The shear ($η$) and bulk ($ζ$) viscosities are calculated in a quasiparticle relaxation time approximation for a hadron matter described within the relativistic mean-field based model with scaled hadron masses and couplings. Comparison with results of other models is presented. We demonstrate that a small value of the shear viscosity to entropy density ratio required for explaining a large elliptic flow observed at RHIC may be reached in the hadron phase. Large values of the bulk viscosity are noted in case of the baryon enriched matter.
The thermodynamic quantities of the ideal gas of hadrons and the $(2+1)$--flavor lattice QCD scaled by the effective degeneracy factors of the corresponding models are compared. We have found that in terms of the scaled variables the quark-hadron duality of the lattice QCD and the hadron resonance gas (HRG) model disappears. However, we have unexpectedly revealed that the scaled variables lead to the quark-hadron duality of the lattice QCD and the quantum ideal gas of kaons and antikaons, namely, the ideal gas of those hadrons that contain all the three quarks $u,d,s$ and their antiquarks. Sat…
The bulk viscosity is calculated for hadron matter produced in heavy-ion collisions, being described in the relaxation time approximation withi n the relativistic mean- field-based model with scaled hadron masses and couplings. W e show how different approximations used in the literature affect the result. Nume rical evaluations of the bulk viscosity with three considered models deviate not much from each other confirming earlier results.
We show how the measurement of appropriately constructed particle-energy/momentum correlations allows access to the bulk viscosity of strongly interacting hadron matter in heavy ion collisions. This measurement can be performed by the LHC and RHIC experiments in events with high-particle multiplicity, following up on existing estimates of the shear viscosity based on elliptic flow.
Shear viscosity ηand entropy density s of a hadronic resonance gas are calculated using the Chapman-Enskog and virial expansion methods using the K-matrix parametrization of hadronic cross sections which preserves the unitarity of the T -matrix. In the π-K-N-η- mixture considered, a total of 57 resonances up to 2 GeV were included. Comparisons are also made to results with other hadronic cross sections such as the Breit-Wigner (BW) and, where available, experimental phase shift parametrizations. Hadronic interactions forming resonances are shown to decrease the shear viscosity and increase the…
We have calculated microscopically bulk viscosity of hadronic matter, where equilibrium thermodynamics for all hadrons in medium are described by Hadron Resonance Gas (HRG) model. Considering pions and nucleons as abundant medium constituents, we have calculated their thermal widths, which inversely control the strength of bulk viscosities for respective components and represent their in-medium scattering probabilities with other mesonic and baryonic resonances, present in the medium. Our calculations show that bulk viscosity increases with both temperature and baryon chemical potential, where…
The shear ($η$) and bulk ($ζ$) viscosities are calculated in a quasiparticle relaxation time approximation. The hadron phase is described within the relativistic mean field based model with scaled hadron masses and couplings. The quark phase is treated in terms of the heavy quark bag model fitted to the lattice data. A two-phase model allowing for the first order phase transition from the hadron phase to the strongly coupled quark gluon plasma is constructed by means of the Gibbs conditions. Temperature and baryon density dependence of the calculated viscosity-to-entropy ratios ($η/s$, $ζ/s$) …
We estimate bulk and shear viscosity at finite temperature and baryon densities of hadronic matter within hadron resonance gas model. For bulk viscosity we use low energy theorems of QCD for the energy momentum tensor correlators. For shear viscosity coefficient, we estimate the same using molecular kinetic theory to relate the shear viscosity coefficient to average momentum of the hadrons in the hot and dense hadron gas. The bulk viscosity to entropy ratio increases with chemical potential and is related to the reduction of velocity of sound at nonzero chemical potential. The shear viscosity …
Quark-Gluon plasmas produced in relativistic heavy-ion collisions quickly expand and cool, entering a phase consisting of multiple interacting hadronic resonances just below the QCD deconfinement temperature. The transport properties of this hot hadron gas are poorly understood, yet they play an important role in our ability to infer transport properties of the quark-gluon plasma, because experimental measurements integrate over the whole system evolution. Assuming that the hot hadron gas can be modeled by a hadron cascade code based on kinetic theory assuming binary interactions, the shear vi…
The bulk viscosity coefficient of hadronic matter has been estimated in this present work, where the thermodynamical equilibrium quantity like speed of sound in the medium has been obtained by using standard hadron resonance gas model. Whereas, the non-equilibrium quantity like thermal widths of medium constituents have been calculated in the framework field theory at finite temperature. Our values of bulk viscosity coefficient are in agreement with some earlier estimations.
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 anisotropi…
The shear viscosity $η$ in the van der Waals excluded volume hadron-resonance gas model is considered. For the shear viscosity the result of the non-relativistic gas of hard-core particles is extended to the mixture of particles with different masses, but equal values of hard-core radius r. The relativistic corrections to hadron average momenta in thermal equilibrium are also taken into account. The ratio of the viscosity $η$ to the entropy density s is studied. It monotonously decreases along the chemical freeze-out line in nucleus-nucleus collisions with increasing collision energy. As a fun…
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 k…
In this paper, we have discussed the transverse momentum dependence of elliptic flow measured in relativistic heavy-ion collisions. The transverse momentum dependence of the number of constituent quarks ($n_{q}$) scaled $v_{2}$ is obtained for all the measured identified hadrons. The $n_{q}$ scaled $ϕ$ $v_{2}$ is found to be similar to $n_{q}$ scaled $Ω$ $v_{2}$. This indicates that both $ϕ$ and $Ω$ are produced through quark recombination at RHIC energies. We also find $n_{q}$ scaled proton $v_{2}$ ($v_{2}$ of light quarks) is higher than $n_{q}$ scaled $ϕ$ and $Ω$ $v_{2}$ ($v_{2}$ of strange…
Using the (2+1)-dimensional viscous hydrodynamic code VISH2+1 with a temperature dependent specific shear viscosity (eta/s)(T), we present a detailed study of the influence of a large hadronic shear viscosity and its corresponding relaxation time tau_pi on the transverse momentum spectra and elliptic flow of hadrons produced in 200 A GeV Au+Au collisions. Although theory, in principle, predicts a well-defined relation T*tau_pi = kappa(T)*(eta/s)(T), the precise form of kappa(T) for the matter created in relativistic heavy-ion collisions is not known. For the popular choice kappa=3 the hadron s…
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 …
We have explored some phenomenological issues during calculations of transport coefficients for hadronic matter, produced in the experiments of heavy ion collisions. Here, we have used an ideal hadron resonance gas model to demonstrate the issues. On the basis of dissipation mechanism, the hadronic zoo is classified into resonance and non-resonance members, who participate in dissipation via strong decay and scattering channels respectively. Imposing our phenomenological restriction, we are able to provide a rough upper and lower bound estimations of transport coefficients. Interestingly, we f…
We extract the specific shear viscosity $η/s$ of nuclear matter for various temperatures and chemical potentials in the hadronic phase using data taken in high energy nuclear collisions. We use a blastwave parameterization of the final state of nuclear collisions, including non-equilibrium deformations of particle distributions due to shear stress in the Navier-Stokes approximation. We fit spectra and elliptic flow of identified hadrons for a variety of collision energies and impact parameters at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The systems analyz…
We study the effect of magnetic field on the transport properties like shear and bulk viscosities of hot and dense hadronic matter within hadron resonance gas model. We estimate the bulk viscosity using low energy theorems for bilocal correlators of the energy momentum tensor generalized to finite temperature, density and magnetic field. We use Gaussian ansatz for the spectral function at low frequency. We estimate shear viscosity coefficient using molecular kinetic theory. We find that vacuum contribution due to finite magnetic field dominates the bulk viscosity (ζ) for the temperatures up to…
We study linear and nonlinear wave propagation in a dense and cold hadron gas and also in a cold quark gluon plasma, taking viscosity into account and using the Navier-Stokes equation. The equation of state of the hadronic phase is derived from the nonlinear Walecka model in the mean field approximation. The quark gluon plasma phase is described by the MIT equation of state. We show that in a hadron gas viscosity strongly damps wave propagation and also hinders shock wave formation. This marked difference between the two phases may have phenomenological consequences and lead to new QGP signatu…
We address a discrepancy between different computations of $η/s$ (shear viscosity over entropy density) of hadronic matter. Substantial deviations of this coefficient are found between transport approaches mainly based on resonance propagation with finite lifetime and other (semi-analytical) approaches with energy-dependent cross-sections, where interactions do not introduce a timescale. We provide an independent extraction of this coefficient by using the newly-developed SMASH (Simulating Many Accelerated Strongly interacting Hadrons) transport code, which is an example of a mainly resonance-…
The changes of hadron properties in dense and/or hot matter are discussed in terms of effective chiral Lagrangians with the parameters of the theory scaled in a simple way. The phenomenologically successful Walecka model is identified as a mean field chiral Lagrangian with the scaled parameters. Kaon condensation and chiral restoration transitions can be described within the same mean field framework.
Lattice calculations of the QCD trace anomaly at temperatures $T<160$ MeV have been shown to match hadron resonance gas model calculations, which include an exponentially rising hadron mass spectrum. In this paper we perform a more detailed comparison of the model calculations to lattice data that confirms the need for an exponentially increasing density of hadronic states. Also, we find that the lattice data is compatible with a hadron density of states that goes as $ρ(m) \sim m^{-a}\exp(m/T_H) $ at large $m$ with $a> 5/2$ (where $T_H \sim 167$ MeV). With this specific subleading contribution…
Knowledge of the equation of state of the baryon matter plays a decisive role in the description of neutron stars. With an increase of the baryon density the filling of Fermi seas of hyperons and $Δ$ isobars becomes possible. Their inclusion into standard relativistic mean-field models results in a strong softening of the equation of state and a lowering of the maximum neutron star mass below the measured values. We extend a relativistic mean-field model with scaled hadron masses and coupling constants developed in our previous works and take into account now not only hyperons but also the $Δ$…
We study the effects of bulk viscosity on pT spectra and elliptic flow in heavy ion collisions. For this purpose we compute the dissipative correction df to the single particle distribution functions in leading-log QCD, and in several simplified models. We consider, in particular, the relaxation time approximation and a kinetic model for the hadron resonance gas. We implement these distribution functions in a hydrodynamic simulation of Au + Au collisions at RHIC. We find significant corrections due to bulk viscosity in hadron pT spectra and the differential elliptic flow parameter v2(pT). Thes…
We estimate the temperature dependence of the bulk viscosity in a relativistic hadron gas. Employing the Green-Kubo formalism in the SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) transport approach, we study different hadronic systems in increasing order of complexity. We analyze the (in)validity of the single exponential relaxation ansatz for the bulk-channel correlation function and the strong influence of the resonances and their lifetimes. We discuss the difference between the inclusive bulk viscosity of an equilibrated, long-lived system, and the effective bulk viscosit…
Here we continue to elaborate properties of the relativistic mean-field based model (SHMC) proposed in ref. [6] where hadron masses and coupling constants depend on the $σ$-meson field. The validity of approximations used in [6] is discussed. We additionally incorporate contribution of meson excitations to the equations of motion. We also estimate the effects of the particle width. It is demonstrated that the inclusion of the baryon-baryon hole and baryon-antibaryon loop terms, if performed perturbatively, destroys the consistency of the model.
We investigate the influence of a temperature-dependent shear viscosity over entropy density ratio eta/s on the transverse momentum spectra and elliptic flow of hadrons in ultrarelativistic heavy-ion collisions. We find that the elliptic flow in sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC is dominated by the viscosity in the hadronic phase and in the phase transition region, but largely insensitive to the viscosity of the quark-gluon plasma (QGP). At the highest LHC energy, the elliptic flow becomes sensitive to the QGP viscosity and insensitive to the hadronic viscosity.
Ultrarelativistic heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) are thought to have produced a state of matter called the Quark-Gluon-Plasma, characterized by a very small shear viscosity to entropy density ratio $η/s$, near the lower bound predicted for that quantity by Anti-deSitter space/Conformal Field Theory (AdS/CFT) methods. As the produced matter expands and cools, it evolves through a phase described by a hadron gas with rapidly increasing $η/s$. We calculate $η/s$ as a function of temperature in this phase and find that its value poses a challenge for viscous rel…
The proposed earlier relativistic mean-field model with hadron masses and coupling constants depending on the $σ$-meson field is generalized to finite temperatures. Within this approach we simulate the in-medium behavior of the hadron masses motivated by the Brown-Rho scaling. The high-lying baryon resonances and boson excitations as well as excitations of the $σ$, $ω$ and $ρ$ fields interacting via mean fields are incorporated into this scheme. Thermodynamic properties of hot and dense hadronic matter are elaborated with the constructed equation of state. Even at zero baryon density, effectiv…
We show that first approximations to the bulk viscosity $η_v$ are expressible in terms of factors that depend on the sound speed $v_s$, the enthalpy, and the interaction (elastic and inelastic) cross section. The explicit dependence of $η_v$ on the factor $(\frac 13 - v_s^2)$ is demonstrated in the Chapman-Enskog approximation as well as the variational and relaxation time approaches. The interesting feature of bulk viscosity is that the dominant contributions at a given temperature arise from particles which are neither extremely nonrelativistic nor extremely relativistic. Numerical results f…
We explore the influence of a temperature-dependent shear viscosity over entropy density ratio $η/s$ on the azimuthal anisotropies v_2 and v_4 of hadrons at various rapidities. We find that in Au+Au collisions at full RHIC energy, $\sqrt{s_{NN}}=200$ GeV, the flow anisotropies are dominated by hadronic viscosity at all rapidities, whereas in Pb+Pb collisions at the LHC energy, $\sqrt{s_{NN}}=2760$ GeV, the flow coefficients are affected by the viscosity both in the plasma and hadronic phases at midrapidity, but the further away from midrapidity, the more dominant the hadronic viscosity is. We …
A theoretical framework for the calculation of shear and bulk viscosities of hadronic matter at finite temperature is presented. The framework is based on the quasi-particle picture. It allows for an arbitrary number of hadron species with point-like interactions, and allows for both elastic and inelastic collisions. Detailed balance is ensured. The particles have temperature dependent masses arising from mean field or potential effects, which maintains self-consistency between the equation of state and the transport coefficients. As an example, we calculate the shear and bulk viscosity in the…
In this article, we will briefly review the recent progress on hydrodynamic modeling and the extraction of the quark-gluon plasma (QGP) specific shear viscosity with an emphasis on results obtained from the hybrid model VISHNU that couples viscous hydrodynamics for the macroscopic expansion of the QGP to the hadron cascade model for the microscopic evolution of the late hadronic stage.
We describe ultra-relativistic heavy ion collisions at RHIC and the LHC with a hybrid model using the IP-Glasma model for the earliest stage and viscous hydrodynamics and microscopic transport for the later stages of the collision. We demonstrate that within this framework the bulk viscosity of the plasma plays an important role in describing the experimentally observed radial flow and azimuthal anisotropy simultaneously. We further investigate the dependence of observables on the temperature below which we employ the microscopic transport description.
We extend the relativistic mean-field models with hadron masses and meson-baryon coupling constants dependent on the scalar $σ$ field, studied previously to incorporate $Δ(1232)$ baryons. Available empirical information is analyzed to put constraints on the couplings of $Δ$s with meson fields. Conditions for the appearance of $Δ$s are studied. We demonstrate that with inclusion of the $Δ$s our equations of state continue to fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, the constraint on the maximum mass of the neutron stars…
We discuss in detail the shear viscosity coefficient eta and the viscosity to entropy density ratio eta/s of a hadronic gas comprised of pions and nucleons. In particular, we study the effects of baryon chemical potential on eta and eta/s. We solve the relativistic quantum Boltzmann equations with binary collisions (pi pi, pi N, and NN) for a state slightly deviated from thermal equilibrium at temperature T and baryon chemical potential mu. The use of phenomenological amplitudes in the collision terms, which are constructed to reproduce experimental data, greatly helps to extend the validity r…
We investigate the consequences of a nonzero bulk viscosity coefficient on the transverse momentum spectra, azimuthal momentum anisotropy, and multiplicity of charged hadrons produced in heavy ion collisions at LHC energies. The agreement between a realistic 3D hybrid simulation and the experimentally measured data considerably improves with the addition of a bulk viscosity coefficient for strongly interacting matter. This paves the way for an eventual quantitative determination of several QCD transport coefficients from the experimental heavy ion and hadron-nucleus collision programs.
Using viscous relativistic hydrodynamics we show that systematic studies of the impact parameter dependence of the eccentricity scaled elliptic flow can distinguish between different models for the calculation of the initial source eccentricity. This removes the largest present uncertainty in the extraction of the specific viscosity of the matter created in relativistic heavy-ion collisions from precise elliptic flow measurements.
We use the excluded volume Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $ηT/w$ at low temperatures and at finite baryon densities $ρ_B$. This $ηT/w$ is then matched to a QCD-based shear viscosity calculation of the QGP for different profiles of $ηT/w$ across {T,$μ_{B}$} including cross-over and critical point transitions. When compared to ideal hydrodynamic trajectories across {T,$μ_{B}$}, we find that the $ηT/w(T,μ_B)$ profiles would require initial conditions at much larger baryon density to reach the same freeze-out point.
We study the influence of a temperature-dependent shear viscosity over entropy density ratio $η/s$, different shear relaxation times $τ_π$, as well as different initial conditions on the transverse momentum spectra of charged hadrons and identified particles. We investigate the azimuthal flow asymmetries as a function of both collision energy and centrality. The elliptic flow coefficient turns out to be dominated by the hadronic viscosity at RHIC energies. Only at higher collision energies the impact of the viscosity in the QGP phase is visible in the flow asymmetries. Nevertheless, the shear …
We study the effects of the shear and bulk viscosities in the hadronic phase on the expansion of the fireball and on the particle production in relativistic heavy ion collisions. Comparing simulation with or without viscosity in the hadronic matter we find that elliptic flow observables strongly dependent on dissipative effects in the late stage. On the other hand, interferometry radii are sensitive, through the early transverse flow, on the value of the viscosity at high temperatures. We present first calculations including the effects of bulk viscosity in the hadronic phase and in the hadron…
The particle spectra and Hanbury-Brown Twiss (HBT) radius of Au+Au collisions at RHIC energy are investigated by a hydrodynamical expanding source with both shear and bulk viscosities ($ζ$). With a large width of the ratio of $ζ$ to entropy density $s$, both the particle transverse momentum spectra and the ratio $R_{out}/R_{side}$ of HBT radii in the direction of the total transverse momentum of detected two particles ($R_{out}$) and perpendicular to both this direction and the beam direction ($R_{side}$) become a little steeper.
Elaborated calculations of the shear and the bulk viscosities in the hadron gas, using the ultrarelativistic quantum molecular dynamics (UrQMD) model cross sections, are made. These cross sections are analyzed and improved. A special treatment of the resonances is implemented additionally. All this allows for better hydrodynamical description of the experimental data. The previously considered approximation of one constant cross section for all hadrons is justified. It's found that the bulk viscosity of the hadron gas is much larger than the bulk viscosity of the pion gas while the shear visco…
Within the relativistic mean-field framework with hadron masses and coupling constants dependent on the mean scalar field we study properties of nuclear matter at finite temperatures, baryon densities and isospin asymmetries relevant for heavy-ion collisions at laboratory energies below 2$A$ GeV. Previously constructed (KVORcut-based and MKVOR-based) models for the description of the cold hadron matter, which differ mainly by the density dependence of the nucleon effective mass and symmetry energy, are extended for finite temperatures. The baryon equation of state, which includes nucleons and …
Current experiments at the Relativistic Heavy Ion Collider (RHIC) are probing finite baryon densities where the shear viscosity to enthalpy ratio $ηT/w$ of the Quark Gluon Plasma remains unknown. We use the Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $ηT/w$ at low temperatures and at finite baryon densities $ρ_B$. We then match $ηT/w$ to a QCD-based shear viscosity calculation within the deconfined phase to create a table across $\left\{T,μ_B\right\}$ for different cross-over and critical point scenarios at a specified location. We find that these new $ηT…
We compute the shear viscosity of two-flavor QCD plasma in an external magnetic field in perturbative QCD at leading log order, assuming that the magnetic field is weak or soft: $eB\sim g^4\log(1/g)T^2$. We show that the shear viscosity takes a form $η=\barη(\bar B)T^3/(g^4\log(1/g))$ with a dimensionless function $\barη(\bar B)$ in terms of a dimensionless variable $\bar B=(eB)/(g^4\log(1/g)T^2)$. The variable $\bar B$ corresponds to the relative strength of the effect of cyclotron motions compared to the QCD collisions: $\bar B\sim l_{mfp}/l_{cyclo}$. We provide a full numerical result for t…
The transport coefficients of a multi-component hadronic gas at zero and non-zero baryon chemical potential are calculated using the Chapman-Enskog method. The calculations are done within the framework of an $S$-matrix based interacting hadron resonance gas model. In this model, the phase-shifts and cross-sections are calculated using $K$-matrix formalism and where required, by parameterizing the experimental phase-shifts. Using the energy dependence of cross-section, we find the temperature dependence of various transport coefficients such as shear viscosity, bulk viscosity, heat conductivit…
We discuss the temperature dependence of the scaled jet quenching parameter of hot gluonic matter within a quasiparticle approach. A pronounced maximum in the vicinity of the transition temperature is observed, where the ratio of the scaled jet quenching parameter and the inverse specific shear viscosity increases above typical values for weakly coupled systems.
We introduce a new scenario for heavy ion collisions that could solve the lingering problems associated with the so-called HBT puzzle. We postulate that the system starts expansion as the perfect quark-gluon fluid but close to freeze-out it splits into clusters, due to a sharp rise of bulk viscosity in the vicinity of the hadronization transition. We then argue that the characteristic cluster size is determined by the viscosity coefficient and the expansion rate. Typically it is much smaller and independent of the total system volume. These clusters maintain the pre-existing outward-going flow…
A hadron resonance gas model including all known particles and resonances with masses $m<2$ GeV and an exponentially rising density of Hagedorn states for $m>2$ GeV is used to obtain an upper bound on the shear viscosity to entropy density ratio, $η/s\approx1/(4π)$, of hadronic matter near $T_c$. We found a large trace anomaly and small speed of sound near $T_c$, which agree well with recent lattice calculations. We comment on the bulk viscosity to entropy density ratio close to $T_c$.
We present an estimate of the behaviour of the shear and bulk viscosity coefficients when the QCD critical point is approached from the hadronic side, describing hadronic matter within the statistical bootstrap model (SBM) of strong interactions. The boostrap model shows critical behavior near the quark-hadron transition temperature if the parameter characterizing the degeneracy of Hagedorn states is properly chosen. We calculate the critical exponents and amplitudes of relevant thermodynamic quantities near the QCD critical point and combine them with an Ansatz for the shear and bulk viscosit…
The new state of matter produced at Relativistic Heavy Ion Collider reveals a strongly coupled quark-gluon plasma with an extremely small shear viscosity to entropy density ratio eta/s. We calculate the eta/s of an equilibrated hadron matter characterized by a relativistic hadron resonance gas with a Hagedorn mass spectrum that grows exponentially with the hadron mass. We find with increase in temperature of the system the eta/s value decreases due to rapid increase in the multiplicity of massive resonances. In the vicinity of the critical temperature for deconfinement transition, the minimum …
In the real-time thermal field theory, the standard expression of shear viscosity for the nucleonic constituents is derived from the two point function of nucleonic viscous stress tensors at finite temperature and density. The finite thermal width or Landau damping is traditionally included in the nucleon propagators. This thermal width is calculated from the in-medium self-energy of nucleon for different possible pion-baryon loops. The dynamical part of nucleon-pion-baryon interactions are taken care by the effective Lagrangian densities of standard hadronic model. The shear viscosity to entr…
We have attempted to review on microscopic calculation of transport coefficients like shear and bulk viscosities in the framework of hadron resonance gas model, where a special attention is explored on the effect of finite system size. The standard expressions of transport coefficients, obtained from relaxation time approximation of kinetic theory or diagrammatic Kubo-type formalism, carry mainly two temperature dependent components -- thermodynamical phase space and relaxation time of medium constituent. Owing to quantum effect of finite system size, thermodynamical phase space can be reduced…
The equation of state of cold baryonic matter is studied within a relativistic mean-field model with hadron masses and coupling constants depending on a scalar field. We demonstrate that if the effective nucleon mass stops to decrease with a density increase at densities $n>n_*>n_0$, where $n_0$ is the nuclear saturation density, the equation of state stiffens for these densities and the limiting neutron star mass increases. The stabilization of the nucleon mass can be realised if in the equation of motion for the scalar mean-field there appear a term sharply varying in a narrow vicinity of th…
The collective behavior of hadrons and of electromagnetic radiation in heavy-ion collisions has been widely used to study the properties of the the Quark-Gluon Plasma (QGP). Indeed this collectivity, as measured by anisotropic flow coefficients, can be used to constrain the transport properties of QGP. The goal of this contribution is to investigate the influence of the specific bulk viscosity ($ζ/s$) on dilepton production, both at Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. We explore the sensitivity of dileptons to dynamical features that bulk viscosity …
The ratio of bulk to shear viscosity is expected to exhibit a different behaviour in weakly and in strongly coupled systems. This can be expressed by its dependence on the squared sound velocity. In the high temperature QCD plasma at small running coupling, the viscosity ratio is uniquely determined by a quadratic dependence on the conformality measure, whereas in certain strongly coupled and nearly conformal theories this dependence is linear. Employing an effective kinetic theory of quasiparticle excitations with medium-modified dispersion relation, we analyze the ratio of bulk to shear visc…
