Nonzero Baryon Chemical Potential Research Articles

Properties of kaon at non-zero temperature and baryon chemical potential

Properties of kaon at non-zero temperature and baryon chemical potential

Effects of the QCD critical point on the spectra and flow coefficients of hadrons

The space-time evolution of the hot and dense fireball of quarks and gluons produced in ultrarelativistic heavy-ion collisions at nonzero baryonic chemical potential and temperature has been studied by using relativistic dissipative hydrodynamics. For this purpose, a numerical code has been developed to solve the relativistic viscous causal hydrodynamics in ($3+1$) dimensions with the inclusion of QCD critical point ($CP$) through the equation of state and scaling behavior of transport coefficients. We compute the transverse momentum spectra, directed and elliptic flow coefficients of pions and protons to comprehend the effect of $CP$ on these observables. It is found that the integration over the entire space-time history of the fireball largely obliterates the effects of $CP$ on the spectra and flow coefficients for the event averaged initial conditions considered here.

Comprehensive simulation of heavy-ion collisions at nonzero baryon chemical potential

We present results of hydrodynamic modelling of Au-Au collisions from $\sqrt{s_{NN}}$ = 7.7 to 200 GeV. Our simulations have three novel components. Firstly, we use a Linear EXtrapolation of Ultrarelativistic nucleon-nucleon Scattering to nucleus-nucleus collisions (LEXUS) inspired Monte-Carlo initial state model. Secondly, we use a crossover equation of state at finite baryon densities without a critical point. Finally, we use departure functions derived from the quasiparticle theory of transport coefficients for hadronic matter at non-zero baryon densities.

Polyakov loop models in the large N limit: Phase diagram at finite density

The 't Hooft-Veneziano limit of various U(N) and SU(N) Polyakov loop models is constructed at finite temperature and non-zero baryon chemical potential. In this paper we calculate the free energy, its derivatives, the Polyakov loop expectation values and the baryon density. The phase diagram is described in details.

Shedding light on thermal photon and dilepton production

Electromagnetic radiation from the quark-gluon plasma (QGP) is an important observable to be considered in heavy ion collision experiments. I will provide an update on recent advancements from perturbation theory and quenched lattice simulations. The resummed next-to-leading order (NLO) emission rate has recently been decomposed into transverse and longitudinal components, and extended to non-zero baryon chemical potential. The associated spectral function has also been tested against the Euclidean correlator, for continuum-extrapolated lattice data (at μB = 0).

Polarization tensor of magnetized quark-gluon plasma at nonzero baryon density

We derive a general expression for the absorptive part of the one-loop photon polarization tensor in a strongly magnetized quark-gluon plasma at nonzero baryon chemical potential. To demonstrate the application of the main result in the context of heavy-ion collisions, we study the effect of a nonzero baryon chemical potential on the photon emission rate. The rate and the ellipticity of photon emission are studied numerically as a function the transverse momentum (energy) for several values of temperature and chemical potential. When the chemical potential is small compared to the temperature, the rates of the quark and antiquark splitting processes (i.e., qrightarrow q +gamma and {bar{q}}rightarrow {bar{q}} +gamma , respectively) are approximately the same. However, the quark splitting gradually becomes the dominant process with increasing the chemical potential. We also find that increasing the chemical potential leads to a growing total photon production rate but has only a small effect on the ellipticity of photon emission. The quark-antiquark annihilation (q+{bar{q}}rightarrow gamma ) also contributes to the photon production, but its contribution remains relatively small for a wide range of temperatures and chemical potentials investigated.

The large N limit of SU(N) integrals in lattice models

The standard U(N) and SU(N) integrals are calculated in the large N limit. Our main finding is that for an important class of integrals this limit is different for two groups. We describe the critical behaviour of SU(N) models and discuss implications of our results for the large N behaviour of SU(N) lattice gauge theories at finite temperatures and non-zero baryon chemical potential. The key ingredients of our approach are 1) expansion of the integrals into a sum over irreducible representations and 2) calculation of sums over partitions of r of products of dimensions of two different representations of a symmetric group Sr.

String breaking, baryons, medium, and gauge/string duality

We consider the string breaking phenomenon within effective string models which purport to mimic QCD with two light flavors, with a special attention to baryon modes. We make some estimates of the string breaking distances at zero and non-zero baryon chemical potentials. Our estimates point towards the enhancement of baryon production in strong decays of heavy mesons in dense baryonic matter. We also suggest that the enhanced production of $\Lambda_c^+$ baryons in PbPb collisions is mainly due to larger values of chemical potential.

Baryon modes in string breaking from gauge/string duality

We consider the string breaking phenomenon within effective string models which purport to mimic QCD with two light flavors, with a special attention to baryon modes. We make some estimates of the string breaking distances at zero and non-zero baryon chemical potentials. Our estimates point towards the enhancement of baryon production in strong decays of heavy mesons in dense baryonic matter. We also suggest that the enhanced production of Λc+ baryons in PbPb collisions is mainly due to larger values of chemical potential.

Brane nucleation instabilities in non-AdS/non-CFT

We speculate that the weak gravity conjecture applied to theories with holographic duals bans the existence of disordered phases at zero temperature. We test this idea by introducing a non-zero baryon chemical potential in a deformation of the SU(Nc) × SU(Nc) Klebanov-Witten gauge theory with broken supersymmetry and conformal invariance. At low temperature, a disordered phase dual to a black brane geometry is unstable for low chemical potentials and metastable for high values. In the metastable phase, states with a partial Higgsing of the gauge group are favored over the normal disordered phase. This is reflected in the properties of the effective potential for color branes in the dual geometry, where the appearance of a global minimum outside the horizon signals the onset of a brane nucleation instability. When the Higgsing involves only one of the group factors, the global minimum remains at a finite distance from the horizon, making it possible to construct holographic duals to metastable “color superconducting” states. We also consider branes dual to excitations with baryon charge, but find that the extremal geometry remains marginally stable against the emission of particles carrying baryon charge independently of the strength of the deformation.

The critical point of Bootstrap and Lattice QCD

It is shown that the hadronic matter formed at high temperatures, according to the prescription of the statistical bootstrap principle, develops a critical point at nonzero baryon chemical potential. The location of the critical point is evaluated with the use of lattice QCD pressure.

Fourier coefficients of the net baryon number density and chiral criticality

We investigate the Fourier coefficients $b_k(T)$ of the net--baryon number density in strongly interacting matter at nonzero temperature and density. The asymptotic behavior of the coefficients at large $k$ is determined by the singularities of the partition function in the complex chemical potential plane. Within a QCD-like effective chiral model, we show that the chiral and deconfinement properties at nonzero baryon chemical potential are reflected in characteristic $k$-- and $T$-- dependences of the Fourier coefficients. We also discuss the influence of the Roberge-Weiss transition on these coefficients. Our results indicate that the Fourier expansion approach can provide interesting insights into the criticality of QCD matter.

Transport coefficients for multicomponent gas of hadrons using Chapman-Enskog method

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 conductivity and diffusion coefficient. We finally compare our results regarding various transport coefficients with previous results in the literature.

Dynamical stabilisation of complex Langevin simulations of QCD

The ability to describe strongly interacting matter at finite temperature and baryon density provides the means to determine, for instance, the equation of state of QCD at non-zero baryon chemical potential. From a theoretical point of view, direct lattice simulations are hindered by the numerical sign problem, which prevents the use of traditional methods based on importance sampling. Despite recent successes, simulations using the complex Langevin method have been shown to exhibit instabilities, which cause convergence to wrong results. We introduce and discuss the method of dynamic stabilisation (DS), a modification of the complex Langevin process aimed at solving these instabilities. We present results of DS being applied to the heavy-dense approximation of QCD, as well as QCD with staggered fermions at zero chemical potential and finite chemical potential at high temperature. Our findings show that DS can successfully deal with the aforementioned instabilities, opening the way for further progress.

Drag force on heavy diquarks and gauge/string duality

We use gauge/string duality to model a doubly heavy diquark in a color antitriplet moving in a thermal plasma at temperatures near the critical. With the assumption that there is no relative motion between the constituents, we calculate the drag force on the diquark. At high enough speed we find that diquark string configurations develop a cusp. In addition, we estimate the spatial string tension at non-zero baryon chemical potential, and also briefly discuss an extension to a triply heavy triquark in a color triplet.

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

The second-order Israel-Stewart-$\mathrm{M}\stackrel{\ifmmode \ddot{}\else \"{}\fi{}}{\mathrm{u}}\mathrm{ller}$ relativistic hydrodynamics was applied to study the effects of causality on the acoustic oscillation in relativistic fluid. Causal dispersion relations have been derived with nonvanishing shear viscosity, bulk viscosity, and thermal conductivity at nonzero temperature and baryonic 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 a limiting case of the second-order theory. The effects of the causality on the fluidity near the transition point and on the viscous horizon are found to be significant. We observe that the inclusion of causality increases the value of fluidity measure of QGP near ${T}_{c}$ and hence makes the flow strenuous. It was also shown that the inclusion of the large magnetic field in the causal hydrodynamics alters the fluidity of QGP.

Thermodynamics and relativistic kinetic theory for q-generalized Bose\u2013Einstein and Fermi\u2013Dirac systems

The thermodynamics and covariant kinetic theory are elaborately investigated in a non-extensive environment considering the non-extensive generalization of Bose–Einstein (BE) and Fermi–Dirac (FD) statistics. Starting with Tsallis’ entropy formula, the fundamental principles of thermostatistics are established for a grand canonical system having q-generalized BE/FD degrees of freedom. Many particle kinetic theory is set up in terms of the relativistic transport equation with q-generalized Uehling–Uhlenbeck collision term. The conservation laws are realized in terms of appropriate moments of the transport equation. The thermodynamic quantities are obtained in a weak non-extensive environment for a massive pion–nucleon and a massless quark–gluon system with non-zero baryon chemical potential. In order to get an estimate of the impact of non-extensivity on the system dynamics, the q-modified Debye mass and hence the q-modified effective coupling are estimated for a quark–gluon system.

Color screening masses from string models

We use gauge/string duality to estimate the Debye screening mass at non-zero temperature and baryon chemical potential. We interpret this mass as the smallest one in the open string channel. Comparisons are made with the results from holography and lattice QCD.

Net baryon fluctuations from a crossover equation of state

We have constructed an equation of state which smoothly interpolates between an excluded volume hadron resonance gas at low energy density to a plasma of quarks and gluons at high energy density. This crossover equation of state agrees very well with lattice calculations at both zero and nonzero baryon chemical potential. We use it to compute the variance, skewness, and kurtosis of fluctuations of baryon number, and compare to measurements of proton number fluctuations in central Au-Au collisions as measured by the STAR collaboration in a beam energy scan at the Relativistic Heavy Ion Collider. The crossover equation of state can reproduce the data if the fluctuations are frozen out at temperatures well below than the average chemical freeze-out.

Existence of the critical endpoint in the vector meson extended linear sigma model

The chiral phase transition of the strongly interacting matter is investigated at nonzero temperature and baryon chemical potential mu_B within an extended (2+1) flavor Polyakov constituent quark-meson model which incorporates the effect of the vector and axial vector mesons. The effect of the fermionic vacuum and thermal fluctuations computed from the grand potential of the model is taken into account in the curvature masses of the scalar and pseudoscalar mesons. The parameters of the model are determined by comparing masses and tree-level decay widths with experimental values in a chi^2-minimization procedure which selects between various possible assignments of scalar nonet states to physical particles. We examine the restoration of the chiral symmetry by monitoring the temperature evolution of condensates and the chiral partners' masses and of the mixing angles for the pseudoscalar eta-eta' and the corresponding scalar complex. We calculate the pressure and various thermodynamical observables derived from it and compare them to the continuum extrapolated lattice results of the Wuppertal-Budapest collaboration. We study the T-mu_B phase diagram of the model and find that a critical end point exists for parameters of the model, which give acceptable values of chi^2.