evolution of spatially anisotropic perturbation created in the system formed after Relativistic Heavy Ion Collisions has been studied. The microscopic evolution of the fluctuations has been examined within the ambit of Boltzmann Transport Equation (BTE) in a hydrodynamically expanding background. The expansion of the background composed of Quark Gluon Plasma (QGP) is treated within the framework of relativistic hydrodynamics. Spatial anisotropic fluctuations with different geometry have been evolved through Boltzmann equation. It is observed that the trace of such fluctuation survive the evolution. Within the relaxation time approximation analytical results have been obtained for the evolution of these anisotropies. Explicit relations between fluctuations and transport coefficients have been derived. The mixing of various Fourier (or $k$) modes of the perturbations during the evolution of the system has been explicitly demonstrated. This study is very useful in understanding the presumption that the measured anisotropies in the data from heavy ion collisions at relativistic energies imitate the initial state effects. The evolution of correlation function for the perturbation in pressure has been studied and shown that the initial correlation between two neighbouring points in real space evolves to a constant value at later time which gives rise to Dirac delta function for the correlation function in Fourier space. The power spectrum of the fluctuation in thermodynamic quantities (like temperature estimated in this work) can be connected to the fluctuation in transverse momentum of the thermal hadrons measured experimentally. The bulk viscous coefficient of the QGP has been estimated by using correlations of pressure fluctuation with the help of Green-Kubo relation. Angular power spectrum of the anisotropies has been estimated in the appendix.

nucl-th↗

arXiv2016

An estimate of the bulk viscosity of the hadronic medium

The bulk viscosity ($ζ$) of the hadronic medium has been estimated within the ambit of the Hadron Resonance Gas (HRG) model including the Hagedorn density of states. The HRG thermodynamics within a grand canonical ensemble provides the mean hadron number as well as its fluctuation. The fluctuation in the chemical composition of the hadronic medium in the grand canonical ensemble can result in non-zero divergence of the hadronic fluid flow velocity, allowing us to estimate the $ζ$ of the hadronic matter upto a relaxation time. We study the influence of the hadronic spectrum on $ζ$ and find its correlation with the conformal symmetry breaking (CSB) measure, $ε-3P$. We estimate $ζ$ along the contours with constant, $S/N_B$ (total entropy/net baryon number) in the $T-μ$ plane (temperature-baryonic chemical potential) for $S/N_B=30, 45$ and 300. We also assess the value of $ζ$ on the chemical freezeout curve for various centre of mass energy ($\sqrt{s_{NN}}$) and find that the bulk viscosity to entropy density ratio, $ζ/s$ is larger at FAIR than LHC energies.

nucl-th↗

arXiv2016

Diffusion of hidden charm mesons in hadronic medium

The drag and diffusion coefficients of a hot hadronic medium have been evaluated by using hidden charm mesons as probes. The matrix elements for the evaluation of these coefficients are calculated using an effective theory as well as from scattering lengths. Although the transport coefficients show a significant rise with temperature its effects on the suppression of $J/ψ$ in hadronic matter is not significant.

nucl-th↗

arXiv2015

Heavy quark diffusion in pre-equilibrium stage of heavy ion collisions

The drag and diffusion coefficients of heavy quarks (HQs) have been evaluated in the pre-equilibrium phase of the evolving fireball produced in heavy ion collisions at RHIC and LHC energies. The KLN and classical Yang-Mills spectra have been used for describing the momentum distributions of the gluons produced just after the collisions but before they thermalize. The interaction of the HQs with these gluons has been treated within the framework of perturbative QCD. We have observed that the HQs are dragged almost equally by the kinetically equilibrated and out-of-equilibrium gluonic systems. We have also noticed that the HQs diffusion in the pre-equilibrium gluonic phase is as fast as in the kinetically equilibrated gluons. Moreover, the diffusion is faster in the pre-equilibrium phase than in the chemically equilibrated quark-gluon plasma. These findings may have significant impact on the analysis of experimental results on the elliptic flow and the high momentum suppression of the open charm and beauty hadrons.

nucl-th↗

arXiv2014

Diffusion of $Λ_c$ in hot hadronic medium and its impact on $Λ_c/D$ ratio

The drag and diffusion coefficients of the $Λ_c(2286$ MeV) have been evaluated in the hadronic medium which is expected to be formed in the later stages of the evolving fire ball produced in heavy ion collisions at RHIC and LHC energies. The interactions between the $Λ_c$ and the hadrons in the medium have been derived from an effective hadronic Lagrangian as well as from the scattering lengths, obtained in the framework of heavy baryon chiral perturbation theory (HB$χ$PT). In both the approaches, the magnitude of the transport coefficients are turn out to be significant. A larger value is obtained in the former approach with respect to the latter. Significant values of the coefficients indicate substantial amount of interaction of the $Λ_c$ with the hadronic thermal bath. Furthermore, the transport coefficients of the $Λ_c$ is found to be different from the transport coefficients of $D$ meson. Present study indicates that the hadronic medium has a significant impact on the $Λ_c/D$ ratio in heavy ion collisions.

nucl-th↗

arXiv2013

Heavy-quark transport coefficients in a hot viscous quark-gluon plasma medium

The heavy-quark (HQ) transport coefficients have been estimated for a viscous quark-gluon plasma medium, utilizing a recently proposed quasi-particle description based on realistic QGP equation of state (EoS). Interactions entering through the equation of state significantly suppress the temperature dependence of the drag coefficient of QGP as compared to that of an ideal system of quarks and gluons. Inclusion of shear and bulk viscosities through the corrections to the thermal phase space factors of the bath particles alters the magnitude of the drag coefficient and the enhancement is significant at lower temperatures. The competition between the effects of realistic EoS and dissipative corrections through phase space factor the former eventually dictate how the drag coefficient would behave as a function of temperature, and how much quantitatively digress from the ideal case. The observations suggest significant impact of both the realistic equation of state, and the viscosities, on the HQs transport at RHIC and the LHC collision energies.

nucl-th↗

arXiv2013

Heavy flavor suppression: role of hadronic matter

The role of hadronic matter in the suppression of open heavy flavored mesons has been studied. The heavy-quarks (HQs) suppression factors have been calculated and contrasted with the experimental data obtained from nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadronic Collider (LHC) experiments. It is found that the suppression in the hadronic phase at RHIC energy is around $20%-25%$ whereas at the LHC it is around $10%-12%$ for the D meson. In case of B meson the hadronic suppression is around $10%-12%$ and $5%-6%$ at RHIC and LHC energies respectively. Present study suggests that the suppression of heavy flavor in the hadronic phase is significant at RHIC. However, the effect of hadronic suppression at LHC is marginal, this makes the characterization of QGP at LHC less complicated.

nucl-th↗

arXiv2013

Gluon bremsstrahlung by heavy quarks - its effects on transport coefficients and equilibrium distribution

The effects of gluon radiation by charm quarks on the transport coefficients {\it e.g.} drag, longitudinal and transverse diffusion and shear viscosity have been studied within the ambit of perturbative quantum chromodynamics (pQCD) and kinetic theory. We found that while the soft gluon radiation has substantial effects on the transport coefficients of the charm quarks in the quark gluon plasma its effects on the equilibrium distribution function is insignificant.

nucl-th↗