We search for isotropic stochastic gravitational-wave background(SGWB)in the International Pulsar Timing Array second data release.By modeling the SGWB as a power-law,we find very strong Bayesian evidence for a common...We search for isotropic stochastic gravitational-wave background(SGWB)in the International Pulsar Timing Array second data release.By modeling the SGWB as a power-law,we find very strong Bayesian evidence for a common-spectrum process,and further this process has scalar transverse(ST)correlations allowed in general metric theory of gravity as the Bayes factor in favor of the ST-correlated process versus the spatially uncorrelated common-spectrum process is 30±2.The median and the 90%equal-tail amplitudes of ST mode are A_(ST)=1.29^(+0.51)_(−0.44)×10^(−15),or equivalently the energy density parameter per logarithm frequency isΩSTGW=2.31^(+2.19)_(−1.30)×10^(−9),at frequency of 1 year−1.However,we do not find any statistically significant evidence for the tensor transverse(TT)mode and then place the 95%upper limits as A_(TT)<3.95×10^(−15),or equivalentlyΩ^(TT)_(GW)<2.16×10^(−9),at frequency of 1 year^(−1).展开更多
The recent stochastic signal observed jointly by NANOGrav,parkes pulsar timing array,European pulsar timing array,and Chinese pulsar timing array can be accounted for by scalarinduced gravitational waves(SIGWs).The so...The recent stochastic signal observed jointly by NANOGrav,parkes pulsar timing array,European pulsar timing array,and Chinese pulsar timing array can be accounted for by scalarinduced gravitational waves(SIGWs).The source of the SIGWs is from the primordial curvature perturbations,and the main contribution to the SIGWs is from the peak of the primordial curvature power spectrum.To effectively model this peak,we apply the Taylor expansion to parameterize it.With the Taylor expansion parameterization,we apply Bayesian methods to constrain the primordial curvature power spectrum based on the NANOGrav 15 year data set.The constraint on the primordial curvature power spectrum possesses a degree of generality,as the Taylor expansion can effectively approximate a wide range of function profiles.展开更多
Understanding the nature of primordial fluctuations is pivotal to unraveling the Universe's early evolution.While these fluctuations are observed to be nearly scale-invariant,quasi-adiabatic,and Gaussian on large ...Understanding the nature of primordial fluctuations is pivotal to unraveling the Universe's early evolution.While these fluctuations are observed to be nearly scale-invariant,quasi-adiabatic,and Gaussian on large scales,their small-scale behavior remains poorly constrained,offering a potential window into new physics.Recent detections of a stochastic gravitational wave background in the nanohertz frequency range by pulsar timing arrays(PTAs),including NANOGrav,PPTA,EPTA+In PTA,and CPTA,align with astrophysical predictions from supermassive black hole binaries but could also encode signatures of primordial phenomena.We investigate whether the observed signal originates from primordial isocurvature or adiabatic fluctuations by fitting them to the latest NANOGrav dataset.Through comprehensive Bayesian model comparison,we evaluate the distinguishability of these scenarios given current PTA sensitivities.Our results demonstrate that existing data cannot conclusively differentiate between isocurvature and adiabatic sources,highlighting the need for enhanced observational capabilities to probe the primordial universe at small scales.展开更多
Several pulsar timing array(PTA) collaborations have recently reported the evidence for a stochastic gravitational-wave background(SGWB), which can unveil the formation of primordial seeds of inhomogeneities in the ea...Several pulsar timing array(PTA) collaborations have recently reported the evidence for a stochastic gravitational-wave background(SGWB), which can unveil the formation of primordial seeds of inhomogeneities in the early universe. With the SGWB parameters inferred from PTAs data, we can make a prediction of the seeds for early galaxy formation from the domain walls in the axion-like particles(ALPs) field distribution. This also naturally provides a solution to the observation of high redshifts by the James Webb Space Telescope. The predicted photon coupling of the ALP is within the reach of future experimental searches.展开更多
In pulsar timing, timing residuals are the differences between the observed times of arrival and predictions from the timing model. A comprehensive timing model will produce featureless resid- uals, which are presumab...In pulsar timing, timing residuals are the differences between the observed times of arrival and predictions from the timing model. A comprehensive timing model will produce featureless resid- uals, which are presumably composed of dominating noise and weak physical effects excluded from the timing model （e.g. gravitational waves）. In order to apply optimal statistical methods for detecting weak gravitational wave signals, we need to know the statistical properties of noise components in the residuals. In this paper we utilize a variety of non-parametric statistical tests to analyze the whiteness and Gaussianity of the North American Nanohertz Observatory for Gravitational Waves （NANOGrav） 5- year timing data, which are obtained from Arecibo Observatory and Green Bank Telescope from 2005 to 2010. We find that most of the data are consistent with white noise; many data deviate from Gaussianity at different levels, nevertheless, removing outliers in some pulsars will mitigate the deviations.展开更多
The underlying physics of QCD phase transition in the early Universe remains largely unknown due to its strong-coupling nature during the quark-gluon plasma/hadron gas transition,yet a holographic model has been propo...The underlying physics of QCD phase transition in the early Universe remains largely unknown due to its strong-coupling nature during the quark-gluon plasma/hadron gas transition,yet a holographic model has been proposed to quantitatively fit the lattice QCD data while with its duration of the first-order phase transition(FoPT)left undetermined.At specific baryon chemical poten-tial,the first-order QCD phase transition agrees with the observational constraint of baryon asymmetry.It,therefore,provides a scenario for phase transition gravitational waves(GWs)within the standard model of particle physics.If these background GWs could contribute dominantly to the recently claimed common-spectrum red noise from pulsar timing array(PTA)observations,the duration of this FoPT can be well constrained,and the associated primordial black holes are still allowed by current observations.展开更多
Recent pulsar timing observations using MeerKAT of the eccentric binary millisecond pulsar,PSR J0514−4002E,have unveiled a companion with a mass in the mass gap,ranging from 2.09 M_(⊙)to 2.71 M_(⊙).This challenges c...Recent pulsar timing observations using MeerKAT of the eccentric binary millisecond pulsar,PSR J0514−4002E,have unveiled a companion with a mass in the mass gap,ranging from 2.09 M_(⊙)to 2.71 M_(⊙).This challenges conventional astrophysical scenarios for black hole formation.In this paper,we present an alternative explanation:PSR J0514−4002E could be in a PBH-NS binary,with the companion potentially being a primordial black hole formed during the early Universe’s first-order phase transition.The associated stochastic gravitational-wave background generated during this phase transition can account for the observed signal from the pulsar timing array,and the abundance of primordial black holes is consistent with constraints from LIGO-VirgoKAGRA.展开更多
We perform the first search for an isotropic non-tensorial gravitational-wave background(GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves(NANOGrav)...We perform the first search for an isotropic non-tensorial gravitational-wave background(GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse(ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is 107 ± 7, but no statistically significant evidence for the tensor transverse, vector longitudinal, and scalar longitudinal polarization modes. The median and the 90% equal-tail amplitudes of ST mode are ■ , or equivalently the energy density parameter per logarithm frequency is ■, at frequency of 1/year.展开更多
Several pulsar timing array(PTA)collaborations,including NANOGrav,EPTA,PPTA,and CPTA,have announced the evidence for a stochastic signal consistent with a stochastic gravitational wave background(SGWB).Supermassive bl...Several pulsar timing array(PTA)collaborations,including NANOGrav,EPTA,PPTA,and CPTA,have announced the evidence for a stochastic signal consistent with a stochastic gravitational wave background(SGWB).Supermassive black hole binaries(SMBHBs)are supposed to be the most promising gravitational-wave(GW)sources for this signal.In this paper,we use the NANOGrav 15-year data set to constrain the parameter space in an astro-informed formation model for SMBHBs.Our results prefer a large turn-over eccentricity of the SMBHB orbit when GWs begin to dominate the SMBHB evolution.Furthermore,the SGWB spectrum is extrapolated to the space-borne GW detector frequency band by including inspiral-merge-cutoff phases of SMBHBs,indicating that the SGWB from SMBHBs should be detected by LISA,Taiji and Tian Qin in the near future.展开更多
Several Pulsar Timing Array(PTA)Collaborations have recently provided strong evidence for a n Hz Stochastic Gravitational-Wave Background(SGWB).Here we investigate the implications of a firstorder phase transition occ...Several Pulsar Timing Array(PTA)Collaborations have recently provided strong evidence for a n Hz Stochastic Gravitational-Wave Background(SGWB).Here we investigate the implications of a firstorder phase transition occurring within the early Universe's dark quantum chromodynamics epoch,specifically within the framework of the mirror twin Higgs dark sector model.Our analysis indicates a distinguishable SGWB signal originating from this phase transition,which can explain the measurements obtained by PTAs.Remarkably,a significant portion of the parameter space for the SGWB signal also effectively resolves the existing tensions in both the H_(0) and S_(8) measurements in Cosmology.This intriguing correlation suggests a possible common origin of these three phenomena for 0.2<ΔN_(eff)<0.5,where the mirror dark matter component constitutes less than 30% of the total dark matter abundance.Nextgeneration CMB experiments such as CMB-S4 can test this parameter region.展开更多
Recently, the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) claimed the detection of a stochastic common-spectrum process of the pulsar timing array(PTA) time residuals from their 12.5 year da...Recently, the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) claimed the detection of a stochastic common-spectrum process of the pulsar timing array(PTA) time residuals from their 12.5 year data, which might be the first detection of the stochastic background of gravitational waves(GWs). We show that the amplitude and the power index of such waves imply that they could be the secondary GWs induced by the peaked curvature perturbation with a dust-like post inflationary era with-0.091 ≤ w ≤ 0.048. Such stochastic background of GWs naturally predicts substantial existence of planet-mass primordial black holes(PBHs), which can be the lensing objects for the ultrashort-timescale microlensing events observed by the Optical Gravitational Lensing Experiment(OGLE).展开更多
基金This work is supported by the National Key Research and Development Program of China Grant No.2020YFC2201502, grants from NSFC (Grant No.11 975 019,11 991 052,12 047 503)Key Research Program of Frontier Sciences, CAS, Grant NO. ZDBS-LY-7009+1 种基金CAS Project for Young Scientists in Basic Research YSBR-006the Key Research Program of the Chinese Academy of Sciences (Grant NO. XDPB15)。
文摘We search for isotropic stochastic gravitational-wave background(SGWB)in the International Pulsar Timing Array second data release.By modeling the SGWB as a power-law,we find very strong Bayesian evidence for a common-spectrum process,and further this process has scalar transverse(ST)correlations allowed in general metric theory of gravity as the Bayes factor in favor of the ST-correlated process versus the spatially uncorrelated common-spectrum process is 30±2.The median and the 90%equal-tail amplitudes of ST mode are A_(ST)=1.29^(+0.51)_(−0.44)×10^(−15),or equivalently the energy density parameter per logarithm frequency isΩSTGW=2.31^(+2.19)_(−1.30)×10^(−9),at frequency of 1 year−1.However,we do not find any statistically significant evidence for the tensor transverse(TT)mode and then place the 95%upper limits as A_(TT)<3.95×10^(−15),or equivalentlyΩ^(TT)_(GW)<2.16×10^(−9),at frequency of 1 year^(−1).
基金supported in part by the National Natural Science Foundation of China under Grant No.12305060the Talent-Introduction Program of Hubei Polytechnic University under Grant No.19xjk25R。
文摘The recent stochastic signal observed jointly by NANOGrav,parkes pulsar timing array,European pulsar timing array,and Chinese pulsar timing array can be accounted for by scalarinduced gravitational waves(SIGWs).The source of the SIGWs is from the primordial curvature perturbations,and the main contribution to the SIGWs is from the peak of the primordial curvature power spectrum.To effectively model this peak,we apply the Taylor expansion to parameterize it.With the Taylor expansion parameterization,we apply Bayesian methods to constrain the primordial curvature power spectrum based on the NANOGrav 15 year data set.The constraint on the primordial curvature power spectrum possesses a degree of generality,as the Taylor expansion can effectively approximate a wide range of function profiles.
基金supported by the National Natural Science Foundation of China(Grant No.12405056)supported by the National Natural Science Foundation of China(Grant No.12433001)the innovative research group of Hunan Province(Grant No.2024JJ1006)。
文摘Understanding the nature of primordial fluctuations is pivotal to unraveling the Universe's early evolution.While these fluctuations are observed to be nearly scale-invariant,quasi-adiabatic,and Gaussian on large scales,their small-scale behavior remains poorly constrained,offering a potential window into new physics.Recent detections of a stochastic gravitational wave background in the nanohertz frequency range by pulsar timing arrays(PTAs),including NANOGrav,PPTA,EPTA+In PTA,and CPTA,align with astrophysical predictions from supermassive black hole binaries but could also encode signatures of primordial phenomena.We investigate whether the observed signal originates from primordial isocurvature or adiabatic fluctuations by fitting them to the latest NANOGrav dataset.Through comprehensive Bayesian model comparison,we evaluate the distinguishability of these scenarios given current PTA sensitivities.Our results demonstrate that existing data cannot conclusively differentiate between isocurvature and adiabatic sources,highlighting the need for enhanced observational capabilities to probe the primordial universe at small scales.
基金supported by the National Natural Science Foundation of China (Grant Nos.12275134,12147228,12335005,and 12275232)by Maxim Khlopov was carried out at Southern Federal University with financial support from the Ministry of Science and Higher Education of the Russian Federation (Grant No.GZ0110/2310-IF)+2 种基金supported by the National Natural Science Foundation of China (Grant Nos.12005180,and 12305113)the Natural Science Foundation of Shandong Province (Grant Nos.ZR2020QA083,and ZR2022QA026)the Project of Shandong Province Higher Educational Science and Technology Program (Grant No.2022KJ271)。
文摘Several pulsar timing array(PTA) collaborations have recently reported the evidence for a stochastic gravitational-wave background(SGWB), which can unveil the formation of primordial seeds of inhomogeneities in the early universe. With the SGWB parameters inferred from PTAs data, we can make a prediction of the seeds for early galaxy formation from the domain walls in the axion-like particles(ALPs) field distribution. This also naturally provides a solution to the observation of high redshifts by the James Webb Space Telescope. The predicted photon coupling of the ALP is within the reach of future experimental searches.
基金supported by the National Science Foundation(NSF)under PIRE grant0968296support by the National Natural Science Foundation of China(Grant Nos.11503007,91636111 and 11690021)+2 种基金partial support through the New York Space Grant Consortiumsupport by NASA through the Einstein Fellowship grant PF4-150120upport from the JPL RTD program
文摘In pulsar timing, timing residuals are the differences between the observed times of arrival and predictions from the timing model. A comprehensive timing model will produce featureless resid- uals, which are presumably composed of dominating noise and weak physical effects excluded from the timing model （e.g. gravitational waves）. In order to apply optimal statistical methods for detecting weak gravitational wave signals, we need to know the statistical properties of noise components in the residuals. In this paper we utilize a variety of non-parametric statistical tests to analyze the whiteness and Gaussianity of the North American Nanohertz Observatory for Gravitational Waves （NANOGrav） 5- year timing data, which are obtained from Arecibo Observatory and Green Bank Telescope from 2005 to 2010. We find that most of the data are consistent with white noise; many data deviate from Gaussianity at different levels, nevertheless, removing outliers in some pulsars will mitigate the deviations.
基金supported by the National Key Research and Development Program of China(Grant Nos.2020YFC2201501,2021YFC2203004,and 2021YFA0718304)the National Natural Science Foundation of China(Grant Nos.12075101,12235016,12122513,12075298,12175243,12105344,11991052,12235019,and 12047503)+2 种基金the Fundamental Research Funds for the Central Universitiesthe Max Planck Partner Group Research Grantthe Science Research Grants from the China Manned Space Project(Grant No.CMS-CSST-2021-B01)。
文摘The underlying physics of QCD phase transition in the early Universe remains largely unknown due to its strong-coupling nature during the quark-gluon plasma/hadron gas transition,yet a holographic model has been proposed to quantitatively fit the lattice QCD data while with its duration of the first-order phase transition(FoPT)left undetermined.At specific baryon chemical poten-tial,the first-order QCD phase transition agrees with the observational constraint of baryon asymmetry.It,therefore,provides a scenario for phase transition gravitational waves(GWs)within the standard model of particle physics.If these background GWs could contribute dominantly to the recently claimed common-spectrum red noise from pulsar timing array(PTA)observations,the duration of this FoPT can be well constrained,and the associated primordial black holes are still allowed by current observations.
基金supported by the National Natural Science Foundation of China(Grant No.12405056)the innovative research group of Hunan Province(Grant No.2024JJ1006)supported by the National Natural Science Foundation of China(Grant No.12433001).
文摘Recent pulsar timing observations using MeerKAT of the eccentric binary millisecond pulsar,PSR J0514−4002E,have unveiled a companion with a mass in the mass gap,ranging from 2.09 M_(⊙)to 2.71 M_(⊙).This challenges conventional astrophysical scenarios for black hole formation.In this paper,we present an alternative explanation:PSR J0514−4002E could be in a PBH-NS binary,with the companion potentially being a primordial black hole formed during the early Universe’s first-order phase transition.The associated stochastic gravitational-wave background generated during this phase transition can account for the observed signal from the pulsar timing array,and the abundance of primordial black holes is consistent with constraints from LIGO-VirgoKAGRA.
基金supported in part by the National Key R&D Program of China(2021YFC2203100)CAS Young Interdisciplinary Innovation Team(JCTD-2022–20)+8 种基金the National Natural Science Foundation of China(11875113,11961131007,12261131497,12003029,11833005,and 12192224)the 111 Project for“Observational and Theoretical Research on Dark Matter and Dark Energy”(B23042)Fundamental Research Funds for Central Universitiesthe Disposizione del Presidente INFN n.24433 in INFN Sezione di MilanoChina Postdoctoral Science Foundation(2023TQ0355)CSC Innovation Talent FundsUSTC Fellowship for International CooperationUSTC Research Funds of the Double First-Class InitiativeCAS project for young scientists in basic research(YSBR-006)。
基金supported by the National Key Research and Development Program of China (Grant No.2020YFC2201502)the National Natural Science Foundation of China (Grant Nos.11975019,11690021,11991052,and 12047503)+2 种基金the Key Research Program of Frontier Sciences,Chinese Academy of Sciences (Grant No.ZDBS-LY-7009)the Chinese Academy of Sciences Project for Young Scientists in Basic Research (Grant No.YSBR006)the Key Research Program of the Chinese Academy of Sciences (Grant No.XDPB15)。
文摘We perform the first search for an isotropic non-tensorial gravitational-wave background(GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse(ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is 107 ± 7, but no statistically significant evidence for the tensor transverse, vector longitudinal, and scalar longitudinal polarization modes. The median and the 90% equal-tail amplitudes of ST mode are ■ , or equivalently the energy density parameter per logarithm frequency is ■, at frequency of 1/year.
基金supported by the National Natural Science Foundation of China(Grant Nos.12250010,11975019,11991052,and 12047503)the Key Research Program of Frontier Sciences,CAS(Grant No.ZDBS-LY-7009)+3 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-006)the Key Research Program of the Chinese Academy of Sciences(Grant No.XDPB15)supported by the National Natural Science Foundation of China(Grant Nos.12247176,and 12247112)the China Postdoctoral Science Foundation Fellowship(Grant No.2022M710429)。
文摘Several pulsar timing array(PTA)collaborations,including NANOGrav,EPTA,PPTA,and CPTA,have announced the evidence for a stochastic signal consistent with a stochastic gravitational wave background(SGWB).Supermassive black hole binaries(SMBHBs)are supposed to be the most promising gravitational-wave(GW)sources for this signal.In this paper,we use the NANOGrav 15-year data set to constrain the parameter space in an astro-informed formation model for SMBHBs.Our results prefer a large turn-over eccentricity of the SMBHB orbit when GWs begin to dominate the SMBHB evolution.Furthermore,the SGWB spectrum is extrapolated to the space-borne GW detector frequency band by including inspiral-merge-cutoff phases of SMBHBs,indicating that the SGWB from SMBHBs should be detected by LISA,Taiji and Tian Qin in the near future.
基金supported by the National Key Research and Development Program of China(2022YFF0503304,and 2022YFF0503301)the National Natural Science Foundation of China(11921003,and 12003069)+1 种基金the New Cornerstone Science Foundation through the XPLORER PRIZE,the Chinese Academy of Sciencesthe Entrepreneurship and Innovation Program of Jiangsu Province。
文摘Several Pulsar Timing Array(PTA)Collaborations have recently provided strong evidence for a n Hz Stochastic Gravitational-Wave Background(SGWB).Here we investigate the implications of a firstorder phase transition occurring within the early Universe's dark quantum chromodynamics epoch,specifically within the framework of the mirror twin Higgs dark sector model.Our analysis indicates a distinguishable SGWB signal originating from this phase transition,which can explain the measurements obtained by PTAs.Remarkably,a significant portion of the parameter space for the SGWB signal also effectively resolves the existing tensions in both the H_(0) and S_(8) measurements in Cosmology.This intriguing correlation suggests a possible common origin of these three phenomena for 0.2<ΔN_(eff)<0.5,where the mirror dark matter component constitutes less than 30% of the total dark matter abundance.Nextgeneration CMB experiments such as CMB-S4 can test this parameter region.
基金supported by the National Key Research and Development Program of China(Grant No.2020YFC2201502)supported by the European Union’s Horizon 2020 Research and Innovation Program under the Marie Sk?odowska-Curie(Grant No.754496)+4 种基金supported by the Key Research Program of the Chinese Academy of Sciences(Grant No.XDPB15)the Chinese Academy of Sciences Project for Young Scientists in Basic Research(Grant No.YSBR-006)the National Natural Science Foundation of China(Grant No.12047503)the Japan Society for the Promotion of Science Grant-in-Aid for Early-Career Scientists(Grant No.JP20K14461)the World Premier International Research Center Initiative(WPI Initiative),MEXT,Japan。
文摘Recently, the North American Nanohertz Observatory for Gravitational Waves(NANOGrav) claimed the detection of a stochastic common-spectrum process of the pulsar timing array(PTA) time residuals from their 12.5 year data, which might be the first detection of the stochastic background of gravitational waves(GWs). We show that the amplitude and the power index of such waves imply that they could be the secondary GWs induced by the peaked curvature perturbation with a dust-like post inflationary era with-0.091 ≤ w ≤ 0.048. Such stochastic background of GWs naturally predicts substantial existence of planet-mass primordial black holes(PBHs), which can be the lensing objects for the ultrashort-timescale microlensing events observed by the Optical Gravitational Lensing Experiment(OGLE).
