Accelerated Expansion Research Articles

A comprehensive parametrization approach for the Hubble parameter in scalar field dark energy models

This study proposes a novel parametrization approach for the dimensionless Hubble parameter i.e. E2(z)=A(z)+β(1+γB(z)) in the context of scalar field dark energy models. The parametrization is characterized by two functions, A(z) and B(z), carefully chosen to capture the behavior of the Hubble parameter at different redshifts. We explore the evolution of cosmological parameters, including the deceleration parameter, density parameter, and equation of state parameter. Observational data from Cosmic Chronometers (CC), Baryonic Acoustic Oscillations (BAO), and the Pantheon＋ datasets are analyzed using MCMC methodology to determine model parameters. The results are compared with the standard ΛCDM model using the Planck observations. Our approach provides a model-independent exploration of dark energy, contributing to a comprehensive understanding of late-time cosmic acceleration.

Cosmic acceleration and turns in the Swampland

We argue that field trajectories, which lead to cosmic acceleration and feature rapid turns near the boundary of the moduli space, are in the Swampland. We obtain this result by assuming the validity of the Swampland Distance Conjecture (SDC) in the presence of a positive scalar potential and by focusing on hyperbolic spaces, as prototype geometries of infinite distance limits of Calabi-Yau compactifications. We find that, in a quasi-de Sitter space with Hubble rate H and acceleration parameter ϵ, the turning rate Ω is upper bounded such as Ω/H < 𝒪(√(ϵ)). Therefore, field trajectories consistent with the SDC can only have a negligible deviation from geodesics. This has direct implications for the realization and consistency of multi-field scenarios in string theory. Moreover, it implies a tension between asymptotic accelerating expansion, consistent with observations, and the de Sitter conjecture.

Expansion and ongoing cosmic ray acceleration in HESS J1731−347

Diffusive shock acceleration in supernova remnants (SNRs) is considered one of the prime mechanisms of galactic cosmic ray (GCR) acceleration. It is still unclear, however, whether SNRs can contribute to the GCR spectrum up to the “knee” (1 PeV) band as acceleration to such energies requires an efficient magnetic field amplification process around the shocks. The presence of such a process is challenging to test observationally. Here, we report on the detection of fast variability in the X-ray synchrotron emission from the forward shock in the SNR HESS J1731−347, which implies the presence of a strong (∼0.2 mG) field exceeding background values, and thus of effective field amplification. We also report a direct measurement of the high forward shock expansion velocity of 4000–5500 km s−1, confirming that the SNR is expanding in a tenuous wind bubble blown by the SNR progenitor, is significantly younger (2.4–9 kyr) than previously assumed by some authors, and only recently started interacting with the dense material outside of the bubble. We finally conclude that there is strong evidence for ongoing hadronic GCR acceleration in this SNR.

Triple crossing positivity bounds, mass dependence and cosmological scalars: Horndeski theory and DHOST

Scalars are widely used in cosmology to model novel phenomena such as the late-time cosmic acceleration. These are effective field theories with highly nonlinear interactions, including Horndeski theory/generalized galileon and beyond. We use the latest fully crossing symmetric positivity bounds to constrain these cosmological EFTs. These positivity bounds, based on fundamental principles of quantum field theory such as causality and unitarity, are able to constrain the EFT coefficients both from above and below. We first map the mass dependence of the fully crossing symmetric bounds, and find that a nonzero mass generically enlarges the positivity regions. We show that fine-tunings in the EFT construction can significantly reduce the viable regions and sometimes can be precarious. Then, we apply the positivity bounds to several models in the Horndeski class and beyond, explicitly listing the ready-to-use bounds with the model parameters, and discuss the implications for these models. The new positivity bounds are found to severely constrain some of these models, in which positivity requires the mass to be parametrically close to the cutoff of the EFT, effectively ruling them out. The examples include massive galileon, the original beyond Horndeski model, and DHOST theory with unity speed of gravity and nearly constant Newton's coupling.

Empowering SME Entrepreneurs: Exploring E-Mind and Financial Self-Efficacy

This study aims to analyze the readiness of SME entrepreneurs in Pangkal Pinang for digital entrepreneurship acceleration and global expansion, taking into consideration the perspectives of Entrepreneurial Mindset (E-Mind) and Financial Self-Efficacy. Data collection was conducted through surveys with in-depth interviews and questionnaires administered to SME entrepreneurs in Pangkal Pinang. Data analysis used a quantitative descriptive approach with IBM SPSS software. The research findings reveal that SME entrepreneurs in Pangkal Pinang possess a strong Entrepreneurial Mindset (E-Mind), as evidenced by their consistent initiative-taking and responsibility for their actions. They are also adept at recognizing and capitalizing on opportunities for business development. The study further highlights the favorable Financial Self-Efficacy among SME entrepreneurs in Pangkal Pinang, characterized by their confidence in financial management and belief in their ability to achieve financial goals in business management.Keywords: E-Mind; Financial Self-Efficacy; Digital Marketing; Financial Technology; Digital Leadership

Reconstructing the distortion function of non-local cosmology: A model-independent approach

We consider non-local modifications of General Relativity given by a distortion function in terms of the inverse of the d’Alembert operator. The inclusion of these terms is motivated by the possibility of reproducing the current accelerated expansion of the Universe starting from non-local gravity. In particular, we propose a model-independent method, based on current observations, to reconstruct the shape of the distortion function, without resorting to a specific cosmological history. We describe a numerical procedure based on Padé polynomials that allows us to study the time evolution of the auxiliary scalar fields introduced to localize non-local gravity action. Thus, adopting suitable boundary conditions, we reconstruct the form of the non-local Lagrangian and infer the best analytical approximation of the numerical outcome. Furthermore, the distortion function turns on during the matter-dominated era and its effects are delayed to the most recent cosmic times. This provides a natural explanation for the late cosmic acceleration, avoiding any fine-tuning problem of the cosmological constant. Finally, we compare our predictions with previous findings based on enforcing the standard ΛCDM background in the reconstruction process.

The dynamics of a hyperbolic solution in [formula omitted] gravity

In this study, our focus is on exploring the dynamics of the universe using a flat FLRW model within the framework of f(R,G) gravity. The specific function f(R,G)=ξR+λR2G2 is considered, with R and G representing the Ricci scalar and Gauss–Bonnet invariant, respectively. To obtain the solution to the gravitational field equations within the f(R,G) formalism, we adopt a specific form for the scale factor, denoted as a=sinh1α(βt) (Nagpal et al., 2019). Here, α and β are parameters of the model that determine the behavior of the scale factor. The proposed model predicts the possibility of eternal cosmic acceleration when 0<α<1.19, indicating a continuous expansion of the universe. On the other hand, for α≥1.19, the model suggests a transition from an early deceleration phase to the current accelerated epoch. This transition aligns with our understanding of the universe’s evolution. Additionally, the model supports the formation of structures in the universe, as it satisfies the Jeans instability condition during the transition from a radiation-dominated era to a matter-dominated era. We focus on analyzing the behavior of the equation of state parameter ω in our model. We investigate the scalar field and analyze the energy conditions about the obtained solution. To validate our model, we employ various diagnostic tools such as the Jerk, Snap, and Lerk parameters, as well as the Om diagnostic, Velocity of sound, and statefinder diagnostic tools. Additionally, we perform cosmological tests to assess the accuracy of our model. A detailed discussion of the results and the model itself is provided.

Late-time attractors and cosmic acceleration

Late-time attractors and cosmic acceleration

Modeling cosmic acceleration with a generalized varying deceleration parameter

Understanding the accelerating expansion of the Universe remains a fundamental challenge in modern cosmology. In this paper, we investigate a cosmological model parametrized by a generalized variable deceleration parameter to elucidate the dynamics driving cosmic acceleration. By employing constraints from the latest observational datasets, including Cosmic Chronometers (CC), Type Ia Supernovae (SNe), and Baryon Acoustic Oscillations (BAO), we assess the compatibility of the model with observational data. The chosen parametrization aligns with thermodynamic constraints on the deceleration parameter, further validating its reliability. Further, we estimate the present value of the Hubble parameter, transition redshift, deceleration parameter, and EoS parameter, which align with observational data. Lastly, our stability analysis confirms the model’s stability against small perturbations.

A Wheeler–DeWitt Non-Commutative Quantum Approach to the Branch-Cut Gravity

In this contribution, motivated by the quest to understand cosmic acceleration, based on the theory of Hořava–Lifshitz and on the branch-cut gravitation, we investigate the effects of non-commutativity of a mini-superspace of variables obeying the Poisson algebra on the structure of the branch-cut scale factor and on the acceleration of the Universe. We follow the guiding lines of a previous approach, which we complement to allow a symmetrical treatment of the Poisson algebraic variables and eliminate ambiguities in the ordering of quantum operators. On this line of investigation, we propose a phase-space transformation that generates a super-Hamiltonian, expressed in terms of new variables, which describes the behavior of a Wheeler–DeWitt wave function of the Universe within a non-commutative algebraic quantum gravity formulation. The formal structure of the super-Hamiltonian allows us to identify one of the new variables with a modified branch-cut quantum scale factor, which incorporates, as a result of the imposed variable transformations, in an underlying way, elements of the non-commutative algebra. Due to its structural character, this algebraic structure allows the identification of the other variable as the dual quantum counterpart of the modified branch-cut scale factor, with both quantities scanning reciprocal spaces. Using the iterative Range–Kutta–Fehlberg numerical analysis for solving differential equations, without resorting to computational approximations, we obtained numerical solutions, with the boundary conditions of the wave function of the Universe based on the Bekenstein criterion, which provides an upper limit for entropy. Our results indicate the acceleration of the early Universe in the context of the non-commutative branch-cut gravity formulation. These results have implications when confronted with information theory; so to accommodate gravitational effects close to the Planck scale, a formulation à la Heisenberg’s Generalized Uncertainty Principle in Quantum Mechanics involving the energy and entropy of the primordial Universe is proposed.

Examining the physical viability of the f(R) gravity via observational constraints

f(R) gravity is an extension of Einstein's General Relativity derived from relaxing the hypothesis that the Hilbert-Einstein action for the gravitational field is strictly linear in the Ricci curvature scalar R and explains the late-time cosmic acceleration of the Universe. We investigate the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) line element filled with two fluids, with the first being pressureless matter and the second being the Renyi holographic dark energy (RHDE) in this study. In this scenario, the Hubble horizon H acts as an Infrared (IR) cutoff. In this regard, the effects of IR cutoff with the Hubble horizon on the traits of RHDE models have been researched. The volumetric power law expansion and the two models of f(R) i.e. f(R)=R+bRm and f(R)=R−μ4R are taken into consideration for the solution of the field equations. The estimated model parameter values that would best fit and work with current observational datasets. This estimation uses 1048 points from the Pantheon supernovae datasets and 30 points from the Hubble datasets. The likelihood function and Bayesian analysis are integrated with the Markov Chain Monte Carlo (MCMC) method at the 1 σ and 2 σ confidence levels. It is crucial to remember that f(R) is a rising function ofR, demonstrating the model's plausibility. For both models, the equation of state (EoS) value is close to a Quintessence zone. The model behaves in a ΛCDM (ΛCold Dark Matter) like manner, as shown by the fact that the statefinder diagnostic pair falls to(r=1,s=0). The Om(z) parameter shows a discrète behaviour.

Investigation on the stability and quantum phase transition of the charged rotating Kiselev Black Hole embedded in Quintessence field with quantum fluctuation of entropy

Immediate local impacts of cosmic acceleration upon a rapidly rotating black hole are very interesting in recent studies. In this paper, the stability of a rapidly rotating black hole and the minimum value of the ratio between the black hole’s angular momentum to it’s mass which ensures the stability, are investigated simultaneously. Also, two modern forms of uncertainty relations are proposed by enhancing the usual Heisenberg algebra with superior terms, in order to supervise on thermodynamic properties of the rotating black hole. An asymptotically flat Kiselev black hole solution, cultivated by quintessence field is chosen for this purpose. The local shifts in spacetime geometry next to the rotating black hole can be resolved from a modified metric, occupying the surrounding spacetime of the black hole. The angular momentum of a rotating black hole depends on the rate of change in acquiring mass by it. On the other hand, at the same time, due to the effect of the quintessence field, there exists repulsive gravitational force inside the black hole. So, there is an uncertainty in the position of innermost stable circular orbit as well as radius of the rotating black hole. This uncertainty is also investigated in our work. Relying on two new forms of uncertainty principle, the modified thermodynamic variables like black hole’s Hawking temperature, heat-capacity, entropy at the black hole’s event horizon, etc. are computed under rotation. Quantum corrections of black hole’s Hawking temperature, entropy, free-energy, etc. are also explored. Further, quantum corrected heat capacity of the rotating black hole is studied and also thermal stability is inquired. The existence of transitions of phase in case of a rapidly rotating black hole are also found out. Again, quantum corrected entropy of black hole contains logarithmic terms and their effects on thermal stability of the rotating black hole are also discussed. Modifications in the mass-temperature, specific heat, etc. of a rotating black hole are also presented according to the modified extension parameters.

FLRW universe in f(Q,T) gravity

A cosmological model is described in this study using [Formula: see text] gravity, and the parameters are restricted using cosmological data sets. We start out by using a well-motivated form of [Formula: see text] as [Formula: see text], where [Formula: see text] and [Formula: see text] are model parameters. To solve the field equations, we use the relation that the deceleration parameter is inversely related to the Hubble parameter. In this case, we find that by parametrizing the cosmological parameters the transition redshift between early deceleration and late time acceleration occurs at [Formula: see text] The positive slope of the Om [Formula: see text] diagnostic analysis indicates that the model is in a phantom phase. Based on the current study, it seems that [Formula: see text] gravity might offer a substitute for dark energy in order to address the current cosmic acceleration.

Causal viscous Universe in Sáez–Ballester theory

In this work, the authors examine the dynamics of viscous Universe in the Sáez–Ballester theory of gravity. The solutions of the Friedmann–Robertson–Walker field equations have been derived within the framework of full causal theories presented by Israel and Stewart using simple parametrization of scale factor a( t), i.e., power law relation a( t) = a0 tα and exponential law a( t) = b0eβ t. The power law cosmological model shows that the Universe transitioned from early cosmic deceleration to the present cosmic acceleration, and the exponential cosmological model shows the accelerated expansion of the Universe. It has been discovered that as time passes, energy density and viscosity decrease while temperature rises. Energy conditions are also investigated in which the strong energy condition is violated. The behaviour of the cosmological parameters such as the Hubble parameter, energy density, pressure, coefficient of viscosity, and state-finder parameter has been presented graphically.

Glutamine Regulates Gene Expression Profiles to Increase the Proliferation of Porcine Intestinal Epithelial Cells and the Expansion of Intestinal Stem Cells.

The intestinal epithelium is known for its rapid self-renewal, and glutamine is crucial in providing carbon and nitrogen for biosynthesis. However, understanding how glutamine affects gene expression in the intestinal epithelium is limited, and identifying the essential genes and signals involved in regulating intestinal epithelial cell growth is particularly challenging. In this study, glutamine supplementation exhibited a robust acceleration of intestinal epithelial cell proliferation and stem cell expansion. RNA sequencing indicated diverse transcriptome changes between the control and glutamine supplementation groups, identifying 925 up-regulated and 1152 down-regulated genes. The up-regulated DEGs were enriched in the KEGG pathway of cell cycle and GO terms of DNA replication initiation, regulation of phosphatidylinositol 3-kinase activity, DNA replication, minichromosome maintenance protein (MCM) complex, and ATP binding, whereas the down-regulated DEGs were enriched in the KEGG pathway of p53 signaling pathway, TNF signaling pathway, and JAK-STAT signaling pathway and GO terms of inflammatory response and intrinsic apoptotic signaling pathway in response to endoplasmic reticulum stress. Furthermore, GSEA analysis revealed a significant up-regulation of the cell cycle, DNA replication initiation, ATP-dependent RNA helicase activity, and down-regulation of the TNF signaling pathway. The protein-protein association network of the intersecting genes highlighted the significance of DNA replication licensing factors (MCM3, MCM6, and MCM10) in promoting intestinal epithelial growth in response to glutamine. Based on these findings, we propose that glutamine may upregulate DNA replication licensing factors, leading to increased PI3K/Akt signaling and the suppression of TNF, JAK-STAT, and p53 pathways. Consequently, this mechanism results in the proliferation of porcine intestinal epithelial cells and the expansion of intestinal stem cells.

Study of Yang–Mills condensate dark energy in the framework of generalized Brans–Dicke theory

The prediction about the accelerating expansion of the universe introduced the concept of dark energy. Since then, a plethora of work has been done to explain the origin and nature of dark energy. This work deals with the possibility of obtaining cosmic acceleration of a new kind of dark energy, viz., Yang–Mills condensate dark energy in generalized Brans–Dicke theory with variable or constant [Formula: see text] (Brans–Dicke parameter) and vanishing and non-vanishing self-interacting potential. We assume the scale factor and scalar field in power law form. Then we investigate the above model to determine whether the universe is accelerating. We obtain a redshift-dependent equation of state parameter, which describes the phase transition of the universe. We notice that the equation of the state parameter meets the [Formula: see text] cold dark matter (CDM) limit in the far future. Then we study the [Formula: see text] analysis to get the thawing or freezing region. We study the stability of the model by studying the square speed of sound. Last, the nature of the scalar field and the potential are analyzed for four cases.

Connecting primordial gravitational waves and dark energy

Cosmic acceleration manifested in the early universe as inflation, generating primordial gravitational waves detectable in the cosmic microwave background (CMB) radiation. Cosmic acceleration is occurring again at present as dark energy, detectable in cosmic distance and structure surveys. We explore the intriguing idea of connecting the two occurrences through quintessential inflation by an α-attractor potential without a cosmological constant. For this model we demonstrate robustness of the connection 1 + w 0 ≈ 4/(3N 2 r) between the present day dark energy equation of state parameter w 0 and the primordial tensor to scalar ratio r for a wide range of initial conditions. Analytic and numerical solutions produce current thawing behavior, resulting in a tight relation w a ≈ -1.53(1 + w 0)≈ -0.2 (4 × 10-3/r). Upcoming CMB and galaxy redshift surveys can test this consistency condition. Within this model, lack of detection of a dark energy deviation from Λ predicts a higher r, and lack of detection of r predicts greater dark energy dynamics.

The role of supernovae inside AGN jets in UHECR acceleration

Context. Jets of active galactic nuclei are potential accelerators of ultra high-energy cosmic rays. Supernovae can occur inside these jets and contribute to cosmic ray acceleration, particularly of heavy nuclei, but that contribution has been hardly investigated so far. Aims. We carried out a first dedicated exploration of the role of supernovae inside extragalactic jets in the production of ultra high-energy cosmic rays. Methods. We characterized the energy budget of supernova-jet interactions, and the maximum possible energies of the particles accelerated in those events, likely dominated by heavy nuclei. This allowed us to assess whether these interactions can be potential acceleration sites of ultra high-energy cosmic rays, or at least of their seeds. For that, we estimated the cosmic ray luminosity for different galaxy types, and compared the injection rate of cosmic ray seeds into the jet with that due to galactic cosmic ray entrainment. Results. Since the supernova is fueled for a long time by the luminosity of the jet, the energy of a supernova-jet interaction can be several orders of magnitude greater than that of an isolated supernova. Thus, despite the low rate of supernovae expected to occur in the jet, they could still provide more seeds for accelerating ultra high-energy particles than cosmic ray entrainment from the host galaxy. Moreover, these interactions can create sufficiently efficient accelerators to be a source of cosmic rays with energies ≳10 EeV. Conclusions. Supernova-jet interactions can contribute significantly to the production of ultra high-energy cosmic rays, either directly by accelerating these particles themselves or indirectly by providing pre-accelerated seeds.

Anisotropic Cosmology in the Local Limit of Nonlocal Gravity

Within the framework of the local limit of nonlocal gravity (NLG), we investigate a class of Bianchi type I spatially homogeneous but anisotropic cosmological models. The modified field equations are presented in this case, and some special solutions are discussed in detail. This modified gravity theory contains a susceptibility function S(x) such that general relativity (GR) is recovered for S = 0. In the modified anisotropic cosmological models, we explore the contribution of S(t) and its temporal derivative to the local anisotropic cosmic acceleration. The implications of our results for observational cosmology are briefly discussed.

The cosmological frame principle and cosmic acceleration

We discuss implications of the cosmological frame principle which states that cosmological effects of modified gravity must be stable as solutions of each of the corresponding sets of dynamical equations holding in the two conformally-related frames. We show that there are such globally stable, ‘frame-independent’ solutions describing cosmic acceleration, suggesting that they may represent a physically relevant effect. This result highlights the importance of further investigation into the implications of the frame principle for cosmological properties that rely on the use of conformal frames.