Pub Date : 2024-04-12DOI: 10.1007/s10714-024-03229-5
B. Eslam Panah, K. Jafarzade, Á. Rincón
Recently, it was shown that the power-Maxwell (PM) theory could remove the singularity of the electric field (B. Eslam Panah, Europhys. Lett. 134, 20005 (2021)). Motivated by a great interest in three-dimensional black holes and a surge of success in studying massive gravity from both the cosmological and astrophysical points of view, we investigate three-dimensional black hole solutions in de Rham, Gabadadze, and Tolley massive theory of gravity in the presence of PM electrodynamics. First, we extract exact three-dimensional solutions in this theory of gravity. Then we study the geometrical properties of these solutions. Calculating conserved and thermodynamic quantities, we check the validity of the first law of thermodynamics for these black holes. We also examine the stability of these black holes in the context of the canonical ensemble. We continue calculating this kind of black hole’s optical features, such as the photon orbit radius, the energy emission rate, and the deflection angle. Considering these optical quantities, finally, we analyze the effective role of the parameters of models on them.
{"title":"Three-dimensional AdS black holes in massive-power-Maxwell theory","authors":"B. Eslam Panah, K. Jafarzade, Á. Rincón","doi":"10.1007/s10714-024-03229-5","DOIUrl":"10.1007/s10714-024-03229-5","url":null,"abstract":"<div><p>Recently, it was shown that the power-Maxwell (PM) theory could remove the singularity of the electric field (B. Eslam Panah, Europhys. Lett. 134, 20005 (2021)). Motivated by a great interest in three-dimensional black holes and a surge of success in studying massive gravity from both the cosmological and astrophysical points of view, we investigate three-dimensional black hole solutions in de Rham, Gabadadze, and Tolley massive theory of gravity in the presence of PM electrodynamics. First, we extract exact three-dimensional solutions in this theory of gravity. Then we study the geometrical properties of these solutions. Calculating conserved and thermodynamic quantities, we check the validity of the first law of thermodynamics for these black holes. We also examine the stability of these black holes in the context of the canonical ensemble. We continue calculating this kind of black hole’s optical features, such as the photon orbit radius, the energy emission rate, and the deflection angle. Considering these optical quantities, finally, we analyze the effective role of the parameters of models on them.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-024-03229-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140547911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-04-09DOI: 10.1007/s10714-024-03234-8
M. Zeeshan Gul, M. Sharif, Adeeba Arooj
This paper explores the viability and stability of compact stellar objects characterized by anisotropic matter in the framework of (f(textrm{Q},textrm{T})) theory, where (textrm{Q}) denotes non-metricity and (textrm{T}) represents the trace of the energy-momentum tensor. We consider a specific model of this theory to obtain explicit expressions for the field equations governing the behavior of matter and geometry in this context. Furthermore, the Karmarkar condition is employed to assess the configuration of static spherically symmetric structures. The values of unknown constants in the metric potentials are determined through matching conditions of the interior and exterior spacetimes. Various physical quantities such as fluid parameters, energy constraints, equation of state parameters, mass, compactness and redshift are graphically analyzed to evaluate the viability of the considered compact stars. The Tolman–Oppenheimer–Volkoff equation is used to examine the equilibrium state of the stellar models. Moreover, the stability of the proposed compact stars is investigated through sound speed and adiabatic index methods. This study concludes that the proposed compact stars analyzed in this theoretical framework are viable and stable, as all the required conditions are satisfied.
{"title":"Physical analysis of spherical stellar structures in (f(textrm{Q},textrm{T})) theory","authors":"M. Zeeshan Gul, M. Sharif, Adeeba Arooj","doi":"10.1007/s10714-024-03234-8","DOIUrl":"10.1007/s10714-024-03234-8","url":null,"abstract":"<div><p>This paper explores the viability and stability of compact stellar objects characterized by anisotropic matter in the framework of <span>(f(textrm{Q},textrm{T}))</span> theory, where <span>(textrm{Q})</span> denotes non-metricity and <span>(textrm{T})</span> represents the trace of the energy-momentum tensor. We consider a specific model of this theory to obtain explicit expressions for the field equations governing the behavior of matter and geometry in this context. Furthermore, the Karmarkar condition is employed to assess the configuration of static spherically symmetric structures. The values of unknown constants in the metric potentials are determined through matching conditions of the interior and exterior spacetimes. Various physical quantities such as fluid parameters, energy constraints, equation of state parameters, mass, compactness and redshift are graphically analyzed to evaluate the viability of the considered compact stars. The Tolman–Oppenheimer–Volkoff equation is used to examine the equilibrium state of the stellar models. Moreover, the stability of the proposed compact stars is investigated through sound speed and adiabatic index methods. This study concludes that the proposed compact stars analyzed in this theoretical framework are viable and stable, as all the required conditions are satisfied.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-024-03234-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140541633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-04-08DOI: 10.1007/s10714-024-03227-7
Eduard Mychelkin, Maxim Makukov, Gulnara Suliyeva, Nosratollah Jafari
The triumph of general relativity under the banner “gravity is geometry” began with confirming the crucial effects within the Solar system and proceeded recently to the strong-field shadow effect for the compact object in the center of the Milky Way. Here, we examine some of those phenomena for the Einstein-scalar equations in the antiscalar regime to reveal the difference from vacuum both in weak and strong fields. As a result, we find that for week-field perihelion shift the difference between vacuum and antiscalar cases proves to be observationally imperceptible in practice, even for S-cluster stars with high eccentricities, except for the S62 star with measurable difference per century. In strong-field case, we reconsider the shadow effect (this time without involving complex-valued scalar field) as the most perspective from an observational viewpoint. Even though the resulting difference is quite appreciable (about 5%), no conclusion can be made until the mass of the central object is known with the accuracy an order of magnitude higher than the currently available.
{"title":"On the weak and strong field effects in antiscalar background","authors":"Eduard Mychelkin, Maxim Makukov, Gulnara Suliyeva, Nosratollah Jafari","doi":"10.1007/s10714-024-03227-7","DOIUrl":"10.1007/s10714-024-03227-7","url":null,"abstract":"<div><p>The triumph of general relativity under the banner “gravity is geometry” began with confirming the crucial effects within the Solar system and proceeded recently to the strong-field shadow effect for the compact object in the center of the Milky Way. Here, we examine some of those phenomena for the Einstein-scalar equations in the antiscalar regime to reveal the difference from vacuum both in weak and strong fields. As a result, we find that for week-field perihelion shift the difference between vacuum and antiscalar cases proves to be observationally imperceptible in practice, even for S-cluster stars with high eccentricities, except for the S62 star with measurable difference per century. In strong-field case, we reconsider the shadow effect (this time without involving complex-valued scalar field) as the most perspective from an observational viewpoint. Even though the resulting difference is quite appreciable (about 5%), no conclusion can be made until the mass of the central object is known with the accuracy an order of magnitude higher than the currently available.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-024-03227-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140538325","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-04-06DOI: 10.1007/s10714-024-03225-9
Juan M. Z. Pretel, Clésio E. Mota
Within the context of Rastall gravity, we investigate the hydrostatic equilibrium and dynamical stability against radial pulsations of compact stars, where a free parameter (beta ) measures the deviations from General Relativity (GR). We derive both the modified Tolman–Oppenheimer–Volkoff (TOV) equations and the Sturm–Liouville differential equation governing the adiabatic radial oscillations. Such equations are solved numerically in order to obtain the compact-star properties for two realistic equations of state (EoSs). For hadronic matter, the fundamental mode frequency (omega _0) becomes unstable almost at the critical central energy density corresponding to the maximum gravitational mass. However, for quark matter, where larger values of (vert beta vert ) are required to observe appreciable changes in the mass-radius diagram, there exist stable stars after the maximum-mass configuration for negative values of (beta ). Using an independent analysis, our results reveal that the emergence of a cusp can be used as a criterion to indicate the onset of instability when the binding energy is plotted as a function of the proper mass. Specifically, we find that the central-density value where the binding energy is a minimum corresponds precisely to (omega _0^2 =0).
{"title":"Compact stars in Rastall gravity: hydrostatic equilibrium and radial pulsations","authors":"Juan M. Z. Pretel, Clésio E. Mota","doi":"10.1007/s10714-024-03225-9","DOIUrl":"10.1007/s10714-024-03225-9","url":null,"abstract":"<div><p>Within the context of Rastall gravity, we investigate the hydrostatic equilibrium and dynamical stability against radial pulsations of compact stars, where a free parameter <span>(beta )</span> measures the deviations from General Relativity (GR). We derive both the modified Tolman–Oppenheimer–Volkoff (TOV) equations and the Sturm–Liouville differential equation governing the adiabatic radial oscillations. Such equations are solved numerically in order to obtain the compact-star properties for two realistic equations of state (EoSs). For hadronic matter, the fundamental mode frequency <span>(omega _0)</span> becomes unstable almost at the critical central energy density corresponding to the maximum gravitational mass. However, for quark matter, where larger values of <span>(vert beta vert )</span> are required to observe appreciable changes in the mass-radius diagram, there exist stable stars after the maximum-mass configuration for negative values of <span>(beta )</span>. Using an independent analysis, our results reveal that the emergence of a cusp can be used as a criterion to indicate the onset of instability when the binding energy is plotted as a function of the proper mass. Specifically, we find that the central-density value where the binding energy is a minimum corresponds precisely to <span>(omega _0^2 =0)</span>.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-024-03225-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140533945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-04-06DOI: 10.1007/s10714-024-03233-9
Rikpratik Sengupta
We obtain a novel model of oscillating non-singular cosmology on the spatially flat Randall–Sundrum (RS) II brane. At early times, the universe is dominated by a scalar field with an inflationary emergent potential (V(phi )=A(e^{Bphi }-1)^2), A and B being constants. Interestingly, we find that such a scalar field can source a non-singular bounce, replacing the big bang on the brane. The turnaround again happens naturally on the brane dominated by a phantom dark energy [favoured by observations (Knop et al. in Astrophys J 598:102, 2003. Spergel et al. in Astrophys J Suppl 148:175, 2003. Tegmark et al. in Phys Rev D 69:103501, 2004) at late times], thus avoiding the big rip singularity and leading upto the following non-singular bounce via a contraction phase. There is a smooth non-singular transition of the brane universe through both the bounce and turnaround, leading to alternate expanding and contracting phases. This is the first model where a single braneworld of positive tension can be made to recycle as discussed in details in the concluding section.
摘要 我们在空间平坦的兰德尔-桑德鲁姆(RS)II(Randall-Sundrum (RS) II brane)上得到了一个振荡非星状宇宙学的新模型。在早期,宇宙是由一个标量场主导的,它具有一个膨胀的突发势 (V(phi )=A(e^{Bphi }-1)^2) ,A 和 B 是常数。A和B是常数。有趣的是,我们发现这样一个标量场可以产生非奇异的反弹,从而取代 "星系大爆炸"。在由幽灵暗能量主导的[观测结果支持(Knop 等,发表于《天体物理学杂志》598:102, 2003. Spergel 等,发表于《天体物理学杂志》598:102, 2003.Spergel 等人在 Astrophys J Suppl 148:175, 2003.Tegmark等人在Phys Rev D 69:103501,2004)],从而避免了大裂解奇点,并通过收缩阶段导致了随后的非奇点反弹。在反弹和回转过程中,"鹤膜宇宙 "都会发生平滑的非奇异过渡,从而导致交替的膨胀和收缩阶段。这是第一个可以使一个具有正张力的单一支链世界循环的模型,详见结论部分的讨论。
{"title":"A novel model of non-singular oscillating cosmology on flat Randall–Sundrum II braneworld","authors":"Rikpratik Sengupta","doi":"10.1007/s10714-024-03233-9","DOIUrl":"10.1007/s10714-024-03233-9","url":null,"abstract":"<div><p>We obtain a <i>novel</i> model of oscillating non-singular cosmology on the spatially flat Randall–Sundrum (RS) II brane. At early times, the universe is dominated by a scalar field with an inflationary emergent potential <span>(V(phi )=A(e^{Bphi }-1)^2)</span>, <i>A</i> and <i>B</i> being constants. Interestingly, we find that such a scalar field can source a non-singular bounce, replacing the big bang on the brane. The turnaround again happens naturally on the brane dominated by a phantom dark energy [favoured by observations (Knop et al. in Astrophys J 598:102, 2003. Spergel et al. in Astrophys J Suppl 148:175, 2003. Tegmark et al. in Phys Rev D 69:103501, 2004) at late times], thus avoiding the big rip singularity and leading upto the following non-singular bounce via a contraction phase. There is a smooth non-singular transition of the brane universe through both the bounce and turnaround, leading to alternate expanding and contracting phases. This is the <i>first</i> model where a single braneworld of positive tension can be made to recycle as discussed in details in the concluding section.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140533924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-04-04DOI: 10.1007/s10714-024-03230-y
Chia-Min Lin
This work proposes more solutions for the Wheeler–DeWitt equation in a flat FLRW minisuperspace. We study quantum cosmology in the framework of the de Broglie–Bohm interpretation and investigate the quantum cosmological effects throughout the evolution of the universe. In a particular solution, the tendency for a scalar field to roll down the potential is balanced by the quantum force, and a Minkowski spacetime is obtained.
{"title":"More solutions for the Wheeler–DeWitt equation in a flat FLRW minisuperspace","authors":"Chia-Min Lin","doi":"10.1007/s10714-024-03230-y","DOIUrl":"10.1007/s10714-024-03230-y","url":null,"abstract":"<div><p>This work proposes more solutions for the Wheeler–DeWitt equation in a flat FLRW minisuperspace. We study quantum cosmology in the framework of the de Broglie–Bohm interpretation and investigate the quantum cosmological effects throughout the evolution of the universe. In a particular solution, the tendency for a scalar field to roll down the potential is balanced by the quantum force, and a Minkowski spacetime is obtained.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140348955","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-04-04DOI: 10.1007/s10714-024-03231-x
Samstuti Chanda, Ranjan Sharma
We study the higher dimensional scenario of an anisotropic compact star using the Buchdahl–Vaidya–Tikekar metric ansatz. In our formalism, the anisotropy is assumed in such a way that, in the absence of it, the solution reduces to Schwarzschild’s interior solution in (D ge 4) dimensions. The model is so developed that it correlates anisotropy to the curvature parameter K which characterizes a departure from spherical geometry of the (t=) constant hypersurface of the associated spacetime when embedded in a 4 dimensional Euclidean space. Due to the particular choice of anisotropy, the pressure balancing equation for hydrostatic equilibrium continues to have the same form in higher dimensions. Consequently, our approach permits extending a four-dimensional solution to a higher dimensional spacetime without deforming the sphericity of the configuration. Making use of the model, we propose a higher dimensional anisotropic analogue of the Buchdahl bound on compactness. We show that additional dimension as well as anisotropy reduce the compactification limit. Our technique helps to regain the original Buchdahl limit in (D=4) dimensions and also, in the absence of anisotropy, the compactification limit in higher dimensions obtained earlier by Leon and Cruz (Gen Relativ Gravit 32:1207–1216, 2000. https://doi.org/10.1023/A:1001982402392). It turns out that the maximum achievable dimension remains model dependent through the causality condition and the compactification limit. We scrutinize the model under all the requisite physical conditions for a relativistic anisotropic fluid sphere which might serve as the internal structure of a compact star in higher dimensions. We analyze the consequences of the departure from homogeneous spherical distribution and dimensionality on the physical behaviour of the star. The EOS becomes stiffer in higher dimensions and comparatively lower anisotropic stress. Our calculation shows that the central density reduces as we move towards higher dimensions and inclusion of anisotropy increases the rate of fall of the density profile. We also note that the two pressures get reduced considerably in higher dimensions. We show that, for a given curvature parameter specifying the sphericity, an extra dimension is analogous to moving towards a homogeneous distribution of an anisotropic star.
我们利用布赫达赫-瓦伊迪亚-蒂凯卡公设解析法研究了各向异性紧凑恒星的高维情况。在我们的形式主义中,各向异性是以这样一种方式假定的:如果没有各向异性,那么解就会还原为施瓦兹柴尔德的内部解(Schwarzschild's interior solution in (Dge 4) dimensions)。这个模型是这样建立的:它把各向异性与曲率参数K联系起来,而曲率参数K是相关时空的(t=)恒定超表面嵌入4维欧几里得空间时偏离球形几何的特征。由于各向异性的特殊选择,流体静力学平衡的压力平衡方程在更高维度中仍然具有相同的形式。因此,我们的方法允许将四维解法扩展到更高维度的时空,而不会改变构型的球形性。利用该模型,我们提出了关于紧凑性的布赫达尔约束的高维各向异性类似物。我们证明,额外维度和各向异性会降低紧凑性极限。我们的技术有助于在(D=4)维度上重新获得原始的布赫达尔极限,而且,在没有各向异性的情况下,也有助于获得莱昂和克鲁兹(Gen Relativ Gravit 32:1207-1216, 2000. https://doi.org/10.1023/A:1001982402392)早先在更高维度上获得的紧凑性极限。事实证明,通过因果关系条件和压缩极限,可达到的最大维度仍然取决于模型。我们在相对论各向异性流体球体的所有必要物理条件下仔细研究了这个模型,该流体球体可能是高维度紧凑恒星的内部结构。我们分析了偏离均匀球形分布和维度对恒星物理行为的影响。各向异性应力相对较低时,各向异性应力在更高维度下会变得更加坚硬。我们的计算表明,随着维数的增加,中心密度会降低,而各向异性会增加密度曲线的下降速度。我们还注意到,在更高的维度上,两个压力会大大减小。我们表明,对于指定球度的给定曲率参数,额外维度类似于各向异性恒星的均匀分布。
{"title":"Compactness bound of Buchdahl–Vaidya–Tikekar anisotropic star in (Dge 4) dimensional spacetime","authors":"Samstuti Chanda, Ranjan Sharma","doi":"10.1007/s10714-024-03231-x","DOIUrl":"10.1007/s10714-024-03231-x","url":null,"abstract":"<div><p>We study the higher dimensional scenario of an anisotropic compact star using the Buchdahl–Vaidya–Tikekar metric ansatz. In our formalism, the anisotropy is assumed in such a way that, in the absence of it, the solution reduces to Schwarzschild’s interior solution in <span>(D ge 4)</span> dimensions. The model is so developed that it correlates anisotropy to the curvature parameter <i>K</i> which characterizes a departure from spherical geometry of the <span>(t=)</span> constant hypersurface of the associated spacetime when embedded in a 4 dimensional Euclidean space. Due to the particular choice of anisotropy, the pressure balancing equation for hydrostatic equilibrium continues to have the same form in higher dimensions. Consequently, our approach permits extending a four-dimensional solution to a higher dimensional spacetime without deforming the sphericity of the configuration. Making use of the model, we propose a higher dimensional anisotropic analogue of the Buchdahl bound on compactness. We show that additional dimension as well as anisotropy reduce the compactification limit. Our technique helps to regain the original Buchdahl limit in <span>(D=4)</span> dimensions and also, in the absence of anisotropy, the compactification limit in higher dimensions obtained earlier by Leon and Cruz (Gen Relativ Gravit 32:1207–1216, 2000. https://doi.org/10.1023/A:1001982402392). It turns out that the maximum achievable dimension remains model dependent through the causality condition and the compactification limit. We scrutinize the model under all the requisite physical conditions for a relativistic anisotropic fluid sphere which might serve as the internal structure of a compact star in higher dimensions. We analyze the consequences of the departure from homogeneous spherical distribution and dimensionality on the physical behaviour of the star. The EOS becomes stiffer in higher dimensions and comparatively lower anisotropic stress. Our calculation shows that the central density reduces as we move towards higher dimensions and inclusion of anisotropy increases the rate of fall of the density profile. We also note that the two pressures get reduced considerably in higher dimensions. We show that, for a given curvature parameter specifying the sphericity, an extra dimension is analogous to moving towards a homogeneous distribution of an anisotropic star.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140348923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-03-29DOI: 10.1007/s10714-024-03226-8
Anastasia V. Lysenko, Oleksandr O. Sobol
We study the Schwinger pair creation of scalar charged particles by a homogeneous electric field in an expanding universe in the quantum kinetic approach. We introduce an adiabatic vacuum for the scalar field based on the Wentzel–Kramers–Brillouin solution to the mode equation in conformal time and apply the formalism of Bogolyubov coefficients to derive a system of quantum Vlasov equations for three real kinetic functions. Compared to the analogous system of equations previously reported in the literature, the new one has two advantages. First, its solutions exhibit a faster decrease at large momenta which makes it more suitable for numerical computations. Second, it predicts no particle creation in the case of conformally coupled massless scalar field in the vanishing electric field, i.e., it respects the conformal symmetry of the system. We identify the ultraviolet divergences in the electric current and energy–momentum tensor of produced particles and introduce the corresponding counterterms in order to cancel them.
{"title":"Quantum kinetic approach to the Schwinger production of scalar particles in an expanding universe","authors":"Anastasia V. Lysenko, Oleksandr O. Sobol","doi":"10.1007/s10714-024-03226-8","DOIUrl":"10.1007/s10714-024-03226-8","url":null,"abstract":"<div><p>We study the Schwinger pair creation of scalar charged particles by a homogeneous electric field in an expanding universe in the quantum kinetic approach. We introduce an adiabatic vacuum for the scalar field based on the Wentzel–Kramers–Brillouin solution to the mode equation in conformal time and apply the formalism of Bogolyubov coefficients to derive a system of quantum Vlasov equations for three real kinetic functions. Compared to the analogous system of equations previously reported in the literature, the new one has two advantages. First, its solutions exhibit a faster decrease at large momenta which makes it more suitable for numerical computations. Second, it predicts no particle creation in the case of conformally coupled massless scalar field in the vanishing electric field, i.e., it respects the conformal symmetry of the system. We identify the ultraviolet divergences in the electric current and energy–momentum tensor of produced particles and introduce the corresponding counterterms in order to cancel them.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140321891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-03-28DOI: 10.1007/s10714-024-03224-w
Thomas Morley, Sivakumar Namasivayam, Elizabeth Winstanley
We study the renormalized stress-energy tensor (RSET) for a massless, conformally coupled scalar field on global anti-de Sitter space-time in four dimensions. Robin (mixed) boundary conditions are applied to the scalar field. We compute both the vacuum and thermal expectation values of the RSET. The vacuum RSET is a multiple of the space-time metric when either Dirichlet or Neumann boundary conditions are applied. Imposing Robin boundary conditions breaks the maximal symmetry of the vacuum state and results in an RSET whose components with mixed indices have their maximum (or maximum magnitude) at the space-time origin. The value of this maximum depends on the boundary conditions. We find similar behaviour for thermal states. As the temperature decreases, thermal expectation values of the RSET approach those for vacuum states and their values depend strongly on the boundary conditions. As the temperature increases, the values of the RSET components tend to profiles which are the same for all boundary conditions. We also find, for both vacuum and thermal states, that the RSET on the space-time boundary is independent of the boundary conditions and determined entirely by the trace anomaly.
{"title":"Renormalized stress-energy tensor on global anti-de Sitter space-time with Robin boundary conditions","authors":"Thomas Morley, Sivakumar Namasivayam, Elizabeth Winstanley","doi":"10.1007/s10714-024-03224-w","DOIUrl":"10.1007/s10714-024-03224-w","url":null,"abstract":"<div><p>We study the renormalized stress-energy tensor (RSET) for a massless, conformally coupled scalar field on global anti-de Sitter space-time in four dimensions. Robin (mixed) boundary conditions are applied to the scalar field. We compute both the vacuum and thermal expectation values of the RSET. The vacuum RSET is a multiple of the space-time metric when either Dirichlet or Neumann boundary conditions are applied. Imposing Robin boundary conditions breaks the maximal symmetry of the vacuum state and results in an RSET whose components with mixed indices have their maximum (or maximum magnitude) at the space-time origin. The value of this maximum depends on the boundary conditions. We find similar behaviour for thermal states. As the temperature decreases, thermal expectation values of the RSET approach those for vacuum states and their values depend strongly on the boundary conditions. As the temperature increases, the values of the RSET components tend to profiles which are the same for all boundary conditions. We also find, for both vacuum and thermal states, that the RSET on the space-time boundary is independent of the boundary conditions and determined entirely by the trace anomaly.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10714-024-03224-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140321847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 : 2024-03-19DOI: 10.1007/s10714-024-03223-x
Jianbo Lu, Mou Xu, Jing Guo, Ruonan Li
Wormholes are considered to be hypothetical tunnels connecting two distant regions of the universe or two different universes. In general relativity (GR), the formation of traversable WH requires the consideration of exotic matter that violates energy conditions (ECs). If the wormhole geometry can be described in modified gravitational theories without introducing exotic matter, it will be significant for studying these theories. In the paper, we analyze some physical properties of static traversable WH within the framework of f(R, T) modified gravitational theory. Firstly, we explore the validity of the null, weak, dominant and strong energy conditions for wormhole matter for the considered (f(R,T)=R+alpha R^2+lambda T) model. Research shows that it is possible to obtain traversable WH geometry without bring in exotic matter that violates the null energy condition (NEC) in the f(R, T) theory. The violation of the dominant energy condition (DEC) in this model may be related to quantum fluctuations or indicates the existence of special matter that violates this EC within the wormhole. Moreover, it is found that in the (f(R,T)=R+alpha R^2+lambda T) model, relative to the GR, the introduction of the geometric term (alpha R^2) has no remarkable impact on the wormhole matter components and their properties, while the appearance of the matter-geometry coupling term (lambda T) can resolve the question that WH matter violates the null, weak and strong energy condition in GR. Additionally, we investigate dependency of the valid NEC on model parameters and quantify the matter components within the wormhole using the “volume integral quantifier”. Lastly, based on the modified Tolman–Oppenheimer–Volkov equation, we find that the traversable WH in this theory is stable. On the other hand, we use the classical reconstruction technique to derive wormhole solution in f(R, T) theory and discuss the corresponding ECs of matter. It is found that all four ECs (NEC, WEC, SEC and DEC) of matter in the traversable wormholes are valid in this reconstructed f(R, T) model, i.e we provide a wormhole solution without introducing the exotic matter and special matter in f(R, T) theory.
{"title":"Investigating the physical properties of traversable wormholes in the modified f(R, T) gravity","authors":"Jianbo Lu, Mou Xu, Jing Guo, Ruonan Li","doi":"10.1007/s10714-024-03223-x","DOIUrl":"10.1007/s10714-024-03223-x","url":null,"abstract":"<div><p>Wormholes are considered to be hypothetical tunnels connecting two distant regions of the universe or two different universes. In general relativity (GR), the formation of traversable WH requires the consideration of exotic matter that violates energy conditions (ECs). If the wormhole geometry can be described in modified gravitational theories without introducing exotic matter, it will be significant for studying these theories. In the paper, we analyze some physical properties of static traversable WH within the framework of <i>f</i>(<i>R</i>, <i>T</i>) modified gravitational theory. Firstly, we explore the validity of the null, weak, dominant and strong energy conditions for wormhole matter for the considered <span>(f(R,T)=R+alpha R^2+lambda T)</span> model. Research shows that it is possible to obtain traversable WH geometry without bring in exotic matter that violates the null energy condition (NEC) in the <i>f</i>(<i>R</i>, <i>T</i>) theory. The violation of the dominant energy condition (DEC) in this model may be related to quantum fluctuations or indicates the existence of special matter that violates this EC within the wormhole. Moreover, it is found that in the <span>(f(R,T)=R+alpha R^2+lambda T)</span> model, relative to the GR, the introduction of the geometric term <span>(alpha R^2)</span> has no remarkable impact on the wormhole matter components and their properties, while the appearance of the matter-geometry coupling term <span>(lambda T)</span> can resolve the question that WH matter violates the null, weak and strong energy condition in GR. Additionally, we investigate dependency of the valid NEC on model parameters and quantify the matter components within the wormhole using the “volume integral quantifier”. Lastly, based on the modified Tolman–Oppenheimer–Volkov equation, we find that the traversable WH in this theory is stable. On the other hand, we use the classical reconstruction technique to derive wormhole solution in <i>f</i>(<i>R</i>, <i>T</i>) theory and discuss the corresponding ECs of matter. It is found that all four ECs (NEC, WEC, SEC and DEC) of matter in the traversable wormholes are valid in this reconstructed <i>f</i>(<i>R</i>, <i>T</i>) model, i.e we provide a wormhole solution without introducing the exotic matter and special matter in <i>f</i>(<i>R</i>, <i>T</i>) theory.</p></div>","PeriodicalId":578,"journal":{"name":"General Relativity and Gravitation","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140161562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}