arXiv subjects

Zong-Hong Zhu

Publications and source records attributed to Zong-Hong Zhu.

At least 73 records · Page 4Linked to original sources

arXiv2022

Direct measurement of the distribution of dark matter with strongly lensed gravitational waves

In this Letter, we present a new idea of probing the distribution of dark matter exhibiting elastic and velocity-independent self-interactions. These interactions might be revealed in multiple measurements of strongly lensed gravitational waves, which can be observationally explored to determine the strength of self-scatterings. Specifically, each individual galactic-scale strong-lensing system whose source is a coalescing compact binary emitting gravitational waves will provide a model-independent measurement of the shear viscosity of dark matter along the line of sight. These individual measurements could be a probe of large-scale distribution of dark matter and its properties. Our results indicate that with 10-1000 strongly lensed gravitational waves from ET and DECIGO, robust constraints on the large-scale distribution of self-interacting dark matter might be produced. More stringent limits on the dark matter scattering cross-section per unit mass ($σ_χ/m_χ$) relevant to galaxy and cluster scales are also expected, compared with the conservative estimates obtained in the electromagnetic domain. Finally, we discuss the effectiveness of our method in the context of self-interacting dark matter particle physics.

astro-ph.CO↗

arXiv2022

Dark photon bursts from compact binary systems and constraints

In this work, we consider the burst signal of the dark photon, the hypothetical vector boson of the $U(1)_B$ or $U(1)_{B-L}$ gauge group, generated by a compact binary star system. The absence of the signal in the laser interferometer puts bounds on the coupling constant $ε$ to the ordinary matter. It turns out that if the dark photon is massless, $ε^2$ is on the order of $10^{-37}-10^{-33}$ at most; in the massive case, the upper bound of $ε^2$ is about $10^{-38}-10^{-31}$ in the mass range from $10^{-19}$ eV to $10^{-11}$ eV. These are the first bounds derived from the interferometer observations independent of the assumption of dark photons being dark matter.

hep-ph↗

arXiv2022

Gravitational memory effects in Chern-Simons modified gravity

The gravitational memory effects of Chern-Simons modified gravity are considered in the asymptotically flat spacetime. If the Chern-Simons scalar does not directly couple with the ordinary matter fields, there are also displacement, spin and center-of-mass memory effects as in general relativity. This is because the term of the action that violates the parity invariance is linear in the scalar field but quadratic in the curvature tensor. This results in the parity violation occuring at the higher orders in the inverse luminosity radius. The scalar field does not induce any new memory effects that can be detected by interferometers or pulsar timing arrays. The asymptotic symmetry is group is also the extended Bondi-Metzner-Sachs group. The constraints on the memory effects excited by the tensor modes are obtained.

gr-qc↗

arXiv2021

DECi-hertz Interferometer Gravitational-wave Observatory: Forecast constraints on the cosmic curvature with LSST strong lenses

In this paper, we aim at using the DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO), a future Japanese space gravitational-wave antenna sensitive to frequency range between LISA and ground-based detectors, to provide gravitational-wave constraints on the cosmic curvature at $z\sim 5$. In the framework of the well-known distance sum rule, the perfect redshift coverage of the standard sirens observed by DECIGO, compared with lensing observations including the source and lens from LSST, makes such cosmological-model-independent test more natural and general. Focusing on three kinds of spherically symmetric mass distributions for the lensing galaxies, we find that the cosmic curvature is expected to be constrained with the precision of $ΔΩ_K \sim 10^{-2}$ in the early universe ($z\sim5.0$), improving the sensitivity of ET constraints by about a factor of 10. However, in order to investigate this further, the mass density profiles of early-type galaxies should be properly taken into account. Specially, our analysis demonstrates the strong degeneracy between the spatial curvature and the lens parameters, especially the redshift evolution of power-law lens index parameter. When the extended power law mass density profile is assumed, the weakest constraint on the cosmic curvature can be obtained. Whereas, the addition of DECIGO to the combination of LSST+DECIGO does improve the constraint on the luminosity density slope and the anisotropy of the stellar velocity dispersion significantly. Therefore, our paper highlights the benefits of synergies between DECIGO and LSST in constraining new physics beyond the standard model, which could manifest itself through accurate determination of the cosmic curvature.

astro-ph.CO↗

arXiv2021

Event rate predictions of strongly lensed gravitational waves with detector networks and more realistic templates

Strong lensing of gravitational waves (GWs) is attracting growing attention of the community. The event rates of lensed GWs by galaxies were predicted in numerous papers, which used some approximations to evaluate the GW strains detectable by a single detector. The joint-detection of GW signals by a network of instruments will increase the detecting ability of fainter and farther GW signals, which could increase the detection rate of the lensed GWs, especially for the 3rd generation detectors, e.g., Einstein Telescope (ET) and Cosmic Explorer (CE). Moreover, realistic GW templates will improve the accuracy of the prediction. In this work, we consider the detection of galaxy-scale lensed GW events under the 2nd, 2.5th, and 3rd generation detectors with the network scenarios and adopt the realistic templates to simulate GW signals. Our forecast is based on the Monte Carlo technique which enables us to take Earth's rotation into consideration. We find that the overall detection rate is improved, especially for the 3rd generation detector scenarios. More precisely, it increases by ~37% adopting realistic templates, and under network detection strategy, further increases by ~58% comparing with adoption of the realistic templates, and we estimate that the 3rd generation GW detectors will detect hundreds lensed events per year. The effect from the Earth's rotation is weakened in the detector network strategy.

astro-ph.GA↗

arXiv2021

Redshift evolution of the Amati relation: calibrated results from the Hubble diagram of quasars at high redshifts

Gamma-ray bursts (GRBs) have long been proposed as a complementary probe to type Ia supernovae (SNe Ia) and cosmic microwave background to explore the expansion history of the high-redshift universe, mainly because they are bright enough to be detected at greater distances. Although they lack definite physical explanations, many empirical correlations between GRB isotropic energy/luminosity and some directly detectable spectral/temporal properties have been proposed to make GRBs standard candles. Since the observed GRB rate falls off rapidly at low redshifts, thus preventing a cosmology independent calibration of these correlations. In order to avoid the circularity problem, SN Ia data are usually used to calibrate the luminosity relations of GRBs in the low redshift region (limited by the redshift range for SN Ia sample), and then extrapolate it to the high redshift region. This approach is based on the assumption of no redshift evolution for GRB luminosity relations. In this work, we suggest the use a complete quasar sample in the redshift range of $0.5<z<5.5$ to test such an assumption. We divide the quasar sample into several sub-samples with different redshift bins, and use each sub-sample to calibrate the isotropic $γ$-ray equivalent energy of GRBs in relevant redshift bins. By fitting the newly calibrated data, we find strong evidence that the most commonly used Amati relation between spectral peak energy and isotropic-equivalent radiated energy shows no, or marginal, evolution with redshift. Indeed, at different redshifts, the coefficients in the Amati relation could have a maximum variation of 0.93\% at different redshifts, and there could be no coincidence in the range of 1$σ$.

astro-ph.HE↗

arXiv2021

Inspiraling double compact object detection and lensing rate -- forecast for DECIGO and B-DECIGO

Emergence of gravitational wave (GW) astronomy revived the interest in exploring the low frequency GW spectrum inaccessible from the ground. Satellite GW observatory DECIGO in its original configuration and the currently proposed smaller scale B-DECIGO are aimed to cover deci-Hertz part of the GW spectrum, which fills the gap between LISA mili-Hertz and deca- to kilo-Hertz range probed by ground-based detectors. In this paper we forecast the detection rates of inspiraling double compact objects (DCOs) and the unresolved confusion noise from these sources in DECIGO and B-DECIGO. In the context of DECIGO we use, for the first time, the population synthesis intrinsic inspiral rates of NS-NS, BH-NS and BH-BH systems. We also estimate the expected gravitational lensing rates of such sources for DECIGO and B-DECIGO. The result is that yearly detection of DCOs inspirals for the DECIGO is of order of $10^4 - 10^5$, while for a much smaller scale B-DECIGO they are about $10^2 - 10^4$ depending on the DCO population considered. Taking into account that considerable part of these events would be detectable by ground-based GW observatories the added value of DECIGO/B-DECIGO could be substantial. DECIGO will also be able to register $5-50$ lensed NS-NS inspirals and up to O(100) BH-BH inspirals. On the contrary, predictions for the B-DECIGO are pessimistic: only the optimistic common envelope scenario of DCO formation could yield a few lensed BH-BH inspirals per year. We also address the question of the magnification bias in the GW event catalogs of DECIGO and B-DECIGO.

astro-ph.HE↗

arXiv2021

Optimized localization for gravitational-waves from merging binaries

The Advanced LIGO and Virgo gravitational wave observatories have opened a new window with which to study the inspiral and mergers of binary compact objects. These observations are most powerful when coordinated with multi-messenger observations. This was underlined by the first observation of a binary neutron star merger GW170817, coincident with a short Gamma-ray burst, GRB170817A, and the identification of the host galaxy NGC~4993 from the optical counterpart AT~2017gfo. Finding the fast-fading optical counterpart critically depends on the rapid production of a sky-map based on LIGO/Virgo data. Currently, a rapid initial sky map is produced followed by a more accurate, high-latency, $\gtrsim{12}{\rm{hr}}$ sky map. We study optimization choices of the Bayesian prior and signal model which can be used alongside other approaches such as reduced order quadrature. We find these yield up to a $60\%$ reduction in the time required to produce the high-latency localisation for binary neutron star mergers.

gr-qc↗

arXiv2021

Diagnosing the cosmic coincidence problem and its evolution with recent observations

In the framework of a phenomenological cosmological model with the assumption of $ρ_{X} \propto ρ_{m} a^ξ$ ($ρ_{X}$ and $ρ_{m} $ are the energy densities of dark energy and matter, respectively.), we intend to diagnose the cosmic coincidence problem by using the recent samples of Type Ia supernovae (SNe Ia), baryon acoustic oscillation (BAO) and cosmic microwave background (CMB). $ξ$ is a key parameter to characterize the severity of the coincidence problem, wherein $ξ=3$ and $0$ correspond to the $Λ$CDM scenario and the self-similar solution without the coincidence problem, respectively. The case of $ξ= Constant$ has been investigated in the previous studies, while we further consider the case of $ξ(z) = ξ_{0} + ξ_{z}*\frac{z}{1+z}$ to explore the possible evolution. A joint analysis of the Pantheon SNe Ia sample with the recent BAO and CMB data figures out that $ξ=3.28\pm0.15$ in the case of $ξ= Constant$ at $68\%$ confidence level (CL), in addition, $ξ_{0} = 2.78_{-1.01}^{+0.28}$ and $ξ_{z} = 0.93_{-0.91}^{+1.56}$ in the case of $ξ(z)$ at $68\%$ CL. It implies that the temporal evolution of the scaling parameter $ξ$ is accepted by the joint sample at $68\%$ CL; however, the joint sample also cannot distinguish whether the scaling parameter $ξ$ is variable or not at 95\% CL. Moreover, the $Λ$CDM scenario is accepted by the joint sample at $95\%$ CL in both cases, and the coincidence problem still exists. In addition, we apply the Bayesian evidence to compare the models with the analysis of the joint sample, it turns out that the $Λ$CDM scenario is most supported by the joint sample; furthermore, the joint sample prefers the scenario with a constant $ξ$ to the one with a variable $ξ(z)$.

astro-ph.CO↗

arXiv2021

Constraining cosmological parameters from strong lensing with DECIGO and B-DECIGO sources

Gravitational lensing has long been used to measure or constrain cosmology models. Although the lensing effect of gravitational waves has not been observed by LIGO/Virgo, it is expected that there can be a few to a few hundreds lensed events to be detected by the future Japanese space-borne interferometers DECIGO and B-DECIGO, if they are running for 4 years. Given the predicted lensed gravitational wave events, one can estimate the constraints on the cosmological parameters via the lensing statistics and the time delay methods. With the lensing statistics method, the knowledge of the lens redshifts, even with the moderate uncertainty, will set the tight bound on the energy density parameter $Ω_M$ for matter, that is, $0.288\lesssimΩ_M\lesssim0.314$ at best. The constraint on the Hubble constant $H_0$ can be determined using the time delay method. It is found out that at $5σ$, $|δH_0|/H_0$ ranges from $3\%$ to $11\%$ for DECIGO, and B-DECIGO will give less constrained results, $8\%-15\%$. In this work, the uncertainties on the luminosity distance and the time delay distance are set to be $10\%$ and $20\%$, respectively. The improvement on measuring these distances will tighten the bounds.

astro-ph.CO↗

arXiv2021

Analyzing the Stability of Non-coplanar Circumbinary Planets using Machine Learning

Exoplanet detection in the past decade by efforts including NASA's Kepler and TESS missions has discovered many worlds that differ substantially from planets in our own Solar system, including more than 400 exoplanets orbiting binary or multi-star systems. This not only broadens our understanding of the diversity of exoplanets, but also promotes our study of exoplanets in the complex binary and multi-star systems and provides motivation to explore their habitability. In this study, we analyze orbital stability of exoplanets in non-coplanar circumbinary systems using a numerical simulation method, with which a large number of circumbinary planet samples are generated in order to quantify the effects of various orbital parameters on orbital stability. We also train a machine learning model that can quickly determine the stability of the circumbinary planetary systems. Our results indicate that larger inclinations of the planet tend to increase the stability of its orbit, but change in the planet's mass range between Earth and Jupiter has little effect on the stability of the system. In addition, we find that Deep Neural Networks (DNNs) have higher accuracy and precision than other machine learning algorithms.

astro-ph.EP↗

arXiv2021

Cosmological consequences of a scalar field with oscillating equation of state. III. Unifying inflation with dark energy and small tensor-to-scalar ratio

We investigate the inflationary consequences of the oscillating dark energy model proposed by Tián [\href{https://doi.org/10.1103/PhysRevD.101.063531}{Phys. Rev. D {\bf 101}, 063531 (2020)}], which aims to solve the cosmological coincidence problem with multi-accelerating Universe (MAU). We point out that the inflationary dynamics belong to slow-roll inflation. The spectral index of scalar perturbations and the tensor-to-scalar ratio $r$ are shown to be consistent with current \textit{Planck} measurements. Especially, this model predicts $r\sim10^{-7}$, which is far below the observation limits. This result motivates us to explore the smallness of $r$ in the general MAU. We propose a quintessential generalization of the original model and prove $r<0.01$ in general. The null detection to date of primordial gravitational waves provides a circumstantial evidence for the MAU. After the end of inflation, the scalar field rolls toward infinity instead of a local minimum, and meanwhile its equation of state is oscillating with an average value larger than $1/3$. In this framework, we show that gravitational particle creation at the end of inflation is capable of reheating the Universe.

astro-ph.CO↗

arXiv2021

Inflationary attractors from a non-canonical kinetic term

We show explicitly how the T-model, E-model, and Hilltop inflations are obtained from the inflation models with a non-canonical kinetic term and an arbitrary potential. By this method, any attractor of observables $n_s$ and $r$ is possible. The presence of attractors poses a challenge to differentiate inflation models.

gr-qc↗

arXiv2021

Hubble diagram at higher redshifts: Model independent calibration of quasars

In this paper, we present a model-independent approach to calibrate the largest quasar sample. Calibrating quasar samples is essentially constraining the parameters of the linear relation between the $\log$ of the ultraviolet (UV) and X-ray luminosities. This calibration allows quasars to be used as standardized candles. There is a strong correlation between the parameters characterizing the quasar luminosity relation and the cosmological distances inferred from using quasars as standardized candles. We break this degeneracy by using Gaussian process regression to model-independently reconstruct the expansion history of the Universe from the latest type Ia supernova observations. Using the calibrated quasar dataset, we further reconstruct the expansion history up to redshift of $z\sim 7.5$. Finally, we test the consistency between the calibrated quasar sample and the standard $\rmΛCDM$ model based on the posterior probability distribution of the GP hyperparameters. Our results show that the quasar sample is in good agreement with the standard $\rmΛCDM$ model in the redshift range of the supernova, despite of mildly significant deviations taking place at higher redshifts. Fitting the standard $\rmΛCDM$ model to the calibrated quasar sample, we obtain a high value of the matter density parameter $Ω_m = 0.382^{+0.045}_{-0.042}$, which is marginally consistent with the constraints from other cosmological observations.

astro-ph.CO↗

arXiv2021

A higher-multipole gravitational waveform model for an eccentric binary black holes based on the effective-one-body-numerical-relativity formalism

We construct a new factorized waveform including $(l,|m|)=(2,2),(2,1),(3,3),(4,4)$ modes based on effective-one-body (EOB) formalism, which is valid for spinning binary black holes (BBH) in general equatorial orbit. When combined with the dynamics of $\texttt{SEOBNRv4}$, the $(l,|m|)=(2,2)$ mode waveform generated by this new waveform can fit the original $\texttt{SEOBNRv4}$ waveform very well in the case of a quasi-circular orbit. We have calibrated our new waveform model to the Simulating eXtreme Spacetimes (SXS) catalog. The comparison is done for BBH with total mass in $(20,200)M_\odot$ using Advanced LIGO designed sensitivity. For the quasi-circular cases we have compared our $(2,2)$ mode waveforms to the 281 numerical relativity (NR) simulations of BBH along quasi-circular orbits. All of the matching factors are bigger than 98\%. For the elliptical cases, 24 numerical relativity simulations of BBH along an elliptic orbit are used. For each elliptical BBH system, we compare our modeled gravitational polarizations against the NR results for different combinations of the inclination angle, the initial orbit phase and the source localization in the sky. We use the the minimal matching factor respect to the inclination angle, the initial orbit phase and the source localization to quantify the performance of the higher modes waveform. We found that after introducing the high modes, the minimum of the minimal matching factor among the 24 tested elliptical BBHs increases from 90\% to 98\%. Following our previous $\texttt{SEOBNRE}$ waveform model, we call our new waveform model $\texttt{SEOBNREHM}$. Our $\texttt{SEOBNREHM}$ waveform model can match all tested 305 SXS waveforms better than 98\% including highly spinning ($χ=0.99$) BBH, highly eccentric ($e\approx0.15$) BBH and large mass ratio ($q=10$) BBH.

gr-qc↗

arXiv2021

Early dark energy in $k$-essence

Early dark energy (EDE) that becomes subdominant around the epoch of matter-radiation equality can be used to ease the Hubble tension. However, there is a theoretical problem that why the energy scale of EDE is in coincidence with that of matter-radiation equality when their physics are completely unrelated. Sakstein and Trodden [Phys. Rev. Lett. 124, 161301 (2020)] proposed a mechanism to solve this coincidence problem with $\mathcal{O}({\rm eV})$-mass neutrino. In this paper, in order to solve the coincidence problem, we propose a new scenario for EDE, in which the onset and ending of EDE are triggered by the radiation-matter transition. The specific example we study is a $k$-essence model. The cosmic evolution equations can be recast into a two-dimensional dynamical system and its main properties are analyzed. Our results suggest that $k$-essence seems unable to realize the new scenario for EDE. However, an EDE model with different scenario is realized in $k$-essence. In this model, the ending of EDE can be triggered by the radiation-matter transition while the onset depends on the initial conditions of the scalar field. Therefore, the obtained model can only be used to solve half of the coincidence problem. The full resolution in the framework of our initial proposed scenario is worthy of more research.

gr-qc↗

arXiv2021

"Conserved charges" of the Bondi-Metzner-Sachs algebra in the Brans-Dicke theory

The asymptotic symmetries in Brans-Dicke theory are analyzed using Penrose's conformal completion method, which is independent of the coordinate system used. These symmetries indeed include supertranslations and Lorentz transformations for an asymptotically flat spacetime. With the Wald-Zoupas formalism, "conserved charges" and fluxes of the Bondi-Metzner-Sachs algebra are computed. The scalar degree of freedom contributes only to the Lorentz boost charge, although it plays a role in various fluxes. The flux-balance laws are further used to constrain displacement memory, spin memory and center-of-mass memory effects.

gr-qc↗

arXiv2021

Lensing rates of gravitational wave signals displaying beat patterns detectable by DECIGO and B-DECIGO

The coherent nature of gravitational wave emanating from a compact binary system makes it possible to detect some interference patterns in two (or more) signals registered simultaneously by the detector. Gravitational lensing effect can be used to bend trajectories of gravitational waves, which might reach the detector at the same time. Once this happens, a beat pattern may form, and can be used to obtain the luminosity distance of the source, the lens mass, and cosmological parameters such as the Hubble constant. Crucial question is how many such kind of events could be detected. In this work, we study this issue for the future space-borne detectors: DECIGO and its downscale version, B-DECIGO. It is found out that there can be a few tens to a few hundreds of lensed gravitational wave events with the beat pattern observed by DECIGO and B-DECIGO per year, depending on the evolution scenario leading to the formation of double compact objects. In particular, black hole-black hole binaries are dominating population of lensed sources in which beat patterns may reveal. However, DECIGO could also register a considerable amount of lensed signals from binary neutron stars, which might be accompanied by electromagnetic counterparts. Our results suggest that, in the future, lensed gravitational wave signal with the beat pattern could play an important role in cosmology and astrophysics.

gr-qc↗