分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2023-07-25
摘要： Strong evidence for a gravitational-wave background (GWB) has been reported in the nano-Hertz band. Interpreting the origin of this background to be scalar-induced gravitational waves (SIGWs), we explore the equation of state (EoS) of the early universe by performing Bayes parameter inferences across the big-bang nucleosynthesis (BBN), cosmic microwave background (CMB), and pulsar timing array (PTA) joint observations for the first time. Assuming a monochromatic power spectrum for primordial curvature perturbations, we obtain the spectral amplitude $A\sim10^{-3}-10^{-1}$ and spectral peak frequency $f_\ast\sim10^{-7}-10^{-6}$ Hz. We find that the radiation domination with EoS $w=1/3$ is compatible with the current observational data, the kination domination with EoS $w=1$ is not forbidden, while the early matter domination with EoS $w=0$ is excluded at more than $2\sigma$ confidence level. These results can be tested with future observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves (GWs) from compact binary coalescences encode the absolute luminosity distances of GW sources. Once the redshifts of GW sources are known, one can use the distance-redshift relation to constrain cosmological parameters. One way to obtain the redshifts is to localize GW sources by GW observations and then use galaxy catalogs to determine redshifts from a statistical analysis of redshift information of the potential host galaxies, and such GW data are commonly referred to as dark sirens. The third-generation (3G) GW detectors are planned to work in the 2030s and will observe numerous compact binary coalescences. Using these GW events as dark sirens requires high-quality galaxy catalogs from future sky survey projects. The China Space Station Telescope (CSST) will be launched in 2024 and will observe billions of galaxies within a 17500 deg$^2$ survey area up to $z\sim 4$, providing photometric and spectroscopic galaxy catalogs. In this work, we simulate the CSST galaxy catalog and the 5-year GW data, and combine them to infer the Hubble constant ($H_0$). Our results show that the measurement precision of $H_0$ could reach better than $0.005\%$, which is an astonishing precision for the Hubble constant measurement. We conclude that the synergy between the 3G GW detectors and CSST will be of far-reaching importance in dark-siren cosmology.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the context of the discrepancies between the early and late universe, we emphasize the importance of independent measurements of the cosmic curvature in the late universe. We present an investigation of the model-independent measurement of the cosmic curvature parameter $\Omega_k$ in the late universe with the latest Hubble parameter $H(z)$ measurements and type Ia supernovae (SNe Ia) data. For that, we use two reconstruction methods, the Gaussian process (GP) and artificial neural network (ANN) methods, to achieve the distance construction from $H(z)$ data. In the results obtained by different combinations of observations and reconstruction methods, the tightest constraint on the cosmic curvature is $\Omega_k=-0.03\pm0.11$, in good agreement with zero curvature. This result is the most precise constraint on the cosmic curvature obtained among the recent related estimations. Our findings suggest that the observational data of the late universe support a flat universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmic curvature $\Omega_{K,0}$, which determines the spatial geometry of
the universe, is an important parameter in modern cosmology. Any deviation from
$\Omega_{K,0}=0$ would have a profound impact on primordial inflation paradigm
and fundamental physics. In this work, we adopt a cosmological
model-independent method to test whether $\Omega_{K,0}$ deviates from zero. We
use the Gaussian process to reconstruct the reduced Hubble parameter $E(z)$ and
the derivative of distance $D'(z)$ from observational data, and then determine
$\Omega_{K,0}$ with a null test relation. The cosmic chronometer (CC) Hubble
data, baryon acoustic oscillation (BAO) Hubble data, and supernovae Pantheon
sample are considered. Our result is consistent with a spatially flat universe
within the domain of reconstruction $01$, it tends to favor a closed universe. In this sense, there is
still a possibility for a closed universe. We also carry out the null test of
the cosmic curvature at $0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ultra-low-frequency gravitational waves (GWs) generated by individual inspiraling supermassive black hole binaries (SMBHBs) in the centers of galaxies may be detected by pulsar timing arrays (PTAs) in the future. These GW signals encoding absolute cosmic distances can serve as bright and dark sirens, having potential to be developed into a precise cosmological probe. Here we show that an SKA-era PTA consisting of 100 millisecond pulsars may observe about 20 bright sirens and 90 dark sirens during a 10-year observation. The bright sirens, together with the CMB data, have comparable capabilities to current mainstream data for measuring the equation of state of dark energy. The dark sirens could make the measurement precision of the Hubble constant far beyond the standard of precision cosmology. Our results indicate that ultra-low-frequency GWs from individual SMBHBs are of great significance in exploring the nature of dark energy and measuring the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this work, we consider a new cosmological model (named $\tilde\Lambda$CDM) in which the vacuum energy interacts with matter and radiation, and test this model using the current cosmological observations. We find that this model can significantly relieve the $H_0$ tension, and at the same time it can also slightly reduce the $S_8$ tension, which cannot be easily observed in other cosmological models. Using the CMB+BAO+SN (CBS) data to constrain the model, we obtain the results of $H_0=70.6^{+1.4}_{-1.7}~\rm{km~s^{-1} Mpc^{-1}}$ and $S_8=0.820\pm 0.011$, and thus the $H_0$ and $S_8$ tensions are relieved to $1.28\sigma$ and $2.67\sigma$, respectively. However, in this case the $\tilde\Lambda$CDM model is not favored by the data, compared with $\Lambda$CDM. We find that when the $H_0$ and $S_8$ data are added into the data combination, the situation is significantly improved. In the CBS+$H_0$ case, we obtain the result of $H_0=72.2\pm 1.2$ ${\rm km~s^{-1}~Mpc^{-1}}$, which relieves the $H_0$ tension to $0.53\sigma$, and in this case the model is favored over $\Lambda$CDM. In the CBS+$H_0$+$S_8$ case, we get a synthetically best situation, $H_0=71.9\pm 1.1$ ${\rm km~s^{-1}~Mpc^{-1}}$ and $S_8=0.8071\pm 0.0099$, in which the $H_0$ and $S_8$ tensions are relived to $0.75\sigma$ and $2.09\sigma$, respectively. In this case, the model is most favored by the data. Therefore, such a cosmological model can greatly relieve the $H_0$ tension, and at the same time it can also effectively alleviate the $S_8$ tension.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Background estimation is essential when studying TeV gamma-ray astronomy for extensive air shower arrays. In this work, by applying four applying four different methods including equi-zenith angle method, surrounding window method, direct integration method, and time-swapping method, the number of the background events is calculated. Based on simulation samples, the statistical significance of the excess signal from different background estimation methods is determined. Following this, we discuss the limits and the applicability of the four methods under different conditions. Under the detector stability assumption with signal, the results from the above four methods are consistent at the 1 sigma level. In the no signal condition, when the acceptance of the detector changes with both space and time, the surrounding window method is most stable and hardly affected. In this acceptance assumption, we find that the background estimation in the direct integration and time-swapping methods are sensitive to the selection of time window, and the shorter time window can reduce the impact on the background estimation to some extent.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： It is intriguing to ask whether the existence of primordial black holes (PBHs) in the early universe could significantly reduce the abundance of certain stable massive particles (SMP) via gravitational capture, after which the PBHs evaporate before BBN to avoid conflict with stringent bounds. For example, this mechanism is relevant to an alternative solution of the monopole problem proposed by Stojkovic and Freese, in which magnetic monopoles produced in the early universe are captured by PBHs, thus freeing inflation from having to occur during or after the corresponding phase transitions that produced the monopoles. In this work, we reanalyze the solution by modelling the capture process in the same way as the coexisting monopole annihilation, which exhibits typical features of a diffusive capture. A monochromatic PBH mass function and a radiation-dominated era before PBH evaporation are assumed. We found that for Pati-Salam monopoles corresponding to a symmetry breaking scale between $10^{10}\,\text{GeV}$ and $10^{15}\,\text{GeV}$, the capture rate is many orders of magnitude below what is needed to cause a significant reduction of the monopole density. The difference with respect to previous literature can be attributed to both the modelling of the capture process and also the assumption on the PBH mass function. Within our assumptions, we also found that the magnetic charge that is large enough to make an extremal magnetic black hole cosmologically stable cannot be obtained from magnetic charge fluctuation via monopole capture. The large magnetic charged required by cosmological stability can nevertheless be obtained from magnetic charge fluctuation at PBH formation, and if later the monopole abundance can be reduced significantly by some non-inflationary mechanism, long-lived near-extremal magnetic black holes of observational relevance might result.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Fast radio bursts (FRBs) can be used to measure the Hubble constant by employing the Macquart relation. However, at present, only a small number of FRB events are localized to their host galaxies with known redshifts. In this paper, we develop a Bayesian method to statistically measure the Hubble constant using unlocalized FRBs and galaxy catalog data, which makes it possible to constrain cosmological parameters by using a large number of FRB data without known redshift information. Using the six FRB events observed by ASKAP combined with the big bang nucleosynthesis result, we obtain $H_0=71.7^{+8.8}_{-7.4}$ km s$^{-1}$ Mpc$^{-1}$ in the simulation-based case and $H_0=71.5^{+10.0}_{-8.1}$ km s$^{-1}$ Mpc$^{-1}$ in the observation-based case ($68\%$ highest-density interval), assuming different host galaxy population parameters. We also estimate that in the next few years, using thousands of FRBs could achieve a $3\%$ precision on the random error of the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： It is intriguing to ask whether the existence of primordial black holes (PBHs) in the early universe could significantly reduce the abundance of certain stable massive particles (SMP) via gravitational capture, after which the PBHs evaporate before BBN to avoid conflict with stringent bounds. For example, this mechanism is relevant to an alternative solution of the monopole problem proposed by Stojkovic and Freese, in which magnetic monopoles produced in the early universe are captured by PBHs, thus freeing inflation from having to occur during or after the corresponding phase transitions that produced the monopoles. In this work, we reanalyze the solution by modelling the capture process in the same way as the coexisting monopole annihilation, which exhibits typical features of a diffusive capture. A monochromatic PBH mass function and a radiation-dominated era before PBH evaporation are assumed. We found that for Pati-Salam monopoles corresponding to a symmetry breaking scale between $10^{10}\,\text{GeV}$ and $10^{15}\,\text{GeV}$, the capture rate is many orders of magnitude below what is needed to cause a significant reduction of the monopole density. The difference with respect to previous literature can be attributed to both the modelling of the capture process and also the assumption on the PBH mass function. Within our assumptions, we also found that the magnetic charge that is large enough to make an extremal magnetic black hole cosmologically stable cannot be obtained from magnetic charge fluctuation via monopole capture. The large magnetic charged required by cosmological stability can nevertheless be obtained from magnetic charge fluctuation at PBH formation, and if later the monopole abundance can be reduced significantly by some non-inflationary mechanism, long-lived near-extremal magnetic black holes of observational relevance might result.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although the cosmic curvature has been tightly constrained in the standard cosmological model using observations of cosmic microwave background anisotropies, it is still of great importance to independently measure this key parameter using only late-universe observations in a cosmological model-independent way. The distance sum rule in strong gravitational lensing (SGL) provides such a way, provided that the three distances in the sum rule can be calibrated by other observations. In this paper, we propose that gravitational waves (GWs) can be used to provide the distance calibration in the SGL method, which can avoid the dependence on distance ladder and cover a wider redshift range. Using the simulated GW standard siren observation by the Einstein Telescope as an example, we show that this scheme is feasible and advantageous. We find that $\Delta\Omega_k\simeq 0.17$ with the current SGL data, which is slightly more precise than the case of using SN to calibrate. Furthermore, we consider the forthcoming LSST survey that is expected to observe many SGL systems, and we find that about $10^4$ SGL data could provide the precise measurement of $\Delta\Omega_k\simeq 10^{-2}$ with the help of GWs. In addition, our results confirm that this method of constraining $\Omega_k$ is strongly dependent on lens models. However, obtaining a more accurate phenomenological model for lens galaxies is highly predictable as future massive surveys observe more and more SGL samples, which will significantly improve the constraint of cosmic curvature.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Background estimation is essential when studying TeV gamma-ray astronomy for extensive air shower arrays. In this work, by applying four applying four different methods including equi-zenith angle method, surrounding window method, direct integration method, and time-swapping method, the number of the background events is calculated. Based on simulation samples, the statistical significance of the excess signal from different background estimation methods is determined. Following this, we discuss the limits and the applicability of the four methods under different conditions. Under the detector stability assumption with signal, the results from the above four methods are consistent at the 1 sigma level. In the no signal condition, when the acceptance of the detector changes with both space and time, the surrounding window method is most stable and hardly affected. In this acceptance assumption, we find that the background estimation in the direct integration and time-swapping methods are sensitive to the selection of time window, and the shorter time window can reduce the impact on the background estimation to some extent.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational waves (GWs) from the compact binary coalescences can be used as standard sirens to explore the cosmic expansion history. In the next decades, it is anticipated that we could obtain the multi-band GW standard siren data (from nanohertz to a few hundred hertz), which are expected to play an important role in cosmological parameter estimation. In this work, we give for the first time the joint constraints on cosmological parameters using the future multi-band GW standard siren observations. We simulate the multi-band GW standard sirens based on the SKA-era pulsar timing array (PTA), the Taiji observatory, and the Cosmic Explorer (CE) to perform cosmological analysis. In the $\Lambda$CDM model, we find that the joint PTA+Taiji+CE data could provide a tight constraint on the Hubble constant with a $0.5\%$ precision. Moreover, PTA+Taiji+CE could break the cosmological parameter degeneracies generated by CMB, especially in the dynamical dark energy models. When combining the PTA+Taiji+CE data with the CMB data, the constraint precisions of $\Omega_{\rm m}$ and $H_0$ are $1.0\%$ and $0.3\%$, meeting the standard of precision cosmology. The joint CMB+PTA+Taiji+CE data give $\sigma(w)=0.028$ in the $w$CDM model and $\sigma(w_0)=0.11$ and $\sigma(w_a)=0.32$ in the $w_0w_a$CDM model, which are comparable with or close to the latest constraint results by the CMB+BAO+SN. In conclusion, it is worth expecting to use the future multi-band GW observations to explore the nature of dark energy and measure the Hubble constant.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： LISA and Taiji are expected to form a space-based gravitational-wave (GW) detection network in the future. In this work, we make a forecast for the cosmological parameter estimation with the standard siren observation from the LISA-Taiji network. We simulate the standard siren data based on a scenario with configuration angle of $40^{\circ}$ between LISA and Taiji. Three models for the population of massive black hole binary (MBHB), i.e., pop III, Q3d, and Q3nod, are considered to predict the events of MBHB mergers. We find that, based on the LISA-Taiji network, the number of electromagnetic (EM) counterparts detected is almost doubled compared with the case of single Taiji mission. Therefore, the LISA-Taiji network's standard siren observation could provide much tighter constraints on cosmological parameters. For example, solely using the standard sirens from the LISA-Taiji network, the constraint precision of $H_0$ could reach $1.3\%$. Moreover, combined with the CMB data, the GW-EM observation based on the LISA-Taiji network could also tightly constrain the equation of state of dark energy, e.g., the constraint precision of $w$ reaches about $4\%$, which is comparable with the result of CMB+BAO+SN. It is concluded that the GW standard sirens from the LISA-Taiji network will become a useful cosmological probe in understanding the nature of dark energy in the future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the near future, the redshift drift observations in optical and radio
bands will provide precise measurements on $H(z)$ covering the redshift ranges
of $2
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Measurements of time-delay cosmography of lensed quasars can provide an independent probe to explore the expansion history of the late-time Universe. In this paper, we employ the time-delay cosmography measurements from seven lenses (here abbreviated as the TD data) to constrain interacting dark energy (IDE) models. We mainly focus on the scenario of vacuum energy (with $w=-1$) interacting with cold dark matter, and consider four typical cases of the interaction form $Q$. When the TD data alone are employed, we find that the IDE models with $Q\propto \rho_{\rm de}$ seem to have an advantage in relieving the $H_{0}$ tension between the cosmic microwave background (CMB) and TD data. When the TD data are added to the CMB$+$BAO$+$SN$+H_0$ data, we find that: (i) the coupling parameter $\beta$ in all the considered IDE models is positive within 1$\sigma$ range, implying a mild preference for the case of cold dark matter decaying into dark energy; (ii) the IDE model with $Q = \beta H_{0} \rho_{\rm c}$ slightly relieves the $S_8$ tension, but the other considered IDE models further aggravate this tension; (iii) the Akaike information criteria of the IDE models with $Q \propto \rho_{\rm c}$ are lower than that of the $\Lambda$CDM model, indicating that these IDE models are more preferred by the current mainstream data. We conclude that the considered IDE models have their own different advantages when the TD data are employed, and none of them can achieve good scores in all aspects.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We investigate an extended cosmological model motivated by the asymptotic safety of gravitational field theory, in which the matter and radiation densities and the cosmological constant receive a correction parametrized by the parameters $\delta_G$ and $\delta_\Lambda$, leading to that both the evolutions of the matter and radiation densities and the cosmological constant slightly deviate from the standard forms. Here we explain this model as a scenario of vacuum energy interacting with matter and radiation. We consider two cases of the model: {(i) ${\tilde\Lambda}$CDM with one additional free parameter $\delta_G$, with $\delta_{\rm G}$ and $\delta_\Lambda$ related by a low-redshift limit relation and (ii) e${\tilde\Lambda}$CDM with two additional free parameters $\delta_G$ and $\delta_\Lambda$ that are independent of each other.} We use two data combinations, CMB+BAO+SN (CBS) and CMB+BAO+SN+$H_0$ (CBSH), to constrain the models. We find that, in the case of using the CBS data, neither ${\tilde\Lambda}$CDM nor e${\tilde\Lambda}$CDM can effectively alleviate the $H_0$ tension. However, it is found that using the CBSH data the $H_0$ tension can be greatly relieved by the models. In particular, in the case of e${\tilde\Lambda}$CDM, the $H_0$ tension can be resolved to 0.71$\sigma$. We conclude that as an interacting dark energy model, ${\tilde\Lambda}$CDM is much better than $\Lambda(t)$CDM in the sense of both relieving the $H_0$ tension and fitting to the current observational data.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Using the 21 cm intensity mapping (IM) technique can efficiently perform
large-scale neutral hydrogen surveys, and this method has great potential for
measuring dark-energy parameters. Some 21 cm IM experiments aiming at measuring
dark energy in the redshift range of $0
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In recent years, a crisis in the standard cosmology has been caused by inconsistencies in the measurements of some key cosmological parameters, Hubble constant $H_0$ and cosmic curvature parameter $\Omega_K$ for example. It is necessary to remeasure them with the cosmological model-independent methods. In this paper, based on the distance sum rule, we present such a way to constrain $H_0$ and $\Omega_K$ simultaneously in the late universe from strong gravitational lensing time delay (SGLTD) data and gravitational wave (GW) standard siren data simulated from the future observation of the Einstein Telescope (ET). Based on the currently 6 observed SGLTD data, we find that the constraint precision of $H_0$ from the combined 100 GW events can be comparable with the measurement from SH0ES collaboration. As the number of GW events increases to 700, the constraint precision of $H_0$ will exceed that of the \textit{Planck} 2018 results. Considering 1000 GW events as the conservative estimation of ET in ten-year observation, we obtain $H_0=73.69\pm 0.36 \mathrm{~km~s^{-1}~Mpc^{-1}}$ with a 0.5\% uncertainty and $\Omega_K=0.076^{+0.068}_{-0.087}$. In addition, we simulate 55 SGL systems with 6.6\% uncertainty for the measurement of time-delay distance. By combining with 1000 GWs, we infer that $H_0=73.65\pm0.35 \mathrm{~km~s^{-1}~Mpc^{-1}}$ and $\Omega_K=0.008\pm0.048$. Our results suggest that this approach can play an important role in exploring cosmological tensions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The neutral hydrogen (HI) intensity mapping (IM) survey is regarded as a promising approach for cosmic large-scale structure (LSS) studies. A major issue for the HI IM survey is to remove the bright foreground contamination. A key to successfully remove the bright foreground is to well control or eliminate the instrumental effects. In this work, we consider the instrumental effect of polarization leakage and use the U-Net approach, a deep learning-based foreground removal technique, to eliminate the polarization leakage effect.In this method, the principal component analysis (PCA) foreground subtraction is used as a preprocessing step for the U-Net foreground subtraction. Our results show that the additional U-Net processing could either remove the foreground residual after the conservative PCA subtraction or compensate for the signal loss caused by the aggressive PCA preprocessing. Finally, we test the robustness of the U-Net foreground subtraction technique and show that it is still reliable in the case of existing constraint error on HI fluctuation amplitude.
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