The current paper reports an investigation of a warm inflationary scenario in the context of $\textit{f}$($\textit{T}$) gravity for a spatially flat FLRW universe. In our model, inflation is driven purely by the torsional sector of $\textit{f}$($\textit{T}$) gravity, without introducing any additional scalar fields. We focus on the high dissipative regime ( $$R \gg 1$$ ), reconstruct the Hubble parameter as a function of the e-folding number $\textit{N}$, and derive the slow-roll parameters $$\varepsilon _1(N)$$ and $$\varepsilon _2(N)$$ . The study has encapsulated the dynamics of inflation and its duration under strong dissipation. The dissipative coefficient $$\Gamma $$ is modeled with a temperature-dependent power-law form, linking the inflationary dynamics to thermal corrections and the particle content of the early universe. The analysis has affirmed that the torsion-induced energy density $$\rho _T$$ successfully transitions to radiation energy density $$\rho _{rad}$$ , facilitating a graceful exit from inflation. Finally, we have validated our model by comparing the scalar spectral index and tensor-to-scalar ratio with Planck 2018 results, demonstrating consistency within observational bounds. Additionally, it is verified that the thermal domination condition $$T_{*}/H > 1$$ and the torsion dominance condition $$\rho _T/\rho _{rad} > 1$$ are satisfied.

India

Moli Ghosh

Türkiye

Can Aktaş

Surajit Chattopadhyay

Reconstructing $\textit{f}$($\textit{T}$) gravity and exploring the torsion driven warm inflationary cosmology

In this work we study the warm inflation mechanism in the presence of the Barrow holographic dark energy model. Warm inflation differs from other forms of inflation primarily in that it assumes that radiation and inflaton fields exist and interact throughout the inflationary process. After the warming process, energy moves from the inflaton to the radiation as a result of the interaction, keeping the cosmos warm. Here we have set up the warm inflationary mechanism using Barrow holographic dark energy as the driving agent. Warm inflation has been explored in a highly dissipative regime and interesting results have been obtained. It is seen that the Barrow holographic dark energy can successfully drive a warm inflationary scenario in the early universe. Finally, the model was compared with the observational data, and compliance was found.

Prabir Rudra

Azerbaijan

Iran

Canada

Behnam Pourhassan

Warm inflation with Barrow holographic dark energy

A four-parameter generalized entropy has recently been developed based on the generalized cut-off of holographic dark energy (HDE) formalism. It reduces to various known entropies for appropriate parameter limits, as shown in recent studies by Odintsov and others. In the current work, we investigate the evolution of the universe in its early and late phases within the framework of entropic cosmology, where the entropic energy density functions are reconstructed within the framework of the equivalence of holographic dark energy and four-parameter generalized entropy ( <math altimg='si1.svg'><msub><mrow><mi mathvariant='script'>S</mi></mrow><mrow><mi>g</mi></mrow></msub></math>). Also, we examined different entropic dark energy models in this regard, including the generalized holographic dark energy with Nojiri-Odintsov(NO) cut-off, the Barrow entropic HDE (BHDE), and the Tsallis entropic HDE (THDE) as IR cut-off, all of three particular cases of the most generalized four parameter entropic holographic dark energy. Inspired by the works of Nojiri and others, our current work reports a study on cosmological parameters and thermodynamics with entropy corrections to cosmological horizon entropy as well as black hole entropy with a highly generalized viscous coupled holographic dark fluid along with its particular cases.

Sanghati Saha

Ertan Güdekli

Gizem Dilara Açan Yildiz

Thermodynamics of the most generalized form of holographic dark energy and some particular cases with corrected entropies

This article presents a new model for anisotropic compact stars that are confined to physical dark matter in the background of <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo stretchy='false'>)</mo></math> teleparallel gravity. The model is based on the equation of state (EoS) of the bag model type and the Bose-Einstein dark matter density profile. The derived solutions meet the energy conditions, the causality conditions, and the required conditions on the stability factor and adiabatic index, indicating that they are physically well-behaved and represent the physical and stable matter configuration. We also determine the maximum mass, surface redshift, and compactness parameter at the surface. Interestingly, all of these numbers fall within the specified range, supporting the physical viability of our proposal. Additionally, the various masses that are derived for varying the model parameter <italic>k</italic> correspond to five compact, realistic compact objects, including LMC X-4, Her X-1, 4U 1538-52, SAX J1808.4-3658, and Cen X-3. We have also illustrated the radially symmetric profiles of energy density and the moment of inertia for non-rotating stars.

Samprity Das

Relativistic model of an anisotropic star with Bose-Einstein dark matter density profile in <italic>f</italic>( <italic>T</italic>) gravity

Assuming that viscous fluid in the form of Barrow holographic dark energy (BHDE) (a particular case of more generalized version of HDE elaborated in Nojiri et al. in Phys Lett B 825:136844, 2022; Symmetry 13(6):928, 2021) and pressure-less dark matter are present across the flat Friedmann–Robertson–Walker universe, we find the precise solutions of viscous BHDE models in non-interacting and interacting scenarios for different choices of scale factor. We show the evolution of the EoS parameters in the viscous non-interacting and interacting situations together with the deceleration parameters for observing the transition time frame. Afterwards, we investigate a bounce inflation model using the analytical results of model’s slow-roll parameters, scalar spectral index, and tensor-to-scalar ratio. We investigated an association between BHDE and scalar field models since inflation is typically attributed to the existence of scalar fields. The evolution of the generated potential from the scalar fields are plotted against time. Finally, we investigated the GSL of the thermodynamics.

A coupled-fluid approach to explore bounce and inflationary cosmology with Barrow holographic as the driving dark fluid

The evaluation of the energy-momentum distribution for a new four-dimensional, spherically symmetric, static and charged black hole spacetime geometry with constant nonzero topological Euler density is performed by using the energy-momentum complexes of Einstein and Møller. This black hole solution was recently developed in the context of the coupled Einstein–nonlinear electrodynamics of the Born-Infeld type. The energy is found to depend on the mass <math id="M1"><mrow><mi>M</mi></mrow></math> and the charge <math id="M2"><mrow><mi>q</mi></mrow></math> of the black hole, the cosmological constant <math id="M3"><mrow><mi>Λ</mi></mrow></math>, and the radial coordinate <math id="M4"><mrow><mi>r</mi></mrow></math>, while in both prescriptions all the momenta vanish. Some limiting and particular cases are analyzed and discussed, illustrating the rather extraordinary character of the spacetime geometry considered.

Romania

Irina Radinschi

Greece

Theophanes Grammenos

Farook Rahaman

Andromahi Spanou

Marius Mihai Cazacu

Italy

Antonio Pasqua

Localization of Energy-Momentum for a Black Hole Spacetime Geometry with Constant Topological Euler Density

The energy-momentum of a new four-dimensional, charged, spherically symmetric, and nonsingular black hole solution constructed in the context of general relativity coupled to a theory of nonlinear electrodynamics is investigated, whereby the nonlinear mass function is inspired by the probability density function of the continuous logistic distribution. The energy and momentum distributions are calculated by use of the Einstein, Landau-Lifshitz, Weinberg, and Møller energy-momentum complexes. In all these prescriptions, it is found that the energy distribution depends on the mass <math id="M1"><mrow><mi>M</mi></mrow></math> and the charge <math id="M2"><mrow><mi>q</mi></mrow></math> of the black hole, an additional parameter <math id="M3"><mrow><mi>β</mi></mrow></math> coming from the gravitational background considered, and the radial coordinate <math id="M4"><mrow><mi>r</mi></mrow></math>. Further, the Landau-Lifshitz and Weinberg prescriptions yield the same result for the energy, while, in all the aforesaid prescriptions, all the momenta vanish. We also focus on the study of the limiting behavior of the energy for different values of the radial coordinate, the parameter <math id="M5"><mrow><mi>β</mi></mrow></math>, and the charge <math id="M6"><mrow><mi>q</mi></mrow></math>. Finally, it is pointed out that, for <math id="M7"><mi>r</mi><mo>→</mo><mi>∞</mi></math> and <math id="M8"><mi>q</mi><mo>=</mo><mn>0</mn></math>, all the energy-momentum complexes yield the same expression for the energy distribution as in the case of the Schwarzschild black hole solution.

Sayeedul Islam

Energy-Momentum for a Charged Nonsingular Black Hole Solution with a Nonlinear Mass Function

This paper reports a study on the truncated Israel-Stewart formalism for bulk viscosity using the extended holographic Ricci dark energy (EHRDE). Under the consideration that the universe is dominated by EHRDE, the evolution equation for the bulk viscous pressure <math id="M1"><mrow><mi>Π</mi></mrow></math> in the framework of the truncated Israel-Stewart theory has been taken as <math id="M2"><mi>τ</mi><mover><mrow><mi>Π</mi></mrow><mo>˙</mo></mover><mo>+</mo><mi>Π</mi><mo>=</mo><mo>-</mo><mn>3</mn><mi>ξ</mi><mi>H</mi></math>, where <math id="M3"><mrow><mi>τ</mi></mrow></math> is the relaxation time and <math id="M4"><mrow><mi>ξ</mi></mrow></math> is the bulk viscosity coefficient. Considering effective pressure as a sum of thermodynamic pressure of EHRDE and bulk viscous pressure, it has been observed that under the influence of bulk viscosity the EoS parameter <math id="M5"><mrow><msub><mrow><mi>w</mi></mrow><mrow><mi>D</mi><mi>E</mi></mrow></msub></mrow></math> is behaving like phantom, that is, <math id="M6"><msub><mrow><mi>w</mi></mrow><mrow><mi>D</mi><mi>E</mi></mrow></msub><mo>≤</mo><mo>-</mo><mn>1</mn></math>. It has been observed that the magnitude of the effective pressure <math id="M7"><msub><mrow><mi>p</mi></mrow><mrow><mi>e</mi><mi>f</mi><mi>f</mi></mrow></msub><mo>=</mo><mi>p</mi><mo>+</mo><mi>Π</mi></math> is decaying with time. We also investigated the case for a specific choice of scale factor; namely, <math id="M8"><mi>a</mi><mo>(</mo><mi>t</mi><mo>)</mo><mo>=</mo><mo>(</mo><mi>t</mi><mo>-</mo><msub><mrow><mi>t</mi></mrow><mrow><mn>0</mn></mrow></msub><msup><mrow><mo>)</mo></mrow><mrow><mi>β</mi><mo>/</mo><mo>(</mo><mn>1</mn><mo>-</mo><mi>α</mi><mo>)</mo></mrow></msup></math>. For this choice we have observed that a transition from quintessence to phantom is possible for the equation of state parameter. However, the <math id="M9"><mrow><mi>Λ</mi></mrow></math>CDM phase is not attainable by the state-finder trajectories for this choice. Finally it has been observed that in both of the cases the generalized second law of thermodynamics is valid for the viscous EHRDE dominated universe enveloped by the apparent horizon.

Israel-Stewart Approach to Viscous Dissipative Extended Holographic Ricci Dark Energy Dominated Universe

The present paper reports a study on the cosmological consequences arising from reconstructing <math id="M2"><mi>f</mi><mo>(</mo><mi>T</mi><mo>)</mo></math> gravity through new holographic polytropic dark energy. We assume two approaches, namely, a particular form of Hubble parameter <math id="M3"><mrow><mi>H</mi></mrow></math> and a solution for <math id="M4"><mi>f</mi><mo>(</mo><mi>T</mi><mo>)</mo></math>. We obtain the deceleration parameter and effective equation of state, as well as torsion equation of state parameters from total density and pressure in both cases. It is interesting to mention here that the deceleration and torsion equation of state represent transition from deceleration to acceleration phase. We study the statefinder parameters under both approaches which result in the fact that statefinder trajectories are found to attain ΛCDM point. The comparison with observational data represents consistent results. Also, we discuss the stability of reconstructed models through squared speed of sound which represents stability in late times.

Pakistan

Abdul Jawad

Shamaila Rani

Holographic Polytropic Gravity Models

Dark energy models are here investigated and studied in the framework of the Chern–Simons modified gravity model. We bring into focus the holographic dark energy model with Granda–Oliveros cut-off, the modified holographic Ricci dark energy model and a model with higher derivatives of the Hubble parameter. The relevant expressions of the scale factor a(t) for a Friedmann–Robertson–Walker Universe are derived and studied, and, in this context, the evolution of the scale factor is shown to be similar to the one displayed by the modified Chaplygin gas in two of the above models.