Abstract We consider the problem of a charged impurity exerting a weak, slowly decaying force on its surroundings, treating the latter as an ideal compressible fluid. In the semiclassical approximation, the ion is described by the Newton equation coupled to the Euler equation for the medium. After linearization, we obtain a simple closed formula for the effective mass of the impurity, depending on the interaction potential, the mean medium density, and sound velocity. Thus, once the interaction and the equation of state of the fluid is known, an estimate of the hydrodynamic effective mass can be quickly provided. Going beyond the classical case, we show that replacing the Newton with Schr"{o}dinger equation induces a different mass renormalization, wherein the surroundings affect the dynamics of the dispersion of the particle's wave packet. The two effective masses may remarkably differ, as, in particular, the scaling of the two Fermi polaron effective masses with the medium density is opposite. Our results are relevant for experimental systems featuring low energy impurities in Fermi or Bose systems, such as ions immersed in neutral atomic gases.

ABSTRACT In this paper, we prove the linear and nonlinear ill‐posedness of the Kelvin–Helmholtz problem for compressible ideal fluids when the Mach number lies in the range between a sufficiently small fixed constant and . Inspired by the approach of Guo and Tice (2011), we establish the failure of local‐in‐time continuous dependence on initial data in high‐order Sobolev spaces for solutions of the Kelvin–Helmholtz problem. To the best of our knowledge, this is the first result that rigorously demonstrates nonlinear instability for the Kelvin–Helmholtz problem for compressible Euler fluids.

Abstract We present a spherically symmetric stellar model within the framework of seven dimensional third order Lovelock gravity for a neutral perfect fluid distribution. The third order Lovelock field equations are generated for such a fluid configuration by imposing pressure isotropy. This condition yields a first order nonlinear differential equation which is an extension of the Abel differential equation. This is due to the additional higher order curvature effects arising in third order Lovelock gravity. We demonstrate new exact solutions that can model a static spherically symmetric star. The energy density and pressure are both variable. We also show that a special case arises, which is a constant density model with a cosmological interpretation. Furthermore, we illustrate the matching conditions to generate a spherically symmetric stellar model in third order Lovelock gravity when the EGB and third order Lovelock coupling constants are related.

Human serum is an ideal body fluid for discovering and monitoring biomarkers for disease diagnosis and treatment response. However, intrinsic proteolytic degradation during sample handling may compromise biomarker integrity, which may affect the accuracy of results. To address this issue, we aimed to test the feasibility of using antibody array technology to evaluate the temporal stability of serum proteins at room temperature. Concentrations of 480 serological proteins were monitored using antibody arrays in samples from 10 healthy donors incubated at 25°C for 0, 6, 12, 24, and 48 h. Linear regression assessed time-dependent concentration changes. Physicochemical properties (molecular weight, isoelectric point, instability index, aliphatic index, hydropathicity) of the proteins were analyzed. Enrichment analyses were performed on degraded proteins. During 48-h incubation, 201 proteins showed a significant negative linear correlation between concentration and time, among which the concentration of 91 proteins reduced over 20% in the first 6 h. Degraded proteins were significantly associated with lower molecular weight (MW < 40 kDa) but no other physicochemical properties. Enrichment analyses revealed degraded proteins associated with various terms and involved in important signaling pathways, like JAK-STAT, PI3K-Akt, and MAPK. Our data demonstrate the feasibility of employing antibody arrays for detecting serum protein degradation. Using this platform, we found some serum proteins with clinical significance rapidly degrade at room temperature, including interleukins (e.g., IL-1β/IL-12p40/IL-17), growth factors (e.g., aFGF, bFGF, and BMP-2), and chemokines (e.g., I-309, 6Ckine, and BLC). These may serve as potential biomarkers for assessing human serum sample quality.

In this investigation, we examine the geometric character of almost Riemann solitons and gradient almost Riemann solitons in the context of perfect fluid solutions of the Einstein equations that admit a torse-forming vector field ζ. We first examine the conditions on the scalar curvature, which are necessary for the existence of an almost Riemann soliton or a gradient almost Riemann soliton in such solutions. We then examine the case of several physically reasonable types of perfect fluids, such as dark fluids, dust-filled universes, and the radiation-dominated epoch. We also show that any spacetime bearing an almost Riemann soliton with a conformal potential vector field must necessarily have an Einstein geometry. In addition, in the case of a perfect fluid spacetime with a torse-forming vector field, given the fulfillment of the almost Riemann soliton compatibility equation and Q·P=0, the scalar curvature of the spacetime must be constant. Finally, a rigidity theorem states that any parallel symmetric (0,2)-tensor defined on the spacetime must be a constant multiple of the metric tensor.

We present a stellar model in the frame of Einstein’s general relativity considering a static and spherically symmetric space time which contains a perfect fluid. The analytical solution is determined starting from a temporal metric function that facilitates the integration of the system. We show that the state equation associated to the model can be approximated in the form [Formula: see text], where [Formula: see text] is the density on the surface of the star. The stability under adiabatic and radial perturbations of static, compact stellar objects with sources of matter from a perfect fluid will determine the maximum value of compactness [Formula: see text], the model also results to be stable according to the criteria of Harrison - Zeldovich - Novikov. In a complementary manner the model is verified for the observational data of the compact object XMMU J173203.3-344518 in HESS J1731-347, of low mass [Formula: see text] and radius [Formula: see text] km, from these we find that the maximum density occurs in the center for its maximum compactness.

We study scalar, electromagnetic and gravitational perturbations of three families of regular black holes, Hayward, Bardeen, and Ayon-Beato-García immersed in a Perfect Fluid Dark Matter (PFDM) background. Using both the sixth-order WKB approximation and the Asymptotic Iteration Method (AIM), we determine the corresponding quasi-normal modes and absorption cross sections. By fixing the horizon radius, we analyze the dependence of the parameters of the black holes and the parameter of PFDM. The computed quasi-normal modes confirm the dynamical stability of the black holes under scalar, electromagnetic and gravitational perturbations. Furthermore, both the real and imaginary parts of the quasi-normal modes increase with the multipole number l, corresponding to higher oscillation frequencies and faster damping rates. On the other hand, absorption cross sections are compared under similar parametric conditions. The results demonstrate that PFDM inuences the dynamical properties of regular black holes.

f(R,φ,X) theory, combination of scalar-tensor and f(R)-class gravity, is examined for perfect fluid in Bianchi Type-I space-time. Hybrid model of Starobinsky-like and kessence is used. Two different forms of solution are obtained and discussed in Bianchi Type-I cosmology. Effective energy densities, effective pressures and necessary statements of energy conditions for both solutions are analyzed. It is discussed whether f(R,φ,X) theory allows expanding or contracting cosmologies for obtained two forms of Bianchi Type-I space-time.

Exact and numerical analysis of accretion dynamics with perfect and polytropic fluids around nonlinear charged black holes

Impact of perfect fluid dark matter on the appearance of rotating black hole

Perfect fluid Bianchi cosmological model admitting conformal motions in f(Q, T) gravity

In relativistic cosmology, the formation of nonlinear inhomogeneities can induce non-negligible backreaction on late-time expansion. Among the important consequences for precision cosmology is the potential impact on the linear growth of large-scale structures. We address this impact by combining covariant spatial averaging with covariant and gauge-invariant perturbation theory. We focus on irrotational dust model spacetimes. The effects of backreaction and nontrivial dynamical curvature on the average cosmological dynamics are formulated as the addition of an effective perfect fluid with pressure. We then introduce an effective background driven by both the averaged dust density and the emergent effective fluid, and derive the general evolution equations for linear perturbations of this system. The residual freedom in this framework amounts to specifying the properties of the effective-fluid perturbations as a closure condition. We analyse two physically motivated choices for this condition. In addition, we clarify the conditions under which the coupling between linear structure growth and perturbations of the effective fluid can be neglected. Finally, we apply this formalism to four examples of averaged cosmological models from the literature, three of which — intended as effective full descriptions of the largest scales — have been shown to provide a good fit to observational data. Our results highlight the importance of backreaction effects in shaping linear structure growth in such models. Neglecting these effects may thus lead to biased predictions for the development of large structures, even when the models provide a good description of the general background observables.

We investigate relativistic Bondi accretion in the Simpson-Visser spacetime, which, via a single parameter ℓ, interpolates between the Schwarzschild, regular black hole, extremal and wormhole regimes. First, we analyse the neutral Simpson-Visser geometry, recovering Schwarzschild at ℓ=0, and then its charged extension of the Reissner-Nordström metric. In both these cases, we derive the conservation equations and analyse two representative fluid models: a barotropic perfect fluid and a constituent with an exponential density profile. By varying the parameters across regimes, we locate critical (sonic) points and integrate velocity, density, and pressure profiles. Although near-horizon inflow velocities are similar across the different solutions, we find that the critical radius, as well as the resulting accretion rates and luminosities, change significantly depending on the value of the parameter and the type of fluid. Remarkably, the barotropic and exponential cases exhibit different trends in the outer regions. Moreover, by extending the analysis to the charged SV spacetime, we find that the presence of a central charge Q produces additional, albeit modest, shifts in the sonic radius which, in combination with those induced by the regularisation parameter ℓ, could provide a double observational marker. In particular, while ℓ acts predominantly on the position of the critical point, in the barotropic fluid case, the electromagnetic contribution of Q slightly dampens the inflow velocity near the horizon.

In this article, we classify pseudo projectively flat space-times and acquire that it represents either an anti- de-Sitter or de-Sitter space-time. Furthermore, we obtain that a pseudo projectively flat perfect fluid space-time represents dark matter era and Robertson-Walker space-time. Next, we establish that a perfect fluid pseudo projectively symmetric space-time represents either a dark matter era, or a static space-time. Also, we examine the effect of pseudo projectively symmetric space-time in [Formula: see text]-gravity by choosing a model and we observe that the null, dominant and weak energy conditions are satisfied, but the strong energy condition has failed, which is also consistent with present observational studies that reveal the universe is expanding. Finally, we apply the flat Friedmann-Robertson-Walker metric to derive a relation between deceleration, jerk and snap parameters.

We investigate weak gravitational lensing and shadow properties of the Konoplya-Zhidenko black hole surrounded by perfect fluid dark matter and a plasma medium. Considering both homogeneous and non-homogeneous (singular isothermal sphere) plasma distributions, we analyze how the dark matter, the deformation parameter, and plasma frequency modify the deflection angle of light rays and black hole’s shadow radius. Our results show that plasma enhances light bending and reduces the shadow size, with the largest shadow in vacuum, followed by non-homogeneous plasma, and the smallest in homogeneous plasma. Comparison with Event Horizon Telescope observations of Sgr A* constrains the allowed parameter space, linking theoretical predictions to measured shadow radii. Additionally, we study Hawking temperature, specific heat, and Gibbs free energy, revealing the roles of perfect fluid dark matter and spacetime deformation in black hole stability and phase behavior. This analysis provides insights into the observational signatures and thermodynamic properties of deformed black holes embedded in realistic galactic environments.

This work deals with a modified gravity theory by extending [Formula: see text] gravity with a general coupling of the torsion scalar T and the trace of the matter energy–momentum tensor [Formula: see text]. In the background of the flat FLRW space-time, the dark energy is considered as a perfect fluid having equation of state [Formula: see text] for the present modified gravity theory. Usually, power law form in each argument has been chosen for the arbitrary function [Formula: see text] in the modified gravity theory. Finally, the present model has been compared with recent observational data.

We provide a comprehensive picture for the formulation of the perfect fluid in the modern effective field theory formalism at both the classical and quantum level. Due to the necessity of decomposing the hydrodynamical variables (\rho, p, u^\mu) ( ρ , p , u μ ) into other internal degrees of freedom, the procedure is inherently not unique. We discuss and compare the different inequivalent formulations. These theories possess a peculiarity: the presence of an infinite dimensional symmetry implying a vanishing dispersion relation \omega = 0 ω = 0 for the transverse modes. This sets the stage for UV-IR mixing in the quantum theory, which we study in the different formulations focussing on the incompressible limit. We observe that the dispersion relation gets modified by quantum effects to become \omega \propto k^2 ω ∝ k 2 , where the fundamental excitations can be viewed as vortex-anti-vortex pairs. The spectrum exhibits infinitely many types of degenerate quanta. The unusual sensitivity to UV quantum fluctuations renders the implementation of the defining infinite symmetry somewhat subtle. However we present a lattice regularization that preserves a deformed version of such symmetry.

This paper investigates pseudo-symmetric space–times within two interrelated frameworks: vacuum f(R)-gravity and Gray’s seven canonical decomposition subspaces. First, it is established that any conformally flat pseudo-symmetric space–time satisfying the vacuum field equations of f(R)-gravity necessarily corresponds to a perfect fluid. Subsequently, a detailed analysis of Gray’s subspaces reveals the following structural results: In the trivial and 𝒜 subspaces, pseudo-symmetric space–times are Ricci-simple and Weyl-harmonic, and thus are necessarily generalized Robertson–Walker space–times. In the B and 𝒜⊕B subspaces, the associated time-like vector field ξl is shown to be an eigenvector of the Ricci tensor with the eigenvalue −R/2. Furthermore, for a perfect fluid pseudo-symmetric space–time obeying f(R)-gravity and belonging to the trivial, 𝒜, B, or 𝒜⊕B subspaces, the isotropic pressure p and energy density σ are proven to be constants. Additionally, it is demonstrated that Gray’s I subspace reduces to the B subspace in the pseudo-symmetric setting. Finally, under specific geometric conditions, pseudo-symmetric space–times in the I⊕𝒜 and I⊕B subspaces are also shown to admit perfect fluid representations. These results collectively clarify the geometric and physical constraints imposed by pseudo-symmetry within f(R)-gravity and Gray’s classification scheme.

Future stability of perfect fluids with extreme tilt and linear equation of state $$p=c_s^2\rho $$ for the Einstein-Euler system with positive cosmological constant: The range $$\frac{1}{3}&lt;c_s^2&lt;\frac{3}{7}$$

We investigate thermal photon production in the quark-gluon plasma (QGP) under strong magnetic fields using a magnetohydrodynamic (MHD) framework. We employ relativistic ideal fluid dynamics under the non-resistive approximation by adopting the Bjorken flow model with power-law decaying magnetic fields , span> a controls the decay rate, , and σ characterizes the initial field strength. The resulting QGP temperature evolution exhibits distinct a- and σ-dependent behaviors. Thermal photon production rates are calculated for three dominant processes: Compton scattering with annihilation (C+A), bremsstrahlung (Brems), and annihilation with additional scattering (A+S). These rates are integrated over the space-time volume to obtain the photon transverse momentum spectrum. Our results demonstrate that increasing a enhances photon yields across all , with (super-fast decay) providing an upper bound. For , a larger σ suppresses yields through accelerated cooling, whereas for , a larger σ enhances yields via prolonged thermal emission. Low- photons receive significant contributions from all QGP evolution stages, while high- photons originate predominantly from early times. The central rapidity region dominates the total yield. This work extends the photon yield studies to the MHD regime under strong magnetic fields, clarifying the magnetic field effects on QGP electromagnetic signatures and establishing foundations for future investigations of magnetization and dissipative phenomena.