arXiv subjects

Shuo Cao

Publications and source records attributed to Shuo Cao.

At least 73 records · Page 4Linked to original sources

arXiv2023

FAST Observations of FRB 20220912A: Burst Properties and Polarization Characteristics

We report the observations of FRB 20220912A using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We conducted 17 observations totaling 8.67 hours and detected a total of 1076 bursts with an event rate up to 390 hr$^{-1}$. The cumulative energy distribution can be well described using a broken power-law function with the lower and higher-energy slopes of $-0.38\pm0.02$ and $-2.07\pm0.07$, respectively. We also report the L band ($1-1.5$ GHz) spectral index of the synthetic spectrum of FRB~20220912A bursts, which is $-2.6\pm0.21$. The average rotation measure (RM) value of the bursts from FRB~20220912A is $-0.08\pm5.39\ \rm rad\,m^{-2}$, close to 0 $\rm rad\,m^{-2}$ and maintain relatively stable over two months. Most bursts have nearly 100\% linear polarization. About 45\% of the bursts have circular polarization with SNR $>$ 3, and the highest circular polarization degree can reach 70\%. Our observations suggest that FRB~20220912A is located in a relatively clean local environment with complex circular polarization characteristics. These various behaviors imply that the mechanism of circular polarization of FRBs likely originates from an intrinsic radiation mechanism, such as coherent curvature radiation or inverse Compton scattering inside the magnetosphere of the FRB engine source (e.g. a magnetar).

astro-ph.HE↗

arXiv2023

Modes mismatch induced variation of quantum coherence for two-mode localized Gaussian states in accelerated frame

Quantum coherence is the basic concept of superposition of quantum states and plays an important role in quantum metrology. We show how a pair of uniformly accelerated observers with a local two-mode Gaussian quantum state affects the Gaussian quantum coherence. We find that the quantum coherence decreases with increasing acceleration, which is due to the Unruh effect that destroys the quantum resource. Essentially, the variation of quantum coherence is caused by the modes mismatch between the input and output mode. Through 2000 randomly generated states, we demonstrate that such mismatch is dominated by the acceleration effect and mildly affected by the waveform parameters. Moreover, the squeezing parameter acted as a suppressor of the reduced coherence, but it tended to be invalid in the high squeezing. In addition, the squeezing parameter can act as a suppressor of the reduced coherence, but the effect of the squeezing parameter tends to be ineffective under high squeezing conditions.

quant-ph↗

arXiv2023

Measuring the speed of light with updated Hubble diagram of high-redshift standard candles

The possible time variation of the fundamental constants of nature has been an active subject of research in modern physics. In this paper, we propose a new method to investigate such possible time variation of the speed of light $c$ using the updated Hubble diagram of high-redshift standard candles including Type Ia Supernovae (SNe Ia) and high-redshift quasars (based on UV-X relation). Our findings show that the SNe Ia Pantheon sample, combined with currently available sample of cosmic chronometers, would produce robust constraints on the speed of light at the level of $c/c_0=1.03\pm0.03$. For the Hubble diagram of UV+X ray quasars acting as a new type of standard candles, we obtain $c/c_0=1.19\pm0.07$. Therefore, our results confirm that there is no strong evidence for the deviation from the constant speed of light up to $z\sim 2$. Moreover, we discuss how our technique might be improved at much higher redshifts ($z\sim5$), focusing on future measurements of the acceleration parameter $X(z)$ with gravitational waves (GWs) from binary neutron star mergers. In particular, in the framework of the second-generation space-based GW detector, DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO), the speed of light is expected to be constrained with the precision of $Δ{c}/c=10^{-3}$.

astro-ph.CO↗

arXiv2023

Time evolution of the local gravitational parameters and gravitational wave polarizations in a relativistic MOND theory

The recently proposed Skordis-Złośnik theory is the first relativistic MOND theory that can recover the success of the standard $Λ$CDM model at matching observations of the cosmic microwave background. This paper aims to revisit the Newtonian and MOND approximations and the gravitational wave analysis of the theory. For the local gravitational parameters, we show that one could obtain both time-varying effective Newtonian gravitational \textit{constant} $G_\textrm{N}$ and time-varying characteristic MOND acceleration scale $a_\textrm{MOND}$, by relaxing the static assumption extensively adopted in the literature. Specially, we successfully demonstrate how to reproduce the redshift dependence of $a_\textrm{MOND}$ observed in the \textit{Magneticum} cold dark matter simulations. For the gravitational waves, we show that there are only two tensor polarizations, and reconfirm that its speed is equal to the speed of light.

gr-qc↗

arXiv2023

Shadow thermodynamics of the Hayward-AdS black hole

In this paper, the phase structure of the Hayward-AdS black hole (BH) is studied using shadow formalism. It has been found that the shadow radius is a monotonic function of the horizon radius and can therefore play an equivalent role to the horizon radius in characterizing the thermodynamics of Hayward-AdS BH. The thermodynamic phase transition (PT) of the Hayward-AdS BH is investigated with the shadow radius. It is shown that as the magnetic charge increases, the shadow radius becomes larger, while the coexistence temperature becomes lower. The thermal profile of the Hayward-AdS BH is established by combining the temperature diagram and the shadow cast diagram, which shows that for a fixed magnetic charge, the temperature of the Hayward-AdS BH increases with the pressure while the region of the thermal profile decreases with the pressure. In particular, the temperature of the Hayward-AdS BH follows an N-type change trend when it is smaller than the critical temperature. This imply that the BH shadow may be used to investigate the thermodynamics of the Hayward-AdS BH.

gr-qc↗

arXiv2022

Direct tests of General Relativity under screening effect with galaxy-scale strong lensing systems

Observations of galaxy-scale strong gravitational lensing (SGL) systems have enabled unique tests of nonlinear departures from general relativity (GR) on the galactic and supergalactic scales. One of the most important cases of such tests is constraints on the gravitational slip between two scalar gravitational potentials. In this paper, we use a newly compiled sample of strong gravitational lenses to test the validity of GR, focusing on the screening effects on the apparent positions of lensed sources relative to the GR predictions. This is the first simultaneous measurement of the Post-Newtonian (PN) parameter ($γ_{PN}$) and the screening radius ($Λ$) without any assumptions about the contents of the Universe. Our results suggest that the measured PPN is marginally consistent with GR ($γ_{PN}=1$) with increasing screening radius ($Λ= 10-300 $kpc), although the choice of lens models may have a significant influence on the final measurements. Based on a well-defined sample of 5000 simulated strong lenses from the forthcoming LSST, our methodology will provide a strong extragalactic test of GR with an accuracy of 0.5\%, assessed up to scales of $Λ\sim 300$ kpc. For the current and future observations of available SGL systems, there is no noticeable evidence indicating some specific cutoff scales on kpc-Mpc scales, beyond which new gravitational degrees of freedom are expressed.

astro-ph.CO↗

arXiv2022

Revisiting the Hubble constant, spatial curvature and cosmography with time-delay and cosmic chronometer observations

In this paper, we go further and propose a cosmological model-independent approach to simultaneously determine the Hubble constant and cosmic curvature with strong lensing time-delay measurements, without any prior assumptions regarding the content of the Universe. The data we use comprises the recent compilation of six well studied strongly lensed quasars, while the cosmic chronometer data are utilized to reconstruct distances via cosmographic parameters. In the framework of third-order Taylor expansion and (2, 1) order Padé approximation for for cosmographic analysis, our results provides model-independent estimation of the Hubble constant $H_0 = 72.24^{+2.73}_{-2.52} ~km~s^{-1}~Mpc^{-1}$ and $H_0 = 72.45^{+1.95}_{-2.02} ~km~s^{-1}~Mpc^{-1}$, which is well consistent with that derived from the local distance ladder by SH0ES collaboration. The measured cosmic curvature $Ω_k=0.062^{+0.117}_{-0.078}$ and $Ω_k=0.069^{+0.116}_{-0.103}$ shows that zero spatial curvature is supported by the current observations of strong lensing time delays and cosmic chronometers. Imposing the prior of spatial flatness leads to more precise (at 1.6$\%$ level) determination of the Hubble constant $H_0=70.47^{+1.14}_{-1.15} ~km~s^{-1}~Mpc^{-1}$ and $H_0=71.66^{+1.15}_{-1.57} ~km~s^{-1}~Mpc^{-1}$, a value located between the results from \textit{Planck} and SH0ES collaboration. If a prior of local (SH0ES) $H_0$ measurement is adopted, the curvature parameter constraint can be further improved to $Ω_k=0.123^{+0.060}_{-0.046}$ and $Ω_k=0.101^{+0.090}_{-0.072}$, supporting no significant deviation from a flat universe. Finally, we also discuss the effectiveness of Padé approximation in reconstructing the cosmic expansion history within the redshift range of $z\sim2.3$, considering its better performance in the Bayes Information Criterion (BIC).

astro-ph.CO↗

arXiv2022

Satellite-based continuous-variable quantum key distribution under the Earth's gravitational field

Long distance communication protocols cannot ignore the existence of the Earth's gravitational field and its effects on quantum states. In this work, we show a very general method to consider the effects of the Earth's gravitational field on continuous-variable quantum key distribution protocols. Our results show that the Earth's gravitational field erodes the ability of the two parties to perform QKD in all the protocols. However, our findings also exhibit some interesting features, i.e., the key rates initially increase for a specific range of height parameter $h\simeq r_A/2$ and then gradually decrease with the increasing of the orbits of satellite $h$. A possible explanation is also provided in our analysis, considering the fact that gravitational frequency shift and special relativistic effects play different roles in the key rates. In addition, our findings show that the change in key rate effected by gravitational frequency shift can be determined at a level of $<1.0\%$ within the satellite height at geostationary Earth orbits. Our work could provide some interesting possibilities to reduce the loss key rate through the control of the orbital height of satellites.

quant-ph↗

arXiv2022

Revising the Hubble constant, spatial curvature and dark energy dynamics with the latest observations of quasars

In this paper, we use a newly compiled sample of ultra-compact structure in radio quasars and strong gravitational lensing systems with quasars acting as background sources to constrain six spatially flat and non-flat cosmological models ($Λ$CDM, PEDE and DGP). These two sets of quasar data (the time-delay measurements of six strong lensing systems and 120 intermediate-luminosity quasars calibrated as standard rulers) could break the degeneracy between cosmological parameters ($H_0$, $Ω_m$ and $Ω_k$) and therefore provide more stringent cosmological constraints for the six cosmological models we study. A joint analysis of the quasar sample provides model-independent estimations of the Hubble constant $H_0$, which is strongly consistent with that derived from the local distance ladder by SH0ES collaboration in the $Λ$CDM and PEDE model. However, in the framework of a DGP cosmology (especially for the flat universe), the measured Hubble constant is in good agreement with that derived from the the recent Planck 2018 results. In addition, our results show that zero spatial curvature is supported by the current lensed and unlensed quasar observations and there is no significant deviation from a flat universe. For most of cosmological model we study (the flat $Λ$CDM, non-flat $Λ$CDM, flat PEDE, and non-flat PEDE models), the derived matter density parameter is completely consistent with $Ω_m\sim 0.30$ in all the data sets, as expected by the latest cosmological observations. Finally, according to the the statistical criteria DIC, although the joint constraints provide substantial observational support to the flat PEDE model, they do not rule out dark energy being a cosmological constant and non-flat spatial hypersurfaces.

astro-ph.CO↗

arXiv2022

Revisiting Chaplygin gas cosmologies with the recent observations of high-redshfit quasars

In this paper, we use the latest observations of quasars covering the redshift range of $0.04<z<5.1$ to investigate a series of Chaplygin gas models as candidates for unified dark matter and dark energy. Based on different combinations of available standard candle and standard ruler data, we put constraints on the generalized Chaplygin gas (GCG), modified Chaplygin gas (MCG), new generalized Chaplygin gas (NGCG) and viscous generalized Chaplygin gas (VGCG) models. Moreover, we apply Jensen-Shannon divergence (JSD), statefinder diagnostics, and the deviance information criterion (DIC) to distinguish these CG models, based on the statistical results derived from Markov chain Monte Carlo method. The results show that (1) The standard ruler data could provide more stringent constraints on the cosmological parameters of different CG models considered in this analysis. Interestingly, the matter density parameter $Ω_{m}$ and Hubble constant $H_{0}$ derived from the available data are well consistent with those from the Planck 2018 results; (2) Based on the statistical criteria JSD, our findings demonstrate the well consistency between Chaplygin gas and the concordance $Λ$CDM model. However, in the framework of statefinder diagnostics, the GCG and NGCG models cannot be distinguished from $Λ$CDM, while MCG and VGCG models show significant deviation from $Λ$CDM in the present epoch; (3) According to the the statistical criteria DIC, we show that the MCG and VGCG models have substantial observational support from high-redshfit quasars, whereas the GCG and NGCG models miss out on the less observational support category but can not be ruled out.

astro-ph.CO↗

arXiv2022

Cosmological-model-independent tests of cosmic distance duality relation with Type Ia supernovae and radio quasars

In this paper, we investigate the possible deviations of the cosmic distance duality relation (CDDR) using the combination of the largest SNe Ia (Pantheon) and compact radio quasar (QSO) samples through two model-independent approaches. The deviation of CDDR is written as $D_L(z)/D_A(z)(1+z)^{-2}=η(z)$ and $η(z)=e^{τ(z)/2}$, with the parameterizations of $F_1$ ($τ(z) = 2ε_1 z$) and $F_2$ ($τ(z) = (1+z)^{2ε_2}-1$). Furthermore, in order to compare the two resulting distances, two cosmological-model-independent methods, i.e., the nearby SNe Ia method and the GP method are employed to match the two distinct data at the same redshift. Our findings indicate that, compared with the results obtained in the literature, there is an improvement in precision when the latest SNe Ia and QSO samples are used. Specially, in the framework of nearby SNe Ia method, the CDDR would be constrained at the precision of $Δε_{1} = 0.013$ in Model $F_1$ and $Δε_{2}=0.018$ in Model $F_2$. Regarding the GP method, one observes that a larger data size would produce more stringent constraints on the CDDR parameters. Therefore, accompanied by further developments in cosmological observations and the analysis methods, our analysis provides an insight into the evidence for unaccounted opacity sources at an earlier stage of the universe, or at the very least the new physics involved.

astro-ph.CO↗

arXiv2022

Comparing the scalar-field dark energy models with recent observations

We investigate the general properties of a class of scalar-field dark energy models (i.e., $ϕ$CDM models) which behave like cosmological trackers at early times. Particularly, we choose three $ϕ$CDM models with typical potentials, i.e., $V(ϕ)\propto ϕ^{-α}$ (inverse power-law (IPL) model), $V(ϕ)\propto \coth^αϕ$ (L-model) and $V(ϕ)\propto \cosh(αϕ)$ (Oscillatory tracker model), where the latter two models are based on the $α$-attractors originated from the study of inflation. These models, which reduce to the $Λ$CDM model with $α\to 0$, are studied and compared with the recent observations, including the Pantheon sample of type Ia supernovae (SNe Ia), baryon acoustic oscillations (BAO) measurements extracted from 6dFGS, BOSS and eBOSS, as well as the temperature and polarization anisotropy power spectra data of cosmic microwave background radiation (CMB) from Planck 2018 results. The observational constraints from the combining sample (SNe Ia + BAO + CMB) indicate that none of the three $ϕ$CDM models exclude the $Λ$CDM model at $68.3\%$ confidence level. We find that the CMB anisotropy data have obvious advantages in constraining the dark energy models compared with other cosmological probes, which is particularly evident in the L-model. Furthermore, we apply the Bayesian evidence to compare the $ϕ$CDM models and the $Λ$CDM model with the analysis of the combining sample. The concordance $Λ$CDM model is still the most supported one. In addition, among the three $ϕ$CDM models, the IPL model is the most competitive one, while the L-model/Oscillatory tacker model is moderately/strongly disfavored.

astro-ph.CO↗

arXiv2022

Multiple measurements of gravitational waves acting as standard probes: model-independent constraints on the cosmic curvature with DECIGO

Although the spatial curvature has been precisely determined via the cosmic microwave background (CMB) observation by Planck satellite, it still suffers from the well-known cosmic curvature tension. As a standard siren, gravitational waves (GWs) from binary neutron star mergers provide a direct way to measure the luminosity distance. In addition, the accelerating expansion of the universe may cause an additional phase shift in the gravitational waveform, which allows us to measure the acceleration parameter. This measurement provides an important opportunity to determine the curvature parameter $Ω_k$ in the GW domain based on the combination of two different observables for the same objects at high redshifts. In this study, we investigate how such an idea could be implemented with future generation of space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) in the framework of two model-independent methods. Our results show that DECIGO could provide a reliable and stringent constraint on the cosmic curvature at a precision of $ΔΩ_k$=0.12, which is comparable to existing results based on different electromagnetic data. Our constraints are more stringent than the traditional electromagnetic method from the Pantheon SNe Ia sample, which shows no evidence for the deviation from the flat universe at $z\sim 2.3$. More importantly, with our model-independent method, such a second-generation space-based GW detector would also be able to explore the possible evolution $Ω_k$ with redshifts, through direct measurements of cosmic curvature at different redshifts ($z\sim 5$). Such a model-independent $Ω_k$ reconstruction to the distance past can become a milestone in gravitational-wave cosmology.

astro-ph.CO↗

arXiv2022

Constraints on the abundance of supermassive primordial black holes from lensing of compact radio sources

The possibility that primordial black holes (PBHs) form a part of dark matter has been considered over a wide mass range from the Planck mass ($10^{-5}~\rm g$) to the level of the supermassive black hole in the center of the galaxy. Primordial origin might be one of the most important formation channel of supermassive black holes. We use the non-detection of lensing effect of very long baseline interferometer observations of compact radio sources with extremely high angular resolution as a promising probe to constrain the abundance of intergalactic PBHs in the mass range $\sim10^4$-$10^9~M_{\odot}$. For a sample of well-measured 543 flat-spectrum compact radio sources, no milli-lensed images are found with angular separations between $1.5$ milli-arcseconds and $50$ milli-arcseconds. From this null search result, we derive that the fraction of dark matter made up of supermassive PBHs in the mass range $\sim10^6$-$10^8~M_{\odot}$ is $\lesssim1.48\%$ at $95\%$ confidence level. This constraints would be significantly improved due to the rapid increase of the number of measured compact radio sources. For instance, on the basis of none confirmed milli-lensing candidate in the latest $\sim14000$ sources, we derive the abundance of supermassive PBHs and obtain that it is $\lesssim0.06\%$ at $95\%$ confidence level.

astro-ph.CO↗

arXiv2022

Direct Estimate of the Post-Newtonian Parameter and Cosmic Curvature from Galaxy-scale Strong Gravitational Lensing

Einstein's theory of general relativity (GR) has been precisely tested on solar system scales, but extragalactic tests are still poorly performed. In this work, we use a newly compiled sample of galaxy-scale strong gravitational lenses to test the validity of GR on kiloparsec scales. In order to solve the circularity problem caused by the preassumption of a specific cosmological model based on GR, we employ the distance sum rule in the Friedmann-Lema\^ıtre-Robertson-Walker metric to directly estimate the parameterized post-Newtonian (PPN) parameter $γ_{\rm PPN}$ and the cosmic curvature $Ω_k$ by combining observations of strong lensing and Type Ia supernovae. This is the first simultaneous measurement of $γ_{\rm PPN}$ and $Ω_k$ without any assumptions about the contents of the universe or the theory of gravity. Our results show that $γ_{\rm PPN}=1.11^{+0.11}_{-0.09}$ and $Ω_{k}=0.48^{+1.09}_{-0.71}$, indicating a strong degeneracy between the two quantities. The measured $γ_{\rm PPN}$, which is consistent with the prediction of 1 from GR, provides a precise extragalactic test of GR with a fractional accuracy better than 9.0\%. If a prior of the spatial flatness (i.e., $Ω_{k}=0$) is adopted, the PPN parameter constraint can be further improved to $γ_{\rm PPN}=1.07^{+0.07}_{-0.07}$, representing a precision of 6.5\%. On the other hand, in the framework of GR (i.e., $γ_{\rm PPN}=1$), our results are still marginally compatible with zero curvature ($Ω_k=-0.12^{+0.48}_{-0.36}$), supporting no significant deviation from a flat universe.

astro-ph.CO↗

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

High precision measurement of cosmic curvature: from gravitational waves and cosmic chronometer

Although the spatial curvature has been measured with very high precision, it still suffers from the well known cosmic curvature tension. In this paper, we propose an improved method to determine the cosmic curvature, by using the simulated data of binary neutron star mergers observed by the second generation space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO). By applying the Hubble parameter observations of cosmic chronometers to the DECIGO standard sirens, we explore different possibilities of making measurements of the cosmic curvature referring to a distant past: one is to reconstruct the Hubble parameters through the Gaussian process without the influence of hypothetical models, and the other is deriving constraints on $Ω_K$ in the framework of non-flat $Λ$ cold dark matter model. It is shown that in the improved method DECIGO could provide a reliable and stringent constraint on the cosmic curvature ($Ω_{K} = -0.007\pm0.016$), while we could only expect the zero cosmic curvature to be established at the precision of $ΔΩ_K=0.12$ in the second model-dependent method. Therefore, our results indicate that in the framework of methodology proposed in this paper, the increasing number of well-measured standard sirens in DECIGO could significantly reduce the bias of estimations for cosmic curvature. Such constraint is also comparable to the precision of Planck 2018 results with the newest cosmic microwave background (CMB) observations ($ΔΩ_{K} \approx 0.018$), based on the concordance $Λ$CDM model.

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↗