Pub Date : 2026-02-01Epub Date: 2026-01-16DOI: 10.1016/j.dark.2026.102225
Yu-Xiang Huang , Sen Guo , En-Wei Liang , Kai Lin
Understanding how dark matter affects the immediate environment of black holes (BHs) is crucial for interpreting horizon-scale observations. We study rotating BHs surrounded by perfect fluid dark matter (PFDM), exploring their observable features through both analytical and numerical approaches. Using the existence criterion of the innermost stable circular orbit (ISCO), we first derive joint constraints on the PFDM intensity parameter k and the spin parameter a. Within the resulting physically allowed parameter regime, we perform high-resolution, general-relativistic ray-tracing simulations of thin accretion disks at 87 GHz and 230 GHz, capturing the detailed brightness morphology and photon ring structure shaped by PFDM. By incorporating angular diameter measurements of M87* and Sgr A* from the Event Horizon Telescope (EHT), we further narrow down the viable parameter space and directly compare synthetic images with EHT observations of M87*. We find that the inclusion of PFDM improves the agreement with the observed compact shadow and asymmetric brightness distribution, suggesting that dark matter may leave observable imprints on horizon-scale images. Our results position PFDM as a physically motivated extension to the Kerr geometry and highlight a promising astrophysical pathway for probing dark matter near BHs with current and future VLBI campaigns.
{"title":"Impact of perfect fluid dark matter on the appearance of rotating black hole","authors":"Yu-Xiang Huang , Sen Guo , En-Wei Liang , Kai Lin","doi":"10.1016/j.dark.2026.102225","DOIUrl":"10.1016/j.dark.2026.102225","url":null,"abstract":"<div><div>Understanding how dark matter affects the immediate environment of black holes (BHs) is crucial for interpreting horizon-scale observations. We study rotating BHs surrounded by perfect fluid dark matter (PFDM), exploring their observable features through both analytical and numerical approaches. Using the existence criterion of the innermost stable circular orbit (ISCO), we first derive joint constraints on the PFDM intensity parameter <em>k</em> and the spin parameter <em>a</em>. Within the resulting physically allowed parameter regime, we perform high-resolution, general-relativistic ray-tracing simulations of thin accretion disks at 87 GHz and 230 GHz, capturing the detailed brightness morphology and photon ring structure shaped by PFDM. By incorporating angular diameter measurements of M87* and Sgr A* from the Event Horizon Telescope (EHT), we further narrow down the viable parameter space and directly compare synthetic images with EHT observations of M87*. We find that the inclusion of PFDM improves the agreement with the observed compact shadow and asymmetric brightness distribution, suggesting that dark matter may leave observable imprints on horizon-scale images. Our results position PFDM as a physically motivated extension to the Kerr geometry and highlight a promising astrophysical pathway for probing dark matter near BHs with current and future VLBI campaigns.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102225"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146022830","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 : 2026-02-01Epub Date: 2026-01-16DOI: 10.1016/j.dark.2026.102224
Wei Yang , Yu-Xuan Kang , Arshad Ali , Tao-Tao Sui , Chen-Hao Wu , Ya-Peng Hu
Scalar perturbations in the inflation can be amplified when the base inflation potential Vb(ϕ) incorporates a local bump f(ϕ) such as . This modification will lead to a peak in the curvature power spectrum, increasing a significant abundance of primordial black holes (PBHs). However, since there is no underlying physical reason for the choice of f(ϕ), it is essential to investigate the effects of various bump functions on PBH generation. In this paper, we choose the well-known Starobinsky potential as the base inflation potential to compare the effects produced by different bumps, specifically focusing on the Lorentz and Gaussian bumps which are widely used. To clearly illustrate the differences between these two bumps, we keep parameters in bump functions the same. We find an interesting and novel result that the Lorentz cases manifest a stronger ability to enhance the power spectrum and produce more abundance of PBHs than Gaussian cases. Moreover, we also investigate the different effects of bump functions on the scalar-induced gravitational waves (SIGWs). The results indicate that the Lorentz bump generates SIGWs with a higher energy density, which can be potentially detected in the future. Our study gives valuable insights into the choice and constraints on the bump functions, and the different effects may distinguish the two bump cases for practical purposes in future experiments.
{"title":"Different effects of the Lorentz and Gaussian bump functions on the formation of primordial black holes and secondary gravitational waves","authors":"Wei Yang , Yu-Xuan Kang , Arshad Ali , Tao-Tao Sui , Chen-Hao Wu , Ya-Peng Hu","doi":"10.1016/j.dark.2026.102224","DOIUrl":"10.1016/j.dark.2026.102224","url":null,"abstract":"<div><div>Scalar perturbations in the inflation can be amplified when the base inflation potential <em>V<sub>b</sub></em>(<em>ϕ</em>) incorporates a local bump <em>f</em>(<em>ϕ</em>) such as <span><math><mrow><mi>V</mi><mrow><mo>(</mo><mi>ϕ</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>V</mi><mi>b</mi></msub><mrow><mo>(</mo><mi>ϕ</mi><mo>)</mo></mrow><mrow><mo>(</mo><mn>1</mn><mo>+</mo><mi>f</mi><mrow><mo>(</mo><mi>ϕ</mi><mo>)</mo></mrow><mo>)</mo></mrow></mrow></math></span>. This modification will lead to a peak in the curvature power spectrum, increasing a significant abundance of primordial black holes (PBHs). However, since there is no underlying physical reason for the choice of <em>f</em>(<em>ϕ</em>), it is essential to investigate the effects of various bump functions on PBH generation. In this paper, we choose the well-known Starobinsky potential as the base inflation potential to compare the effects produced by different bumps, specifically focusing on the Lorentz and Gaussian bumps which are widely used. To clearly illustrate the differences between these two bumps, we keep parameters in bump functions the same. We find an interesting and novel result that the Lorentz cases manifest a stronger ability to enhance the power spectrum and produce more abundance of PBHs than Gaussian cases. Moreover, we also investigate the different effects of bump functions on the scalar-induced gravitational waves (SIGWs). The results indicate that the Lorentz bump generates SIGWs with a higher energy density, which can be potentially detected in the future. Our study gives valuable insights into the choice and constraints on the bump functions, and the different effects may distinguish the two bump cases for practical purposes in future experiments.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102224"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146022831","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 : 2026-02-01Epub Date: 2025-12-21DOI: 10.1016/j.dark.2025.102195
Oem Trivedi , Abraham Loeb
Primordial Black Holes (PBHs) represent one of the more interesting ways to address dark matter, at the interface of both cosmology and quantum gravity. It is no surprise then that testing PBHs is a venue of active interest, with several cosmological and astrophysical probes constraining different mass ranges. In this work, we propose novel Solar System scale searches for PBHs, motivated by the unique precision and coverage of local observables. We show that asteroid to dwarf planet mass PBHs can induce measurable dipolar timing signatures in pulsar timing arrays, while planetary mass PBHs can generate detectable ADAF accretion flares through interactions with Kuiper Belt bodies. Together, these complementary approaches open a new observational frontier for probing PBHs across mass ranges that remain unconstrained by conventional cosmological methods.
{"title":"Novel solar system probes for primordial black holes","authors":"Oem Trivedi , Abraham Loeb","doi":"10.1016/j.dark.2025.102195","DOIUrl":"10.1016/j.dark.2025.102195","url":null,"abstract":"<div><div>Primordial Black Holes (PBHs) represent one of the more interesting ways to address dark matter, at the interface of both cosmology and quantum gravity. It is no surprise then that testing PBHs is a venue of active interest, with several cosmological and astrophysical probes constraining different mass ranges. In this work, we propose novel Solar System scale searches for PBHs, motivated by the unique precision and coverage of local observables. We show that asteroid to dwarf planet mass PBHs can induce measurable dipolar timing signatures in pulsar timing arrays, while planetary mass PBHs can generate detectable ADAF accretion flares through interactions with Kuiper Belt bodies. Together, these complementary approaches open a new observational frontier for probing PBHs across mass ranges that remain unconstrained by conventional cosmological methods.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102195"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145883991","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}
We examine the shadow properties of the rotating Fang-Wang black hole (RFWBH)-a regular black hole solution constructed via the Newman-Janis algorithm from a spherically symmetric solution in general relativity with nonlinear electrodynamics–described by the parameters mass, spin, and a deviation parameter M, a, and l respectively. In turn, we analyse the horizon structure and the ergoregion, demonstrating how l modifies these features compared to the Kerr solution. The shadow of a black hole is studied using celestial coordinates, revealing that increasing l reduces the shadow size and distorts its shape. By employing shadow observables - oblateness D and area A—we estimate the parameters a and l. We further constrain the RFWBH parameter space using recent Event Horizon Telescope (EHT) observations of Sgr A* and M87*, particularly through measurements of the angular shadow diameter. For M87*, at inclination , (a/M, l/M) ≤ [0.59, 0.07953], with l/M upper bounded for 0.59 ≤ a ≤ 0.8428 lowering with spin; at , (a/M, l/M) ≤ [0.39, 0.09869] with similar upper bounds on l/M for 0.39 ≤ a ≤ 0.8164. In the case of Sgr A*, the parameter space is constrained as follows: at inclination , the allowed range for a/M and l/M are [0,0.6692] and [0,0.0305], respectively; and for 90∘, the allowed ranges for a/M and l/M are [0,0.759] and [0,0.03075], respectively. We also analyse the energy emission rate, finding that the deviation parameter l subdues high-energy emission. Our results indicate that RFWBHs are consistent with current EHT observations and represent viable alternatives to astrophysical black hole models.
我们研究了旋转Fang-Wang黑洞（RFWBH）的阴影特性，这是一个由广义相对论中具有非线性电动力学的球对称解通过Newman-Janis算法构造的规则黑洞解，分别由参数质量、自旋和偏差参数M、a和l描述。反过来，我们分析了视界结构和遍历区域，演示了与Kerr解决方案相比，l如何修改这些特征。利用天体坐标研究了黑洞的阴影，发现增加l会减小阴影的大小并扭曲其形状。通过使用阴影观测值——扁率D和面积a，我们估计了参数a和l。我们利用事件视界望远镜（EHT）最近对Sgr a *和M87*的观测，特别是通过测量角阴影直径，进一步限制了RFWBH参数空间。对于M87*，在倾角θ=17°时，（a/M, l/M） ≤ [0.59,0.07953]，l/M上限为0.59 ≤ a ≤ 0.8428随自旋降低；θ=90°，（a/M, l/M） ≤ [0.39,0.09869]，l/M的上界为0.39 ≤ a ≤ 0.8164。在Sgr A*的情况下，参数空间受如下限制：在倾角θ=50°时，A /M和l/M的允许范围分别为[0,0.6692]和[0,0.0305]；对于90°，a/M和l/M的允许范围分别为[0,0.759]和[0,0.03075]。我们还分析了能量发射速率，发现偏差参数l抑制了高能发射。我们的研究结果表明，RFWBHs与目前的EHT观测结果一致，并代表了天体物理学黑洞模型的可行替代方案。
{"title":"Observational constraints on the rotating Fang-Wang black hole from EHT shadow imaging of M87* and Sgr A*","authors":"Himanshi Gulia , J.K. Singh , Farruh Atamurotov , Sushant G. Ghosh","doi":"10.1016/j.dark.2025.102203","DOIUrl":"10.1016/j.dark.2025.102203","url":null,"abstract":"<div><div>We examine the shadow properties of the rotating Fang-Wang black hole (RFWBH)-a regular black hole solution constructed via the Newman-Janis algorithm from a spherically symmetric solution in general relativity with nonlinear electrodynamics–described by the parameters mass, spin, and a deviation parameter <em>M, a</em>, and <em>l</em> respectively. In turn, we analyse the horizon structure and the ergoregion, demonstrating how <em>l</em> modifies these features compared to the Kerr solution. The shadow of a black hole is studied using celestial coordinates, revealing that increasing <em>l</em> reduces the shadow size and distorts its shape. By employing shadow observables - oblateness <em>D</em> and area <em>A</em>—we estimate the parameters <em>a</em> and <em>l</em>. We further constrain the RFWBH parameter space using recent Event Horizon Telescope (EHT) observations of Sgr A* and M87*, particularly through measurements of the angular shadow diameter. For M87*, at inclination <span><math><mrow><mi>θ</mi><mo>=</mo><msup><mn>17</mn><mo>∘</mo></msup></mrow></math></span>, (<em>a</em>/<em>M, l</em>/<em>M</em>) ≤ [0.59, 0.07953], with <em>l</em>/<em>M</em> upper bounded for 0.59 ≤ <em>a</em> ≤ 0.8428 lowering with spin; at <span><math><mrow><mi>θ</mi><mo>=</mo><msup><mn>90</mn><mo>∘</mo></msup></mrow></math></span>, (<em>a</em>/<em>M, l</em>/<em>M</em>) ≤ [0.39, 0.09869] with similar upper bounds on <em>l</em>/<em>M</em> for 0.39 ≤ <em>a</em> ≤ 0.8164. In the case of Sgr A*, the parameter space is constrained as follows: at inclination <span><math><mrow><mi>θ</mi><mo>=</mo><msup><mn>50</mn><mo>∘</mo></msup></mrow></math></span>, the allowed range for <em>a</em>/<em>M</em> and <em>l</em>/<em>M</em> are [0,0.6692] and [0,0.0305], respectively; and for 90<sup>∘</sup>, the allowed ranges for <em>a</em>/<em>M</em> and <em>l</em>/<em>M</em> are [0,0.759] and [0,0.03075], respectively. We also analyse the energy emission rate, finding that the deviation parameter <em>l</em> subdues high-energy emission. Our results indicate that RFWBHs are consistent with current EHT observations and represent viable alternatives to astrophysical black hole models.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102203"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145926339","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}
In this paper, we investigate the motion of test particles around a black hole (BH) characterized by spontaneous Lorentz symmetry breaking, parameterized by α. We begin by outlining the theoretical framework underlying such BH geometries and subsequently analyze the corresponding dynamics of massive test particles. By applying the effective potential, we determine the exact conditions for circular trajectories and analyze the properties of the innermost stable circular orbits (ISCOs) parameters. In addition, the effective force acting on particles is studied, which gives further insight into orbital stability. Also, we are testing the BH shadow with M87* and Sgr A* under the influence of BH parameters.. Furthermore, we explore oscillatory phenomena associated with small perturbations around circular orbits, calculating the frequencies as measured by both local and distant observers, as well as the periastron precession. In this context, these results shed light on possible observational signatures of Lorentz-symmetry breaking in strong gravitational regimes and contribute to the understanding of modified BH physics.
{"title":"Stability analysis and oscillatory behavior of orbits around Lorentz-violating black holes","authors":"Rana Muhammad Zulqarnain , Abdelmalek Bouzenada , Farruh Atamurotov , Ikhtiyor Saidov , A.S. Alqahtani , Phongpichit Channuie","doi":"10.1016/j.dark.2025.102200","DOIUrl":"10.1016/j.dark.2025.102200","url":null,"abstract":"<div><div>In this paper, we investigate the motion of test particles around a black hole (BH) characterized by spontaneous Lorentz symmetry breaking, parameterized by <em>α</em>. We begin by outlining the theoretical framework underlying such BH geometries and subsequently analyze the corresponding dynamics of massive test particles. By applying the effective potential, we determine the exact conditions for circular trajectories and analyze the properties of the innermost stable circular orbits (ISCOs) parameters. In addition, the effective force acting on particles is studied, which gives further insight into orbital stability. Also, we are testing the BH shadow with M87* and Sgr A* under the influence of BH parameters.. Furthermore, we explore oscillatory phenomena associated with small perturbations around circular orbits, calculating the frequencies as measured by both local and distant observers, as well as the periastron precession. In this context, these results shed light on possible observational signatures of Lorentz-symmetry breaking in strong gravitational regimes and contribute to the understanding of modified BH physics.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102200"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145926343","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}
This study examines the behavior of compact astrophysical objects within a matter-geometry coupled f(R) gravity model. The modified field equations are expressed for a static interior spacetime with an anisotropic matter distribution. Applying two well-defined radial components of the metric ansatz and anisotropic pressures allows for analytical solutions to these equations. In both theoretical models, integrating the differential equations introduces constants, which are fixed using boundary conditions. Furthermore, the condition of null radial pressure at the boundary is used to determine these constants. Additionally, we visually assess certain important features that ensure the physical acceptability of the proposed model and support our analysis with observational data from LMC X-4. Our theoretical research shows that both models meet the physical viability and stability requirements. Further, our investigation also contributes to the knowledge of how the modified gravity model influences the interior structure of compact stars, paving the way for future studies.
{"title":"Dual impact of matter coupling on LMC X-4 pulsar observations and stability","authors":"Asifa Ashraf , Tayyab Naseer , Hammad Afzal , Chengxun Yuan , Ozodbek Rahimov , Ahmadjon Abdujabbarov","doi":"10.1016/j.dark.2026.102230","DOIUrl":"10.1016/j.dark.2026.102230","url":null,"abstract":"<div><div>This study examines the behavior of compact astrophysical objects within a matter-geometry coupled <em>f</em>(<em>R</em>) gravity model. The modified field equations are expressed for a static interior spacetime with an anisotropic matter distribution. Applying two well-defined radial components of the metric ansatz and anisotropic pressures allows for analytical solutions to these equations. In both theoretical models, integrating the differential equations introduces constants, which are fixed using boundary conditions. Furthermore, the condition of null radial pressure at the boundary is used to determine these constants. Additionally, we visually assess certain important features that ensure the physical acceptability of the proposed model and support our analysis with observational data from LMC X-4. Our theoretical research shows that both models meet the physical viability and stability requirements. Further, our investigation also contributes to the knowledge of how the modified gravity model influences the interior structure of compact stars, paving the way for future studies.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102230"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146077972","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 : 2026-02-01Epub Date: 2025-12-25DOI: 10.1016/j.dark.2025.102201
Cemsinan Deliduman , Furkan Şakir Dilsiz , Selinay Sude Binici
To better distinguish the nature of H0 and S8 tensions, it is necessary to separate the effects of expansion and the growth of structure. The growth index γ was identified as the most important parameter that characterizes the growth of density fluctuations independently of the effects of cosmic expansion. In the ΛCDM model, analyses performed with various cosmological datasets indicate that the growth index has to be larger than its theoretically predicted value. Cosmological models based on f(R) gravity theories have scale-dependent growth indices, whose values are even more at odds with the growth rate data. In this work, we evaluate the growth index in the γδCDM model both theoretically and numerically. Although based on f(R) gravity theory, we show through several analyses with different combinations of datasets that the growth index in the γδCDM model is very close in value to the ΛCDM and the ωCDM models. The growth of structure is suppressed in the γδCDM model, which is formulated with the extended gravitational growth framework. Upon analyzing cosmological data, we ascertain that the γδCDM model is equally competitive as the ΛCDM and the ωCDM models.
{"title":"Growth index in the γδCDM model","authors":"Cemsinan Deliduman , Furkan Şakir Dilsiz , Selinay Sude Binici","doi":"10.1016/j.dark.2025.102201","DOIUrl":"10.1016/j.dark.2025.102201","url":null,"abstract":"<div><div>To better distinguish the nature of <em>H</em><sub>0</sub> and <em>S</em><sub>8</sub> tensions, it is necessary to separate the effects of expansion and the growth of structure. The growth index <em>γ</em> was identified as the most important parameter that characterizes the growth of density fluctuations independently of the effects of cosmic expansion. In the ΛCDM model, analyses performed with various cosmological datasets indicate that the growth index has to be larger than its theoretically predicted value. Cosmological models based on <em>f</em>(<em>R</em>) gravity theories have scale-dependent growth indices, whose values are even more at odds with the growth rate data. In this work, we evaluate the growth index in the <em>γδ</em>CDM model both theoretically and numerically. Although based on <em>f</em>(<em>R</em>) gravity theory, we show through several analyses with different combinations of datasets that the growth index in the <em>γδ</em>CDM model is very close in value to the ΛCDM and the <em>ω</em>CDM models. The growth of structure is suppressed in the <em>γδ</em>CDM model, which is formulated with the extended gravitational growth framework. Upon analyzing cosmological data, we ascertain that the <em>γδ</em>CDM model is equally competitive as the ΛCDM and the <em>ω</em>CDM models.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102201"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145883992","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 : 2026-02-01Epub Date: 2025-12-30DOI: 10.1016/j.dark.2025.102208
Wasif Husain
In this study, the impact of neutron decay into dark matter and various dark matter self-interaction strengths on neutron star properties have been explored. Using the quark-meson coupling (QMC) model for nucleon-only equations of state (EoSs), the effects of different matter compositions have been compared, including strange matter and self-interacting dark matter. The results demonstrate that increasing DM-DM self-repulsion stiffens the EoS, influencing the mass-radius relationship and stability of neutron stars. Furthermore, fundamental mode (f-mode) oscillations have been analyzed, which serve as a diagnostic tool for probing neutron star interiors. The f-mode frequencies follow universal relations, reinforcing their applicability for constraining dense matter properties. It has been shown that neutron stars composed of nucleons-only and self-interacting dark matter exhibit a universal behavior in damping time and angular frequency, whereas strange matter and non-self-interacting dark matter deviate from this trend. Importantly, it has been shown that for a GW energy release of E ∼ 1052 erg and a source distance of 25 Mpc, the characteristic strain and signal-to-noise ratio exceed the ET-D sensitivity threshold below ∼ 2.1 kHz for all models except the non-interacting DM case, demonstrating that neutron-to-dark matter decay scenarios, including the role of DM self-interactions, can be tested through next-generation gravitational-wave asteroseismology, offering a new probe of DM physics and the neutron lifetime anomaly.
{"title":"F-mode oscillations of neutron stars with dark matter from neutron decay: Implications for gravitational-wave detectability","authors":"Wasif Husain","doi":"10.1016/j.dark.2025.102208","DOIUrl":"10.1016/j.dark.2025.102208","url":null,"abstract":"<div><div>In this study, the impact of neutron decay into dark matter and various dark matter self-interaction strengths on neutron star properties have been explored. Using the quark-meson coupling (QMC) model for nucleon-only equations of state (EoSs), the effects of different matter compositions have been compared, including strange matter and self-interacting dark matter. The results demonstrate that increasing DM-DM self-repulsion stiffens the EoS, influencing the mass-radius relationship and stability of neutron stars. Furthermore, fundamental mode (f-mode) oscillations have been analyzed, which serve as a diagnostic tool for probing neutron star interiors. The f-mode frequencies follow universal relations, reinforcing their applicability for constraining dense matter properties. It has been shown that neutron stars composed of nucleons-only and self-interacting dark matter exhibit a universal behavior in damping time and angular frequency, whereas strange matter and non-self-interacting dark matter deviate from this trend. Importantly, it has been shown that for a GW energy release of <em>E</em> ∼ 10<sup>52</sup> erg and a source distance of 25 Mpc, the characteristic strain and signal-to-noise ratio exceed the ET-D sensitivity threshold below ∼ 2.1 kHz for all models except the non-interacting DM case, demonstrating that neutron-to-dark matter decay scenarios, including the role of DM self-interactions, can be tested through next-generation gravitational-wave asteroseismology, offering a new probe of DM physics and the neutron lifetime anomaly.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102208"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146022829","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 : 2026-02-01Epub Date: 2026-01-08DOI: 10.1016/j.dark.2026.102213
Taishi Katsuragawa , Shin’ichi Nojiri , Sergei D. Odintsov
We study wormhole geometries embedded in an expanding universe within a four-scalar non-linear σ model, where the target-space metric is identified with the spacetime Ricci tensor. In this framework, wormholes can remain stable even when conventional energy conditions are violated. However, once cosmological expansion is included, the effective energy density and pressure are modified by the cosmological fluid, enabling the energy conditions to be satisfied. We further present intriguing geometries in which a finite future singularity appears in our universe but not in another universe connected by the wormhole. Near the throat, the hypersurface becomes timelike, allowing trajectories to traverse to the other universe before the singularity and return afterwards. We also construct wormhole solutions motivated by galactic dark-matter halo profiles, where the required non-vanishing pressure arises naturally from the four-scalar non-linear σ model.
{"title":"Wormhole spacetimes in an expanding universe: Energy conditions and future singularities","authors":"Taishi Katsuragawa , Shin’ichi Nojiri , Sergei D. Odintsov","doi":"10.1016/j.dark.2026.102213","DOIUrl":"10.1016/j.dark.2026.102213","url":null,"abstract":"<div><div>We study wormhole geometries embedded in an expanding universe within a four-scalar non-linear <em>σ</em> model, where the target-space metric is identified with the spacetime Ricci tensor. In this framework, wormholes can remain stable even when conventional energy conditions are violated. However, once cosmological expansion is included, the effective energy density and pressure are modified by the cosmological fluid, enabling the energy conditions to be satisfied. We further present intriguing geometries in which a finite future singularity appears in our universe but not in another universe connected by the wormhole. Near the throat, the hypersurface becomes timelike, allowing trajectories to traverse to the other universe before the singularity and return afterwards. We also construct wormhole solutions motivated by galactic dark-matter halo profiles, where the required non-vanishing pressure arises naturally from the four-scalar non-linear <em>σ</em> model.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102213"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145977318","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 : 2026-02-01Epub Date: 2025-12-30DOI: 10.1016/j.dark.2025.102209
Long-Yue Li , Xia-Yuan Liu , Rong-Gen Cai , Yungui Gong , Wenting Zhou
We study images of spacetimes containing continuous photon spheres (CPS). For a self-gravitating, isotropic, spherically symmetric spacetime with CPS, we find that a thin accretion disk produces images that closely resemble those of a Schwarzschild black hole, despite significant differences in photon dynamics. More generally, for any static, spherically symmetric spacetime with a luminous CPS core, the image profile is universal: members of this class produce identical image shapes, differing only by an overall normalization factor. This universality is, however, sensitive to the nature of the accretion flow and breaks down for spherically symmetric infalling accretion, where Doppler shifts and non-static emission introduce image features that depend on the flow dynamics and the metric. Finally, we investigate photon regions in a rotating CPS spacetime and find that unlike in Kerr spacetime, the photon region appears as one or two angular sectors in a constant-ϕ cross section. These distinctive photon region properties could produce observable signatures that distinguish rotating CPS spacetimes from the Kerr one.
{"title":"Images and photon regions of continuous photon sphere spacetime","authors":"Long-Yue Li , Xia-Yuan Liu , Rong-Gen Cai , Yungui Gong , Wenting Zhou","doi":"10.1016/j.dark.2025.102209","DOIUrl":"10.1016/j.dark.2025.102209","url":null,"abstract":"<div><div>We study images of spacetimes containing continuous photon spheres (CPS). For a self-gravitating, isotropic, spherically symmetric spacetime with CPS, we find that a thin accretion disk produces images that closely resemble those of a Schwarzschild black hole, despite significant differences in photon dynamics. More generally, for any static, spherically symmetric spacetime with a luminous CPS core, the image profile is universal: members of this class produce identical image shapes, differing only by an overall normalization factor. This universality is, however, sensitive to the nature of the accretion flow and breaks down for spherically symmetric infalling accretion, where Doppler shifts and non-static emission introduce image features that depend on the flow dynamics and the metric. Finally, we investigate photon regions in a rotating CPS spacetime and find that unlike in Kerr spacetime, the photon region appears as one or two angular sectors in a constant-<em>ϕ</em> cross section. These distinctive photon region properties could produce observable signatures that distinguish rotating CPS spacetimes from the Kerr one.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"51 ","pages":"Article 102209"},"PeriodicalIF":6.4,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145926340","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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