Pub Date : 2023-05-16DOI: 10.1142/s0218271823500578
S. Qazi, F. Hussain, M. Ramzan, S. Haq
{"title":"Conformal motions of anisotropic exact Bianchi type II models admitting energy conditions in f(T) gravity","authors":"S. Qazi, F. Hussain, M. Ramzan, S. Haq","doi":"10.1142/s0218271823500578","DOIUrl":"https://doi.org/10.1142/s0218271823500578","url":null,"abstract":"","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41611877","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 : 2023-05-15DOI: 10.1142/s0218271823420178
T. McMaken
Vacuum models of charged or spinning black holes possess two horizons, the inner of which has the oft-overlooked property that gravitational tidal forces initially spaghettifying a freely falling observer will eventually change signs and flatten the observer like a pancake. Inner horizons also induce a classical blueshift instability known as mass inflation, and a number of recent studies have found that inner horizons exhibit even stronger quantum singular behavior. In this essay we explore the quantum effect of Hawking radiation, which in the presence of compressive tidal forces seems to predict negative temperatures. By analyzing the interaction of quantum fields with black hole geometries, we can come to a closer semiclassical understanding of what really happens near a black hole's inner horizon.
{"title":"Pancakification and negative Hawking temperatures","authors":"T. McMaken","doi":"10.1142/s0218271823420178","DOIUrl":"https://doi.org/10.1142/s0218271823420178","url":null,"abstract":"Vacuum models of charged or spinning black holes possess two horizons, the inner of which has the oft-overlooked property that gravitational tidal forces initially spaghettifying a freely falling observer will eventually change signs and flatten the observer like a pancake. Inner horizons also induce a classical blueshift instability known as mass inflation, and a number of recent studies have found that inner horizons exhibit even stronger quantum singular behavior. In this essay we explore the quantum effect of Hawking radiation, which in the presence of compressive tidal forces seems to predict negative temperatures. By analyzing the interaction of quantum fields with black hole geometries, we can come to a closer semiclassical understanding of what really happens near a black hole's inner horizon.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43790984","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 : 2023-05-15DOI: 10.1142/s0218271823420051
J. Jaramillo, B. Krishnan, C. Sopuerta
The waveform of a binary black hole coalescence appears to be both simple and universal. In this essay we argue that the dynamics should admit a separation into 'fast and slow' degrees of freedom, such that the latter are described by an integrable system of equations, accounting for the simplicity and universality of the waveform. Given that Painlev'e transcendents are a smoking gun of integrable structures, we propose the Painlev'e-II transcendent as the key structural element threading a hierarchy of asymptotic models aiming at capturing different (effective) layers in the dynamics. Ward's conjecture relating integrable and (anti)self-dual solutions can provide the avenue to encode background binary black hole data in (non-local) twistor structures.
{"title":"Universality in Binary Black Hole Dynamics: An Integrability Conjecture","authors":"J. Jaramillo, B. Krishnan, C. Sopuerta","doi":"10.1142/s0218271823420051","DOIUrl":"https://doi.org/10.1142/s0218271823420051","url":null,"abstract":"The waveform of a binary black hole coalescence appears to be both simple and universal. In this essay we argue that the dynamics should admit a separation into 'fast and slow' degrees of freedom, such that the latter are described by an integrable system of equations, accounting for the simplicity and universality of the waveform. Given that Painlev'e transcendents are a smoking gun of integrable structures, we propose the Painlev'e-II transcendent as the key structural element threading a hierarchy of asymptotic models aiming at capturing different (effective) layers in the dynamics. Ward's conjecture relating integrable and (anti)self-dual solutions can provide the avenue to encode background binary black hole data in (non-local) twistor structures.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42696753","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 : 2023-05-15DOI: 10.1142/s0218271823410043
S. Hod
In this essay, it is proved that there are black holes that are dangerously cold. In particular, by analyzing the emission spectra of highly charged black holes we reveal the fact that near-extremal black holes whose Bekenstein–Hawking temperatures lie in the regime [Formula: see text] may turn into horizonless naked singularities, thus violating the cosmic censorship principle, if they emit a photon with the characteristic thermal energy [Formula: see text] (here [Formula: see text] are, respectively, the proper mass and the electric charge of the electron, the lightest charged particle). We therefore raise here the conjecture that, in the yet unknown quantum theory of gravity, the temperatures of well-behaved black-hole spacetimes are fundamentally bounded from below by the relation [Formula: see text].
{"title":"Black holes that are too cold to respect cosmic censorship","authors":"S. Hod","doi":"10.1142/s0218271823410043","DOIUrl":"https://doi.org/10.1142/s0218271823410043","url":null,"abstract":"In this essay, it is proved that there are black holes that are dangerously cold. In particular, by analyzing the emission spectra of highly charged black holes we reveal the fact that near-extremal black holes whose Bekenstein–Hawking temperatures lie in the regime [Formula: see text] may turn into horizonless naked singularities, thus violating the cosmic censorship principle, if they emit a photon with the characteristic thermal energy [Formula: see text] (here [Formula: see text] are, respectively, the proper mass and the electric charge of the electron, the lightest charged particle). We therefore raise here the conjecture that, in the yet unknown quantum theory of gravity, the temperatures of well-behaved black-hole spacetimes are fundamentally bounded from below by the relation [Formula: see text].","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42606317","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 : 2023-05-14DOI: 10.1142/s0218271823420075
H. Nguyen
Circa 1962 Hans A. Buchdahl pioneered a program -- and made significant progress -- seeking vacuo configurations in pure $mathcal{R}^{2}$ gravity [H. A. Buchdahl, Nuovo Cimento 23, 141 (1962)]. Unfortunately, he deemed the final step in his calculations impassable and prematurely suspended his pursuit. Since then, his achievements on this front have faded into dormancy. Unbeknownst to Buchdahl himself, the $mathcal{R}^{2}$ vacua that he sought were within $textit{his}$ striking distance. In our recent three-paper body of work published in Phys. Rev. D, we broke this six-decades-old impasse and accomplished his goal: A novel class of metrics, describing non-Schwarzschild spacetimes in quadratic gravity and carrying a hallmark of higher-derivative characteristic. Intriguing properties of Buchdahl-inspired spacetimes and their associated Morris-Thorne-Buchdahl wormholes -- summarized herein -- embody a new branch of phenomenology that transcends the Einstein-Hilbert paradigm.
Circa 1962 Hans A.Buchdahl开创了一个在纯$mathcal｛R｝^｛2｝$引力中寻找真空构型的计划，并取得了重大进展[H.A.Buchdahl，Nuovo Cimento 23141（1962）]。不幸的是，他认为自己计算的最后一步是走不通的，并过早地中止了他的追求。从那时起，他在这方面的成就就沉寂了。Buchdahl自己并不知道，他所寻找的$mathcal｛R｝^｛2｝$真空在$textit｛他的｝$打击距离之内。在我们最近发表在Phys上的三篇论文中。D牧师，我们打破了60年来的僵局，实现了他的目标：一类新颖的度量，在二次引力中描述非史瓦西时空，并具有更高导数特征。布赫达尔启发的时空及其相关的Morris Thorne Buchdahl虫洞的有趣特性——在此总结——体现了超越爱因斯坦-希尔伯特范式的现象学的一个新分支。
{"title":"Buchdahl-inspired spacetimes and wormholes: Unearthing Hans Buchdahl's other 'hidden' treasure trove","authors":"H. Nguyen","doi":"10.1142/s0218271823420075","DOIUrl":"https://doi.org/10.1142/s0218271823420075","url":null,"abstract":"Circa 1962 Hans A. Buchdahl pioneered a program -- and made significant progress -- seeking vacuo configurations in pure $mathcal{R}^{2}$ gravity [H. A. Buchdahl, Nuovo Cimento 23, 141 (1962)]. Unfortunately, he deemed the final step in his calculations impassable and prematurely suspended his pursuit. Since then, his achievements on this front have faded into dormancy. Unbeknownst to Buchdahl himself, the $mathcal{R}^{2}$ vacua that he sought were within $textit{his}$ striking distance. In our recent three-paper body of work published in Phys. Rev. D, we broke this six-decades-old impasse and accomplished his goal: A novel class of metrics, describing non-Schwarzschild spacetimes in quadratic gravity and carrying a hallmark of higher-derivative characteristic. Intriguing properties of Buchdahl-inspired spacetimes and their associated Morris-Thorne-Buchdahl wormholes -- summarized herein -- embody a new branch of phenomenology that transcends the Einstein-Hilbert paradigm.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47257705","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 : 2023-05-13DOI: 10.1142/s0218271823420191
G. Heymans, N. Svaiter, G. Krein
Using results of statistical field theory for systems with an anisotropic disorder, we present an analog model for Euclidean wormholes and topological fluctuation effects in a Riemannian space $mathcal{M}^mathrm{d}$. The contribution of wormholes and topological fluctuations to the Euclidean gravitational functional integral is modeled by quenched randomness defined in the $mathbb{R}^{mathrm{d}}$ manifold. We obtain a disorder-averaged free energy by taking the average over all the realizations of the random fields. In the scenario of topology fluctuation, there appears a superposition of infinite branes that contribute to the physical quantities. All topology fluctuations can be understood as two distinct kinds of Euclidean wormholes: wormholes confined to one brane, and wormholes connecting different branes.
{"title":"Analog Model for Euclidean Wormholes Effects","authors":"G. Heymans, N. Svaiter, G. Krein","doi":"10.1142/s0218271823420191","DOIUrl":"https://doi.org/10.1142/s0218271823420191","url":null,"abstract":"Using results of statistical field theory for systems with an anisotropic disorder, we present an analog model for Euclidean wormholes and topological fluctuation effects in a Riemannian space $mathcal{M}^mathrm{d}$. The contribution of wormholes and topological fluctuations to the Euclidean gravitational functional integral is modeled by quenched randomness defined in the $mathbb{R}^{mathrm{d}}$ manifold. We obtain a disorder-averaged free energy by taking the average over all the realizations of the random fields. In the scenario of topology fluctuation, there appears a superposition of infinite branes that contribute to the physical quantities. All topology fluctuations can be understood as two distinct kinds of Euclidean wormholes: wormholes confined to one brane, and wormholes connecting different branes.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48401810","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 : 2023-05-13DOI: 10.1142/s0218271823420063
Julio Arrechea, Carlos Barcel'o
We show that the repulsive effects associated to the zero-point energies of quantum fields are capable of supporting ultracompact stars that overcome the compactness limits present in general relativity for any object in hydrostatic equilibrium. These objects are exact self-consistent solutions in semiclassical gravity that incorporate the backreaction of the renormalized stress-energy tensor (RSET) of quantum fields in vacuum. We arrive at stars of striking qualitative agreement through two independent modelings of the RSET, evidencing the generality and robustness of this result. The main physical properties of these novel black hole mimickers are reviewed.
{"title":"Stellar equilibrium on a physical vacuum soil","authors":"Julio Arrechea, Carlos Barcel'o","doi":"10.1142/s0218271823420063","DOIUrl":"https://doi.org/10.1142/s0218271823420063","url":null,"abstract":"We show that the repulsive effects associated to the zero-point energies of quantum fields are capable of supporting ultracompact stars that overcome the compactness limits present in general relativity for any object in hydrostatic equilibrium. These objects are exact self-consistent solutions in semiclassical gravity that incorporate the backreaction of the renormalized stress-energy tensor (RSET) of quantum fields in vacuum. We arrive at stars of striking qualitative agreement through two independent modelings of the RSET, evidencing the generality and robustness of this result. The main physical properties of these novel black hole mimickers are reviewed.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46579259","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 : 2023-05-12DOI: 10.1142/s0218271823420099
J. Tabatabaei, Abdolali Banihashemi, S. Baghram, B. Mashhoon
Nonlocal gravity (NLG), a classical extension of Einstein's theory of gravitation, has been studied mainly in linearized form. In particular, nonlinearities have thus far prevented the treatment of cosmological models in NLG. In this essay, we discuss the local limit of NLG and apply this limit to the expanding homogenous and isotropic universe. The theory only allows spatially flat cosmological models; furthermore, de Sitter spacetime is forbidden. The components of the model will have different dynamics with respect to cosmic time as compared to the standard $Lambda$CDM model; specifically, instead of the cosmological constant, the modified flat model of cosmology involves a dynamic dark energy component in order to account for the accelerated phase of the expansion of the universe.
{"title":"Dynamic Dark Energy from the Local Limit of Nonlocal Gravity","authors":"J. Tabatabaei, Abdolali Banihashemi, S. Baghram, B. Mashhoon","doi":"10.1142/s0218271823420099","DOIUrl":"https://doi.org/10.1142/s0218271823420099","url":null,"abstract":"Nonlocal gravity (NLG), a classical extension of Einstein's theory of gravitation, has been studied mainly in linearized form. In particular, nonlinearities have thus far prevented the treatment of cosmological models in NLG. In this essay, we discuss the local limit of NLG and apply this limit to the expanding homogenous and isotropic universe. The theory only allows spatially flat cosmological models; furthermore, de Sitter spacetime is forbidden. The components of the model will have different dynamics with respect to cosmic time as compared to the standard $Lambda$CDM model; specifically, instead of the cosmological constant, the modified flat model of cosmology involves a dynamic dark energy component in order to account for the accelerated phase of the expansion of the universe.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46961591","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 : 2023-05-11DOI: 10.1142/s0218271823410055
Neil Lu, S. Scott, K. Wette
Neutron stars are one of the most mysterious wonders in the Universe. Their extreme densities hint at new and exotic physics at work within. Gravitational waves could be the key to unlocking their secrets. In particular, a first detection of gravitational waves from rapidly-spinning, deformed neutron stars could yield new insights into the physics of matter at extreme densities and under strong gravity. Once a first detection is made, a critical challenge will be to robustly extract physically interesting information from the detected signals. In this essay, we describe initial research towards answering this challenge, and thereby unleashing the full power of gravitational waves as an engine for the discovery of new physics.
{"title":"What are neutron stars made of? Gravitational waves may reveal the answer","authors":"Neil Lu, S. Scott, K. Wette","doi":"10.1142/s0218271823410055","DOIUrl":"https://doi.org/10.1142/s0218271823410055","url":null,"abstract":"Neutron stars are one of the most mysterious wonders in the Universe. Their extreme densities hint at new and exotic physics at work within. Gravitational waves could be the key to unlocking their secrets. In particular, a first detection of gravitational waves from rapidly-spinning, deformed neutron stars could yield new insights into the physics of matter at extreme densities and under strong gravity. Once a first detection is made, a critical challenge will be to robustly extract physically interesting information from the detected signals. In this essay, we describe initial research towards answering this challenge, and thereby unleashing the full power of gravitational waves as an engine for the discovery of new physics.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48494943","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 : 2023-05-11DOI: 10.1142/s0218271823420117
Jens Boos
The entropy of a Schwarzschild black hole, as computed via the semiclassical Euclidean path integral in a stationary phase approximation, is determined not by the on-shell value of the action (which vanishes), but by the Gibbons--Hawking--York boundary term evaluated on a suitable hypersurface, which can be chosen arbitrarily far away from the horizon. For this reason, the black hole singularity seemingly has no influence on the Bekenstein--Hawking area law. In this Essay we estimate how a regular black hole core, deep inside a Euclidean black hole of mass $M$ and generated via a UV regulator length scale $ell>0$, affects the black hole entropy. The contributions are suppressed by factors of $ell/(2GM)$; demanding exact agreement with the area law as well as a self-consistent first law of black hole thermodynamics at all orders, however, demands that these contributions vanish identically via uniformly bounded curvature. This links the limiting curvature hypothesis to black hole thermodynamics.
施瓦西黑洞的熵，通过在定相近似下的半经典欧几里得路径积分计算，不是由作用的壳上值(它消失了)决定的，而是由吉本斯-霍金-约克边界项在一个合适的超表面上评估决定的，这个超表面可以任意选择远离视界。因此，黑洞奇点似乎对贝肯斯坦-霍金面积定律没有影响。在本文中，我们估计了在质量为$M$的欧几里得黑洞深处，通过紫外调节器长度尺度$ well > $产生的规则黑洞核心如何影响黑洞熵。贡献被$ well /(2GM)$的因素抑制;然而，要求在所有阶上与面积定律以及自洽的黑洞热力学第一定律完全一致，要求这些贡献通过均匀有界曲率完全消失。这将极限曲率假说与黑洞热力学联系起来。
{"title":"Black hole entropy contributions from Euclidean cores","authors":"Jens Boos","doi":"10.1142/s0218271823420117","DOIUrl":"https://doi.org/10.1142/s0218271823420117","url":null,"abstract":"The entropy of a Schwarzschild black hole, as computed via the semiclassical Euclidean path integral in a stationary phase approximation, is determined not by the on-shell value of the action (which vanishes), but by the Gibbons--Hawking--York boundary term evaluated on a suitable hypersurface, which can be chosen arbitrarily far away from the horizon. For this reason, the black hole singularity seemingly has no influence on the Bekenstein--Hawking area law. In this Essay we estimate how a regular black hole core, deep inside a Euclidean black hole of mass $M$ and generated via a UV regulator length scale $ell>0$, affects the black hole entropy. The contributions are suppressed by factors of $ell/(2GM)$; demanding exact agreement with the area law as well as a self-consistent first law of black hole thermodynamics at all orders, however, demands that these contributions vanish identically via uniformly bounded curvature. This links the limiting curvature hypothesis to black hole thermodynamics.","PeriodicalId":50307,"journal":{"name":"International Journal of Modern Physics D","volume":" ","pages":""},"PeriodicalIF":2.2,"publicationDate":"2023-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42284319","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}
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