Measuring the anisotropies in astrophysical and cosmological gravitational-wave backgrounds with Taiji and LISA networks

We investigate the capabilities of space-based gravitational-wave detector networks,specifically Taiji and LISA,to measure the anisotropies in stochastic gravitational-wave background(SGWB),which are characterized by the angular power spectrum.We find that a detector network can improve the measurement precision of anisotropies by at most fourteen orders of magnitude,depending on the angular multipoles.By doing so,we can enhance our understanding of the physical origins of SGWB,both in astrophysical and cosmological contexts.We assess the prospects of the detector networks for measuring the parameters of angular power spectrum.We further find an inevitable effect of cosmic variance,which can be suppressed by a better angular resolution,strengthening the importance of configuring detector networks.Our findings also suggest a potential detection of the kinematic dipole due to Doppler boosting of SGWB.

Prospects for improving cosmological parameter estimation with gravitational-wave standard sirens from Taiji

Taiji,a space-based gravitational-wave observatory,consists of three satellites forming an equilateral triangle with arm length of 3×10^6 km,orbiting around the Sun.Taiji is able to observe the gravitationalwave standard siren events of massive black hole binary(MBHB)merger,which is helpful in probing the expansion of the universe.In this paper,we preliminarily forecast the capability of Taiji for improving cosmological parameter estimation with the gravitational-wave standard siren data.We simulate fiveyear standard siren data based on three fiducial cosmological models and three models of MBHB’s formation and growth.It is found that the standard siren data from Taiji can effectively break the cosmological parameter degeneracies generated by the cosmic microwave background(CMB)anisotropies data,especially for dynamical dark energy models.The constraints on cosmological parameters are significantly improved by the data combination CMB+Taiji,compared to the CMB data alone.Compared to the current optical cosmological observations,Taiji can still provide help in improving the cosmological parameter estimation to some extent.In addition,we consider an ideal scenario to investigate the potential of Taiji on constraining cosmological parameters.We conclude that the standard sirens of MBHB from Taiji will become a powerful cosmological probe in the future.

Configuration uncertainty propagation of gravitational-wave observatory using a directional state transition tensor

Configuration stability is essential for a space-based Gravitational-Wave(GW)observatory,which can be impacted by orbit insertion uncertainties.Configuration uncertainty propagation is vital for investigating the influences of uncertainties on configuration stability and can be potentially useful in the navigation and control of GW observatories.Current methods suffer from drawbacks related to high computational burden.To this end,a Radial-Tangential-Ddirectional State Transition Tensor(RT-DSTT)-based configuration uncertainty propagation method is proposed.First,two sensitive directions are found by capturing the dominant secular terms.Considering the orbit insertion errors along the two sensitive directions only,a reduced-order RT-DSTT model is developed for orbital uncertainty propagation.Then,the relationship between the uncertainties in the orbital states and the uncertainties in the configuration stability indexes is mapped using highorder derivatives.The result is a semi-analytical solution that can predict the deviations in the configuration stability indexes given orbit insertion errors.The potential application of the proposed RT-DSTT-based method in calculating the feasible domain is presented.The performance of the proposed method is validated on the Laser Interferometer Space Antenna(LISA)project.Simulations show that the proposed method can provide similar results to the STT-based method but requires only half of the computational time.

Parameter estimation for Einstein-dilaton-Gauss-Bonnet gravity with ringdown signals

Future space-based gravitational-wave detectors will detect gravitational waves with high sensitivity in the millihertz frequency band,providing more opportunities to test theories of gravity than ground-based detectors.The study of quasinormal modes(QNMs)and their application in gravity theory testing have been an important aspect in the field of gravitational physics.In this study,we investigate the capability of future space-based gravitational wave detectors,such as LISA,TaiJi,and TianQin,to constrain the dimensionless deviating parameter for Einsteindilaton-Gauss-Bonnet(EdGB)gravity with ringdown signals from the merger of binary black holes.The ringdown signal is modeled by the two strongest QNMs in EdGB gravity.Considering time-delay interferometry,we calculate the signal-to-noise ratio of different space-based detectors for ringdown signals to analyze their capabilities.The Fisher information matrix is employed to analyze the accuracy of parameter estimation,with particular focus on the dimensionless deviating parameter for EdGB gravity.The impact of the parameters of gravitational wave sources on the estimation accuracy of the dimensionless deviating parameter is also studied.We find that the constraint ability of EdGB gravity is limited because the uncertainty of the dimensionless deviating parameter increases with a decrease in the dimensionless deviating parameter.LISA and TaiJi offer more advantages in constraining the dimensionless deviating parameter to a more accurate level for massive black holes,whereas TianQin is more suited to less massive black holes.The Bayesian inference method is used to perform parameter estimation on simulated data,which verifies the reliability of the conclusion.