If nonrelativistic dark matter and radiation are allowed to interact, reaching an approximate thermal equilibrium, this interaction induces a bulk viscous pressure changing the effective one-fluid description of the universe dynamics, permitted by the existence of a common temperature. It has been shown that by modelling such components as perfect fluids, a cosmologically relevant bulk viscous pressure, expressed in terms of the Eckart formalism, emerges for dark matter particle masses in the range of 1 eV-10 eV keeping thermal equilibrium with the radiation. Such a transient bulk viscosity introduces significant effects in the expansion rate near the matter-radiation equality redshift (zeq 3400), impacting also late times leading to a higher inferred value of the Hubble constant H0. Since this mechanism also impacts the sound speed of the baryon-photon fluid, we use the recent DESI DR2 BAO measurements, reported relative to a fiducial Lambda CDM cosmology, to place an upper bound on the logarithm of the free parameter of the model tau eq which represents the time scale in which each component follows its own internal perfect fluid dynamics until thermalization occurs. Our main result is encoded in the bound log10(tau eq [s])-9.76 (2), with the corresponding dimensionless bulk coefficient xi H0/Heq 5.94 & times; 10-4 (2 sigma). The obtained constraints show that DESI DR2 data do not support such an interaction between radiation and dark matter prior to the recombination epoch, precluding the model from solving the cosmic tensions.

The superflow of water at nanoscale remains an open problem. Classical hydrodynamics predicts flow rates that are 2 to 5 orders of magnitude lower than those observed experimentally. Therefore, it is natural to question the validity of such models while exploring alternative approaches. In this work, we investigate the behavior of viscoplastic fluids, particularly Bingham fluids, from the perspective of de Broglie–Bohm quantum mechanics, incorporating the effects of a quantum potential (quantum hydrodynamics). We phenomenologically assume that the physics behind these unexplained experimental results might be associated to an effective quantum potential which properties that can be associated to an effective anti-dissipative hydrodynamical term in the classical approach. We combine a theoretical approach with its numerical solutions to understand the interplay between the Navier–Stokes-Bingham hydrodynamical system and the quantum hydrodynamics. Our results indicate that the quantum potential can be directly associated with the increased flow velocity, reinforcing that quantum effects may play a significant role in the dynamics of fluids confined within nanotubes. Moreover, well-behaved solutions for the system’s wavefunction were identified even in the exotic case of anti-dissipative fluid flow. This evidence provides a possible theoretical explanation for the superflux phenomenon, reinforcing the hypothesis that quantum effects may underlie the discrepancies relative to classical hydrodynamic predictions.

We study electro-acoustic perturbative modes in homogeneous, isotropic and expanding – dubbed as Friedmann-Lemaitre-Robertson-Walker (FLRW) – Jellium models, thereby mimicking density perturbations in analogous Newtonian cosmological expansions. We present both novel analytic solutions for linear perturbations in specific analogue cosmological expansions and full numerical evaluations that characterize the temporal evolution of the electro-acoustic modes capturing their full dynamical behavior across the linear and the nonlinear regimes. For both the case of pressure supported evolution or modes sourced by nonadiabatic contributions, we also characterize the temporal evolution of such perturbations by introducing their scale dependent particle number fluctuation power spectrum which can act as a tool to connect theory and experiments. The dependence of the latter on the physical parameters of the model is demonstrated in detail.

In this work, we propose a geometric description of the quantum dynamics of a free particle based on phase perturbations. Using the hydrodynamic formalism and Bohmian quantum mechanics, and assuming a certain class of conditions/restrictions on the quantum potential, we derive an effective pseudo-Riemannian metric whose conformal factor is determined by the probability density, allowing the quantum dynamics to be reinterpreted in terms of the geodesic propagation of perturbations. This framework establishes a geometric structure that connects the causal propagation of such perturbations to the conditions under which they can influence Bohmian trajectories, providing a new perspective on the dynamical independence of different branches of the wave function and their possible interaction through the guiding equation. We apply this approach to a Gaussian wave packet, analyzing the resulting effective geometry and the associated causal horizon, as well as the conditions under which perturbations compatible with the adopted probability density cease to exert significant influence on the dynamics in question, so that the particle’s trajectory becomes effectively insensitive to additional fluctuations of the wave function.

We explore an extension to Newtonian gravity through a generalised Lagrangian function with the introduction of a second dynamical scalar field. Building on previous research into gravity with variable gravitational coupling, the work derives the complete field equations and applies a weak-field approximation. This leads to an effective post-Newtonian gravitational potential that includes key aspects of relativistic theories. The resulting N-body equations of motion highlight differences among inertial and gravitational masses, which can constrain the theory's free parameter through data from the Nordtvedt effect. By employing the method of osculating orbits for a two-body system, the study calculates the secular variation of the orbital pericenter and aligns this with the latest data on Mercury's perihelion shift, for another observational constraint on the model. Furthermore, a few examples of theories are discussed.

Bose-Einstein condensates are formed when a bosonic gas is cooled to a temperature near absolute zero. When this occurs, quantum properties that are microscopic become macroscopic, facilitating their study. We have studied matter waves in the Gross-Pitaevskii equation subject to a trap Kapitza potential, which is a quantum analog of the classical inverse Kapitza pendulum. Since this specific system was recently experimentally realized with ultracold atoms for the first time, exploring the theoretical models of this system is, therefore, significant and up-to-date. To find the analytical solutions of the corresponding Gross-Pitaevskii equation with such potential, the extended hyperbolic tangent function method was chosen, which leads to soliton solutions. The new class of solutions found in this work, written in terms of Mathieu functions, was used to analyze the influence of the Kapitza potential free model parameters on the soliton dynamics within the condensate. These mainly include dark and dark-bright solitons. Our findings suggest that there are specific classes of parameters of the system for which bright solitons do not exist.

Recently, the experimental realization of a Kapitza potential in a Bose–Einstein condensate (BEC) was reported for the first time in the literature, motivating further theoretical investigations of such a system. At the same time, in the astrophysical context, BEC dark matter models have been widely studied as a possible phenomenological explanation for the dark matter phenomena. We model the galactic structure with an inner cored profile obtained from the ground state equilibrium solution of the Schrödinger–Poisson together with a Kapitza–BEC-like interaction for the tail region. We find reasonable agreement of the model with representative galaxy rotation curves available in the SPARC catalogue.

A Newtonian-like theory inspired by the Brans-Dicke gravitational Lagrangian has been recently proposed in Ref. [1]. We propose here a new variant of this theory such that the usual Newtonian second law is preserved. The cosmological solutions are analysed and accelerated background expansion can be obtained even in a pure matter dominated universe. This happens due to the dynamic character of the effective gravitational coupling which is sourced by a time evolving scalar field . We also analyse the matter density perturbations and find they exhibit an enhanced growth in comparison with the usual Newtonian like behavior in Einstein-de Sitter model.

The structure of astrophysical objects is usually modeled under the assumption of hydrostatic equilibrium. However, actual configurations may deviate from perfect spherical or isotropic properties. Consequently, cosmic objects are expected to exhibit some degree of anisotropy. This consideration also extends to hypothetical dark structures, such as dark stars and dark matter halos. Although the nature of dark matter remains unknown, axion-like particles (ALPs) are strong candidates, suggesting that dark matter halos may have originated from bosonic configurations undergoing gravitational collapse, sustained by boson-boson interactions in the condensate state. This system is described by the Gross-Pitaevskii-Poisson equation. Furthermore, within the framework of the Bohm-de Broglie approach, quantum effects,encapsulated in the so-called quantum potential, may play a significant role in equilibrium astrophysical configurations. In this study, we examine a class of static anisotropic boson stars which are non-minimally coupled to gravity. By including all these factors, we derive a generalized Lane-Emden-like equation and conduct a detailed analysis of the maximum degree of anisotropy that such systems can sustain, thereby identifying physically viable equilibrium configurations. Apart from focusing on the impact of anisotropic contributions, we find that for the so-called Quantum Polytropes (when the quantum potential is the main responsible for the equilibrium condition), the anisotropic factor and the gravitational field have opposite roles compared to the classical case. This leads to a new class of hydrostatic equilibrium objects.

Theories based on the Ricci and the trace of the energy-momentum tensor, or the short name Ricci-trace-based (RTB) theories, represent a gravitational approach based on the Ricci scalar R, and the trace of the energy-momentum tensor g mu nu T mu nu = T. This theory fits into gravitational models of the type f (R, T) = R+ f (T), where f (T) is an arbitrary function of T. In this study, we explore a cosmological scenario within the context of RTB models, investigating in detail the cosmological consequences of the coupling between matter and geometry. In order to address this issue, we propose a toy model in which the non-relativistic cosmological neutrino transition plays a role in the cosmic evolution since the effective total energy-momentum tensor trace is affected in this process. We raise questions about the coupling of neutrinos with geometry during this transition, providing a detailed analysis of how RTB gravity deals with this phenomenon and the impact of neutrinos on cosmological dynamics. In summary, we show that the coupling of cosmological neutrinos with T dependent cosmologies is severely challenged.

This note revisits and corrects a previous analysis on gravitational radiation in compact binary systems within the framework of Brans-Dicke-f(R) theories-models featuring both massless and effectively massive scalar fields. We correct the lower bound on the Brans-Dicke coupling parameter ω_0 presented in prior work, identifying teh issue that led to inverted constraints. By reanalyzing data from the binary system PSR J1012+5307, we present revised bounds on ω_0 as a function of the geometrical scalar field mass m_f, emphasizing that the role of ω_0 differs from its traditional interpretation in standard BD theory.

AbstractThe structure of unimodular gravity (UG) is invariant to a subclass of diffeomorphism, the transverse diffeomorphism, due to the unimodular condition $$\sqrt{-g}=\epsilon $$ - g = ϵ . Consequently, there is a freedom to define how the conservation laws of the energy–momentum tensor in unimodular gravity in the cosmological context. One of the main characteristics of the complete system of equations that describe cosmological dynamics in UG is that they form an underdetermined system if the usual conservation law of the energy–momentum tensor is not considered in your structure. In this article, we propose the construction of a background cosmological model based on the description of a holographic dark energy component with a cutoff of the order of Ricci scalar in non-conservative UG. This choice means that the complete set of equations remains underdetermined, however, the new feature of this cosmological model is the appearance of an interaction between matter and dark energy. Indeed, this is a well-known characteristic of cosmological models in which we have holographic dark energy density. Consequently, we propose an ansatz to the interaction term $$Q=\beta H \rho _{m}$$ Q = β H ρ m , and obtain the cosmological parameters of our model. We found a viable universe model with similar characteristics to the $$\Lambda \textrm{CDM}$$ Λ CDM model. We performed statistical analysis of the background model using the “Cosmic Chronometer” (CC) data for H(z), and obtain as a result using AIC, and the BIC as model selection criteria that $$\Lambda \textrm{CDM}$$ Λ CDM prevails as the best model. However, the proposed model is competitive when compared to the cosmological model $$\omega \textrm{CDM}$$ ω CDM .

We study scalar cosmological perturbations in $f(R, T)$ modified gravity theories being $T$ the trace of the energy-momentum tensor. We provide detailed equations for the matter energy density contrast. We solve then numerically to promote a comparison with available large scale structure (LSS) formation observational data on $f \sigma_8$ and also addressing the $S_8$ tension. We identify $f(R,T)$ models that lead either to growth enhancement or suppression. Since recent results in the literature indicate a preference for the latter feature, this type of analysis is quite useful to select viable modifications of gravity. We studied class of such $f(R,T)$ models are either ruled out or severely restricted.

We review the status of f(R,T) cosmological models, where T is the trace of the energy momentum tensor Tμν. We start focusing on the modified Friedmann equations for the minimally coupled gravitational Lagrangian of the type f(R,T)=R+αeβT+γnTn. We show that in such a minimally coupled case there exists a useful constraining relation between the effective fractionary total matter density with an arbitrary equation of state parameter and the modified gravity parameters. With this association the modified gravity sector can be independently constrained using estimations of the gas mass fraction in galaxy clusters. Using cosmological background cosmic chronometers data and demanding the universe is old enough to accommodate the existence of Galactic globular clusters with ages of at least ∼14 Gyrs we find a narrow range of the modified gravity free parameter space in which this class of theories remains viable for the late time cosmological evolution. This preferred parameter space region accommodates the ΛCDM limit of f(R,T) models. We also work out the non-minimally coupled case in the metric-affine formalism and find that there are no viable cosmologies in the latter situation. However, when analyzing the cosmological dynamics including a radiation component, we find that this energy density interacts with the matter field and it does not scale according to the typical behavior. We conclude stating that f(R,T) gravity is not able to provide a full cosmological scenario and should be ruled out as a modified gravity alternative to the dark energy phenomena.

We investigate Eigen's model for the evolution of the genetic code of microorganisms using a novel method based on population dynamics analysis. This model, for a given number of offspring, determines long-term survival as a function of the "genetic" information length and copy error probability. There exists a maximum threshold for the quantity of information that can be consistently preserved through the process of evolution within a population of perfectly replicating sequences, meaning no errors are allowed. With our formula, we expand upon the traditional error threshold formula of Eigen's theory and introduce a new expression for general cases where the self-reproduction process allows up to any integer number of copying errors per digit per replication step.

We have derived analytical solutions using Jacobi elliptic functions for bound and nearly bound photon orbits in Kerr-de Sitter and Kerr-de Sitter revisited spacetimes. Leveraging our obtained solutions, we have conducted an analytic ray-tracing in both spacetimes. We have obtained direct images, lensing rings and photon rings for equatorial disks considering inclined locally static observers. Images corresponding to n=(2,3) exhibit a significantly closer resemblance to the critical curve as compared to the n=1 image. This highlights the remarkable potential of these higher-order images as robust testing grounds for general relativity. Furthermore in both spacetimes, we have obtained analytical solutions for the critical parameters governing the structure of the photon ring and analyzed these parameters in details.

Unimodular gravity is one of the oldest geometric gravity theories and alternatives to general relativity. Essentially, it is based on the Einstein–Hilbert Lagrangian with an additional constraint on the determinant of the metric. It can be explicitly shown that unimodular gravity can be recast as general relativity in the presence of a cosmological constant. This fact has led to many discussions on the equivalence of both theories at the classical and quantum levels. Here, we present an analysis focused on the classical scalar perturbations around a cosmological background. We focus on the unusual situation in which the typical conservation laws are not adopted. The discussion is extended to the case where a non-minimal coupled scalar field is introduced. We also present a gauge-invariant analysis showing that perturbations in unimodular gravity display instabilities. Our results reinforce that the equivalence is not verified completely at a cosmological perturbative level.

Unimodular gravity (UG) is often deemed comparable to General Relativity (GR) in many respects, despite the theory exhibiting invariance under a more limited set of diffeomorphic transformations. The discussion we propose in this work relies on the criteria for establishing the equivalence between these two formulations, specifically exploring UG’s application to static and spherically symmetric configurations with the energy-momentum tensor originating from either a scalar field or an electromagnetic field. We find that the equivalence between UG and GR might be disrupted when scrutinizing the stability of solutions at a perturbative level.