Pub Date : 2025-02-01DOI: 10.1016/j.dark.2024.101785
Shin’ichi Nojiri , S.D. Odintsov
<div><div>We investigate the radii of the photon sphere and the black hole shadow in the framework of <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> gravity. For this purpose, we derive the field equation for the corresponding theory when the general spherically symmetric and static configuration is considered. This equation is the third-order differential equation with respect to <span><math><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo>≡</mo><msub><mrow><mfenced><mrow><mfrac><mrow><mi>d</mi><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow><mrow><mi>d</mi><mi>R</mi></mrow></mfrac></mrow></mfenced></mrow><mrow><mi>R</mi><mo>=</mo><mi>R</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></msub></mrow></math></span>, where <span><math><mi>r</mi></math></span> is the radial coordinate. Solving the equation, we find <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> as a function of <span><math><mi>r</mi></math></span>, <span><math><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mo>=</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></math></span>. By using the assumed and obtained geometry, one can calculate the scalar curvature <span><math><mi>R</mi></math></span> as a function of <span><math><mi>r</mi></math></span>, <span><math><mrow><mi>R</mi><mo>=</mo><mi>R</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></math></span>, which could be solved with respect to <span><math><mi>r</mi></math></span> as <span><math><mrow><mi>r</mi><mo>=</mo><mi>r</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span>. Then one finds the functional form of <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub></math></span> as a function of the scalar curvature <span><math><mi>R</mi></math></span>, <span><math><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mo>=</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow><mo>=</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mfenced><mrow><mi>r</mi><mo>=</mo><mi>r</mi><mfenced><mrow><mi>R</mi></mrow></mfenced></mrow></mfenced></mrow></math></span>.</div><div>We then solve the corresponding equation perturbatively by assuming the variation of the geometry from the Schwarzschild spacetime could be small and also the deviation of <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> gravity from Einstein’s gravity is small. As a result, we obtain an inhomogeneous linear differential equation and solve the equation in the region around the radius of the photon sphere. This is a quite general approach which may be adopted for any modified gravity. With the help of the obtained solutions, we calculate the radii of the photon sph
{"title":"Black holes and their shadows in F(R) gravity","authors":"Shin’ichi Nojiri , S.D. Odintsov","doi":"10.1016/j.dark.2024.101785","DOIUrl":"10.1016/j.dark.2024.101785","url":null,"abstract":"<div><div>We investigate the radii of the photon sphere and the black hole shadow in the framework of <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> gravity. For this purpose, we derive the field equation for the corresponding theory when the general spherically symmetric and static configuration is considered. This equation is the third-order differential equation with respect to <span><math><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo>≡</mo><msub><mrow><mfenced><mrow><mfrac><mrow><mi>d</mi><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow><mrow><mi>d</mi><mi>R</mi></mrow></mfrac></mrow></mfenced></mrow><mrow><mi>R</mi><mo>=</mo><mi>R</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></msub></mrow></math></span>, where <span><math><mi>r</mi></math></span> is the radial coordinate. Solving the equation, we find <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> as a function of <span><math><mi>r</mi></math></span>, <span><math><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mo>=</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></math></span>. By using the assumed and obtained geometry, one can calculate the scalar curvature <span><math><mi>R</mi></math></span> as a function of <span><math><mi>r</mi></math></span>, <span><math><mrow><mi>R</mi><mo>=</mo><mi>R</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></math></span>, which could be solved with respect to <span><math><mi>r</mi></math></span> as <span><math><mrow><mi>r</mi><mo>=</mo><mi>r</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span>. Then one finds the functional form of <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub></math></span> as a function of the scalar curvature <span><math><mi>R</mi></math></span>, <span><math><mrow><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mo>=</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow><mo>=</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>R</mi></mrow></msub><mfenced><mrow><mi>r</mi><mo>=</mo><mi>r</mi><mfenced><mrow><mi>R</mi></mrow></mfenced></mrow></mfenced></mrow></math></span>.</div><div>We then solve the corresponding equation perturbatively by assuming the variation of the geometry from the Schwarzschild spacetime could be small and also the deviation of <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> gravity from Einstein’s gravity is small. As a result, we obtain an inhomogeneous linear differential equation and solve the equation in the region around the radius of the photon sphere. This is a quite general approach which may be adopted for any modified gravity. With the help of the obtained solutions, we calculate the radii of the photon sph","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101785"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143155699","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 : 2025-02-01DOI: 10.1016/j.dark.2024.101751
Karim H. Seleim , Richa Arya , Sergio E. Jorás
Modified theories of gravity have been investigated for quite a long time in the literature as a possible explanation for the inflationary period of the universe. The correspondence to General Relativity with an extra scalar field in the so-called Einstein Frame via a conformal transformation is a major tool in this class of theories. Since the trivial forms of theory of gravity have already been ruled out from observations, the quest for the “correct” remains unfinished. We argue that the function can be more soundly justified if one starts from its corresponding potential in the Einstein Frame. To shed some light on the subject, we focus on the phase of preheating in this work. We assume three suitably chosen potentials in the Einstein Frame and a conformal-like coupling in the Jordan Frame, from which we then obtain both a non-trivial and a non-trivial coupling between the fields and that yield Parametric Resonance in the Einstein Frame. We propose that a corresponding so-called vacuum awakening mechanism in the Jordan frame explains the exponential amplification of the field. This study is a first step towards building an important relationship between the two frames that will allow further investigations on the production of primordial gravitational waves and black holes during preheating.
{"title":"Parametric resonance in the Einstein frame: The Jordan-frame Doppelgänger","authors":"Karim H. Seleim , Richa Arya , Sergio E. Jorás","doi":"10.1016/j.dark.2024.101751","DOIUrl":"10.1016/j.dark.2024.101751","url":null,"abstract":"<div><div>Modified <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> theories of gravity have been investigated for quite a long time in the literature as a possible explanation for the inflationary period of the universe. The correspondence to General Relativity with an extra scalar field <span><math><mover><mrow><mi>ϕ</mi></mrow><mrow><mo>̃</mo></mrow></mover></math></span> in the so-called Einstein Frame via a conformal transformation is a major tool in this class of theories. Since the trivial forms of <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> theory of gravity have already been ruled out from observations, the quest for the “correct” <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> remains unfinished. We argue that the function <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> can be more soundly justified if one starts from its corresponding potential <span><math><mrow><mi>V</mi><mrow><mo>(</mo><mover><mrow><mi>ϕ</mi></mrow><mrow><mo>̃</mo></mrow></mover><mo>)</mo></mrow></mrow></math></span> in the Einstein Frame. To shed some light on the subject, we focus on the phase of preheating in this work. We assume three suitably chosen potentials in the Einstein Frame and a conformal-like coupling <span><math><mrow><mo>∼</mo><mi>R</mi><msup><mrow><mi>ψ</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span> in the Jordan Frame, from which we then obtain both a non-trivial <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> and a non-trivial coupling between the fields <span><math><mover><mrow><mi>ϕ</mi></mrow><mrow><mo>̃</mo></mrow></mover></math></span> and <span><math><mover><mrow><mi>ψ</mi></mrow><mrow><mo>̃</mo></mrow></mover></math></span> that yield Parametric Resonance in the Einstein Frame. We propose that a corresponding so-called vacuum awakening mechanism in the Jordan frame explains the exponential amplification of the <span><math><mi>ψ</mi></math></span> field. This study is a first step towards building an important relationship between the two frames that will allow further investigations on the production of primordial gravitational waves and black holes during preheating.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101751"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143156652","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 : 2025-02-01DOI: 10.1016/j.dark.2024.101782
Dinesh Chandra Maurya
<div><div>We discover the cosmic acceleration and physical characteristics of dark energy models in Hoyle–Narlikar’s theory of gravity with observational constraints. We identify analytical solutions for the modified field equations of a barotropic fluid source within a flat Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime metric, and subsequently apply observational constraints using the cosmic chronometer (CC) Hubble data points and apparent magnitude from Pantheon SNe sample. We investigate the dark energy behavior of creation field theory using <span><math><mrow><mi>C</mi><mo>∝</mo><mi>t</mi></mrow></math></span>. We investigate the behavior of scale factor <span><math><mrow><mi>a</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span>, deceleration parameter <span><math><mrow><mi>q</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span>, effective equation of state parameter <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mi>e</mi><mi>f</mi><mi>f</mi></mrow></msub></math></span>, and energy conditions over the cosmic time <span><math><mi>t</mi></math></span>. We also investigate causality and statefinder diagnostic for the model. We have found the value of Hubble constant <span><math><mrow><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>=</mo><mn>68</mn><mo>.</mo><msubsup><mrow><mn>9</mn></mrow><mrow><mo>−</mo><mn>2</mn><mo>.</mo><mn>7</mn></mrow><mrow><mo>+</mo><mn>3</mn><mo>.</mo><mn>1</mn></mrow></msubsup></mrow></math></span> Km/s/Mpc and matter density parameter <span><math><mrow><msub><mrow><mi>Ω</mi></mrow><mrow><mi>m</mi><mn>0</mn></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>280</mn><mo>±</mo><mn>0</mn><mo>.</mo><mn>086</mn></mrow></math></span> for barotropic fluid <span><math><mrow><mn>0</mn><mo>≤</mo><mi>ω</mi><mo><</mo><mn>1</mn></mrow></math></span> with dark energy density parameter <span><math><mrow><msub><mrow><mi>Ω</mi></mrow><mrow><mi>C</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>72</mn><mo>±</mo><mn>0</mn><mo>.</mo><mn>014</mn></mrow></math></span>. We found a constraint on creation-field coupling constant <span><math><mrow><mi>f</mi><mo>></mo><mfrac><mrow><mrow><mo>(</mo><mn>1</mn><mo>+</mo><mn>3</mn><mi>ω</mi><mo>)</mo></mrow><msubsup><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow><mrow><mn>2</mn></mrow></msubsup></mrow><mrow><mn>4</mn><mi>π</mi><mrow><mo>(</mo><mn>1</mn><mo>−</mo><mi>ω</mi><mo>)</mo></mrow></mrow></mfrac></mrow></math></span> for transit phase accelerating universe. We found the transition age <span><math><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi>r</mi></mrow></msub><mo>=</mo><mn>6</mn><mo>.</mo><mn>9</mn><mo>,</mo><mspace></mspace><mn>6</mn><mo>.</mo><mn>7</mn></mrow></math></span> giga years with transition redshift <span><math><mrow><msub><mrow><mi>z</mi></mrow><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi>r</mi></mrow></msub></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>595</mn><mo>,</mo><mspace></mspace><mn>0</mn><mo>.</mo><mn>603</mn
{"title":"Transit dark energy models in Hoyle–Narlikar gravity with observational constraints","authors":"Dinesh Chandra Maurya","doi":"10.1016/j.dark.2024.101782","DOIUrl":"10.1016/j.dark.2024.101782","url":null,"abstract":"<div><div>We discover the cosmic acceleration and physical characteristics of dark energy models in Hoyle–Narlikar’s theory of gravity with observational constraints. We identify analytical solutions for the modified field equations of a barotropic fluid source within a flat Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime metric, and subsequently apply observational constraints using the cosmic chronometer (CC) Hubble data points and apparent magnitude from Pantheon SNe sample. We investigate the dark energy behavior of creation field theory using <span><math><mrow><mi>C</mi><mo>∝</mo><mi>t</mi></mrow></math></span>. We investigate the behavior of scale factor <span><math><mrow><mi>a</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span>, deceleration parameter <span><math><mrow><mi>q</mi><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span>, effective equation of state parameter <span><math><msub><mrow><mi>ω</mi></mrow><mrow><mi>e</mi><mi>f</mi><mi>f</mi></mrow></msub></math></span>, and energy conditions over the cosmic time <span><math><mi>t</mi></math></span>. We also investigate causality and statefinder diagnostic for the model. We have found the value of Hubble constant <span><math><mrow><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>=</mo><mn>68</mn><mo>.</mo><msubsup><mrow><mn>9</mn></mrow><mrow><mo>−</mo><mn>2</mn><mo>.</mo><mn>7</mn></mrow><mrow><mo>+</mo><mn>3</mn><mo>.</mo><mn>1</mn></mrow></msubsup></mrow></math></span> Km/s/Mpc and matter density parameter <span><math><mrow><msub><mrow><mi>Ω</mi></mrow><mrow><mi>m</mi><mn>0</mn></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>280</mn><mo>±</mo><mn>0</mn><mo>.</mo><mn>086</mn></mrow></math></span> for barotropic fluid <span><math><mrow><mn>0</mn><mo>≤</mo><mi>ω</mi><mo><</mo><mn>1</mn></mrow></math></span> with dark energy density parameter <span><math><mrow><msub><mrow><mi>Ω</mi></mrow><mrow><mi>C</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>72</mn><mo>±</mo><mn>0</mn><mo>.</mo><mn>014</mn></mrow></math></span>. We found a constraint on creation-field coupling constant <span><math><mrow><mi>f</mi><mo>></mo><mfrac><mrow><mrow><mo>(</mo><mn>1</mn><mo>+</mo><mn>3</mn><mi>ω</mi><mo>)</mo></mrow><msubsup><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow><mrow><mn>2</mn></mrow></msubsup></mrow><mrow><mn>4</mn><mi>π</mi><mrow><mo>(</mo><mn>1</mn><mo>−</mo><mi>ω</mi><mo>)</mo></mrow></mrow></mfrac></mrow></math></span> for transit phase accelerating universe. We found the transition age <span><math><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi>r</mi></mrow></msub><mo>=</mo><mn>6</mn><mo>.</mo><mn>9</mn><mo>,</mo><mspace></mspace><mn>6</mn><mo>.</mo><mn>7</mn></mrow></math></span> giga years with transition redshift <span><math><mrow><msub><mrow><mi>z</mi></mrow><mrow><msub><mrow><mi>t</mi></mrow><mrow><mi>r</mi></mrow></msub></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>595</mn><mo>,</mo><mspace></mspace><mn>0</mn><mo>.</mo><mn>603</mn","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101782"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143156655","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 : 2025-02-01DOI: 10.1016/j.dark.2024.101776
Jorge L. Rodríguez-Monteverde , Santiago Jaraba , Juan García-Bellido
In this paper, we use numerical relativity to study the spin induction effect within close hyperbolic encounters of initially spinning black holes. We review the initially non-spinning case and explore the cases of initially aligned, anti-aligned and orthogonal spins with respect to the orbital angular momentum . We find that, for a given initial effective spin, the black hole with a smaller initial spin acquires a greater spin-up than the other black hole after the interaction. We study three different scenarios regarding initial effective spin (), using three different scattering angles in order to obtain maximally spin-inducing scenarios. We also find that the final effective spin-ups with respect to the initial spins are well-fitted by a parabola. For spins orthogonal to , we observe that the black hole spins precess, and that the induced spin in the -direction depends quadratically on the value of the initial spins. These phenomena suggest that dense black hole clusters present a rich spin dynamics, where black hole spins may acquire non-trivial distributions.
{"title":"Spin induction from scattering of two spinning black holes in dense clusters","authors":"Jorge L. Rodríguez-Monteverde , Santiago Jaraba , Juan García-Bellido","doi":"10.1016/j.dark.2024.101776","DOIUrl":"10.1016/j.dark.2024.101776","url":null,"abstract":"<div><div>In this paper, we use numerical relativity to study the spin induction effect within close hyperbolic encounters of initially spinning black holes. We review the initially non-spinning case and explore the cases of initially aligned, anti-aligned and orthogonal spins with respect to the orbital angular momentum <span><math><mover><mrow><mi>L</mi></mrow><mo>→</mo></mover></math></span>. We find that, for a given initial effective spin, the black hole with a smaller initial spin acquires a greater spin-up than the other black hole after the interaction. We study three different scenarios regarding initial effective spin (<span><math><mrow><msub><mrow><mi>χ</mi></mrow><mrow><mi>eff</mi></mrow></msub><mo>=</mo><mo>−</mo><mn>0</mn><mo>.</mo><mn>1</mn><mo>,</mo><mspace></mspace><mn>0</mn><mo>.</mo><mn>0</mn><mo>,</mo><mspace></mspace><mn>0</mn><mo>.</mo><mn>1</mn></mrow></math></span>), using three different scattering angles in order to obtain maximally spin-inducing scenarios. We also find that the final effective spin-ups with respect to the initial spins are well-fitted by a parabola. For spins orthogonal to <span><math><mover><mrow><mi>L</mi></mrow><mo>→</mo></mover></math></span>, we observe that the black hole spins precess, and that the induced spin in the <span><math><mi>z</mi></math></span>-direction depends quadratically on the value of the initial spins. These phenomena suggest that dense black hole clusters present a rich spin dynamics, where black hole spins may acquire non-trivial distributions.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101776"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143099706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-01DOI: 10.1016/j.dark.2024.101763
Orhan Donmez
Studying the gravitational collapse of dust particles toward newly formed black holes has gained popularity following the observation of gravitational waves resulting from black hole mergers. In this paper, we focus on modeling the descent of dust debris toward a black hole using a numerical code that incorporates relativistic hydrodynamics within the framework of General Relativity and Einstein–Gauss–Bonnet gravity. We explore the influence of various parameters, such as the black hole’s rotation parameter and the EGB coupling constant , on the curvature effects observed. Both parameters significantly impact the dynamics of the accretion disk formed around the black holes. Furthermore, we discuss the gravitational collapse process in two distinct scenarios. It is also observed that the mass accretion rate is significantly influenced by these two parameters. The rate at which mass is accreted onto a black hole directly impacts the black hole’s growth and evolutionary trajectory.
{"title":"The gravitational collapse of the dust toward the newly formed rotating black holes in Kerr and 4-D Einstein–Gauss–Bonnet Gravities","authors":"Orhan Donmez","doi":"10.1016/j.dark.2024.101763","DOIUrl":"10.1016/j.dark.2024.101763","url":null,"abstract":"<div><div>Studying the gravitational collapse of dust particles toward newly formed black holes has gained popularity following the observation of gravitational waves resulting from black hole mergers. In this paper, we focus on modeling the descent of dust debris toward a black hole using a numerical code that incorporates relativistic hydrodynamics within the framework of General Relativity and Einstein–Gauss–Bonnet gravity. We explore the influence of various parameters, such as the black hole’s rotation parameter <span><math><mi>a</mi></math></span> and the EGB coupling constant <span><math><mi>α</mi></math></span>, on the curvature effects observed. Both parameters significantly impact the dynamics of the accretion disk formed around the black holes. Furthermore, we discuss the gravitational collapse process in two distinct scenarios. It is also observed that the mass accretion rate is significantly influenced by these two parameters. The rate at which mass is accreted onto a black hole directly impacts the black hole’s growth and evolutionary trajectory.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101763"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143099709","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 : 2025-02-01DOI: 10.1016/j.dark.2024.101768
Amna Ali , Shafqat Ul Islam , Sushant G. Ghosh , Ammuthavali Ramasamya
<div><div>We explore strong-gravitational lensing by spherically symmetric Dyon black holes, characterized by the parameters <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span>, which are releated to the electric and magnetic charges within low-energy string theory. Our study reveals that as the values of <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> increase, there is a decrease in the photon sphere radius (<span><math><msub><mrow><mi>x</mi></mrow><mrow><mi>m</mi></mrow></msub></math></span>), the critical impact parameter (<span><math><msub><mrow><mi>u</mi></mrow><mrow><mi>m</mi></mrow></msub></math></span>), and the angular position (<span><math><msub><mrow><mi>θ</mi></mrow><mrow><mi>∞</mi></mrow></msub></math></span>). Additionally, the flux ratio (<span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>m</mi><mi>a</mi><mi>g</mi></mrow></msub></math></span>) of the first image to all other images decreases with increasing <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span>. In contrast to Schwarzschild black holes (where <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> approach 0), these Dyon black holes show a smaller deflection angle (<span><math><msub><mrow><mi>α</mi></mrow><mrow><mi>D</mi></mrow></msub></math></span>), which further decreases as <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> increase. Furthermore, the time delay for black holes such as Sgr A* and M87* can reach up to approximately 10.011 and 15133.1 min, respectively, deviating from Schwarzschild black holes by about 1.4858 and 2245.8 min. For Sgr A* and M87*, the angular position (<span><math><msub><mrow><mi>θ</mi></mrow><mrow><mi>∞</mi></mrow></msub></math></span>) is found to be within the range of (13.07–26.50) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span> and (10.11–20.51) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span>, respectively, with angular separations (<span><math><mi>s</mi></math></span>) ranging from (0.017–0.406) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span> for Sgr A* and (0.013–0.314) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span> for M87*. The Event Horizon Telescope (EHT) constraints on <span><math><msub><mrow><mi>θ</mi></mrow><mrow><mi>s</mi><mi>h</mi></mrow></msub></math></span> for Sgr A* and M87* within the 1<span><math><mi>σ</mi></math></span> region limit the parameters <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> such that the allowed values of <span><math><mi>β</mi></math></span> depend on the parameter <span><math><mi>λ</mi></math></span>. For Sgr A* <span><math><mrow><mn>0</mn><mo>.</mo><mn>184</mn><msup><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msup><mo><</mo><mi>β</mi><mo><</mo><mn>0</mn><mo>.</mo><mn>508</mn><msup><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span> and <span><math
{"title":"Testing low energy string theory with strong gravitational lensing by black holes and constraints from EHT observations","authors":"Amna Ali , Shafqat Ul Islam , Sushant G. Ghosh , Ammuthavali Ramasamya","doi":"10.1016/j.dark.2024.101768","DOIUrl":"10.1016/j.dark.2024.101768","url":null,"abstract":"<div><div>We explore strong-gravitational lensing by spherically symmetric Dyon black holes, characterized by the parameters <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span>, which are releated to the electric and magnetic charges within low-energy string theory. Our study reveals that as the values of <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> increase, there is a decrease in the photon sphere radius (<span><math><msub><mrow><mi>x</mi></mrow><mrow><mi>m</mi></mrow></msub></math></span>), the critical impact parameter (<span><math><msub><mrow><mi>u</mi></mrow><mrow><mi>m</mi></mrow></msub></math></span>), and the angular position (<span><math><msub><mrow><mi>θ</mi></mrow><mrow><mi>∞</mi></mrow></msub></math></span>). Additionally, the flux ratio (<span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>m</mi><mi>a</mi><mi>g</mi></mrow></msub></math></span>) of the first image to all other images decreases with increasing <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span>. In contrast to Schwarzschild black holes (where <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> approach 0), these Dyon black holes show a smaller deflection angle (<span><math><msub><mrow><mi>α</mi></mrow><mrow><mi>D</mi></mrow></msub></math></span>), which further decreases as <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> increase. Furthermore, the time delay for black holes such as Sgr A* and M87* can reach up to approximately 10.011 and 15133.1 min, respectively, deviating from Schwarzschild black holes by about 1.4858 and 2245.8 min. For Sgr A* and M87*, the angular position (<span><math><msub><mrow><mi>θ</mi></mrow><mrow><mi>∞</mi></mrow></msub></math></span>) is found to be within the range of (13.07–26.50) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span> and (10.11–20.51) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span>, respectively, with angular separations (<span><math><mi>s</mi></math></span>) ranging from (0.017–0.406) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span> for Sgr A* and (0.013–0.314) <span><math><mrow><mi>μ</mi><mi>as</mi></mrow></math></span> for M87*. The Event Horizon Telescope (EHT) constraints on <span><math><msub><mrow><mi>θ</mi></mrow><mrow><mi>s</mi><mi>h</mi></mrow></msub></math></span> for Sgr A* and M87* within the 1<span><math><mi>σ</mi></math></span> region limit the parameters <span><math><mi>λ</mi></math></span> and <span><math><mi>β</mi></math></span> such that the allowed values of <span><math><mi>β</mi></math></span> depend on the parameter <span><math><mi>λ</mi></math></span>. For Sgr A* <span><math><mrow><mn>0</mn><mo>.</mo><mn>184</mn><msup><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msup><mo><</mo><mi>β</mi><mo><</mo><mn>0</mn><mo>.</mo><mn>508</mn><msup><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span> and <span><math","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101768"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143099712","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 : 2025-02-01DOI: 10.1016/j.dark.2024.101784
Salih Kibaroğlu
In this paper, we investigate anisotropic cosmological solutions within the framework of Born–Infeld- gravity, a modification of general relativity that incorporates higher-order curvature invariants. Specifically, we focus on the analysis of Bianchi type-I solutions, which provide a valuable framework for studying the evolution of spatial anisotropies in cosmology. By introducing a reconstruction scheme for this model, we explore the behavior of these solutions, analyze various cosmic evolution scenarios, including Starobinsky inflation, de Sitter-like expansion, power-law dynamics, and Big Rip-like evolution. Additionally, we examine the exponential and power-law behavior of the auxiliary metric function to illustrate its impact on the dynamics of cosmic evolution. Our analysis elucidates how the modifications introduced by Born–Infeld- gravity influence anisotropic dynamics, offering new perspectives on the late-time behavior of the universe and potential future singularities.
{"title":"Anisotropic Born–Infeld-f(R) cosmologies","authors":"Salih Kibaroğlu","doi":"10.1016/j.dark.2024.101784","DOIUrl":"10.1016/j.dark.2024.101784","url":null,"abstract":"<div><div>In this paper, we investigate anisotropic cosmological solutions within the framework of Born–Infeld-<span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> gravity, a modification of general relativity that incorporates higher-order curvature invariants. Specifically, we focus on the analysis of Bianchi type-I solutions, which provide a valuable framework for studying the evolution of spatial anisotropies in cosmology. By introducing a reconstruction scheme for this model, we explore the behavior of these solutions, analyze various cosmic evolution scenarios, including Starobinsky inflation, de Sitter-like expansion, power-law dynamics, and Big Rip-like evolution. Additionally, we examine the exponential and power-law behavior of the auxiliary metric function to illustrate its impact on the dynamics of cosmic evolution. Our analysis elucidates how the modifications introduced by Born–Infeld-<span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>)</mo></mrow></mrow></math></span> gravity influence anisotropic dynamics, offering new perspectives on the late-time behavior of the universe and potential future singularities.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101784"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143100213","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 : 2025-02-01DOI: 10.1016/j.dark.2025.101808
Hanlin Song , Bo-Qiang Ma
Lorentz invariance violation in photons can be quantified by measuring the difference in arrival times between high- and low-energy photons originating from gamma-ray bursts (GRBs). When analyzing data, it is crucial to consider the inherent time delay in the emission of these photons at the source of the GRB. In a recent study, three distinct models were evaluated to explain the intrinsic emission times of high-energy photons by analyzing 14 multi-GeV photon events detected from 8 GRBs using the Fermi Gamma-ray Space Telescope (FGST). In this study, we examine three remarkable GRB photons recorded by different observatories: the 99.3 GeV photon from GRB 221009A observed by FGST, the 1.07 TeV photon from GRB 190114C detected by the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope, and the 12.2 TeV photon from GRB 221009A observed by the Large High Altitude Air-shower Observatory (LHAASO). Our analysis indicates that the newly proposed model with a linear relationship between photon energy and intrinsic emission time can offer a consistent framework to explain the behavior of all three exceptional photons with a Lorentz violation scale GeV.
{"title":"Examining Lorentz invariance violation with three remarkable GRB photons","authors":"Hanlin Song , Bo-Qiang Ma","doi":"10.1016/j.dark.2025.101808","DOIUrl":"10.1016/j.dark.2025.101808","url":null,"abstract":"<div><div>Lorentz invariance violation in photons can be quantified by measuring the difference in arrival times between high- and low-energy photons originating from gamma-ray bursts (GRBs). When analyzing data, it is crucial to consider the inherent time delay in the emission of these photons at the source of the GRB. In a recent study, three distinct models were evaluated to explain the intrinsic emission times of high-energy photons by analyzing 14 multi-GeV photon events detected from 8 GRBs using the Fermi Gamma-ray Space Telescope (FGST). In this study, we examine three remarkable GRB photons recorded by different observatories: the 99.3 GeV photon from GRB 221009A observed by FGST, the 1.07 TeV photon from GRB 190114C detected by the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope, and the 12.2 TeV photon from GRB 221009A observed by the Large High Altitude Air-shower Observatory (LHAASO). Our analysis indicates that the newly proposed model with a linear relationship between photon energy and intrinsic emission time can offer a consistent framework to explain the behavior of all three exceptional photons with a Lorentz violation scale <span><math><mrow><msub><mrow><mi>E</mi></mrow><mrow><mi>LV</mi></mrow></msub><mo>∼</mo><mn>3</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>17</mn></mrow></msup></mrow></math></span> GeV.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101808"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143100673","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 properties of a Schwarzschild black hole (BH) immersed in a Dehnen-(1,4,0) type dark matter (DM) halo. We focus on analyzing the time-like geodesics of massive particles and their epicyclic motion around the Schwarzschild BH surrounded by a Dehnen-type DM halo. We further explore the impact of DM halo parameters on the particle trajectory and the innermost stable circular orbits (ISCOs). It is shown that the effect of the DM halo increases the radius of the ISCO and alters the nature of the particle trajectory, changing it from an escaping trajectory to a captured one. We derive a generic expression for the orbital velocity and epicyclic frequencies of particles moving in circular orbits around the BH. We show that an increase in DM halo parameters enhances orbital velocities and influences the frequencies of astrophysical quasi-periodic oscillations (QPOs). Interestingly, we find that radial oscillations decrease while latitudinal oscillations increase under the influence of the DM halo, leading to changes in the QPO characteristics. Finally, we compare our results with observational QPO data obtained from three selected galactic microquasars, “GRO J1655-40”, “GRS 1915+105”, and “XTE 1550-564” of X-ray binary systems to provide the best-fit constraints for the DM halo parameters by applying a Markov Chain Monte Carlo (MCMC) analysis.
{"title":"Quasiperiodic oscillations around a Schwarzschild black hole surrounded by a Dehnen type dark matter halo","authors":"Tursunali Xamidov , Uktamjon Uktamov , Sanjar Shaymatov , Bobomurat Ahmedov","doi":"10.1016/j.dark.2024.101805","DOIUrl":"10.1016/j.dark.2024.101805","url":null,"abstract":"<div><div>In this paper, we investigate the properties of a Schwarzschild black hole (BH) immersed in a Dehnen-(1,4,0) type dark matter (DM) halo. We focus on analyzing the time-like geodesics of massive particles and their epicyclic motion around the Schwarzschild BH surrounded by a Dehnen-type DM halo. We further explore the impact of DM halo parameters on the particle trajectory and the innermost stable circular orbits (ISCOs). It is shown that the effect of the DM halo increases the radius of the ISCO and alters the nature of the particle trajectory, changing it from an escaping trajectory to a captured one. We derive a generic expression for the orbital velocity and epicyclic frequencies of particles moving in circular orbits around the BH. We show that an increase in DM halo parameters enhances orbital velocities and influences the frequencies of astrophysical quasi-periodic oscillations (QPOs). Interestingly, we find that radial oscillations decrease while latitudinal oscillations increase under the influence of the DM halo, leading to changes in the QPO characteristics. Finally, we compare our results with observational QPO data obtained from three selected galactic microquasars, “GRO J1655-40”, “GRS 1915+105”, and “XTE 1550-564” of X-ray binary systems to provide the best-fit constraints for the DM halo parameters by applying a Markov Chain Monte Carlo (MCMC) analysis.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101805"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143100674","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 : 2025-02-01DOI: 10.1016/j.dark.2025.101825
G. Mustafa , Faisal Javed , S.K. Maurya , Assmaa Abd-Elmonem , Farruh Atamurotov , Neissrien Alhubieshi , Phongpichit Channuie
We study the dynamics of test particles around a non-rotating Barrow’s nonlinear charged black hole, and examine how the parameters of the model influence particle motion. The black hole is characterized by three parameters, the mass of the black hole, the charge of the black hole, and the parameters . Using the effective potential approach, we discuss the stability of equatorial circular orbits. We derive the analytical expressions for the energy and angular momentum of test particles as functions of black hole parameters. The innermost stable circular orbits and the effective forces exerted on the particles are also studied. Furthermore, we numerically integrate the equations of motion to examine the particle trajectories. Epicyclic oscillations of test particles near the equatorial plane are explored, and analytical expressions for radial, vertical, and orbital frequencies have also been derived. We also study the frequency of periastron precession. Lastly, we analyze particle collisions near the horizon of the black hole and calculate the center-of-mass energy. Our findings show that the black hole model’s parameters significantly impact particle motion, revealing interesting aspects of their dynamics.
{"title":"Impact of Barrow’s nonlinear charged on particle motion, trajectories, QPOs, and center of mass energy around a black hole","authors":"G. Mustafa , Faisal Javed , S.K. Maurya , Assmaa Abd-Elmonem , Farruh Atamurotov , Neissrien Alhubieshi , Phongpichit Channuie","doi":"10.1016/j.dark.2025.101825","DOIUrl":"10.1016/j.dark.2025.101825","url":null,"abstract":"<div><div>We study the dynamics of test particles around a non-rotating Barrow’s nonlinear charged black hole, and examine how the parameters of the model influence particle motion. The black hole is characterized by three parameters, the mass <span><math><mi>M</mi></math></span> of the black hole, the charge <span><math><mi>Q</mi></math></span> of the black hole, and the parameters <span><math><mi>α</mi></math></span>. Using the effective potential approach, we discuss the stability of equatorial circular orbits. We derive the analytical expressions for the energy and angular momentum of test particles as functions of black hole parameters. The innermost stable circular orbits and the effective forces exerted on the particles are also studied. Furthermore, we numerically integrate the equations of motion to examine the particle trajectories. Epicyclic oscillations of test particles near the equatorial plane are explored, and analytical expressions for radial, vertical, and orbital frequencies have also been derived. We also study the frequency of periastron precession. Lastly, we analyze particle collisions near the horizon of the black hole and calculate the center-of-mass energy. Our findings show that the black hole model’s parameters significantly impact particle motion, revealing interesting aspects of their dynamics.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"47 ","pages":"Article 101825"},"PeriodicalIF":5.0,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143100688","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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