Pub Date : 2025-12-12DOI: 10.1016/j.dark.2025.102190
S. Khan , Mohammad Alshammari , Othman Abdullah Almatroud , Z. Yousaf
The use of nonmetricity for modeling self-gravitational stellar fluids has become a compelling topic in relativistic astrophysics. In this respect, this study explores some viable non-static compact stellar configurations within the principles of linear and non-linear models of theory. In particular, we formulate anisotropic, self-gravitational models (both dissipative and non-dissipative) using the well-motivated relativistic constraints known as the complexity-free configuration, along with the quasi-homologous condition. The resulting compact star models reveal important outcomes for the physical characteristics and evolution of dynamical, compact models exhibiting anisotropic stresses and non-uniform density distributions. Our work provides a fresh perspective on the development of highly dense matter objects under non-Riemannian geometrical influences by exploring the interaction between anisotropy, nonmetricity, quasi-homologous symmetry, and the complexity factor.
{"title":"Quasi-homologous evolution of dynamical relativistic stars in nonmetricity-induced gravity","authors":"S. Khan , Mohammad Alshammari , Othman Abdullah Almatroud , Z. Yousaf","doi":"10.1016/j.dark.2025.102190","DOIUrl":"10.1016/j.dark.2025.102190","url":null,"abstract":"<div><div>The use of nonmetricity for modeling self-gravitational stellar fluids has become a compelling topic in relativistic astrophysics. In this respect, this study explores some viable non-static compact stellar configurations within the principles of linear and non-linear models of <span><math><mrow><mi>f</mi><mo>(</mo><mi>Q</mi><mo>)</mo></mrow></math></span> theory. In particular, we formulate anisotropic, self-gravitational models (both dissipative and non-dissipative) using the well-motivated relativistic constraints known as the complexity-free configuration, along with the quasi-homologous condition. The resulting compact star models reveal important outcomes for the physical characteristics and evolution of dynamical, compact models exhibiting anisotropic stresses and non-uniform density distributions. Our work provides a fresh perspective on the development of highly dense matter objects under non-Riemannian geometrical influences by exploring the interaction between anisotropy, nonmetricity, quasi-homologous symmetry, and the complexity factor.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102190"},"PeriodicalIF":6.4,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145790923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-09DOI: 10.1016/j.dark.2025.102189
Miguel Aparicio Resco
We investigate asymptotic Schwarzschild exterior solutions in the context of modified gravity theories, specifically within the framework of f(R) gravity, where the asymptotic behavior recovers the standard Schwarzschild solution of General Relativity. Unlike previous studies that rely mainly on analytical approximations, our approach combines asymptotic analysis with numerical integration of the underlying differential equations. Using these solutions, we analyze strong lensing effects to obtain the photon sphere radius and the corresponding capture parameter. Considering rings produced by total reflection, we define the photon sphere width as the difference between the first total reflection and the capture parameter; and study how it is modified in the f(R) scenario. Our results show that the photon sphere width increases in the presence of f(R)-type modifications, indicating deviations from GR that could be observable in the strong-field regime.
{"title":"Asymptotic Schwarzschild solutions in f(R) gravity and their observable effects on the photon sphere of black holes","authors":"Miguel Aparicio Resco","doi":"10.1016/j.dark.2025.102189","DOIUrl":"10.1016/j.dark.2025.102189","url":null,"abstract":"<div><div>We investigate asymptotic Schwarzschild exterior solutions in the context of modified gravity theories, specifically within the framework of <em>f</em>(<em>R</em>) gravity, where the asymptotic behavior recovers the standard Schwarzschild solution of General Relativity. Unlike previous studies that rely mainly on analytical approximations, our approach combines asymptotic analysis with numerical integration of the underlying differential equations. Using these solutions, we analyze strong lensing effects to obtain the photon sphere radius and the corresponding capture parameter. Considering rings produced by total reflection, we define the photon sphere width as the difference between the first total reflection and the capture parameter; and study how it is modified in the <em>f</em>(<em>R</em>) scenario. Our results show that the photon sphere width increases in the presence of <em>f</em>(<em>R</em>)-type modifications, indicating deviations from GR that could be observable in the strong-field regime.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102189"},"PeriodicalIF":6.4,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145790921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1016/j.dark.2025.102188
Abdulmohsen Daham Alruwaili , Abdul Jawad , Shama Sadiq
In this paper, we study the theoretical as well as observational aspects of warm inflation inspired by different potentials named as β-exponential potential, E-potential, natural inflation potential which generalize the well known power law inflation. In this scenario, the inflation field decays into radiation during the inflationary phase. We analyze inflationary parameters and swampland conjectures in the presence of f(ϕ, T) gravity. In our study, we calculate the scalar spectral index ns, tensor-to-scalar ratio (r) and modified form of de-Sitter conjectures . We also observed their graphical behavior for different values of inflationary decay rate a such as respectively. It is found that inflationary parameters lie within the recently predicted observational ranges.
{"title":"Physical constraining the warm inflationary parameters in f(ϕ, T) modified gravity","authors":"Abdulmohsen Daham Alruwaili , Abdul Jawad , Shama Sadiq","doi":"10.1016/j.dark.2025.102188","DOIUrl":"10.1016/j.dark.2025.102188","url":null,"abstract":"<div><div>In this paper, we study the theoretical as well as observational aspects of warm inflation inspired by different potentials named as <em>β</em>-exponential potential, E-potential, natural inflation potential which generalize the well known power law inflation. In this scenario, the inflation field decays into radiation during the inflationary phase. We analyze inflationary parameters and swampland conjectures in the presence of <em>f</em>(<em>ϕ, T</em>) gravity. In our study, we calculate the scalar spectral index <em>n<sub>s</sub></em>, tensor-to-scalar ratio (<em>r</em>) and modified form of de-Sitter conjectures <span><math><mfrac><mrow><msup><mover><mi>T</mi><mo>¯</mo></mover><mo>′</mo></msup><mi>V</mi></mrow><mrow><mover><mi>T</mi><mo>¯</mo></mover><msup><mi>V</mi><mo>′</mo></msup></mrow></mfrac></math></span>. We also observed their graphical behavior for different values of inflationary decay rate <em>a</em> such as <span><math><mrow><mi>a</mi><mo>=</mo><mn>0</mn><mo>,</mo><mspace></mspace><mn>1</mn><mo>,</mo><mspace></mspace><mo>−</mo><mn>1</mn></mrow></math></span> respectively. It is found that inflationary parameters lie within the recently predicted observational ranges.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102188"},"PeriodicalIF":6.4,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145790919","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-02DOI: 10.1016/j.dark.2025.102186
Andrei Lazanu
We use two subsets of 2000 and 1000 Quijote simulations to build two power spectrum emulators, allowing for fast computations of the non-linear matter power spectrum. The first emulator is built in terms of seven cosmological parameters: the matter and baryon fraction of the energy density of the Universe Ωm and Ωb, the reduced Hubble constant h, the scalar spectral index ns, the amplitude of matter density fluctuations σ8, the total neutrino mass Mν and the dark energy equation of state parameter w, on scales . The power spectra can be directly determined at redshifts 0, 0.5, 1, 2 and 3, while for intermediate redshifts these can be interpolated. The second emulator is based on five cosmological parameters, Ωm, h, ns, σ8 and the amplitude of equilateral non-Gaussianity , at redshifts 0, 0.503, 0.733, 0.997 for . The emulators are built on machine learning techniques. In both cases we have investigated both neural networks and tree-based methods and we have shown that the best accuracy is obtained for a neural network with two hidden layers. Both emulators achieve a root-mean-squared relative error of less then 5 % for all the redshifts considered on the scales discussed.
{"title":"Power spectrum emulators from neural networks and tree-based methods","authors":"Andrei Lazanu","doi":"10.1016/j.dark.2025.102186","DOIUrl":"10.1016/j.dark.2025.102186","url":null,"abstract":"<div><div>We use two subsets of 2000 and 1000 <span>Quijote</span> simulations to build two power spectrum emulators, allowing for fast computations of the non-linear matter power spectrum. The first emulator is built in terms of seven cosmological parameters: the matter and baryon fraction of the energy density of the Universe Ω<sub><em>m</em></sub> and Ω<sub><em>b</em></sub>, the reduced Hubble constant <em>h</em>, the scalar spectral index <em>n<sub>s</sub></em>, the amplitude of matter density fluctuations <em>σ</em><sub>8</sub>, the total neutrino mass <em>M<sub>ν</sub></em> and the dark energy equation of state parameter <em>w</em>, on scales <span><math><mrow><mi>k</mi><mo>∈</mo><mrow><mo>[</mo><mn>0.015</mn><mo>,</mo><mn>1.8</mn><mo>]</mo></mrow><mspace></mspace><mi>h</mi><mo>/</mo><mrow><mrow><mi>M</mi></mrow><mi>p</mi><msup><mi>c</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></mrow></math></span>. The power spectra can be directly determined at redshifts 0, 0.5, 1, 2 and 3, while for intermediate redshifts these can be interpolated. The second emulator is based on five cosmological parameters, Ω<sub><em>m</em></sub>, <em>h, n<sub>s</sub>, σ</em><sub>8</sub> and the amplitude of equilateral non-Gaussianity <span><math><msubsup><mi>f</mi><mrow><mrow><mi>N</mi></mrow><mi>L</mi></mrow><mrow><mrow><mi>e</mi></mrow><mi>q</mi></mrow></msubsup></math></span>, at redshifts 0, 0.503, 0.733, 0.997 for <span><math><mrow><mi>k</mi><mo>∈</mo><mrow><mo>[</mo><mn>0.015</mn><mo>,</mo><mn>1.8</mn><mo>]</mo></mrow><mspace></mspace><mi>h</mi><mo>/</mo><mrow><mrow><mi>M</mi></mrow><mi>p</mi><msup><mi>c</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></mrow></math></span>. The emulators are built on machine learning techniques. In both cases we have investigated both neural networks and tree-based methods and we have shown that the best accuracy is obtained for a neural network with two hidden layers. Both emulators achieve a root-mean-squared relative error of less then 5 % for all the redshifts considered on the scales discussed.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102186"},"PeriodicalIF":6.4,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145685713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-02DOI: 10.1016/j.dark.2025.102187
Mattia Dubbini , Orlando Luongo , Marco Muccino
We extend the framework of spontaneous baryogenesis by investigating the generation of baryon asymmetry when the inflaton, θ, is minimally coupled with a complex spectator scalar field ϕ, as θ2|ϕ|2. We also consider ϕ non-minimally coupled with the Ricci scalar curvature R, since in previous works a Yukawa-like interaction with gravity has already been shown to provide a significant contribution to the production of baryon asymmetry. We do not consider further interactions of the spectator field with the fermions of the Standard Model, considering it de facto as a dark scalar field. In evaluating the violation of the baryon-number conservation during the reheating epoch, in a perfectly homogeneous and isotropic universe, we follow a semiclassical approach, where θ, ϕ and gravity are considered as classical fields, whereas the fermions are quantized. We solve the equations of motion for the inflaton and spectator fields, respectively at first and zero-order in perturbation theory, neglecting at first stage the expansion of the universe. Afterwards, we quantify how the spectator field modifies the inflationary dynamics and thus find the baryon asymmetry produced via the inflaton decays into fermion-antifermion pairs by computing the corresponding decay amplitudes. In particular, the coupling term θ2|ϕ|2 acts as an additional contribution to the square effective mass of the inflaton, increasing its decay amplitudes into fermion-antifermion pairs. Consequently, we expect this to affect the production of the net baryon asymmetry. We therefore obtain small first order correction to standard spontaneous baryogenesis and finally discuss the mass-mixing between fermions. Accordingly, the effects of considering the universe expansion are accounted, showing when the coupling between ϕ and R becomes noticeable in altering the overall baryon asymmetry.
{"title":"Impact of a complex scalar spectator field on baryon asymmetry within spontaneous baryogenesis","authors":"Mattia Dubbini , Orlando Luongo , Marco Muccino","doi":"10.1016/j.dark.2025.102187","DOIUrl":"10.1016/j.dark.2025.102187","url":null,"abstract":"<div><div>We extend the framework of spontaneous baryogenesis by investigating the generation of baryon asymmetry when the inflaton, <em>θ</em>, is minimally coupled with a complex spectator scalar field <em>ϕ</em>, as <em>θ</em><sup>2</sup>|<em>ϕ</em>|<sup>2</sup>. We also consider <em>ϕ</em> non-minimally coupled with the Ricci scalar curvature <em>R</em>, since in previous works a Yukawa-like interaction with gravity has already been shown to provide a significant contribution to the production of baryon asymmetry. We do not consider further interactions of the spectator field with the fermions of the Standard Model, considering it <em>de facto</em> as a dark scalar field. In evaluating the violation of the baryon-number conservation during the reheating epoch, in a perfectly homogeneous and isotropic universe, we follow a semiclassical approach, where <em>θ, ϕ</em> and gravity are considered as classical fields, whereas the fermions are quantized. We solve the equations of motion for the inflaton and spectator fields, respectively at first and zero-order in perturbation theory, neglecting at first stage the expansion of the universe. Afterwards, we quantify how the spectator field modifies the inflationary dynamics and thus find the baryon asymmetry produced via the inflaton decays into fermion-antifermion pairs by computing the corresponding decay amplitudes. In particular, the coupling term <em>θ</em><sup>2</sup>|<em>ϕ</em>|<sup>2</sup> acts as an additional contribution to the square effective mass of the inflaton, increasing its decay amplitudes into fermion-antifermion pairs. Consequently, we expect this to affect the production of the net baryon asymmetry. We therefore obtain small first order correction to standard spontaneous baryogenesis and finally discuss the mass-mixing between fermions. Accordingly, the effects of considering the universe expansion are accounted, showing when the coupling between <em>ϕ</em> and <em>R</em> becomes noticeable in altering the overall baryon asymmetry.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102187"},"PeriodicalIF":6.4,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145738733","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-01DOI: 10.1016/j.dark.2025.102185
Rahima Mokeddem , Maria Lopes , Felipe Avila , Armando Bernui , Wiliam S. Hipólito-Ricaldi
In this study we investigate potential large-angle anisotropies in the angular distribution of the cosmological parameters H0 (the Hubble constant) and Ωm (the matter density) in the flat-ΛCDM framework, using the Pantheon+SH0ES supernovae catalog. For this we perform a directional analysis by dividing the celestial sphere into a set of directions, and estimate the best-fit cosmological parameters across the sky using a MCMC approach. Our results show a dominant dipolar pattern for both parameters in study, suggesting a preferred axis in the universe expansion and in the distribution of matter. However, we also found that for z ≳ 0.015, this dipolar behavior is not statistically significant, confirming the expectation –in the ΛCDM scenario– of an isotropic expansion and a uniform angular distribution of matter (both results at 1 σ confidence level). Nevertheless, for nearby supernovae, at distances ≲ 60 Mpc or z ≲ 0.015, the peculiar velocities introduce a highly significant dipole in the angular distribution of H0. Furthermore, we perform various robustness tests that support our findings, and consistency tests of our methodology.
{"title":"Probing cosmic isotropy: Hubble constant and matter density large-angle variations with the Pantheon+SH0ES data","authors":"Rahima Mokeddem , Maria Lopes , Felipe Avila , Armando Bernui , Wiliam S. Hipólito-Ricaldi","doi":"10.1016/j.dark.2025.102185","DOIUrl":"10.1016/j.dark.2025.102185","url":null,"abstract":"<div><div>In this study we investigate potential large-angle anisotropies in the angular distribution of the cosmological parameters <em>H</em><sub>0</sub> (the Hubble constant) and Ω<sub><em>m</em></sub> (the matter density) in the flat-ΛCDM framework, using the Pantheon+SH0ES supernovae catalog. For this we perform a directional analysis by dividing the celestial sphere into a set of directions, and estimate the best-fit cosmological parameters across the sky using a MCMC approach. Our results show a dominant dipolar pattern for both parameters in study, suggesting a preferred axis in the universe expansion and in the distribution of matter. However, we also found that for <em>z</em> ≳ 0.015, this dipolar behavior is not statistically significant, confirming the expectation –in the ΛCDM scenario– of an isotropic expansion and a uniform angular distribution of matter (both results at 1 <em>σ</em> confidence level). Nevertheless, for nearby supernovae, at distances ≲ 60 Mpc or <em>z</em> ≲ 0.015, the peculiar velocities introduce a highly significant dipole in the angular distribution of <em>H</em><sub>0</sub>. Furthermore, we perform various robustness tests that support our findings, and consistency tests of our methodology.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102185"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145738734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-30DOI: 10.1016/j.dark.2025.102175
M. Sharif , M. Zeeshan Gul , I. Hashim
This study investigates the Rényi Holographic dark energy, Sharma-Mittal Holographic dark energy and Generalized Holographic dark energy models in the framework of f(R, T2) gravity, where R denotes the Ricci scalar and T2 represents the self-contraction of the stress-energy tensor. For this purpose we employed two horizons as infrared cut-offs, such as Hubble horizon and Ricci horizon. The analysis is conducted for a non-interacting scenario in a spatially flat Friedmann-Robertson-Walker universe. By considering a specific form of this modified gravity, we reconstruct the corresponding gravitational models based on these selected dark energy formulations. Additionally, a stability analysis is performed for all cases and the evolution of the equation of state parameter is examined. Our finding indicates that the reconstructed f(R, T2) models effectively describe both the phantom and quintessence phases of cosmic evolution, aligning with the observed accelerated expansion of the universe. This study highlights the deep interconnections between holographic dark energy models and modified gravity theories, offering valuable insights into the large scale dynamics of the cosmos.
{"title":"Comparative analysis of holographic dark energy models in f(R, T2) gravity","authors":"M. Sharif , M. Zeeshan Gul , I. Hashim","doi":"10.1016/j.dark.2025.102175","DOIUrl":"10.1016/j.dark.2025.102175","url":null,"abstract":"<div><div>This study investigates the Rényi Holographic dark energy, Sharma-Mittal Holographic dark energy and Generalized Holographic dark energy models in the framework of <em>f</em>(<em>R, T</em><sup>2</sup>) gravity, where <em>R</em> denotes the Ricci scalar and <em>T</em><sup>2</sup> represents the self-contraction of the stress-energy tensor. For this purpose we employed two horizons as infrared cut-offs, such as Hubble horizon and Ricci horizon. The analysis is conducted for a non-interacting scenario in a spatially flat Friedmann-Robertson-Walker universe. By considering a specific form of this modified gravity, we reconstruct the corresponding gravitational models based on these selected dark energy formulations. Additionally, a stability analysis is performed for all cases and the evolution of the equation of state parameter is examined. Our finding indicates that the reconstructed <em>f</em>(<em>R, T</em><sup>2</sup>) models effectively describe both the phantom and quintessence phases of cosmic evolution, aligning with the observed accelerated expansion of the universe. This study highlights the deep interconnections between holographic dark energy models and modified gravity theories, offering valuable insights into the large scale dynamics of the cosmos.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102175"},"PeriodicalIF":6.4,"publicationDate":"2025-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145665512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-29DOI: 10.1016/j.dark.2025.102183
Abdulmohsen Daham Alruwaili , Abdul Jawad , Ruqia Arif
This paper explores the stability analysis of Friedmann-like spacetimes using dynamical system methods. In this context, we begin by considering a modified cosmological scenario based on Tsallis entropy corrections. These entropic formulations modify the cosmological field equations that govern the universes dynamics. To analyze the dynamics of the adjusted Friedmann equations, we first transform them into an autonomous system of first-order differential equations. This formulation allows us to locate and examine the critical points, which represent the system’s equilibrium states. We consider the various linear and non-linear forms of interaction between cosmological fluids. For each model, we calculate the critical points and discuss their behavior associated with eigenvalues. We investigate the different stages in the universe’s evolution including dust and radiation dominated era of the universe as well as quintessence, ΛCDM and phantom regimes. In addition, we develop the phase space portraits of all the interaction models revealing the stable, unstable and saddle behavior of critical points. In most of the cases, the system supports stable critical points.
{"title":"Testing cosmic stability phenomenon of Tsallis entropy corrected universe","authors":"Abdulmohsen Daham Alruwaili , Abdul Jawad , Ruqia Arif","doi":"10.1016/j.dark.2025.102183","DOIUrl":"10.1016/j.dark.2025.102183","url":null,"abstract":"<div><div>This paper explores the stability analysis of Friedmann-like spacetimes using dynamical system methods. In this context, we begin by considering a modified cosmological scenario based on Tsallis entropy corrections. These entropic formulations modify the cosmological field equations that govern the universes dynamics. To analyze the dynamics of the adjusted Friedmann equations, we first transform them into an autonomous system of first-order differential equations. This formulation allows us to locate and examine the critical points, which represent the system’s equilibrium states. We consider the various linear and non-linear forms of interaction between cosmological fluids. For each model, we calculate the critical points and discuss their behavior associated with eigenvalues. We investigate the different stages in the universe’s evolution including dust and radiation dominated era of the universe as well as quintessence, ΛCDM and phantom regimes. In addition, we develop the phase space portraits of all the interaction models revealing the stable, unstable and saddle behavior of critical points. In most of the cases, the system supports stable critical points.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102183"},"PeriodicalIF":6.4,"publicationDate":"2025-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145738732","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-27DOI: 10.1016/j.dark.2025.102178
Iqra Ibrar , Eman M. Moneer , M. Sharif , Euaggelos E. Zotos
This paper investigates a new model that describes the structure of spherically symmetric anisotropic compact stars in the framework of f(Q, T) gravity, where Q represents non-metricity and T is the trace of the energy-momentum tensor. We use the Tolman-Durgapal-V metric as the seed solution and apply the MIT bag model equation of state to obtain a closed form solution. To test the physical validity of our model, we apply it to two well-known compact star candidates: SAX J 178.9-2021 and 4U 1538-52. Using graphical features, we analyze key physical properties such as matter density, pressure profiles, anisotropy, equation of state parameters, energy conditions, mass function and important stability parameters including compactness, gravitational redshift, causality, Herrera’s cracking condition and the adiabatic index. The results demonstrate that our model is free from singularities and accurately describes a variety of observed compact stars.
{"title":"Imprints of the MIT bag equation of state on the compact stars in the framework of f(Q, T) gravity","authors":"Iqra Ibrar , Eman M. Moneer , M. Sharif , Euaggelos E. Zotos","doi":"10.1016/j.dark.2025.102178","DOIUrl":"10.1016/j.dark.2025.102178","url":null,"abstract":"<div><div>This paper investigates a new model that describes the structure of spherically symmetric anisotropic compact stars in the framework of <em>f</em>(<em>Q, T</em>) gravity, where <em>Q</em> represents non-metricity and <em>T</em> is the trace of the energy-momentum tensor. We use the <em>Tolman-Durgapal-V</em> metric as the seed solution and apply the <em>MIT bag</em> model equation of state to obtain a closed form solution. To test the physical validity of our model, we apply it to two well-known compact star candidates: SAX J 178.9-2021 and 4U 1538-52. Using graphical features, we analyze key physical properties such as matter density, pressure profiles, anisotropy, equation of state parameters, energy conditions, mass function and important stability parameters including compactness, gravitational redshift, causality, Herrera’s cracking condition and the adiabatic index. The results demonstrate that our model is free from singularities and accurately describes a variety of observed compact stars.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102178"},"PeriodicalIF":6.4,"publicationDate":"2025-11-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145790920","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-11-23DOI: 10.1016/j.dark.2025.102182
Dong-Hoon Kim
We consider a situation in which light emitted from the neighborhood of a binary interacts with gravitational waves from the binary (e.g., a supermassive black hole binary in a quasar, a binary pulsar, etc.). The effect is cumulative over the long path lengths of light propagation and might be appreciable if the interaction initially takes place close to the source of gravitational waves, where the strain amplitude can be large. This situation can be modeled effectively using spherical gravitational waves (i.e., transverse-traceless radially propagating waves), with the strain amplitude varying with the distance from the source to a field point where the two wavefronts of light and gravitational waves meet each other. Our analysis employs geometrical-optics methods in curved spacetime, where the curvature is due to gravitational waves propagating in a flat spacetime background. We place a particular focus on the effect of gravitational Faraday rotation (or Skrotskii/Rytov effect) resulting from the interaction between light and gravitational waves from binaries.
{"title":"Geometrical-optics analysis of the interaction between light and gravitational waves from binaries","authors":"Dong-Hoon Kim","doi":"10.1016/j.dark.2025.102182","DOIUrl":"10.1016/j.dark.2025.102182","url":null,"abstract":"<div><div>We consider a situation in which light emitted from the neighborhood of a binary interacts with gravitational waves from the binary (e.g., a supermassive black hole binary in a quasar, a binary pulsar, etc.). The effect is cumulative over the long path lengths of light propagation and might be appreciable if the interaction initially takes place close to the source of gravitational waves, where the strain amplitude can be large. This situation can be modeled effectively using spherical gravitational waves (i.e., transverse-traceless radially propagating waves), with the strain amplitude varying with the distance from the source to a field point where the two wavefronts of light and gravitational waves meet each other. Our analysis employs geometrical-optics methods in curved spacetime, where the curvature is due to gravitational waves propagating in a flat spacetime background. We place a particular focus on the effect of gravitational Faraday rotation (or Skrotskii/Rytov effect) resulting from the interaction between light and gravitational waves from binaries.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102182"},"PeriodicalIF":6.4,"publicationDate":"2025-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145665511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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