Pub Date : 2025-02-19DOI: 10.1088/1361-6382/adb2d6
Tong Huang, Rui-Qi Liu, Rui-Jie Li, Ling-Ling Yang, Yan-Jie Zhang, Qiang-Bing Mao and Qing Li
The Newtonian gravitational constant G is one of the most fundamental constants in nature. In G measurement with the angular acceleration feedback method, the largest error comes from the distances between the geometric centers of the source masses. In the on-going experiment, the silicon spheres with a more homogeneous density are used as the source masses. Here a scheme of measuring the geometric distances between the silicon spheres with the laser interferometer is proposed. The measurement principle is analyzed, and the error sources, such as the laser, the sphere, the alignment of optical path, and the environment are evaluated. With this method, the horizontal and vertical geometric distances can be measured with uncertainties of 11 nm and 9 nm, respectively. The simulation is performed to verify the theoretical model of measuring the distance, where the maximum deviation between the simulation result and the theoretical one is only −2.7 nm. When the sphericities of the four silicon spheres are at the level of 0.1 µm, the uncertainty of each distance after considering the sphericity is about 0.1 µm, corresponds to a combined uncertainty of 0.6 ppm for G measurement with the angular acceleration feedback method. This provides an effective method to reduce the measurement uncertainty of geometric distance between the silicon spheres, and makes it possible to measure G with a higher precision.
{"title":"Theoretical analysis and simulation verification for measuring the geometric distances between the silicon spheres with the laser interferometer in G measurement","authors":"Tong Huang, Rui-Qi Liu, Rui-Jie Li, Ling-Ling Yang, Yan-Jie Zhang, Qiang-Bing Mao and Qing Li","doi":"10.1088/1361-6382/adb2d6","DOIUrl":"https://doi.org/10.1088/1361-6382/adb2d6","url":null,"abstract":"The Newtonian gravitational constant G is one of the most fundamental constants in nature. In G measurement with the angular acceleration feedback method, the largest error comes from the distances between the geometric centers of the source masses. In the on-going experiment, the silicon spheres with a more homogeneous density are used as the source masses. Here a scheme of measuring the geometric distances between the silicon spheres with the laser interferometer is proposed. The measurement principle is analyzed, and the error sources, such as the laser, the sphere, the alignment of optical path, and the environment are evaluated. With this method, the horizontal and vertical geometric distances can be measured with uncertainties of 11 nm and 9 nm, respectively. The simulation is performed to verify the theoretical model of measuring the distance, where the maximum deviation between the simulation result and the theoretical one is only −2.7 nm. When the sphericities of the four silicon spheres are at the level of 0.1 µm, the uncertainty of each distance after considering the sphericity is about 0.1 µm, corresponds to a combined uncertainty of 0.6 ppm for G measurement with the angular acceleration feedback method. This provides an effective method to reduce the measurement uncertainty of geometric distance between the silicon spheres, and makes it possible to measure G with a higher precision.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"1 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143443250","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-18DOI: 10.1088/1361-6382/adb2d4
K Andrzejewski
We analyse the motion of the spinning body (in the pole–dipole approximation) in the gravitational and electromagnetic fields described by the Mathisson–Papapetrou–Dixon–Souriau equations. First, we define a novel spin condition for the body with the magnetic dipole moment proportional to spin, which generalizes the one proposed by Ohashi–Kyrian–Semerák for gravity. As a result, we get the whole family of charged spinning particle models in the curved spacetime with remarkably simple dynamics (momentum and velocity are parallel). Applying the reparametrization procedure, for a specific dipole moment, we obtain equations of motion with constant mass and gyromagnetic factor. Next, we show that these equations follow from an effective Hamiltonian formalism, previously interpreted as a classical model of the charged Dirac particle.
{"title":"Revisiting the dynamics of a charged spinning body in curved spacetime","authors":"K Andrzejewski","doi":"10.1088/1361-6382/adb2d4","DOIUrl":"https://doi.org/10.1088/1361-6382/adb2d4","url":null,"abstract":"We analyse the motion of the spinning body (in the pole–dipole approximation) in the gravitational and electromagnetic fields described by the Mathisson–Papapetrou–Dixon–Souriau equations. First, we define a novel spin condition for the body with the magnetic dipole moment proportional to spin, which generalizes the one proposed by Ohashi–Kyrian–Semerák for gravity. As a result, we get the whole family of charged spinning particle models in the curved spacetime with remarkably simple dynamics (momentum and velocity are parallel). Applying the reparametrization procedure, for a specific dipole moment, we obtain equations of motion with constant mass and gyromagnetic factor. Next, we show that these equations follow from an effective Hamiltonian formalism, previously interpreted as a classical model of the charged Dirac particle.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"24 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-18DOI: 10.1088/1361-6382/adb2d3
Somnath Saha, Subhajit Saha and Nilanjana Mahata
This paper deals with gravitational thermodynamics on the dynamical apparent horizon of an Friedmann–Lemaitre–Robertson–Walker (FLRW) Universe with dissipation. The dissipation is assumed to arise due to adiabatic gravitational particle creation. For the thermodynamic study, we consider the Bekenstein–Hawking formalism and also assume a nonzero curvature κ for a general study. In particular, we study the unified first law, the generalized second law, and thermodynamic stability in our model. The specific heat capacities are taken into account for the study of thermodynamic stability. Our study reveals a nice result! The ratio of the specific heat capacity at constant pressure and that at constant volume in a flat FLRW Universe with dissipation is nothing but the negative of the deceleration parameter. In classical thermodynamics, this ratio is known as the isentropic expansion factor or (for ideal gases) the adiabatic index. A more interesting fact that has come to light is that this relation is independent of the cosmological model used. So, this is actually a generic result in big bang cosmology. We discuss the implications of this result on the evolution of the Universe. Finally, we determine the constraints on the effective equation of state and the particle creation rate which guarantees thermodynamic stability in our model.
{"title":"For a flat Universe, C P /...","authors":"Somnath Saha, Subhajit Saha and Nilanjana Mahata","doi":"10.1088/1361-6382/adb2d3","DOIUrl":"https://doi.org/10.1088/1361-6382/adb2d3","url":null,"abstract":"This paper deals with gravitational thermodynamics on the dynamical apparent horizon of an Friedmann–Lemaitre–Robertson–Walker (FLRW) Universe with dissipation. The dissipation is assumed to arise due to adiabatic gravitational particle creation. For the thermodynamic study, we consider the Bekenstein–Hawking formalism and also assume a nonzero curvature κ for a general study. In particular, we study the unified first law, the generalized second law, and thermodynamic stability in our model. The specific heat capacities are taken into account for the study of thermodynamic stability. Our study reveals a nice result! The ratio of the specific heat capacity at constant pressure and that at constant volume in a flat FLRW Universe with dissipation is nothing but the negative of the deceleration parameter. In classical thermodynamics, this ratio is known as the isentropic expansion factor or (for ideal gases) the adiabatic index. A more interesting fact that has come to light is that this relation is independent of the cosmological model used. So, this is actually a generic result in big bang cosmology. We discuss the implications of this result on the evolution of the Universe. Finally, we determine the constraints on the effective equation of state and the particle creation rate which guarantees thermodynamic stability in our model.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"64 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143435046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-17DOI: 10.1088/1361-6382/ada2d3
Jan Niklas Reinhardt, Olaf Hartwig and Gerhard Heinzel
Space-based gravitational-wave detectors, such as the Laser Interferometer Space Antenna (LISA), record interferometric measurements on widely separated satellites. Their clocks are not synced actively. Instead, clock synchronization is performed in on-ground data processing. It relies on measurements of the so-called pseudoranges, which entangle the interspacecraft light travel times (LTTs) with the clock desynchronizations between emitting and receiving spacecraft. For interspacecraft clock synchronization, we need to isolate the differential clock desynchronizations, i.e. disentangle the pseudoranges. This further yields estimates for the interspacecraft LTTs, which are required as delays for the laser frequency noise suppression via time-delay interferometry (TDI). Previous studies on pseudorange disentanglement apply various simplifications in the pseudorange modeling and the data simulation. In contrast, this article derives an accurate pseudorange model in the barycentric celestial reference system, complemented by realistic state-of-the-art LISA data simulations. Concerning pseudorange disentanglement, this leads to an a priori under-determined system. We demonstrate how on-ground orbit determinations, as well as onboard transmission and on-ground reception time tags of the telemetry data, can be used to resolve this degeneracy. We introduce an algorithm for pseudorange disentanglement based on a nonstandard Kalman filter specially designed for clock synchronization in systems where pseudorange measurements are conducted in different time frames. This algorithm achieves interspacecraft clock synchronization and LTT estimation with submeter accuracy, thus fulfilling the requirements of TDI.
{"title":"Clock synchronization and light-travel-time estimation for space-based gravitational-wave detectors","authors":"Jan Niklas Reinhardt, Olaf Hartwig and Gerhard Heinzel","doi":"10.1088/1361-6382/ada2d3","DOIUrl":"https://doi.org/10.1088/1361-6382/ada2d3","url":null,"abstract":"Space-based gravitational-wave detectors, such as the Laser Interferometer Space Antenna (LISA), record interferometric measurements on widely separated satellites. Their clocks are not synced actively. Instead, clock synchronization is performed in on-ground data processing. It relies on measurements of the so-called pseudoranges, which entangle the interspacecraft light travel times (LTTs) with the clock desynchronizations between emitting and receiving spacecraft. For interspacecraft clock synchronization, we need to isolate the differential clock desynchronizations, i.e. disentangle the pseudoranges. This further yields estimates for the interspacecraft LTTs, which are required as delays for the laser frequency noise suppression via time-delay interferometry (TDI). Previous studies on pseudorange disentanglement apply various simplifications in the pseudorange modeling and the data simulation. In contrast, this article derives an accurate pseudorange model in the barycentric celestial reference system, complemented by realistic state-of-the-art LISA data simulations. Concerning pseudorange disentanglement, this leads to an a priori under-determined system. We demonstrate how on-ground orbit determinations, as well as onboard transmission and on-ground reception time tags of the telemetry data, can be used to resolve this degeneracy. We introduce an algorithm for pseudorange disentanglement based on a nonstandard Kalman filter specially designed for clock synchronization in systems where pseudorange measurements are conducted in different time frames. This algorithm achieves interspacecraft clock synchronization and LTT estimation with submeter accuracy, thus fulfilling the requirements of TDI.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"21 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143426973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-17DOI: 10.1088/1361-6382/adb23c
Jordan Gué, Aurélien Hees and Peter Wolf
We propose a simple modification of space-based gravitational wave (GW) detector optical benches which would enable the measurement of vacuum birefringence of light induced by axion dark matter through its coupling to electromagnetism. Specifically, we propose to change a half-wave plate by a circular polarizer. While marginally affecting the sensitivity to GW by a factor , we show that such an adjustment would make future detectors such as LISA, TianQin, Taiji and Big-Bang Observer the most sensitive experiments at low axion masses.
{"title":"Probing the axion–photon coupling with space-based gravitational wave detectors","authors":"Jordan Gué, Aurélien Hees and Peter Wolf","doi":"10.1088/1361-6382/adb23c","DOIUrl":"https://doi.org/10.1088/1361-6382/adb23c","url":null,"abstract":"We propose a simple modification of space-based gravitational wave (GW) detector optical benches which would enable the measurement of vacuum birefringence of light induced by axion dark matter through its coupling to electromagnetism. Specifically, we propose to change a half-wave plate by a circular polarizer. While marginally affecting the sensitivity to GW by a factor , we show that such an adjustment would make future detectors such as LISA, TianQin, Taiji and Big-Bang Observer the most sensitive experiments at low axion masses.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"4 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143426975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-17DOI: 10.1088/1361-6382/adaf00
Samantha Parry Kenyon, Stephen Apple, John Siu, Peter J Wass and John W Conklin
A gravitational wave detector in space, the Laser Interferometer Space Antenna (LISA) will be able to detect gravitational waves in the frequency range of 0.1 mHz–1 Hz, adding to humanity’s knowledge of the dark cosmos. The LISA gravitational reference sensor contains a test mass (TM) and is used to determine the local inertial reference frame and as endpoints for the interferometry. The TM is surrounded by an electrode housing to detect changes in TM position and orientation, which is fed back to the spacecraft thrusters for drag-free control. As seen on LISA Pathfinder, the TM builds up charge over time from the space environment and needs to be discharged in order to keep the resulting force noise as low as possible. The operation of intelligently discharging the TM is known as charge control, and is one area of improvement to be explored for LISA. To explore new methods of TM discharge, UV LEDs will be pulsed synchronized with an existing 100 kHz high frequency electric field to facilitate photoelectron current direction and to achieve lower UV light powers by duty cycling. This paper addresses new pulsed methods for the LISA Charge Management System, which require in-depth modeling, analysis, and testing because space environment validation will not be possible prior to LISA launch. Therefore, it is necessary to model the dynamics of charge movement to determine the force noise contribution of pulsed continuous charge control. The charge dynamics model is described, and simulation results featured for charge control efficacy in a deep space radiation environment. Experimental testing of the simulation results could be done in the University of Florida Torsion Pendulum, a key technology to testing GRS performance in a space-like environment.
{"title":"Advanced charge control dynamics simulation for the LISA gravitational reference sensor","authors":"Samantha Parry Kenyon, Stephen Apple, John Siu, Peter J Wass and John W Conklin","doi":"10.1088/1361-6382/adaf00","DOIUrl":"https://doi.org/10.1088/1361-6382/adaf00","url":null,"abstract":"A gravitational wave detector in space, the Laser Interferometer Space Antenna (LISA) will be able to detect gravitational waves in the frequency range of 0.1 mHz–1 Hz, adding to humanity’s knowledge of the dark cosmos. The LISA gravitational reference sensor contains a test mass (TM) and is used to determine the local inertial reference frame and as endpoints for the interferometry. The TM is surrounded by an electrode housing to detect changes in TM position and orientation, which is fed back to the spacecraft thrusters for drag-free control. As seen on LISA Pathfinder, the TM builds up charge over time from the space environment and needs to be discharged in order to keep the resulting force noise as low as possible. The operation of intelligently discharging the TM is known as charge control, and is one area of improvement to be explored for LISA. To explore new methods of TM discharge, UV LEDs will be pulsed synchronized with an existing 100 kHz high frequency electric field to facilitate photoelectron current direction and to achieve lower UV light powers by duty cycling. This paper addresses new pulsed methods for the LISA Charge Management System, which require in-depth modeling, analysis, and testing because space environment validation will not be possible prior to LISA launch. Therefore, it is necessary to model the dynamics of charge movement to determine the force noise contribution of pulsed continuous charge control. The charge dynamics model is described, and simulation results featured for charge control efficacy in a deep space radiation environment. Experimental testing of the simulation results could be done in the University of Florida Torsion Pendulum, a key technology to testing GRS performance in a space-like environment.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"49 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143427130","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-17DOI: 10.1088/1361-6382/adaf02
Johanna Borissova, Bianca Dittrich, Dongxue Qu and Marc Schiffer
Simplicial approaches to quantum gravity such as Quantum Regge Calculus and Spin Foams include configurations where bulk edges can become arbitrarily large while keeping the lengths of the boundary edges small. Such configurations pose significant challenges in Euclidean Quantum Regge Calculus, as they lead to infinities for the partition function and length expectation values. Here we investigate such configurations in three-dimensional Lorentzian Quantum Regge Calculus, and find that the partition function and length expectation values remain finite. This shows that the Lorentzian approach can avoid a key issue of the Euclidean approach. We also find that the space of configurations, for which bulk edges can become very large, is much richer than in the Euclidean case. In particular, it includes configurations with irregular light-cone structures, which lead to imaginary terms in the Regge action and branch cuts along the Lorentzian path integral contour. Hence, to meaningfully define the Lorentzian Regge path integral, one needs to clarify how such configurations should be handled.
{"title":"Spikes and spines in 3D Lorentzian simplicial quantum gravity","authors":"Johanna Borissova, Bianca Dittrich, Dongxue Qu and Marc Schiffer","doi":"10.1088/1361-6382/adaf02","DOIUrl":"https://doi.org/10.1088/1361-6382/adaf02","url":null,"abstract":"Simplicial approaches to quantum gravity such as Quantum Regge Calculus and Spin Foams include configurations where bulk edges can become arbitrarily large while keeping the lengths of the boundary edges small. Such configurations pose significant challenges in Euclidean Quantum Regge Calculus, as they lead to infinities for the partition function and length expectation values. Here we investigate such configurations in three-dimensional Lorentzian Quantum Regge Calculus, and find that the partition function and length expectation values remain finite. This shows that the Lorentzian approach can avoid a key issue of the Euclidean approach. We also find that the space of configurations, for which bulk edges can become very large, is much richer than in the Euclidean case. In particular, it includes configurations with irregular light-cone structures, which lead to imaginary terms in the Regge action and branch cuts along the Lorentzian path integral contour. Hence, to meaningfully define the Lorentzian Regge path integral, one needs to clarify how such configurations should be handled.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"64 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143426974","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-14DOI: 10.1088/1361-6382/adae4a
Germain Tobar, Igor Pikovski, Michael E Tobar
We propose a multi-mode bar consisting of mass elements of decreasing size for the implementation of a gravitational version of the photo-electric effect through the stimulated absorption of up to kHz gravitons from a binary neutron star merger and post-merger. We find that the multi-mode detector has normal modes that retain the coupling strength to the gravitational wave of the largest mass-element, while only having an effective mass comparable to the mass of the smallest element. This allows the normal modes to have graviton absorption rates due to the tonne-scale largest mass, while the single graviton absorption process in the normal mode could be resolved through energy measurements of a mass-element in-principle smaller than pico-gram scale. We argue the feasibility of directly counting gravito-phonons in the bar through energy measurements of the end mass. This improves the transduction of the single-graviton signal, enhancing the feasibility of detecting single gravitons.
{"title":"Detecting kHz gravitons from a neutron star merger with a multi-mode resonant mass detector","authors":"Germain Tobar, Igor Pikovski, Michael E Tobar","doi":"10.1088/1361-6382/adae4a","DOIUrl":"https://doi.org/10.1088/1361-6382/adae4a","url":null,"abstract":"We propose a multi-mode bar consisting of mass elements of decreasing size for the implementation of a gravitational version of the photo-electric effect through the stimulated absorption of up to kHz gravitons from a binary neutron star merger and post-merger. We find that the multi-mode detector has normal modes that retain the coupling strength to the gravitational wave of the largest mass-element, while only having an effective mass comparable to the mass of the smallest element. This allows the normal modes to have graviton absorption rates due to the tonne-scale largest mass, while the single graviton absorption process in the normal mode could be resolved through energy measurements of a mass-element in-principle smaller than pico-gram scale. We argue the feasibility of directly counting gravito-phonons in the bar through energy measurements of the end mass. This improves the transduction of the single-graviton signal, enhancing the feasibility of detecting single gravitons.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"63 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143417297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-14DOI: 10.1088/1361-6382/adaa4a
Eleni-Alexandra Kontou, Nicolai Rothe
In this work, we analyze the cosmological model in which the expansion is driven by a classical, free Klein–Gordon field on a flat, four-dimensional Friedmann–Lemaître—Robertson–Walker spacetime. The model allows for arbitrary mass, non-zero cosmological constant and coupling to curvature. We find that there are strong restrictions to the parameter space, due to the requirement for the reality of the field values. At early cosmological times, we observe Big Bang singularities, solutions where the scale factor asymptotically approaches zero, and Small Bangs. The latter are solutions for which the Hubble parameter diverges at a finite value of the scale factor. They appear generically in our model for certain curvature couplings. An early inflationary era is observed for a specific value of the curvature coupling without further assumptions (unlike in many other inflationary models). A late-time Dark Energy period is present for all solutions with positive cosmological constant, numerically suggesting that a ‘cosmic no-hair’ theorem holds under more general assumptions than the original Wald version which relies on classical energy conditions. The classical fields in consideration can be viewed as resembling one-point functions of a semiclassical model, in which the cosmological expansion is driven by a quantum field.
{"title":"A new approach in classical Klein–Gordon cosmology: ‘Small Bangs’, inflation and Dark Energy","authors":"Eleni-Alexandra Kontou, Nicolai Rothe","doi":"10.1088/1361-6382/adaa4a","DOIUrl":"https://doi.org/10.1088/1361-6382/adaa4a","url":null,"abstract":"In this work, we analyze the cosmological model in which the expansion is driven by a classical, free Klein–Gordon field on a flat, four-dimensional Friedmann–Lemaître—Robertson–Walker spacetime. The model allows for arbitrary mass, non-zero cosmological constant and coupling to curvature. We find that there are strong restrictions to the parameter space, due to the requirement for the reality of the field values. At early cosmological times, we observe Big Bang singularities, solutions where the scale factor asymptotically approaches zero, and Small Bangs. The latter are solutions for which the Hubble parameter diverges at a finite value of the scale factor. They appear generically in our model for certain curvature couplings. An early inflationary era is observed for a specific value of the curvature coupling without further assumptions (unlike in many other inflationary models). A late-time Dark Energy period is present for all solutions with positive cosmological constant, numerically suggesting that a ‘cosmic no-hair’ theorem holds under more general assumptions than the original Wald version which relies on classical energy conditions. The classical fields in consideration can be viewed as resembling one-point functions of a semiclassical model, in which the cosmological expansion is driven by a quantum field.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"5 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143417296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-13DOI: 10.1088/1361-6382/adadbf
Erik Jensko
In this work we study the Friedmann–Lemaître–Robertson–Walker cosmologies with arbitrary spatial curvature for the symmetric teleparallel theories of gravity, giving the first presentation of their coincident gauge form. Our approach explicitly starts with the cosmological Killing vectors and constructs the coincident gauge coordinates adapted to these Killing vectors. We then obtain three distinct spatially flat branches and a single spatially curved branch. Contrary to some previous claims, we show that all branches can be studied in this gauge-fixed formalism, which offers certain conceptual advantages. We also identify common flaws that have appeared in the literature regarding the coincident gauge. Using this approach, we find that both the flat and spatially curved solutions in f(Q) gravity can be seen as equivalent to the metric teleparallel f(T) models, demonstrating a deeper connection between these theories. This is accomplished by studying the connection equation of motion, which can be interpreted as a consistency condition in the gauge-fixed approach. Finally, we discuss the role of diffeomorphism invariance and local Lorentz invariance in these geometric modifications of gravity.
{"title":"Spatial curvature in coincident gauge f(Q) cosmology","authors":"Erik Jensko","doi":"10.1088/1361-6382/adadbf","DOIUrl":"https://doi.org/10.1088/1361-6382/adadbf","url":null,"abstract":"In this work we study the Friedmann–Lemaître–Robertson–Walker cosmologies with arbitrary spatial curvature for the symmetric teleparallel theories of gravity, giving the first presentation of their coincident gauge form. Our approach explicitly starts with the cosmological Killing vectors and constructs the coincident gauge coordinates adapted to these Killing vectors. We then obtain three distinct spatially flat branches and a single spatially curved branch. Contrary to some previous claims, we show that all branches can be studied in this gauge-fixed formalism, which offers certain conceptual advantages. We also identify common flaws that have appeared in the literature regarding the coincident gauge. Using this approach, we find that both the flat and spatially curved solutions in f(Q) gravity can be seen as equivalent to the metric teleparallel f(T) models, demonstrating a deeper connection between these theories. This is accomplished by studying the connection equation of motion, which can be interpreted as a consistency condition in the gauge-fixed approach. Finally, we discuss the role of diffeomorphism invariance and local Lorentz invariance in these geometric modifications of gravity.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":"16 1","pages":""},"PeriodicalIF":3.5,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143401463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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