Ratio Of Shear Viscosity Research Articles

Hydrodynamics of arcsin AdS black brane

In this paper, we explore a modified black brane within AdS space–time, characterized by the Lagrangian density [Formula: see text]. Due to the absence of an analytic solution, we approach the Einstein equations using a perturbative method, extending our analysis to the second order in q. Subsequently, we compute the ratio of shear viscosity to entropy density. Our results suggest that the KSS Bound is not saturated in this model.

Jet transport coefficients by elastic and radiative scatterings in the strongly interacting quark-gluon plasma

We extend the investigation of jet transport coefficients within the effective dynamical quasiparticle model (DQPM)—constructed to describe nonperturbative QCD phenomena of the strongly interacting quark-gluon plasma (sQGP) in line with the lattice QCD equation of state—by accounting for inelastic 2→3 reactions with gluon radiation in addition to the elastic scattering of partons. The elastic and inelastic reactions are calculated explicitly within leading-order Feynman diagrams with effective propagators and vertices from the DQPM by accounting for all channels and their interferences. We present the results for the jet transport coefficients such as the transverse momentum transfer squared q̂ per unit length as well as the energy loss dE/dx per unit length in the sQGP and investigate their dependence on the temperature T and momentum of the jet parton depending on the choice of the strong coupling constant αs in thermal, jet parton, and radiative vertices. For the latter, we consider different scenarios used in the literature and find a very strong dependence of q̂ and dE/dx on the choice of αs. Moreover, we explore the relation of q̂/T3 to the ratio of specific shear viscosity to entropy density η/s and show that the ratio T3/q̂ to η/s has a strong T dependence—especially when approaching Tc—on the choice of αs in scattering vertices. Published by the American Physical Society 2024

R2 corrections on screening length

We study finite-coupling corrections on the screening length of a heavy quark-antiquark (QQ¯) pair moving in strongly coupled Super Yang-Mills plasma. We performed the analysis by computing the Wilson loop in a general AdS5 space with curvature-squared (R2) corrections and the Gauss-Bonnet (GB) background, respectively. For the general case, it is shown that the screening length with R2 corrections can be larger or smaller than that without R2 corrections depending on the correction coefficients, and these effects are more pronounced for the perpendicular case compared with parallel case. For the GB case, it turns out that increasing λGB (a dimensionless parameter in GB gravity) leads to decreasing the screening length thus reducing the binding energy of QQ¯ pair. In addition, we discuss how the screening length changes with the ratio of shear viscosity to entropy density at strong coupling under GB corrections.

Spatial diffusion of heavy quarks in a background magnetic field

The ratio of shear viscosity to entropy density shows a valley-shaped pattern well-known in the community of heavy-ion physics. Diffusion coefficients of heavy quark and meson show a similar structure, and both sketches have become quite popular in the community. Present work has attempted a finite magnetic field extension of the diffusion coefficients of heavy quark and meson. Using Einstein's diffusion relation, we calculated heavy quark and heavy meson diffusion by the ratio of conductivity to susceptibility in the kinetic theory framework of relaxation time approximation. The relaxation time of heavy quark and meson are tuned from the knowledge of earlier works on spatial diffusion estimations, and then we have extended the framework for a finite magnetic field, where our outcomes have revealed two aspects—anisotropic and quantum aspects of diffusion with future possibilities of phenomenological signature. Published by the American Physical Society 2024

Holographic aspects of non-minimal R F F AdS black brane

In this paper, we study the holographic dual to an asymptotically anti-de Sitter black brane in an Einstein–Yang–Mills model with a non-minimal coupling between the Riemann and Yang–Mills fields. First, we construct a planar black hole solution of this model up to the first order of the non-minimal coupling of the Yang–Mills field with the Riemann–Christoffel tensor, denoted as q 2. Then, we calculate the color non-abelian direct current conductivity and the ratio of shear viscosity to entropy density for this solution. Our result for the shear viscosity η to entropy density s ratio saturates the Kovtun, Son, and Starinets bound, which is proportional to . However, our result for the conductivity is new up to the first order of q 2.

Holographic aspects of non-minimal RFμα(a)F(a)μα black brane

In this paper, we consider Einstein–Hilbert gravity in the presence of cosmological constant and an electric field of Yang–Mills type, which is minimally coupled to gravity. We couple the Ricci scalar to the Yang–Mills invariant to obtain a modified theory of gravity. The black brane solution of this model is introduced up to the first order of the [Formula: see text] term. Then, the color non-Abelian direct current (DC) conductivity and the ratio of shear viscosity to entropy density are calculated for this solution. Our results recover the Yang–Mills Schwarzschild AdS black brane in the limit of [Formula: see text].

Two-particle transverse momentum correlations in pp and p -Pb collisions at energies available at the CERN Large Hadron Collider

Two-particle transverse momentum differential correlators, recently measured in Pb--Pb collisions at energies available at the CERN Large Hadron Collider (LHC), provide an additional tool to gain insights into particle production mechanisms and infer transport properties, such as the ratio of shear viscosity to entropy density, of the medium created in Pb-Pb collisions. The longitudinal long-range correlations and the large azimuthal anisotropy measured at low transverse momenta in small collision systems, namely pp and p-Pb, at LHC energies resemble manifestations of collective behaviour. This suggests that locally equilibrated matter may be produced in these small collision systems, similar to what is observed in Pb-Pb collisions. In this work, the same two-particle transverse momentum differential correlators are exploited in pp and p-Pb collisions at $\sqrt{s} = 7$ TeV and $\sqrt{s_{\rm NN}} = 5.02$ TeV, respectively, to seek evidence for viscous effects. Specifically, the strength and shape of the correlators are studied as a function of the produced particle multiplicity to identify evidence for longitudinal broadening that might reveal the presence of viscous effects in these smaller systems. The measured correlators and their evolution from pp and p--Pb to Pb--Pb collisions are additionally compared to predictions from Monte Carlo event generators, and the potential presence of viscous effects is discussed.

Exploring the self interacting dark matter properties from low redshift observations

We calculate the shear (eta ) and bulk viscosity (zeta ) of Self Interacting Dark Matter (SIDM) fluid using the kinetic theory formalism. Using the astrophysical constraints on dark matter self-interaction cross section over mass sigma /m , we demonstrate that viscous SIDM fluid violates the lower bound on the ratio of shear viscosity to its entropy density, eta /mathfrak {s}=frac{1}{4pi }. Then, considering the eta /mathfrak {s} bound as universal, we derive a theoretical upper limit on the ratio of velocity average dark matter self interaction cross-section to its mass and also estimate an upper limit on SIDM mass. We report that mass of the SIDM particle should be sub-GeV scale. Furthermore, with the assumption of a power-law form of eta and zeta , we study its evolution in the light of low redshift observations. We show that at the large redshift, the SIDM viscosity is small, but at the small redshift, it becomes sufficiently large and contributes significantly to cosmic dissipation. As a consequence, viscous SIDM can explain the low redshift observations and also consistent with the standard cosmological prediction.

Boltzmann collision operator for polyatomic gases in agreement with experimental data and DSMC method

This paper is concerned with the Boltzmann equation based on a continuous internal energy variable to model polyatomic gases with constant specific heats. We propose a family of models for the collision kernel and evaluate the nonlinear Boltzmann collision operator to get explicit expressions for transport coefficients like shear and bulk viscosities, thermal conductivity, depending on the collision kernel parameters. This model is shown to contain as a special case the collision kernel used in the direct simulation Monte Carlo method with the variable hard sphere cross section. Then, we show that it is possible to choose parameters in such a way that we recover various physical phenomena, in particular, experimental data for the shear viscosity, Prandtl number and the ratio of bulk and shear viscosities at the same time.

Lingering Dynamics of Type 2 Diabetes Mellitus Red Blood Cells in Retinal Arteriolar Bifurcations.

It has been proven that the deformability of red blood cells (RBC) is reduced owing to changes in mechanical properties, such as diabetes mellitus and hypertension. To probe the effects of RBC morphological and physical parameters on the flow field in bifurcated arterioles, three types of RBC models with various degrees of biconcave shapes were built based on the in vitro experimental data. The dynamic behaviors of the RBCs in shear flow were simulated to validate the feasibility of the finite element-Arbitrary Lagrangian-Eulerian method with a moving mesh. The influences of the shear rate and viscosity ratios on RBC motions were investigated. The motion of RBCs in arteriolar bifurcations was further simulated. Abnormal variations in the morphological and physical parameters of RBCs may lead to diminished tank-tread motion and enhanced tumbling motion in shear flow. Moreover, abnormal RBC variations can result in slower RBC motion at the bifurcation with a longer transmit time and greater flow resistance, which may further cause inadequate local oxygen supply. These findings would provide useful insights into the microvascular complications in diabetes mellitus.

Microstructural Dynamics and Rheology of Worm-like Diblock Copolymer Nanoparticle Dispersions under a Simple Shear and a Planar Extensional Flow.

We investigate the shear and extensional flow behavior of dispersions composed of two types of worm-like nanoparticles (WLNPs) with comparable cross-sectional diameters, similar persistence lengths but differing contour lengths, and thus differing flexibility. By measuring the flow-induced birefringence (FIB) of WLNP dispersions in two contrasting microfluidic devices, we obtain an experimental quantification of the role of shearing and planar extensional flows at aligning a short and stiff WLNP (S-WLNP) and a relatively long and flexible WLNP (L-WLNP). We show that shear and extensional flows induce the alignment of both types of WLNPs. However, extensional deformations are more effective than shear deformations at triggering the onset of alignment of the WLNP. The difference between shear and extensional deformations for WLNP alignment is explained based on the ratio of extensional and shear viscosity of the solvent fluid (Trouton ratio of the solvent) and a structural parameter related to the WLNP extensibility and flexibility. Under shear flow, these WLNP dispersions display shear-thinning behavior, with an exponential reduction in viscosity with increasing alignment. Under extensional flow, the WLNP alignment leads to extensional thinning, making WLNP ideal additives for industrial and biotechnology formulations exposed to extensional dominated flows (e.g., jetting, spraying, and printing processes).

Comparative study on the role of PAM and PANA on the property of fresh cement paste

Both polyacrylamide (PAM) and sodium polyacrylate (PANA) are polypropylene based polymer, however it is still uncertain whether there are some differences between their roles on the property of fresh cement paste. Thus this work aimed to compare the property of fresh cement pastes with them, such as shear viscosity, fluidity, bleeding and water evaporation loss ratio. Meanwhile, the ultraviolet visible spectra, infrared spectroscopy and thermogravimetry were carried out to explore the mechanisms that are responsible for these differences. The experimental results indicate that as compared with PANA, PAM increases the shear viscosity and reduces the fluidity of cement paste more significantly. However, PANA more significantly reduces bleeding and water evaporation loss ratio. These differences are in conjunction with their different behaviors in the fresh cement paste, such as promotion in the cement hydration at early age and reaction with cement hydration product.

Impact of fragment formation on shear viscosity in the nuclear liquid-gas phase transition region

The dimensionless ratio of shear viscosity to entropy density $\ensuremath{\eta}/s$ typically has a minimum at a phase transition as observed in many atomic and molecular systems. This quantity has been under intense study in high-energy heavy-ion collisions as a sign of a QCD phase transition or rapid crossover between hadronic and quark-gluon degrees of freedom. The authors perform numerical simulations of matter at lower density and temperature associated with a minimum in $\ensuremath{\eta}/s$ which may shed light on the nuclear liquid-gas phase transition and its connection to the QCD transition.

Shock-wave structure in non-polar diatomic and polyatomic dense gases under rotation and vibration

This study investigates the effect of rotation and vibration on the structure of shock waves in moderately dense diatomic and polyatomic non-polar gases using the one-temperature Navier–Stokes–Fourier approach. The modified Enskog equation of state of the gas is taken to include the denseness and shielding effects. The specific heat at constant volume has been taken to be temperature-dependent. The shear viscosity, the bulk viscosity, and the thermal conductivity have been assumed to follow the temperature-dependent power-law model. Nitrogen and oxygen gas have been taken as the test cases for diatomic gases while carbon dioxide was taken for the polyatomic gases. The implicit system of equations is derived and solved numerically for density and temperature. The inclusion of denseness, rotational, and vibrational modes of molecular motion have a significant effect on the density and temperature profiles, the inverse shock thickness, the bulk to shear viscosity ratio, and the molar specific heat at constant pressure. The gas having a low characteristic vibrational temperature has been found to have a high value of inverse shock thickness. The inverse shock thickness, the bulk to shear viscosity ratio, and the molar specific heat at constant pressure for nitrogen and carbon dioxide are found to be in good agreement with the experimental values.

Evaluation of Layer Adhesion and Uniformity in Poly(lactic acid) and Thermoplastic Starch Multilayered Films

Multilayered films of poly(lactic acid) (PLA) and thermoplastic starch (TPS) offer complementary characteristics that are promising for sustainable packaging applications. In this study, an in-house designed three-line coextrusion process was developed to fabricate layered films. These films were produced at varying shear rates and viscosity ratios with and without compatibilizers. Rheological and thermal analyses were used to investigate adhesion strength and uniformity. Results showed the processing shear rate has a significant effect up to 136% on adhesion strength, its maximum at 10.6 s–1. Viscosity ratio, varied by plasticizer content in TPS, impacted adhesion strength up to 48% within the studied ranges, showing its maximum at 25 wt % added plasticizers. Results showed that 2.5 wt % of compatibilizer, maleic anhydride, within TPS increased adhesion strength up to 35%. Thermal analysis of layers at different locations along the cross-section revealed that the viscosity ratio had a defining impact on layer uniformity of TPS within PLA layers. This study highlights the importance of material and processing parameters in designing a biobased sustainable packaging solution.

Construction of a pseudo-Newtonian potential for a spinning black hole embedded in quintessence background: Brief accretion studies

It is found difficult to construct a complete general relativistic theory for an accretion disc around a relativistic compact star. There exists a trend to reproduce the effects of general relativistic attraction by using a pseudo-Newtonian approach. One such pseudo-Newtonian force for a spinning black hole sitting in quintessence background is constructed in this paper. Comparison with general relativity at different parametric values is picturised thoroughly. Next, an accretion model using this newly constructed pseudo-Newtonian force is built. The radial inward speed gradient is found to be expressed as a ratio of two functions. It can be realized easily that among these two functions, the denominator might vanish for a particular value of radial speed in the interval zero to speed of light. To make the flow physical, the numerator should vanish at the same radial distance. This will ultimately generate two speed profiles starting from the particular radial distance. This is the cause of generation for accretion and wind branches. It has been followed that the disc is truncated at a finite distance due to the fact that the specific angular momentum becomes larger than the Keplerian angular momentum beyond that. Effects of the spin of the central gravitating object are followed along with the intense effect of the quintessence parameters concerned. Accretion and wind density profiles are also studied to find the density variations near the central engine. Ratio of shear viscosity to entropy density is analyzed in the presence of quintessence for viscous accretion flows.

Holographic approach to transport in dense QCD matter

The transport properties of dense QCD matter play a crucial role in the physics of neutron stars and their mergers, but are notoriously difficult to study with traditional quantum field theory tools. Specializing to the case of unpaired quark matter in beta equilibrium, we approach the problem through the machinery of holography, in particular the V-QCD and D3-D7 models, and derive results for the electrical and thermal conductivities and the shear and bulk viscosities. In addition we compare the bulk to shear viscosity ratio to the speed of sound and find that it violates the so-called Buchel bound. Our results differ dramatically from earlier predictions of perturbative QCD, the root causes and implications of which we analyze in detail.

Total and Partial Shear Viscosity in Heavy-Ion Collisions at Energies of BES, FAIR and NICA

We calculated the shear viscosity of hot and dense nuclear matter produced in a symmetric system of central gold–gold collisions at energies of BES RHIC, FAIR and NICA. For calculations of the collisions, the transport model UrQMD was employed. The shear viscosity was obtained within the Green–Kubo formalism. The hadron resonance gas model was used to determine temperature and chemical potentials of baryon charge and strangeness out of microscopic model calculations. In contrast to our previous works, we determined the partial viscosity of the main hadron species, such as nucleons, pions, kaons and Lambdas, via the nucleon–nucleon, pion–pion and so forth, correlators. A decrease in the beam energy from Elab=40 to 10 AGeV leads a to rise in baryon shear viscosity accompanied by a drop in the shear viscosity of mesons. The ratio of total shear viscosity to entropy density also decreases.

Reexamination of local spin polarization beyond global equilibrium in relativistic heavy ion collisions

We study local spin polarization in the relativistic hydrodynamic model. Generalizing the Wigner functions previously obtained from chiral kinetic theory by Y. Hidaka et al. [Phys. Rev. D 97, 016004 (2018)] to the massive case, we present the possible contributions up to the order of $\hbar$ from thermal vorticity, shear viscous tensor, other terms associated with the temperature and chemical-potential gradients, and electromagnetic fields to the local spin polarization. We then implement the (3+1)-dimensional viscous hydrodynamic model to study the spin polarizations from these sources with a small chemical potential and ignorance of electromagnetic fields by adopting an equation of state different from those in other recent studies. Although the shear correction alone upon the local polarization results in a sign and azimuthal-angle dependence more consistent with experimental observations, as also discovered in other recent studies, it is mostly suppressed by the contributions from thermal vorticity and other terms that yield an opposite trend. It is found that the total local spin polarization can be very sensitive to the equation of states, the ratio of shear viscosity to entropy density, and the freeze-out temperature.

QCD at finite chemical potential in and out-of equilibrium

We review the transport properties of the strongly interacting quark-gluon plasma (QGP) created in heavy-ion collisions at ultrarelativistic energies, i.e. out-of equilibrium, and compare them to the equilibrium properties. The description of the strongly interacting (non-perturbative) QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature T c from lattice QCD. We study the transport coefficients such as the ratio of shear viscosity and bulk viscosity over entropy density, diffusion coefficients, electric conductivity etc versus temperature T and baryon chemical potential μ B . Based on a microscopic transport description of heavy-ion collisions we, furthermore, discuss which observables are sensitive to the QGP formation and its properties.