This letter reports a gravitational redshift measurement experiment using a satellite-based compact passive hydrogen maser(PHM)in a lunar distant retrograde orbit(DRO).In March 2024,the Chinese Academy of Sciences lau...This letter reports a gravitational redshift measurement experiment using a satellite-based compact passive hydrogen maser(PHM)in a lunar distant retrograde orbit(DRO).In March 2024,the Chinese Academy of Sciences launched the DRO-A/B twin satellites,which entered a DRO in July 2024.This orbit has a geocentric distance of approximately 300,000–450,000 kilometers and a 2:1 resonance ratio.Employing microwave dual one-way ranging(DOWR),satellite-ground time-frequency comparisons were successfully achieved in April 2025 using the PHM aboard the DRO-A satellite.This study validated the in-orbit performance of the compact PHM and supported tests of the Einstein Equivalence Principle.The gravitational redshift measurement result is(8.74±4.17)×10^(−3).As the world’s first fundamental physics experiment to deploy PHMs in a lunar DRO,this study provides significant new engineering approaches for testing gravitational theories in cislunar space.展开更多
The detection of gravitational waves by the LIGO-Virgo-KAGRA collaboration has ushered in a new era of observational astronomy,emphasizing the need for rapid and detailed parameter estimation and population-level anal...The detection of gravitational waves by the LIGO-Virgo-KAGRA collaboration has ushered in a new era of observational astronomy,emphasizing the need for rapid and detailed parameter estimation and population-level analyses.Traditional Bayesian inference methods,particularly Markov chain Monte Carlo,face significant computational challenges when dealing with the high-dimensional parameter spaces and complex noise characteristics inherent in gravitational wave data.This review examines the emerging role of simulation-based inference methods in gravitational wave astronomy,with a focus on approaches that leverage machine-learning techniques such as normalizing flows and neural posterior estimation.We provide a comprehensive overview of the theoretical foundations underlying various simulation-based inference methods,including neural posterior estimation,neural ratio estimation,neural likelihood estimation,flow matching,and consistency models.We explore the applications of these methods across diverse gravitational wave data processing scenarios,from single-source parameter estimation and overlapping signal analysis to testing general relativity and conducting population studies.Although these techniques demonstrate speed improvements over traditional methods in controlled studies,their model-dependent nature and sensitivity to prior assumptions are barriers to their widespread adoption.Their accuracy,which is similar to that of conventional methods,requires further validation across broader parameter spaces and noise conditions.展开更多
Our analysis is particularly motivated by its relevance to understanding compact object instabilities,gravitational collapse thresholds,and the formation of dense structures under the influence of modified gravity the...Our analysis is particularly motivated by its relevance to understanding compact object instabilities,gravitational collapse thresholds,and the formation of dense structures under the influence of modified gravity theories.The interplay of anisotropic pressures,perturbative dynamics,and modified gravity contributions offers insight into both the stable configuration of dense fluids and the mechanisms leading to dynamical instability.Such considerations directly contribute to the aims of high energy density profiles,particularly in modeling physical systems where extreme pressure,curvature,and matter interactions co-exist.We consider an axially symmetric,dense structure with anisotropic matter content and employ a specific equation of state(EoS)to examine the interplay between static and dynamic quantities via the adiabatic index.To address the complex dynamics of the collapse process,a perturbative scheme is utilized under Newtonian and post-Newtonian approximations,enabling a detailed examination of the stability and structural evolution of the system under the influence of the considered minimally coupled gravity.Our results demonstrate that hydrostatic equilibrium is maintained when effective pressure,gravitational,and anti-gravitational forces are balanced,while deviations from this balance initiate dynamical instability.Graphical representations of stable and unstable regimes are presented,revealing how the choice of gravity functions significantly affects the outcome.This work provides insight into the behavior of dense,self-gravitating configurations under modified gravity,offering broader implications for the modeling of compact astrophysical objects and contributing to the understanding of gravitational collapse in energy density regimes.展开更多
The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payl...The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.展开更多
Tilt-to-length(TTL)coupling noise is a critical issue in space-based gravitational wave detection due to its complex dependence on multiple interacting factors,which complicates the identification of dominant paramete...Tilt-to-length(TTL)coupling noise is a critical issue in space-based gravitational wave detection due to its complex dependence on multiple interacting factors,which complicates the identification of dominant parameters.To address this challenge,we develop a simulation model of the Taiji scientific interferometer,generating noise datasets under multiparameter conditions.Given the uniqueness of the telescope as well as the convergence behavior of the algorithm,the analysis is structured hierarchically:(i)the telescope level and(ii)the optical bench level.A hierarchical framework combining XGBoost and SHapley Additive exPlanations(SHAP)values is employed to model the intricate relationships between parameters and TTL coupling noise,supplemented by sensitivity analysis.Our results identify pointing jitter and telescope radius as the dominant parameters at the telescope level,while the angles of the plane mirrors and beam splitters are most influential at the optical bench level.The parameter space is reduced from 86 dimensions to 14 dimensions without sacrificing model accuracy.This approach offers actionable insights for optimizing the Taiji interferometer design.展开更多
White dwarfs,one of the compact objects in the Universe,play a crucial role in astrophysical research and provide a platform for exploring nuclear physics.In this work,we extend the relativistic mean field approach by...White dwarfs,one of the compact objects in the Universe,play a crucial role in astrophysical research and provide a platform for exploring nuclear physics.In this work,we extend the relativistic mean field approach by using a Walecka-type quantum hadrodynamics model to capture the intricate structure of white dwarfs.We calculate nuclear properties,Coulomb energy,and photon energy within white dwarfs in a unified framework.By carefully calibrating the model parameters to align with nuclear matter properties,we successfully reproduce the structures of several elements in white dwarfs,such as the isotopes of C and ^(16)O,except for the unnaturally deeply bound state 4 He.Furthermore,we predict the characteristics of white dwarfs composed of atom-like units and the gravitational waves stemming from binary white dwarf inspirals incorporating tidal deformability contributions up to the 2.5 post-Newtonian order.These results shed light on the structure of white dwarfs and provide valuable information for future gravitational wave detection.This methodological advancement allows for a cohesive analysis of white dwarfs,neutron stars,and the nuclear pasta within a unified theoretical framework.展开更多
Relic gravitational waves(RGWs)from the early Universe carry crucial and fundamental cosmological information.Therefore,it is of extraordinary importance to investigate potential RGW signals in the data from observato...Relic gravitational waves(RGWs)from the early Universe carry crucial and fundamental cosmological information.Therefore,it is of extraordinary importance to investigate potential RGW signals in the data from observatories such as the LIGO-Virgo-KAGRA network.Here,focusing on typical RGWs from the inflation and the first-order phase transition(by sound waves and bubble collisions),effective and targeted deep learning neural networks are established to search for these RGW signals within the real LIGO data(O2,O3a and O3b).Through adjustment and adaptation processes,we develop suitable Convolutional Neural Networks(CNNs)to estimate the likelihood(characterized by quantitative values and distributions)that the focused RGW signals are present in the LIGO data.We find that if the constructed CNN properly estimates the parameters of the RGWs,it can determine with high accuracy(approximately 94%to 99%)whether the samples contain such RGW signals;otherwise,the likelihood provided by the CNN cannot be considered reliable.After testing a large amount of LIGO data,the findings show no evidence of RGWs from:1)inflation,2)sound waves,or 3)bubble collisions,as predicted by the focused theories.The results also provide upper limits of their GW spectral energy densities of h^(2)Ω_(gw)~10^(-5),respectively for parameter boundaries within 1)[β∈(-1.87,-1.85)×α∈(0.005,0.007)],2)[β/H_(pt)∈(0.02,0.16)×α∈(1,10)×T_(pt)∈(5*10^(9),10^(10))Gev],and 3)[β/H_(pt)∈(0.08,0.2)×α∈(1,10)×T_(pt)∈(5*10^(9),8*10^(10))Gev].In short,null results and upper limits are obtained,and the analysis suggests that our developed methods and neural networks to search for typical RGWs in the LIGO data are effective and reliable,providing a viable scheme for exploring possible RGWs from the early Universe and placing constraints on relevant cosmological theories.展开更多
In the framework of general relativity(GR), gravitational waves(GWs) travel at the speed of light across all frequencies. However, massive gravity and weak equivalence principle(WEP)violation may lead to frequency-dep...In the framework of general relativity(GR), gravitational waves(GWs) travel at the speed of light across all frequencies. However, massive gravity and weak equivalence principle(WEP)violation may lead to frequency-dependent variations in the propagation speed of GWs, which can be examined by comparing the theoretical and observed discrepancies in the arrival times of GW signals at various frequencies. This provides us with an opportunity to test these theories.For massive gravity, we consider that gravitons may have a nonzero rest mass. For WEP violations, we hypothesize that different massless particles exposed to the same gravitational source should exhibit varying gravitational time delays. The gravitational time delay induced by massive gravitational sources is proportional to γ + 1, where the parameter γ = 1 in GR.Therefore, we can quantify these two deviations using phenomenological parameters mg and |Δγ|, respectively. In this study, we use selected GW data from binary black hole coalescences in the LIGO-Virgo catalogs GWTC-2.1 and GWTC-3 to place constraints on the parameters mg and |Δγ|. We also compute Bayes factors for models that assume the existence of graviton mass and WEP violation compared to the standard GW model, respectively. The absolute value of the natural logarithm of the Bayes factor is generally less than two. Our analysis reveals no significant preference for either model. Additionally, the Bayes factors between these two models do not provide obvious evidence in favor of either one.展开更多
The chiral gravitational wave background(GWB)can be produced by axion-like fields in the early universe.We perform parameter estimation for two types of chiral GWB with the LISATaiji network:axion-dark photon coupling...The chiral gravitational wave background(GWB)can be produced by axion-like fields in the early universe.We perform parameter estimation for two types of chiral GWB with the LISATaiji network:axion-dark photon coupling and axion-Nieh–Yan coupling.We estimate the spectral parameters of these two mechanisms induced by the axion and determine the normalized model parameters using the Fisher information matrix.For highly chiral GWB signals that we choose to analyze in the mHz band,the normalized model parameters are constrained with a relative error less than 6.7%(dark photon coupling)and 2.2%(Nieh–Yan coupling)at the onesigma confidence level.The circular polarization parameters are constrained with a relative error around 21%(dark photon coupling)and 6.2%(Nieh–Yan coupling)at the one-sigma confidence level.展开更多
文摘This letter reports a gravitational redshift measurement experiment using a satellite-based compact passive hydrogen maser(PHM)in a lunar distant retrograde orbit(DRO).In March 2024,the Chinese Academy of Sciences launched the DRO-A/B twin satellites,which entered a DRO in July 2024.This orbit has a geocentric distance of approximately 300,000–450,000 kilometers and a 2:1 resonance ratio.Employing microwave dual one-way ranging(DOWR),satellite-ground time-frequency comparisons were successfully achieved in April 2025 using the PHM aboard the DRO-A satellite.This study validated the in-orbit performance of the compact PHM and supported tests of the Einstein Equivalence Principle.The gravitational redshift measurement result is(8.74±4.17)×10^(−3).As the world’s first fundamental physics experiment to deploy PHMs in a lunar DRO,this study provides significant new engineering approaches for testing gravitational theories in cislunar space.
基金supported by the National Key Research and Development Program of China(2021YFC2203004)the National Natural Science Foundation of China(NSFC)(12405076,12247187,and 12147103)+1 种基金the National Astronomical Data Center(NADC2023YDS-01)the Fundamental Research Funds for the Central Universities.
文摘The detection of gravitational waves by the LIGO-Virgo-KAGRA collaboration has ushered in a new era of observational astronomy,emphasizing the need for rapid and detailed parameter estimation and population-level analyses.Traditional Bayesian inference methods,particularly Markov chain Monte Carlo,face significant computational challenges when dealing with the high-dimensional parameter spaces and complex noise characteristics inherent in gravitational wave data.This review examines the emerging role of simulation-based inference methods in gravitational wave astronomy,with a focus on approaches that leverage machine-learning techniques such as normalizing flows and neural posterior estimation.We provide a comprehensive overview of the theoretical foundations underlying various simulation-based inference methods,including neural posterior estimation,neural ratio estimation,neural likelihood estimation,flow matching,and consistency models.We explore the applications of these methods across diverse gravitational wave data processing scenarios,from single-source parameter estimation and overlapping signal analysis to testing general relativity and conducting population studies.Although these techniques demonstrate speed improvements over traditional methods in controlled studies,their model-dependent nature and sensitivity to prior assumptions are barriers to their widespread adoption.Their accuracy,which is similar to that of conventional methods,requires further validation across broader parameter spaces and noise conditions.
文摘Our analysis is particularly motivated by its relevance to understanding compact object instabilities,gravitational collapse thresholds,and the formation of dense structures under the influence of modified gravity theories.The interplay of anisotropic pressures,perturbative dynamics,and modified gravity contributions offers insight into both the stable configuration of dense fluids and the mechanisms leading to dynamical instability.Such considerations directly contribute to the aims of high energy density profiles,particularly in modeling physical systems where extreme pressure,curvature,and matter interactions co-exist.We consider an axially symmetric,dense structure with anisotropic matter content and employ a specific equation of state(EoS)to examine the interplay between static and dynamic quantities via the adiabatic index.To address the complex dynamics of the collapse process,a perturbative scheme is utilized under Newtonian and post-Newtonian approximations,enabling a detailed examination of the stability and structural evolution of the system under the influence of the considered minimally coupled gravity.Our results demonstrate that hydrostatic equilibrium is maintained when effective pressure,gravitational,and anti-gravitational forces are balanced,while deviations from this balance initiate dynamical instability.Graphical representations of stable and unstable regimes are presented,revealing how the choice of gravity functions significantly affects the outcome.This work provides insight into the behavior of dense,self-gravitating configurations under modified gravity,offering broader implications for the modeling of compact astrophysical objects and contributing to the understanding of gravitational collapse in energy density regimes.
基金the National Key Research&Development Program of China(Grant No.2022YFC2203901)the State Key Laboratory of Spatial Datum(Grant No.SKLSD2025-KF-03)+1 种基金Fundamental Research Funds for the Central UniversitiesSun Yat-sen University for the support。
文摘The space gravitational wave detection aims to detect gravitational waves in the mHz band in order to study supermassive black hole mergers,galaxy evolution and the structure of the early universe.One of its core payloads is a transponder-type interstellar laser interferometer,designed to measure relative displacement changes at the pico-meter level.Among its components,phasemeter is tasked with extracting the phase and frequency of the interference signal.Currently,phase-locked loop(PLL)phasemeters are commonly employed.However,the second harmonic signal generated by the mixer can restrict both the dynamic range and phase measurement accuracy of the phasemeter.This paper analyzes the interstellar laser interferometer and the impact of the second harmonic signal on the phasemeter's performance.To address these challenges,a phasemeter incorporating a second harmonic signal filter is proposed.This new design mitigates second harmonic disturbances within the phasemeter's bandwidth by dynamically adjusting the filter's cutoff frequency to track the input signal frequency,thereby suppressing the second harmonic signal in real time.Theoretical and simulation analyses demonstrate that the proposed phasemeter with a second harmonic filter significantly enhances the dynamic range.Finally,experimental results verify that the phasemeter can achieve the tracking of sudden frequency changes up to4.8 MHz.
基金Project supported by the National Key Research and Development Program of China(Grant No.2020YFC2200100)the CAS's Strategic Pioneer Program on Space Science(Grant No.XDA1502110201)。
文摘Tilt-to-length(TTL)coupling noise is a critical issue in space-based gravitational wave detection due to its complex dependence on multiple interacting factors,which complicates the identification of dominant parameters.To address this challenge,we develop a simulation model of the Taiji scientific interferometer,generating noise datasets under multiparameter conditions.Given the uniqueness of the telescope as well as the convergence behavior of the algorithm,the analysis is structured hierarchically:(i)the telescope level and(ii)the optical bench level.A hierarchical framework combining XGBoost and SHapley Additive exPlanations(SHAP)values is employed to model the intricate relationships between parameters and TTL coupling noise,supplemented by sensitivity analysis.Our results identify pointing jitter and telescope radius as the dominant parameters at the telescope level,while the angles of the plane mirrors and beam splitters are most influential at the optical bench level.The parameter space is reduced from 86 dimensions to 14 dimensions without sacrificing model accuracy.This approach offers actionable insights for optimizing the Taiji interferometer design.
基金supported in part by the National Key R&D Program of China under Grant No.2021YFC2202900supported in part by the National Key Research and Development Program of China under Grant No.2020YFC2201501+2 种基金the National Science Foundation of China(NSFC)under Grant Nos.12347103 and 11875147the National Science Foundation of China(NSFC)under Grants Nos.12347103,12147103 and 11821505the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No.XDB23030100。
文摘White dwarfs,one of the compact objects in the Universe,play a crucial role in astrophysical research and provide a platform for exploring nuclear physics.In this work,we extend the relativistic mean field approach by using a Walecka-type quantum hadrodynamics model to capture the intricate structure of white dwarfs.We calculate nuclear properties,Coulomb energy,and photon energy within white dwarfs in a unified framework.By carefully calibrating the model parameters to align with nuclear matter properties,we successfully reproduce the structures of several elements in white dwarfs,such as the isotopes of C and ^(16)O,except for the unnaturally deeply bound state 4 He.Furthermore,we predict the characteristics of white dwarfs composed of atom-like units and the gravitational waves stemming from binary white dwarf inspirals incorporating tidal deformability contributions up to the 2.5 post-Newtonian order.These results shed light on the structure of white dwarfs and provide valuable information for future gravitational wave detection.This methodological advancement allows for a cohesive analysis of white dwarfs,neutron stars,and the nuclear pasta within a unified theoretical framework.
基金supported in part by the National Natural Science Foundation of China under Grant Nos.11605015,12347101 and 12147102the Natural Scienceof Chongqing under Grant No.cstc2020jcyjmsxm X0944the Research Funds for the Central Universities under Grant No.2022CDJXY-002。
文摘Relic gravitational waves(RGWs)from the early Universe carry crucial and fundamental cosmological information.Therefore,it is of extraordinary importance to investigate potential RGW signals in the data from observatories such as the LIGO-Virgo-KAGRA network.Here,focusing on typical RGWs from the inflation and the first-order phase transition(by sound waves and bubble collisions),effective and targeted deep learning neural networks are established to search for these RGW signals within the real LIGO data(O2,O3a and O3b).Through adjustment and adaptation processes,we develop suitable Convolutional Neural Networks(CNNs)to estimate the likelihood(characterized by quantitative values and distributions)that the focused RGW signals are present in the LIGO data.We find that if the constructed CNN properly estimates the parameters of the RGWs,it can determine with high accuracy(approximately 94%to 99%)whether the samples contain such RGW signals;otherwise,the likelihood provided by the CNN cannot be considered reliable.After testing a large amount of LIGO data,the findings show no evidence of RGWs from:1)inflation,2)sound waves,or 3)bubble collisions,as predicted by the focused theories.The results also provide upper limits of their GW spectral energy densities of h^(2)Ω_(gw)~10^(-5),respectively for parameter boundaries within 1)[β∈(-1.87,-1.85)×α∈(0.005,0.007)],2)[β/H_(pt)∈(0.02,0.16)×α∈(1,10)×T_(pt)∈(5*10^(9),10^(10))Gev],and 3)[β/H_(pt)∈(0.08,0.2)×α∈(1,10)×T_(pt)∈(5*10^(9),8*10^(10))Gev].In short,null results and upper limits are obtained,and the analysis suggests that our developed methods and neural networks to search for typical RGWs in the LIGO data are effective and reliable,providing a viable scheme for exploring possible RGWs from the early Universe and placing constraints on relevant cosmological theories.
基金supported by the National Key R&D Program of China (Grant No. 2021YFC 2203002)the National Natural Science Foundation of China (Grant Nos. 12173071 and 12473075)。
文摘In the framework of general relativity(GR), gravitational waves(GWs) travel at the speed of light across all frequencies. However, massive gravity and weak equivalence principle(WEP)violation may lead to frequency-dependent variations in the propagation speed of GWs, which can be examined by comparing the theoretical and observed discrepancies in the arrival times of GW signals at various frequencies. This provides us with an opportunity to test these theories.For massive gravity, we consider that gravitons may have a nonzero rest mass. For WEP violations, we hypothesize that different massless particles exposed to the same gravitational source should exhibit varying gravitational time delays. The gravitational time delay induced by massive gravitational sources is proportional to γ + 1, where the parameter γ = 1 in GR.Therefore, we can quantify these two deviations using phenomenological parameters mg and |Δγ|, respectively. In this study, we use selected GW data from binary black hole coalescences in the LIGO-Virgo catalogs GWTC-2.1 and GWTC-3 to place constraints on the parameters mg and |Δγ|. We also compute Bayes factors for models that assume the existence of graviton mass and WEP violation compared to the standard GW model, respectively. The absolute value of the natural logarithm of the Bayes factor is generally less than two. Our analysis reveals no significant preference for either model. Additionally, the Bayes factors between these two models do not provide obvious evidence in favor of either one.
基金supported by the National Key Research and Development Program of China(Grant Nos.2023YFC2206200 and 2021YFC2201901)the National Natural Science Foundation of China(Grant Nos.12375059 and12405074)。
文摘The chiral gravitational wave background(GWB)can be produced by axion-like fields in the early universe.We perform parameter estimation for two types of chiral GWB with the LISATaiji network:axion-dark photon coupling and axion-Nieh–Yan coupling.We estimate the spectral parameters of these two mechanisms induced by the axion and determine the normalized model parameters using the Fisher information matrix.For highly chiral GWB signals that we choose to analyze in the mHz band,the normalized model parameters are constrained with a relative error less than 6.7%(dark photon coupling)and 2.2%(Nieh–Yan coupling)at the onesigma confidence level.The circular polarization parameters are constrained with a relative error around 21%(dark photon coupling)and 6.2%(Nieh–Yan coupling)at the one-sigma confidence level.
