Classical and Quantum Gravity最新文献

{"title":"Anti-de Sitter momentum space in 3D and 4D quantum gravity","authors":"Giovanni Amelino-Camelia, I. Lobo, Giovanni Palmisano","doi":"10.1088/1361-6382/ad3163","DOIUrl":"https://doi.org/10.1088/1361-6382/ad3163","url":null,"abstract":"\u0000 There has been strong interest in the possibility that in the quantum-gravity realm momentum space might be curved, mainly focusing, especially for what concerns phenomenological implications, on the case of a de Sitter momentum space. We here take as starting point the known fact that quantum gravity coupled to matter in $2+1$ spacetime dimensions gives rise to an effective picture characterized by a momentum space with anti-de Sitter geometry, and we point out some key properties of $2+1$-dimensional anti-de Sitter momentum space. We observe that it is impossible to implement all of these properties in theories with a $3+1$-dimensional anti-de Sitter momentum space, and we then investigate, with the aim of providing guidance to the relevant phenomenology focusing on possible modified laws of conservation of momenta, the implications of giving up, in the $3+1$-dimensional case, some of the properties of the $2+1$-dimensional case.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140077411","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}

{"title":"Bulk viscous late acceleration under near equilibrium conditions in f(R; T ) gravity with mixed dark matter.","authors":"Vishnu A Pai, Titus K. Mathew","doi":"10.1088/1361-6382/ad3082","DOIUrl":"https://doi.org/10.1088/1361-6382/ad3082","url":null,"abstract":"\u0000 Numerous studies have tried to explain the observed late acceleration of the Universe as being caused by the bulk viscosity associated with the dark matter component. However, for driving the said accelerated expansion, all such models require a violation of Near Equilibrium Conditions (NEC) associated with the background viscous theory. But recently, it was found that, with the aid of a cosmological constant, it is possible to maintain NEC for the bulk viscous warm dark matter during certain evolutionary epochs of the Universe. Nevertheless, this negated the possibility of having a ‘solely’ viscous-driven late acceleration in Einstein gravity within the NEC limit. In the present study, we investigate a model of the universe composed of mixed dark matter components, with viscous dark matter (vDM), and inviscid cold dark matter (CDM) as its constituents, in the context of R + 2λTvm gravity, and show that the model predicts late acceleration by satisfying NEC, critical energy condition (CEC) and second law of thermodynamics (SLT) throughout the evolution, even in the absence of a cosmological constant. One intriguing feature observed in this model is the possibility of having a negative bulk viscous coefficient and yet satisfying the second law of thermodynamics. Finally, by applying both theoretical and observational constraints on the model parameters, we determined the best-fit values of model parameters and thereby analyzed the evolutionary behavior of some relevant cosmological observables.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140261317","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}

{"title":"An approximate application of quantum gravity to the rotation problem","authors":"Richard Michael Jones","doi":"10.1088/1361-6382/ad3083","DOIUrl":"https://doi.org/10.1088/1361-6382/ad3083","url":null,"abstract":"\u0000 {Arbitrary initial conditions allow solutions of Einstein's field equations for General Relativity to have arbitrarily large relative rotation of matter and inertial frames. The ``Rotation Problem'' is to explain why the measured relative rotation rate is so small. As it turns out, nearly any reasonable theory of quantum gravity can solve the rotation problem by phase interference.} Even as early as {}{about a quarter of a second after the initial simgularity, quantum cosmology would limit the cosmologies that contribute significantly to a path integral calculation to have relative rms rotation rates less than about} {{}}{$10^{-51}$ radians per year.} Those calculations are based on using 50 e-foldings during inflation. For 55 or 60 e-foldings, the cosmologies contributing significantly to the path integral would have even smaller relative rotation rates. In addition, although inflation dominates the calculation, even if there had been no inflation, the cosmologies contributing significantly to the path integral would have relative rotation rates less than about {}{$10^{-32}$ radians per year at about a quarter of a second after the initial singularity.} These calculations are insensitive to the details of the theory of quantum gravity because the main factor depends only on the size of the visible universe, the Planck time, the free-space speed of light, the Hubble parameter, and the number of e-foldings during inflation. These calculations use the Einstein-Hilbert action in quantum gravity, {{}}{including} large-scale relative rotation of inertial frames and the matter distribution, in which each ``path'' is a cosmology with a different rms relative rotation rate. The calculations include inflation for 50, 55, and 60 e-foldings, and for values of the dependence of relative rotation rate on cosmological scale factor $a$ as $a^{-m}$ for various values of $m$. The calculation shows that the action is an extremum at zero rms relative rotation rate.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140078340","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}

{"title":"A torsion balance as a weak-force testbed for novel optical inertial sensors","authors":"Gerald Bergmann, Carolin Cordes, Christoph Gentemann, V. Händchen, Qinglan Wang, Hao Yan, K. Danzmann, G. Heinzel, Moritz Mehmet","doi":"10.1088/1361-6382/ad29e8","DOIUrl":"https://doi.org/10.1088/1361-6382/ad29e8","url":null,"abstract":"\u0000 <jats:p>Torsion balances (TBs) are versatile instruments known for their ability to measure tiny forces and accelerations with high precision. We are currently commissioning a new TB facility to support the development and testing of novel optical inertial sensor units for future gravity-related space missions. Here, we report on the status of our apparatus and present first sensitivity curves that demonstrate acceleration and torque sensitivities of <jats:inline-formula>\u0000 <jats:tex-math><?CDATA $5,cdot,10^{-11},mathrm{m},mathrm{s}^{-2}$?></jats:tex-math>\u0000 <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\">\u0000 <mml:mn>5</mml:mn>\u0000 <mml:mo>⋅</mml:mo>\u0000 <mml:msup>\u0000 <mml:mn>10</mml:mn>\u0000 <mml:mrow>\u0000 <mml:mo>−</mml:mo>\u0000 <mml:mn>11</mml:mn>\u0000 </mml:mrow>\u0000 </mml:msup>\u0000 <mml:mrow>\u0000 <mml:mi mathvariant=\"normal\">m</mml:mi>\u0000 </mml:mrow>\u0000 <mml:msup>\u0000 <mml:mrow>\u0000 <mml:mi mathvariant=\"normal\">s</mml:mi>\u0000 </mml:mrow>\u0000 <mml:mrow>\u0000 <mml:mo>−</mml:mo>\u0000 <mml:mn>2</mml:mn>\u0000 </mml:mrow>\u0000 </mml:msup>\u0000 </mml:math>\u0000 <jats:inline-graphic xmlns:xlink=\"http://www.w3.org/1999/xlink\" xlink:href=\"cqgad29e8ieqn1.gif\" xlink:type=\"simple\" />\u0000 </jats:inline-formula> and <jats:inline-formula>\u0000 <jats:tex-math><?CDATA $1,cdot,10^{-12},mathrm{Nm},sqrt{mathrm{Hz}}^{-1}$?></jats:tex-math>\u0000 <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\" overflow=\"scroll\">\u0000 <mml:mn>1</mml:mn>\u0000 <mml:mo>⋅</mml:mo>\u0000 <mml:msup>\u0000 <mml:mn>10</mml:mn>\u0000 <mml:mrow>\u0000 <mml:mo>−</mml:mo>\u0000 <mml:mn>12</mml:mn>\u0000 </mml:mrow>\u0000 </mml:msup>\u0000 <mml:mrow>\u0000 <mml:mi mathvariant=\"normal\">N</mml:mi>\u0000 <mml:mi mathvariant=\"normal\">m</mml:mi>\u0000 </mml:mrow>\u0000 <mml:msup>\u0000 <mml:msqrt>\u0000 <mml:mrow>\u0000 <mml:mi mathvariant=\"normal\">H</mml:mi>\u0000 <mml:mi mathvariant=\"normal\">z</mml:mi>\u0000 </mml:mrow>\u0000 </mml:msqrt>\u0000 ","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140079700","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}

{"title":"The mass gap in five dimensional Einstein–Gauss–Bonnet black holes: a geometrical explanation","authors":"C. Hansraj, R. Goswami, S. D. Maharaj","doi":"10.1088/1361-6382/ad28f8","DOIUrl":"https://doi.org/10.1088/1361-6382/ad28f8","url":null,"abstract":"\u0000 It is well known that, unlike in higher dimensional general relativity (GR), we cannot have a black hole with an arbitrarily small mass in five dimensional Einstein–Gauss–Bonnet gravity. When we study the dynamical black hole formation via the radiation collapse in the radiating Boulware–Deser spacetime in five dimensions, the central zero mass singularity is weak, conical and naked, and the horizon forms only when a finite amount of matter, that depends on the coupling constant of the Gauss–Bonnet term, falls into the central singularity. To understand this phenomenon transparently and geometrically, we study the radiating Boulware–Deser spacetime in five dimensions using a 1+1+3 spacetime decomposition, for the first time. We find that the geometric and thermodynamic quantities can be expressed in terms of the gravitational mass and the Gauss–Bonnet (GB) parameter and separate each of them into their Gauss–Bonnet and matter parts. Drawing comparisons with five dimensional GR at every step, we explicitly show how the mass gap arises for a general mass function M(v) and what functions for M(v) make certain geometrical quantities well defined at the central singularity. We show in the case of self-similar radiation collapse in the modified theory, the central singularity is not a sink for timelike geodesics and is extendable. This clearly demonstrates how the GB invariant affects the nature of the final state of a continual collapse in this modified theory.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140090337","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}

{"title":"A quantum of information in black hole evaporation","authors":"M. V. van Putten","doi":"10.1088/1361-6382/ad2319","DOIUrl":"https://doi.org/10.1088/1361-6382/ad2319","url":null,"abstract":"\u0000 Black holes evolve by evaporation of their event horizon. While this process is believed to be unitary, there is no consensus on the recovery of information in black hole entropy. A missing link is a unit of information in black hole evaporation. Distinct from Hawking radiation, we identify evaporation in entangled pairs by $mathbb{P}^2$ topology of the event horizon consistent with the Bekenstein-Hawking entropy in a uniformly spaced horizon area. It derives by continuation of $mathbb{P}^2$ in Rindler spacetime prior to gravitational collapse, subject to a tight correlation of the fundamental frequency of Quasi-Normal-Mode (QNM) ringing in gravitational and electromagnetic radiation. Information extraction from entangled pairs by detecting one over the surface spanned by three faces of a large cube carries a quantum of information of $2k_Blog3$ upon including measurement of spin.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139595107","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}

{"title":"ΛCDM-Rastall cosmology revisited: constraints from a recent quasars datasample","authors":"Jesús Astorga Moreno, K. Jacobo, Salvador Arteaga, M. A. García-Aspeitia, Alberto Hernández Almada","doi":"10.1088/1361-6382/ad1fca","DOIUrl":"https://doi.org/10.1088/1361-6382/ad1fca","url":null,"abstract":"\u0000 In this paper we study the impact of a recent quasar datasample in the constraint of the free parameters of an extension of general relativity. As a ruler to test, we use Rastall gravity in the context of background cosmology being a simple extension to general relativity. We compare the results from quasars dataset with other known samples such as cosmic chronometers, supernovae of the Ia type, baryon acoustic oscillations, HII galaxies, and also a joint analysis. Results are consistent with the standard cosmological model emphasizing that Rastall gravity is equivalent to General Relativity. According to the constraints provided from the joint sample, the age of the Universe is τU = 12.601+0.067 −0.066 Gyrs and the transition to an accelerated phase occurs at zT = 0.620 ± 0.025 in the redshift scale, being only the phase transition consistent with the standard paradigm and having a younger Universe. With the quasars sample, the universe age differs with that expected in ΛCDM having a result of τU = 11.958+0.139 −0.109 Gyrs with a transition at zT = 0.652 ± 0.032 this last consistent with standard cosmology. A remarkable result is that quasars constraints has the capability to differentiate among general relativity and Rastall gravity due to the result for the parameter λ = −2.231+0.785 −0.546. Moreover, the parameter j under quasars constraints suggests that the cause of the late universe’s acceleration is a dark energy fluid different from a cosmological constant.","PeriodicalId":505126,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139617661","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}