In this article, we formulate three different solutions by extending the regular Hayward black hole in the background of gravitational decoupling, a well-known approach to extend the existing solutions to the more generalized domain. To do this, we consider a seed perfect fluid spherical source and add an extra matter content in the Einstein’s field equations. This makes the gravitational equations more complex and thus we are required to implement the decoupling technique, resulting in two subsystems. For solving first of them representing perfect fluid setup, we consider Hayward black hole. As the other system is concerned, three constraints are taken into account to find the deformation function which completes the solution. A particular combination of both these solutions leads to a novel extension analogous to the total fluid distribution. Afterwards, we choose multiple values of the decoupling parameter to graphically analyze the physical attributes for our resulting solutions. Some thermodynamic characteristics are also discussed. Finally, we conclude that the stability for all three models remains preserved according to the specific heat and Hessian matrix criteria.

Pakistan

Azerbaijan

Tayyab Naseer

Malta

Jackson Said

M. Sharif

Saudi Arabia

Abdel-Haleem Abdel-Aty

Thermodynamic properties of non-singular Hayward black hole through the lens of minimal gravitational decoupling

In this paper, we introduce the $$\phi $$ CDM model, and we compare to the concordance model. We provide their epoch evolution, we perform a dynamical analysis to each model, and a comparative analysis between the two models. We revitalise these two models, since we study them in systems with higher number of variables. Furthermore, the $$\phi $$ CDM model is more complete than the one that we found in the literature, since we take into account all the so far discovered epochs, radiation, matter, and dark energy epochs. In contrast in the literature there is no study including the radiation epoch for this model. We find that both models can describe the generally accepted scenario of cosmic evolution, and current observations. Both models, describe qualitative and quantitative current observations about the epoch behaviour of the species of the universe. We find the $$\phi $$ CDM model has the following exotic transition from a epoch and a epoch, towards a epoch, in the matter-potential-scalar plane.

France

Pierros Ntelis

Exploring $$\phi $$ CDM model dynamics

A well-known problem in cosmology is the ‘Hubble tension’ problem, i.e. different estimates for the Hubble constant  $$H_0$$  <math> <msub> <mi>H</mi> <mn>0</mn> </msub> </math>   are not concordant with each other. This work investigates different statistical methods for estimating this value using cosmic chronometer, type Ia supernova and baryonic acoustic data. We start by making use of methods already established in the literature for this purpose, namely Gaussian process regression and Markov chain Monte Carlo (MCMC) methods based on the concordance  $$\varLambda $$  <math> <mi>Λ</mi> </math>  CDM model. We also consider two novel approaches; the first makes use of non-parametric MCMC inference on the hyperparameters of a Gaussian process kernel, independently of any cosmological model. The second approach is Student’s t-process regression, which is a generalised version of Gaussian process regression that makes use of the multivariate Student’s t-distribution instead of the multivariate Gaussian distribution. We also consider variants of these two methods which account for heteroscedasticity within the data. A comparison of the different approaches is made. In particular, the model-independent techniques investigated mostly agree with predictions based on the  $$\varLambda $$  <math> <mi>Λ</mi> </math>  CDM model. Moreover, Gaussian process regression is highly sensitive to the prior specification, while Student’s t-process regression and the heteroscedastic variants of both methods are more robust to this. Student’s t-process regression and both heteroscedastic models suggest a lower value of the Hubble constant. Across all the estimates obtained for the Hubble constant within this work, the median value is  $$\hat{H}_0^{med} = 68.85 \pm 1.67$$  <math> <mrow> <msubsup> <mover> <mi>H</mi> <mo>^</mo> </mover> <mn>0</mn> <mrow> <mi>med</mi> </mrow> </msubsup> <mo>=</mo> <mn>68.85</mn> <mo>±</mo> <mn>1.67</mn> </mrow> </math>   km s $$^{-1}$$  <math> <mmultiscripts> <mrow></mrow> <mrow></mrow> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </mmultiscripts> </math>   Mpc $$^{-1}$$  <math> <mmultiscripts> <mrow></mrow> <mrow></mrow> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </mmultiscripts> </math>  .

Samuel Zammit

David Suda

Fiona Sammut

Estimation of the Hubble constant using Gaussian process regression and viable alternatives

In this paper, we explore the existence of various non-singular compact stellar solutions influenced by the Maxwell field within the matter-geometry coupling based modified gravity. We start this analysis by considering a static spherically symmetric spacetime which is associated with the isotropic matter distribution. We then determine the field equations corresponding to two specific functions of this modified theory. Along with these models, we also adopt different forms of the matter Lagrangian. We observe several unknowns in these equations such as the metric potentials, charge and fluid parameters. Thus, the embedding class-one condition and a particular realistic equation of state is used to construct their corresponding solutions. The former condition provides the metric components possessing three constants, and we calculate them through junction conditions. Further, four developed models are graphically analyzed under different parametric values. Finally, we find all our developed solutions well-agreeing with the physical requirements, offering valuable insights for future explorations of the stellar compositions in this theory.

Existence of non-singular stellar solutions within the context of electromagnetic field: a comparison between minimal and non-minimal gravity models

A unified Chew-Mandelstam description of single-pion photoproduction data, together with pion- and <math><mi>η</mi></math>-hadroproduction data, has been extended to include measurements carried out over the last decade. We consider photodecay amplitudes evaluated at the pole with particular emphasis on <math><mrow><mi>n</mi><mi>γ</mi></mrow></math> couplings and the influence of weighting on our fits. Both energy-dependent and single-energy analysis (energy-binned data) are considered.

United States

William J. Briscoe

Axel Schmidt

Igor Strakovsky

Ron L. Workman

Croatia

Alfred Švarc

Extended SAID partial-wave analysis of pion photoproduction

The pursuit of understanding the mysteries surrounding dark energy has sparked significant interest within the field of cosmology. While conventional approaches, such as the cosmological constant, have been extensively explored, alternative theories incorporating scalar field-based models and modified gravity have emerged as intriguing avenues. Among these, teleparallel theories of gravity, specifically the  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   formulation, have gained prominence as a means to comprehend dark energy within the framework of teleparallelism. In this study, we investigate two well-studied models of teleparallel dark energy and examine the presence of cosmological singularities within these scenarios. Using the Goriely–Hyde procedure, we examine the dynamical systems governing the cosmological equations of these models. Our analysis reveals that both models exhibit Type IV singularities, but only for a limited range of initial conditions. These results could indicate a potential edge for teleparallel cosmological models over their other modified gravity counterparts, as the models we examine seem to be only allowing for weak singularities that too under non general conditions.

India

Oem Trivedi

Russia

Maxim Khlopov

Brazil

Rafael Nunes

Cosmological singularities in  $$f(T,\phi ) $$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   gravity

In this work, we reconstruct the Hubble diagram using various data sets, including correlated ones, in artificial neural networks (ANN). Using ReFANN, that was built for data sets with independent uncertainties, we expand it to include non-Guassian data points, as well as data sets with covariance matrices among others. Furthermore, we compare our results with the existing ones derived from Gaussian processes and we also perform null tests in order to test the validity of the concordance model of cosmology.

Greece

Romania

Konstantinos Dialektopoulos

Purba Mukherjee

Jurgen Mifsud

Neural network reconstruction of cosmology using the Pantheon compilation

The Noether Symmetry approach is applied to study an extended teleparallel  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   gravity that contains the torsion scalar T and the scalar field  $$\phi $$  <math> <mi>ϕ</mi> </math>   in the context of an Friedmann–Lemaître–Robertson–Walker space-time. We investigate the Noether symmetry approach in  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   gravity formalism with the specific form of  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   and analyze how to demonstrate a nontrivial Noether vector. The Noether symmetry method is a helpful resource for generating models and finding out the exact solution of the Lagrangian. In this article, we go through how the Noether symmetry approach enables us to define the form of the function  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   and obtain exact cosmological solutions. We also find the analytical cosmological solutions to the field equations, that is consistent with the Noether symmetry. Our results demonstrate that the obtained solutions enable an accelerated expansion of the Universe. We have also obtained the present value of the Hubble parameter, deceleration parameter, and effective equation of state parameter, which is fit in the range of current cosmological observations.

L. Duchaniya

B. Mishra

Noether symmetry approach in scalar-torsion  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   gravity

The study of cosmological perturbation theory in f(T) gravity is a topic of great interest in teleparallel gravity since this is one of the simplest generalizations of the theory that modifies the teleparallel equivalent of general relativity. In this work, we explore the possibility of a non-flat FLRW background solution and perform perturbations for positively as well as negatively curved spatial geometries, together with a comparison to the flat case. We determine the generalized behaviour of the perturbative modes for this non-flat FLRW setting for arbitrary f(T) models, when the most general homogeneous and isotropic background tetrads are used. We also identify propagating modes in this setup, and relate this with the case of a flat cosmology.

Estonia

Japan

Sebastian Bahamonde

Kazakhstan

Manuel Hohmann

Germany

Christian Pfeifer

China

Emmanuel Saridakis

Perturbations in non-flat cosmology for f(T) gravity

Teleparallel based cosmological models provide a description of gravity in which torsion is the mediator of gravitation. Several extensions have been made within the so-called teleparallel equivalent of general relativity which is equivalent to general relativity at the level of the equations of motion where attempts are made to study the extensions of this form of gravity and to describe more general functions of the torsion scalar T. One of these extensions is  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   gravity; T and  $$\phi $$  <math> <mi>ϕ</mi> </math>   respectively denote the torsion scalar and scalar field. In this work, the dynamical system analysis has been performed for this class of theories to obtain the cosmological behaviour of a number of models. Two models are presented here with some functional form of the torsion scalar and the critical points are obtained. For each critical point, the stability behaviour and the corresponding cosmology are shown. Through the graphical representation, the equation of state parameter and the density parameters for matter-dominated, radiation-dominated and dark energy phase are also presented for both the models.

S. Kadam

Dynamical systems analysis in  $$f(T,\phi )$$  <math> <mrow> <mi>f</mi> <mo>(</mo> <mi>T</mi> <mo>,</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </math>   gravity