Pub Date : 2024-07-24DOI: 10.1088/1361-6382/ad672c
Stefano Colace, Shima Samandari, M. Granata, Alex Amato, M. Caminale, Christophe Michel, G. Gemme, Laurent Pinard, Maurizio Canepa, M. Magnozzi
Thermal annealing plays a key role in optimizing the properties of amorphous optical coatings. In the field of gravitational wave detection (GWD), however, the effects of annealing protocols on the interferometry mirror coatings have been explored primarily by ex post analysis. As a result, the dynamics of the coatings properties during annealing is still poorly known, potentially leading to suboptimal performance. Here, using real-time, in situ spectroscopic ellipsometry (SE) we have tracked the refractive index and thickness of a titania-tantala coating during controlled annealing. We have tested the material and the annealing protocol used in current GWD mirrors. The annealing cycle consisted of a heating ramp from room temperature to 500 °C, followed by a 10-hour plateau at the same temperature and the final cooling ramp. SE measurements have been run continuously during the entire cycle. Significant variations in the thickness and refractive index, which accompany the coating structural relaxation, have been recorded during the heating ramp. These variations start around 200 °C, slightly above the deposition temperature, and show an increased rate in the range 250-350 °C. A smaller, continuous evolution has been observed during the 10-hour high-temperature plateau. The results offer suggestions to modify the current annealing protocol for titania-tantala coatings, for example by increasing the time duration of the high-temperature plateau. They also suggest an increase in the substrate temperature at deposition. The approach presented here paves the way for systematic, real-time investigations to clarify how the annealing parameters shape the properties of optical coatings, and can be leveraged to define and optimize the annealing protocol of new candidate materials for GWD mirrors.
热退火在优化非晶态光学镀膜性能方面发挥着关键作用。然而，在引力波探测（GWD）领域，退火协议对干涉镜涂层的影响主要是通过事后分析来探索的。因此，人们对退火过程中涂层性能的动态变化仍然知之甚少，这有可能导致性能不理想。在这里，我们使用实时原位光谱椭偏仪（SE）跟踪了受控退火过程中二氧化钛-钽涂层的折射率和厚度。我们测试了当前 GWD 反射镜使用的材料和退火协议。退火周期包括从室温加热到 500 °C，然后在相同温度下保持 10 小时，最后冷却。SE 测量在整个周期内连续进行。伴随着涂层结构的松弛，在加热斜坡期间记录到厚度和折射率的显著变化。这些变化从 200 °C 左右开始，略高于沉积温度，并在 250-350 °C 范围内呈现上升趋势。在 10 小时的高温高原期间，观察到了较小的连续变化。这些结果为修改当前的二氧化钛-钽涂层退火方案提供了建议，例如延长高温稳定阶段的时间。他们还建议提高沉积时的基底温度。本文介绍的方法为进行系统、实时的研究铺平了道路，以阐明退火参数如何影响光学镀膜的性能，并可用于确定和优化 GWD 镜新候选材料的退火方案。
{"title":"Monitoring the evolution of optical coatings during thermal annealing with real-time, in situ spectroscopic ellipsometry","authors":"Stefano Colace, Shima Samandari, M. Granata, Alex Amato, M. Caminale, Christophe Michel, G. Gemme, Laurent Pinard, Maurizio Canepa, M. Magnozzi","doi":"10.1088/1361-6382/ad672c","DOIUrl":"https://doi.org/10.1088/1361-6382/ad672c","url":null,"abstract":"\u0000 Thermal annealing plays a key role in optimizing the properties of amorphous optical coatings. In the field of gravitational wave detection (GWD), however, the effects of annealing protocols on the interferometry mirror coatings have been explored primarily by ex post analysis. As a result, the dynamics of the coatings properties during annealing is still poorly known, potentially leading to suboptimal performance. Here, using real-time, in situ spectroscopic ellipsometry (SE) we have tracked the refractive index and thickness of a titania-tantala coating during controlled annealing. We have tested the material and the annealing protocol used in current GWD mirrors. The annealing cycle consisted of a heating ramp from room temperature to 500 °C, followed by a 10-hour plateau at the same temperature and the final cooling ramp. SE measurements have been run continuously during the entire cycle. Significant variations in the thickness and refractive index, which accompany the coating structural relaxation, have been recorded during the heating ramp. These variations start around 200 °C, slightly above the deposition temperature, and show an increased rate in the range 250-350 °C. A smaller, continuous evolution has been observed during the 10-hour high-temperature plateau. The results offer suggestions to modify the current annealing protocol for titania-tantala coatings, for example by increasing the time duration of the high-temperature plateau. They also suggest an increase in the substrate temperature at deposition. The approach presented here paves the way for systematic, real-time investigations to clarify how the annealing parameters shape the properties of optical coatings, and can be leveraged to define and optimize the annealing protocol of new candidate materials for GWD mirrors.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-23DOI: 10.1088/1361-6382/ad66a8
Francesco Benetti, A. Lapi, G. Gandolfi, Stefano Liberati
In a series of recent papers we put forward a “fractional gravity” framework striking an intermediate course between a modified gravity theory and an exotic dark matter (DM) scenario, which envisages the DM component in virialized halos to feel a non-local interaction mediated by gravity. The remarkable success of this model in reproducing several aspects of DM phenomenology motivates us to look for a general relativistic extension. Specifically, we propose a theory, dubbed Relativistic Scalar Fractional Gravity or RSFG, in which the trace of the DM stressenergy tensor couples to the scalar curvature via a non-local operator constructed with a fractional power of the d’Alembertian. We derive the field equations starting from an action principle, and then we investigate their weak field limit, demonstrating that in the Newtonian approximation the fractional gravity setup of our previous works is recovered. We compute the first-order post-Newtonian parameter γ and its relation with weak lensing, showing that although in RSFG the former deviates from its GR values of unity, the latter is unaffected. We also perform a standard scalar-vectortensor-decomposition of RSFG in the weak field limit, to highlight that gravitational waves propagate at the speed of light, though also an additional scalar mode becomes dynamical. Finally, we derive the modified conservation laws of the DM stress energy tensor in RSFG, showing that a new non-local force emerges, and hence that the DM fluid deviates from the geodesic solutions of the field equations.
{"title":"A relativistic scalar model for fractional interaction between dark matter and gravity","authors":"Francesco Benetti, A. Lapi, G. Gandolfi, Stefano Liberati","doi":"10.1088/1361-6382/ad66a8","DOIUrl":"https://doi.org/10.1088/1361-6382/ad66a8","url":null,"abstract":"\u0000 In a series of recent papers we put forward a “fractional gravity” framework striking an intermediate course between a modified gravity theory and an exotic dark matter (DM) scenario, which envisages the DM component in virialized halos to feel a non-local interaction mediated by gravity. The remarkable success of this model in reproducing several aspects of DM phenomenology motivates us to look for a general relativistic extension. Specifically, we propose a theory, dubbed Relativistic Scalar Fractional Gravity or RSFG, in which the trace of the DM stressenergy tensor couples to the scalar curvature via a non-local operator constructed with a fractional power of the d’Alembertian. We derive the field equations starting from an action principle, and then we investigate their weak field limit, demonstrating that in the Newtonian approximation the fractional gravity setup of our previous works is recovered. We compute the first-order post-Newtonian parameter γ and its relation with weak lensing, showing that although in RSFG the former deviates from its GR values of unity, the latter is unaffected. We also perform a standard scalar-vectortensor-decomposition of RSFG in the weak field limit, to highlight that gravitational waves propagate at the speed of light, though also an additional scalar mode becomes dynamical. Finally, we derive the modified conservation laws of the DM stress energy tensor in RSFG, showing that a new non-local force emerges, and hence that the DM fluid deviates from the geodesic solutions of the field equations.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141812844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-15DOI: 10.1088/1361-6382/ad6389
Z. Yousaf, K. Bamba, Bander Almutairi, S. Khan, M. Z. Bhatti
We investigate spherically symmetric classes of anisotropic solutions within the realm of a schematic gravitational decoupling scheme, primarily decoupling through minimal geometric deformation, applied to non-rotating, ultra-compact, self-gravitational fluid distributions. In this respect, we employ the minimal complexity factor scheme to generate physically realistic models for anisotropic matter distributions, using a well-behaved model. The zero-complexity factor condition enables us to determine the deformation function for solving the decoupled system. We explore all the structure-defining scalar variables, such as density inhomogeneity, strong energy condition, density homogeneity, and the complexity factor (an alloy of density inhomogeneity and pressure anisotropy) for the decoupling constant ranging between $0$ and $1$. We observe that the anisotropy vanishes when the coupling constant is set to unity. This finding holds significance as it implies that, in the context of a zero-complexity factor approach, an anisotropic matter distribution becomes perfect without requiring any isotropy requirements. This work effectively explored the impact of complexity on the composition of self-gravitational stellar distributions. This effective approach enables the development of new, physically realistic isotropic stellar models for anisotropic matter distributions. Additionally, our findings indicate that the complexity factor in static, spherically symmetric self-gravitational objects can significantly affect the nature of the matter distribution within these systems. It is concluded that the minimally deformed Durgapal-IV model features an increasing pressure profile, and the local anisotropy of pressure vanishes throughout the model under complexity-free conditions.
{"title":"Role of complexity on the minimal deformation of black holes","authors":"Z. Yousaf, K. Bamba, Bander Almutairi, S. Khan, M. Z. Bhatti","doi":"10.1088/1361-6382/ad6389","DOIUrl":"https://doi.org/10.1088/1361-6382/ad6389","url":null,"abstract":"\u0000 We investigate spherically symmetric classes of anisotropic solutions within the realm of a schematic gravitational decoupling scheme, primarily decoupling through minimal geometric deformation, applied to non-rotating, ultra-compact, self-gravitational fluid distributions. In this respect, we employ the minimal complexity factor scheme to generate physically realistic models for anisotropic matter distributions, using a well-behaved model. The zero-complexity factor condition enables us to determine the deformation function for solving the decoupled system. We explore all the structure-defining scalar variables, such as density inhomogeneity, strong energy condition, density homogeneity, and the complexity factor (an alloy of density inhomogeneity and pressure anisotropy) for the decoupling constant ranging between $0$ and $1$. We observe that the anisotropy vanishes when the coupling constant is set to unity. This finding holds significance as it implies that, in the context of a zero-complexity factor approach, an anisotropic matter distribution becomes perfect without requiring any isotropy requirements. This work effectively explored the impact of complexity on the composition of self-gravitational stellar distributions. This effective approach enables the development of new, physically realistic isotropic stellar models for anisotropic matter distributions. Additionally, our findings indicate that the complexity factor in static, spherically symmetric self-gravitational objects can significantly affect the nature of the matter distribution within these systems. It is concluded that the minimally deformed Durgapal-IV model features an increasing pressure profile, and the local anisotropy of pressure vanishes throughout the model under complexity-free conditions.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141648627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-15DOI: 10.1088/1361-6382/ad638a
Harkirat Singh Sahota
Sharply peaked quantum states are conjectured to be conducive to the notion of a quantum-corrected spacetime. We investigate this conjecture for a flat-FLRW model with perfect fluid, where a generalized ordering scheme is considered for the gravitational Hamiltonian. We study the implications of different ordering choices on the dynamics of the quantum universe. We demonstrate that the imprints of the operator ordering ambiguity are minimal, and quantum fluctuations are small in the case of sharply peaked states, leading to a consistent notion of a quantum-corrected spacetime defined via the expectation value of the scale factor. Surprisingly, the ordering imprints survive far away from the singularity through the quantum fluctuations in the quantum-corrected spacetime for broadly peaked states.
{"title":"Imprints of the operator ordering ambiguity on the dynamics of perfect fluid dominated quantum universe","authors":"Harkirat Singh Sahota","doi":"10.1088/1361-6382/ad638a","DOIUrl":"https://doi.org/10.1088/1361-6382/ad638a","url":null,"abstract":"\u0000 Sharply peaked quantum states are conjectured to be conducive to the notion of a quantum-corrected spacetime. We investigate this conjecture for a flat-FLRW model with perfect fluid, where a generalized ordering scheme is considered for the gravitational Hamiltonian. We study the implications of different ordering choices on the dynamics of the quantum universe. We demonstrate that the imprints of the operator ordering ambiguity are minimal, and quantum fluctuations are small in the case of sharply peaked states, leading to a consistent notion of a quantum-corrected spacetime defined via the expectation value of the scale factor. Surprisingly, the ordering imprints survive far away from the singularity through the quantum fluctuations in the quantum-corrected spacetime for broadly peaked states.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141645563","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-10DOI: 10.1088/1361-6382/ad61b5
Federico Manzoni
Gravitational solitons (gravisolitons) are particular exact solutions of Einstein field equation in vacuum build on a given background solution. Their interpretation is not yet fully clear but they contain many of the physically relevant solutions low N-solitons solutions. However, a systematic study and characterization of gravisolitons solution for every N is lacking and their relevance in a theory of quantum gravity is not fully understood. This work aims to investigate and characterize some properties of N-axialsoliton solutions such as their asymptotically behaviour and asymptotic symmetries given minimal assumptions on the background metric. We develop an explicit systematic asymptotically expansion for the N-axialsoliton solution and we compute the leading order of the asymptotic killing vectors. Moreover, in the perspective to better understand the role of gravisolitons in quantum gravity we make a link, and a one of the first explicit test, to the corner symmetry proposal deriving which subalgebra of the universal corner symmetry algebra is generated by the asymptotic Killing vectors of N-axialsoliton solution. In the spirit of the corner proposal, the axialgravisoliton corner symmetry algebra (agcsa) can be useful for the quantization of the non-asymptotically flat sector of gravity while, in the spirit of IR triangle, new soft theorems and memory effects could emerge.
引力孤子（gravvisolitons）是建立在给定背景解基础上的爱因斯坦真空场方程的特殊精确解。对它们的解释还不完全清楚，但它们包含了许多与物理相关的低 N 孤子解。然而，目前还缺乏对每一个 N 的引力索解的系统研究和特征描述，对它们在量子引力理论中的相关性也不完全了解。这项工作旨在研究和描述 N 轴玻色子解的一些特性，如它们的渐近行为和渐近对称性，前提是对背景度量的最小假设。我们为 N-axialsoliton 解建立了明确的系统渐近展开，并计算了渐近杀伤向量的前阶。此外，为了更好地理解引力子在量子引力中的作用，我们首次明确检验了角对称性提议，推导出 N-axialsoliton 解的渐近基林向量生成了通用角对称性代数的哪个子代数。本着拐角提议的精神，轴向索里顿拐角对称代数（agcsa）可用于引力非渐近平坦扇形的量子化，而本着红外三角的精神，新的软定理和记忆效应可能会出现。
{"title":"Axialgravisolitons at infinite corner","authors":"Federico Manzoni","doi":"10.1088/1361-6382/ad61b5","DOIUrl":"https://doi.org/10.1088/1361-6382/ad61b5","url":null,"abstract":"\u0000 Gravitational solitons (gravisolitons) are particular exact solutions of Einstein field equation in vacuum build on a given background solution. Their interpretation is not yet fully clear but they contain many of the physically relevant solutions low N-solitons solutions. However, a systematic study and characterization of gravisolitons solution for every N is lacking and their relevance in a theory of quantum gravity is not fully understood. This work aims to investigate and characterize some properties of N-axialsoliton solutions such as their asymptotically behaviour and asymptotic symmetries given minimal assumptions on the background metric. We develop an explicit systematic asymptotically expansion for the N-axialsoliton solution and we compute the leading order of the asymptotic killing vectors. Moreover, in the perspective to better understand the role of gravisolitons in quantum gravity we make a link, and a one of the first explicit test, to the corner symmetry proposal deriving which subalgebra of the universal corner symmetry algebra is generated by the asymptotic Killing vectors of N-axialsoliton solution. In the spirit of the corner proposal, the axialgravisoliton corner symmetry algebra (agcsa) can be useful for the quantization of the non-asymptotically flat sector of gravity while, in the spirit of IR triangle, new soft theorems and memory effects could emerge.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141661259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-09DOI: 10.1088/1361-6382/ad6129
Zhong-Wu Xia, Hao Yang, Yan-Gang Miao
The rotating loop quantum gravity black hole is a newly proposed non-singular black hole, which eliminates spacetime singularities owing to the introduction of a regular parameter through loop quantum corrections. This regular parameter leads to many observable effects. In this paper, the dynamical behavior of a scalar field near a rotating loop quantum gravity black hole is investigated. Given a small initial perturbation by a massless scalar field, we obtain the waveform of the massless scalar field evolving over time. By analyzing the waveform, we find that the regular parameter only affects the decaying oscillation of waveform, which is mainly described by quasi-normal modes. Moreover, we calculate the quasi-normal modes of a massive scalar field by three numerical methods, which are the Prony, WKB, and shooting methods, respectively. Our results indicate that the regular parameter has a significant influence on quasi-normal modes, but the loop quantum black holes remain stable under scalar field perturbations. Finally, we study the amplification effect of rotating loop quantum gravity black holes on scalar fields, i.e., the superradiance effect. Our results indicate the existence of stronger superradiance around loop quantum gravity black holes than that around Kerr ones.
{"title":"Scalar fields around a rotating loop quantum gravity black hole: Waveform, quasi-normal modes and superradiance","authors":"Zhong-Wu Xia, Hao Yang, Yan-Gang Miao","doi":"10.1088/1361-6382/ad6129","DOIUrl":"https://doi.org/10.1088/1361-6382/ad6129","url":null,"abstract":"\u0000 The rotating loop quantum gravity black hole is a newly proposed non-singular black hole, which eliminates spacetime singularities owing to the introduction of a regular parameter through loop quantum corrections. This regular parameter leads to many observable effects. In this paper, the dynamical behavior of a scalar field near a rotating loop quantum gravity black hole is investigated. Given a small initial perturbation by a massless scalar field, we obtain the waveform of the massless scalar field evolving over time. By analyzing the waveform, we find that the regular parameter only affects the decaying oscillation of waveform, which is mainly described by quasi-normal modes. Moreover, we calculate the quasi-normal modes of a massive scalar field by three numerical methods, which are the Prony, WKB, and shooting methods, respectively. Our results indicate that the regular parameter has a significant influence on quasi-normal modes, but the loop quantum black holes remain stable under scalar field perturbations. Finally, we study the amplification effect of rotating loop quantum gravity black holes on scalar fields, i.e., the superradiance effect. Our results indicate the existence of stronger superradiance around loop quantum gravity black holes than that around Kerr ones.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141664182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-04DOI: 10.1088/1361-6382/ad5f71
Muxin Han, Chen-Hung Hsiao, Qiaoyin Pan
In this paper, we develop a quantum theory of homogeneously curved tetrahedron geometry, by applying the combinatorial quantization to the phase space of tetrahedron shapes defined in cite{Haggard:2015ima}. Our method is based on the relation between this phase space and the moduli space of SU(2) flat connections on a 4-punctured sphere. The quantization results in the physical Hilbert space as the solution of the quantum closure constraint, which quantizes the classical closure condition $M_4M_3M_2M_1=1$, $M_nuin SU(2)$, for the homogeneously curved tetrahedron. The quantum group $mathcal{U}_q(mathfrak{su}(2))$ emerges as the gauge symmetry of a quantum tetrahedron. The physical Hilbert space of the quantum tetrahedron coincides with the Hilbert space of 4-valent intertwiners of $mathcal{U}_q(mathfrak{su}(2))$. In addition, we define the area operators quantizing the face areas of the tetrahedron and compute the spectrum. The resulting spectrum is consistent with the usual Loop-Quantum-Gravity area spectrum in the large spin regime but is different for small spins. This work closely relates to 3+1 dimensional Loop Quantum Gravity in presence of cosmological constant and provides a justification for the emergence of quantum group in the theory.
{"title":"Quantum group intertwiner space from quantum curved tetrahedron","authors":"Muxin Han, Chen-Hung Hsiao, Qiaoyin Pan","doi":"10.1088/1361-6382/ad5f71","DOIUrl":"https://doi.org/10.1088/1361-6382/ad5f71","url":null,"abstract":"\u0000 In this paper, we develop a quantum theory of homogeneously curved tetrahedron geometry, by applying the combinatorial quantization to the phase space of tetrahedron shapes defined in cite{Haggard:2015ima}. Our method is based on the relation between this phase space and the moduli space of SU(2) flat connections on a 4-punctured sphere. The quantization results in the physical Hilbert space as the solution of the quantum closure constraint, which quantizes the classical closure condition $M_4M_3M_2M_1=1$, $M_nuin SU(2)$, for the homogeneously curved tetrahedron. The quantum group $mathcal{U}_q(mathfrak{su}(2))$ emerges as the gauge symmetry of a quantum tetrahedron. The physical Hilbert space of the quantum tetrahedron coincides with the Hilbert space of 4-valent intertwiners of $mathcal{U}_q(mathfrak{su}(2))$. In addition, we define the area operators quantizing the face areas of the tetrahedron and compute the spectrum. The resulting spectrum is consistent with the usual Loop-Quantum-Gravity area spectrum in the large spin regime but is different for small spins. This work closely relates to 3+1 dimensional Loop Quantum Gravity in presence of cosmological constant and provides a justification for the emergence of quantum group in the theory.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141680101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-02DOI: 10.1088/1361-6382/ad5e30
R. R. Cuzinatto, E. de Morais, Bruto Max Pimentel
In this paper we recall the static and spherically symmetric solution derived within LyST gravity. LyST stands for “Lyra Scalar-Tensor” and is a scalar-tensor proposal for the gravitational interaction modifying general relativity by adopting Lyra manifold as the spacetime substrate. Lyra manifold is characterized both by the metric tensor gµν(x) and the scale φ(x); the latter being an integral part of the definition of reference frame. In a previous work, we have launched the formal geometrical basis of LyST, we have proposed an associated action integral for the gravitational interaction, we have derived the field equations generalizing Einstein field equation, and we have solved these equation to obtain the generalized version of Schwarzschild line element in Lyra manifold. This lead us to Lyra-Schwarzschild spacetime, which is further explored in the present paper. Herein, the trajectories of test particles is thoroughly studied. This is done for both massive particles and massless particles. The geodesic equations are built and solved. The effective potential associated to the motion of these particles around the source is determined and characterized. The possible trajectories include gravitational capture, scattering, bounded orbits, stable and unstable circular orbits, near-horizon motion. The innermost circular orbit allowed for massive particles is determined and compared to the one predicted by GR. The last photon orbit is also calculated for Lyra-Schwarzschild metric. The equation for the periastron shift in the context of Lyra-Schwarzschild solution is constructed; its application to observational data could be useful to constrain the parameters typical of LyST, telling it apart from GR.
{"title":"Particle and light motion in Lyra-Schwarzschild spacetime","authors":"R. R. Cuzinatto, E. de Morais, Bruto Max Pimentel","doi":"10.1088/1361-6382/ad5e30","DOIUrl":"https://doi.org/10.1088/1361-6382/ad5e30","url":null,"abstract":"\u0000 In this paper we recall the static and spherically symmetric solution derived within LyST gravity. LyST stands for “Lyra Scalar-Tensor” and is a scalar-tensor proposal for the gravitational interaction modifying general relativity by adopting Lyra manifold as the spacetime substrate. Lyra manifold is characterized both by the metric tensor gµν(x) and the scale φ(x); the latter being an integral part of the definition of reference frame. In a previous work, we have launched the formal geometrical basis of LyST, we have proposed an associated action integral for the gravitational interaction, we have derived the field equations generalizing Einstein field equation, and we have solved these equation to obtain the generalized version of Schwarzschild line element in Lyra manifold. This lead us to Lyra-Schwarzschild spacetime, which is further explored in the present paper. Herein, the trajectories of test particles is thoroughly studied. This is done for both massive particles and massless particles. The geodesic equations are built and solved. The effective potential associated to the motion of these particles around the source is determined and characterized. The possible trajectories include gravitational capture, scattering, bounded orbits, stable and unstable circular orbits, near-horizon motion. The innermost circular orbit allowed for massive particles is determined and compared to the one predicted by GR. The last photon orbit is also calculated for Lyra-Schwarzschild metric. The equation for the periastron shift in the context of Lyra-Schwarzschild solution is constructed; its application to observational data could be useful to constrain the parameters typical of LyST, telling it apart from GR.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141686997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-11DOI: 10.1088/1361-6382/ad56f0
A. Ditta, G. Mustafa, S. Maurya, D. Sofuoğlu, Asif Mahmood
This manuscript is the first investigation of dark energy celestial phenomena in the modified gravity theory by examining dark energy compact stars within the context of modified $f(T,mathcal{T})$ gravity. In order to compare the outcomes of the $f(T,mathcal{T})$ and $f(T)$ gravity theories, the model $f(T,mathcal{T})=alpha T(r)+beta mathcal{T}(r)+phi$ is selected. This model is then simplified to $f(T)$ gravity by setting $beta=0$. The $f(T)$ gravity is torsion-based gravity, while in $f(T,mathcal{T}$) gravity trace of energy-momentum tensor is coupled with torsion. Moreover, we note that we have more dense object formation in $f(T,mathcal{T})$ gravity as compared to $f(T$)-gravity. The spherically symmetric space-time inside the internal geometry is analyzed using a conformally flat condition, while the Schwarzschild geometry represents the outer space-time. Numerous characteristics of dark energy stars are examined, including equation of state components, energy conditions, and dark energy pressure components. Empirical evidence for the existence of dark energy in stellar configurations is presented by the results for pressure components in dark energy, which show a significant negative tendency in these stellar parameters. A complete analysis is performed by thoroughly investigating energy conditions, pressure profiles, sound speeds, gradients, adiabatic index, TOV equation, mass function, compactness, and redshift function. The mass-radius relation is also discussed via $M-R$ curves. This confirms that the studied star configuration is realistic and acceptable.
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Pub Date : 2024-06-11DOI: 10.1088/1361-6382/ad56ef
Jean-Baptiste Roux
Using the ADM formalism, we demonstrate that the Hamiltonian formulation of Quantum Gravity is exactly in the form of a worldline (WL) formalism in the superspace. We then show that the Keldysh partition function reduces to the partition function of Euclidean 3D gravity. After discussing the meaning of the time parameter, we show that in the gauge fields formalism, our Keldysh partition function reduces to a generating functional of a 2D Conformal Field Theory (CFT). This functional exhibits a minimal time-lapse proportional to the square root of the cosmological constant. From the viewpoint of the Chern-Simons/Liouville correspondence, we calculate the exchange of virtual gravitons between two massive probes from the cosmological boundary.
{"title":"Superspace worldline formalism approach to Quantum Gravity: dimensional reduction and Holography","authors":"Jean-Baptiste Roux","doi":"10.1088/1361-6382/ad56ef","DOIUrl":"https://doi.org/10.1088/1361-6382/ad56ef","url":null,"abstract":"\u0000 Using the ADM formalism, we demonstrate that the Hamiltonian formulation of Quantum Gravity is exactly in the form of a worldline (WL) formalism in the superspace. We then show that the Keldysh partition function reduces to the partition function of Euclidean 3D gravity. After discussing the meaning of the time parameter, we show that in the gauge fields formalism, our Keldysh partition function reduces to a generating functional of a 2D Conformal Field Theory (CFT). This functional exhibits a minimal time-lapse proportional to the square root of the cosmological constant. From the viewpoint of the Chern-Simons/Liouville correspondence, we calculate the exchange of virtual gravitons between two massive probes from the cosmological boundary.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141355968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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