Narrow Results

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 0.1 GeV and increases with magnetic field while ratio ζ/s decreases with magnetic field. We also find that shear viscosity coefficient of hadronic matter decreases with magnetic field.

The thermodynamic properties of a non-interacting ideal hadron resonance gas (HRG) of finite volume have been studied in the presence of an external magnetic field. The inclusion of background magnetic field in the calculation of thermodynamic potential is done by the modification of the dispersion relations of the charged hadrons in terms of Landau quantization. The generalized Matsubara prescription has been employed to take into account the finite size effects in which a periodic (anti-periodic) boundary conditions is considered for the mesons (baryons). We find significant effects of the magnetic field as well as system size on the temperature dependence of energy density, longitudinal and transverse pressure especially in low temperature regions. The HRG is found to exhibit diamagnetism (paramagnetism) in the low (high) temperature region whereas the finite size effect is seen to strengthen the diamagnetic behavior of the medium.

In this paper, we investigate the effect of repulsive interaction between hadrons on the susceptibilities of conserved charges, namely baryon number (B), electric charge (Q) and strangeness (S). We estimate second-, fourth- and sixth-order susceptibilities of conserved charges, their differences, ratios and correlations within ambit of mean-field hadron resonance gas (MFHRG) model. We consider repulsive mean-field interaction among meson pairs, baryon pairs and antibaryon pairs separately and constrain them by confronting the results of various susceptibilities with the recent lattice quantum chromodynamics (LQCD) data. We find that the repulsive interactions between baryon–baryon pairs and antibaryon–antibaryon pairs are sufficient to describe the baryon susceptibilities of hadronic matter at temperatures below QCD transition temperature. However, small but finite mesonic repulsive interaction is needed to describe electric charge and strangeness susceptibilities. We finally conclude that the repulsive interaction between hadrons play a very important role in describing the thermodynamic properties of hadronic matter, especially near the quark–hadron phase transition temperature ($T_c$). The mean-field parameter for baryons ($K_B$) should be constrained in the range $0.40\le K_B\le 0.450\mathrm{\text{GeV}}{\mathrm{\text{fm}}}^3$ to get a good agreement of baryon susceptibilities with the LQCD results, whereas meson mean-field parameter $K_M\sim 0.05\mathrm{\text{GeV}}{\mathrm{\text{fm}}}^3$ must be included with $K_B$ to get a reasonable agreement of MFHRG model with the LQCD results for electric charge and strangeness susceptibilities.

At thermal equilibrium, different chemical freeze-out conditions have been proposed so far. They have an ultimate aim of proposing a universal description for the chemical freeze-out parameters ($T_{ch}$ and ${\mu }_b$), which are to be extracted from the statistical fitting of different particle ratios measured at various collision energies with calculations from thermal models. A systematic comparison between these conditions is presented. The physical meaning of each of them and their sensitivity to the hadron mass cuts are discussed. Based on availability, some of them are compared with recent lattice calculations. We found that most of these conditions are thermodynamically equivalent, especially at small baryon chemical potential. We propose that further crucial consistency tests should be performed at low energies. The fireball thermodynamics is another way of guessing conditions describing the chemical freeze-out parameters extracted from high-energy experiments. We endorse the possibility that the various chemical freeze-out conditions should be interpreted as different aspects of one universal condition.

An overview of a hadron resonance gas (HRG) model that includes van der Waals (vdW) interactions between hadrons is presented. Applications of the excluded volume HRG model to heavy-ion collision data and lattice quantum chromodynamics (QCD) equation of state are discussed. A recently developed quantum vdW HRG model is covered as well. Applications of this model in the context of the QCD critical point are elaborated.

From the analysis of light (anti)nuclei multiplicities that were measured recently by the ALICE collaboration in Pb+Pb collisions at the center-of-mass collision energy $\sqrt{s_{NN}}=2.76$TeV, there arose a highly nontrivial question about the excluded volume of composite particles. Surprisingly, the hadron resonance gas model (HRGM) is able to perfectly describe the light (anti) nuclei multiplicities under various assumptions. Thus, one can consider the (anti)nuclei with a vanishing hard-core radius (as the point-like particles) or with the hard-core radius of proton, but the fit quality is the same for these assumptions. It is clear, however, that such assumptions are unphysical. Hence we obtain a formula for the classical excluded volume of loosely bound light nuclei consisting of A baryons. To implement a new formula into the HRGM, we have to modify the induced surface tension concept to treat the hadrons and (anti)nuclei on the same footing. We perform a thorough analysis of hadronic and (anti)nuclei multiplicities measured by the ALICE collaboration. The HRGM with the induced surface tension allows us to verify different assumptions on the values of hard-core radii and different scenarios of chemical freeze-out of (anti)nuclei. It is shown that the unprecedentedly high quality of fit ${\chi }_{\mathrm{\text{tot}}}^2/\mathrm{\text{dof}}\simeq 0.724$ is achieved, if the chemical freeze-out temperature of hadrons is about $T_h=150$MeV, while the one for all (anti)nuclei is $T_A=174-175.2$MeV.

Here, we present new results obtained for the equation of state with induced surface and curvature tensions. The explicit formulas for the first five virial coefficients of system pressure and for the induced surface and curvature tension coefficients are derived and their possible applications are briefly discussed.

The particle ratios $k^{+}/{\pi }^{+}$, ${\pi }^{-}/K^{-}$, $\bar{p}/{\pi }^{-}$, $\mathrm{\Lambda }/{\pi }^{-}$, $\mathrm{\Omega }/{\pi }^{-}$, $p/{\pi }^{+}$, ${\pi }^{-}/{\pi }^{+}$, $K^{-}/K^{+}$, $\bar{p}/p$, $\bar{\mathrm{\Lambda }}/\mathrm{\Lambda }$, $\bar{\mathrm{\Sigma }}/\mathrm{\Sigma }$, $\bar{\mathrm{\Omega }}/\mathrm{\Omega }$ measured at AGS, SPS and RHIC energies are compared with large statistical ensembles of 100,000 events deduced from the CRMC EPOS $1.99$ and the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) hybrid model. In the UrQMD hybrid model two types of phase transitions are taken into account. All these data are then confronted with the ideal Hadron Resonance Gas Model. The two types of phase transitions are apparently indistinguishable. Apart from $k^{+}/{\pi }^{+}$, $k^{-}/{\pi }^{-}$, $\mathrm{\Omega }/{\pi }^{-}$, $\bar{p}/{\pi }^{+}$ and $\bar{\mathrm{\Omega }}/\mathrm{\Omega }$, the UrQMD hybrid model agrees well with the CRMC EPOS $1.99$. We also conclude that the CRMC EPOS $1.99$ seems to largely underestimate $k^{+}/{\pi }^{+}$, $k^{-}/{\pi }^{-}$, $\mathrm{\Omega }/{\pi }^{-}$ and $\bar{p}/{\pi }^{+}$.