Search

The Hubble tension refers to the significant discrepancy in the Hubble constant $H_{0}$ obtained from two different measurement methods in cosmology. One method derives data from the Cosmic Microwave Background (CMB) observations by the Planck satellite, yielding a value of $67.4\pm{0.5} \ \mathrm{km\ s^{-1}} \mathrm{Mpc^{-1}} $, while the other method relies on direct measurements of Type Ia supernovae, producing a value $73.04\pm{1.04} \ \mathrm{km\ s^{-1}} \mathrm{Mpc^{-1}} $. This issue has persisted for several years. To theoretically explore potential solutions to this problem, this paper examines a model within the framework of Einstein-Cartan (EC) theory, where torsion is introduced with spin as the corresponding entity, allowing for the assumption $H = -\alpha \phi$. By employing the Markov Chain Monte Carlo (MCMC) algorithm and utilizing Cosmic Chronometers (CC) data, we impose parameter constraints on various parameters in the Friedmann equations, particularly focusing on the curvature density parameter $\Omega_k$, to assess whether the model remains stable under this assumption and whether the estimated parameters align more closely with either of the observational results. In conclusion, we find that the parameter constraints in the model incorporating torsion ($ H_0 = 67.6^{+2.1}_{-2.7} \ \mathrm{km\ s^{-1}\ Mpc^{-1}}$, obtained under the Big Bang Nucleosynthesis (BBN) constraint with $\Omega_{k}=0$; $ H_0 = 66.2^{+4.4}_{-2.9} \ \mathrm{km\ s^{-1}\ Mpc^{-1}}$, obtained under same constraint but set $\Omega_{k}$ as a free variable; $ H_0 = 68.8^{+2.9}_{-4.2} \ \mathrm{km\ s^{-1}\ Mpc^{-1}}$, obtained under the Planck constraint) are more consistent with the value derived from CMB data, favoring the lower $H_0$ value., Comment: 13 pages,5 figures

The Varying Speed of Light (VSL) model describes how the speed of light in a vacuum changes with cosmological redshift. Despite numerous models, there is little observational evidence for this variation. While the speed of light can be accurately measured by physical means, cosmological methods are rarely used. Previous studies quantified the speed of light at specific redshifts using Gaussian processes and reconstructed the redshift-dependent function $c(z)$. It is crucial to quantify the speed of light across varying redshifts. We use the latest data on angular diameter distances $D_A(z)$ and Hubble parameters $H(z)$ from baryon acoustic oscillation (BAO) and cosmic chronometer measurements in the redshift interval $z\in[0.07,1.965]$. The speed of light $c(z)$ is determined using Gaussian and deep Gaussian processes to reconstruct $H(z)$, $D_A(z)$, and $D^{\prime}_A(z)$. Furthermore, we conduct comparisons across three distinct models, encompassing two renowned VSL models. We get the result of the parameters constraints in the models (1) for the ``$c$-c" model, $c_0=29492.6 \pm^{6.2}_{5.3} \mathrm{~km} \mathrm{~s}^{-1}$. (2) For the ``$c$-cl" model, $c_0=29665.5 \pm^{11.2}_{11.4}\mathrm{~km} \mathrm{~s}^{-1}$ and $n=0.05535 \pm^{0.00008}_{0.00007}$. (3) For the ``$c$-CPL" model, $c_0=29555.7 \pm^{13.3}_{13.2} \mathrm{~km} \mathrm{~s}^{-1}$ and $n=-0.0607 \pm 0.0001$. Based on our findings, it may be inferred that Barrow's classical VSL model is not a suitable fit for our data. In contrast, the widely recognized Chevallier-Polarski-Linder (CPL) VSL model, under some circumstances, as well as the universal ``c is constant" model, demonstrate a satisfactory ability to account for our findings., Comment: 15 pages, 9 figures; Accepted for publication in MNRAS

Since the commencement of the first SETI observation in 2019, China's Search for Extraterrestrial Intelligence program has garnered momentum through domestic support and international collaborations. Several observations targeting exoplanets and nearby stars have been conducted with the FAST. In 2023, the introduction of the Far Neighbour Project(FNP) marks a substantial leap forward, driven by the remarkable sensitivity of the FAST telescope and some of the novel observational techniques. The FNP seeks to methodically detect technosignatures from celestial bodies, including nearby stars, exoplanetary systems, Milky Way globular clusters, and more. This paper provides an overview of the progress achieved by SETI in China and offers insights into the distinct phases comprising the FNP. Additionally, it underscores the significance of this project's advancement and its potential contributions to the field., Comment: Submitted for publication in Journal of Physics: Conference Series (HAPP 10th Anniversary Commemorative Volume). Invited talk online discussion panel on "Searching for Extraterrestrial Intelligence Over a Century" at the Centre for the History and Philosophy of Physics (HAPP) at the University of Oxford on Saturday 27th November 2021

Accurately measuring the Hubble parameter is vital for understanding the expansion history and properties of the universe. In this paper, we propose a new method that supplements the covariance between redshift pairs to improve the reconstruction of the Hubble parameter using the OHD dataset. Our approach utilizes a cosmological model-independent radial basis function neural network (RBFNN) to describe the Hubble parameter as a function of redshift effectively. Our experiments show that this method results in a reconstructed Hubble parameter of $H_0 = 67.1\pm9.7~\mathrm{km~s^{-1}~Mpc^{-1}}$ , which is more noise-resistant and fits better with the $\Lambda$CDM model at high redshifts. Providing the covariance between redshift pairs in subsequent observations will significantly improve the reliability and accuracy of Hubble parametric data reconstruction. Future applications of this method could help overcome the limitations of previous methods and lead to new advances in our understanding of the universe., Comment: 10 pages, 2 tables, 5 figures. Matches the published version

Search for extraterrestrial intelligence (SETI) has been mainly focused on nearby stars and their planets in recent years. Barnard's star is the second closest star system to the sun and the closest star in the FAST observable sky which makes the minimum Equivalent Isotropic Radiated Power (EIRP) required for a hypothetical radio transmitter from Barnard's star to be detected by FAST telescope a mere 4.36x10^8 W. In this paper, we present the Five-hundred-meter Aperture Spherical radio Telescope (FAST) telescope as the most sensitive instrument for radio SETI observations toward nearby star systems and conduct a series of observations to Barnard's star (GJ 699). By applying the multi-beam coincidence matching (MBCM) strategy on the FAST telescope, we search for narrow-band signals (~Hz) in the frequency range of 1.05-1.45 GHz, and two orthogonal linear polarization directions are recorded. Despite finding no evidence of radio technosignatures in our series of observations, we have developed predictions regarding the hypothetical extraterrestrial intelligence (ETI) signal originating from Barnard's star. These predictions are based on the star's physical properties and our observation strategy., Comment: 10 pages, 5 figures. matches the published version. arXiv admin note: text overlap with arXiv:2208.02421

The study of massive neutrinos and their interactions is a critical aspect of contemporary cosmology. Recent advances in parallel computation and high-performance computing provide new opportunities for accurately constraining Large-Scale Structures (LSS). In this paper, we introduce the TianNu cosmological N-body simulation during the co-evolution of massive neutrino and cold dark matter components via the CUBEP$^3$M code running on the supercomputer Tianhe-2 and TianNu's connected works. We start by analyzing $2.537\times10^7$ dark halos from the scientific data of TianNu simulation, and compare their angular momentum with the matched halos from neutrino-free TianZero, revealing a dependence of angular momentum modulus on neutrino injection at scales below 50 Mpc and around 10 Mpc., Comment: 11 pages(without ref.), 10 figures, 2 tables. The review of related works about the TianNu simulation

Narrowband radio search for extraterrestrial intelligence (SETI) in the 21st century suffers severely from radio frequency interference (RFI), resulting in a high number of false positives, and it could be the major reason why we have not yet received any messages from space. We thereby propose a novel observation strategy, called MultiBeam Point-source Scanning (MBPS), to revolutionize the way RFI is identified in narrowband radio SETI and provide a prominent solution to the current situation. The MBPS strategy is a simple yet powerful method that sequentially scans over the target star with different beams of a telescope, hence creating real-time references in the time domain for cross-verification, thus potentially identifying all long-persistent RFI with a level of certainty never achieved in any previous attempts. By applying the MBPS strategy during the observation of TRAPPIST-1 with the FAST telescope, we successfully identified all 16,645 received signals as RFI using the solid criteria introduced by the MBPS strategy. Therefore we present the MBPS strategy as a promising tool that should bring us much closer to the first discovery of a genuine galactic greeting., Comment: 8 pages, 6 figures, published in The Astronomical Journal on Nov 15, 2023

Massive neutrinos are expected to affect the large-scale structure formation, including the major component of solid substances, dark matter halos. How halos are influenced by neutrinos is vital and interesting, and angular momentum (AM) as a significant feature provides a statistical perspective for this issue. Exploring halos from TianNu N-body cosmological simulation with the co-evolving neutrino particles, we obtain some concrete conclusions. First, by comparing the same halos with and without neutrinos, in contrast to the neutrino-free case, over 89.71\% of halos have smaller halo moduli, over 71.06\% have smaller particle-mass-reduced (PMR) AM moduli, and over 95.44\% change their orientations of less than $0.65^\circ$. Moreover, the relative variation of PMR modulus is more visible for low-mass halos. Second, to explore the PMR moduli of halos in dense or sparse areas, we divide the whole box into big cubes, and search for halos within a small spherical cell in a single cube. From the two-level divisions, we discover that in denser cubes, the variation of PMR moduli with massive neutrinos decreases more significantly. This distinction suggests that neutrinos exert heavier influence on halos' moduli in compact regions. With massive neutrinos, most halos (86.60\%) have lower masses than without neutrinos., Comment: 12 pages(without ref.), 12 figures. The statistical research of the angular momentum moduli of dark halos in TianNu N-body simulation. Second update only corrects the author name on the arXiv page

The "search for extraterrestrial intelligence" (SETI) commensal surveys aim to scan the sky to find possible technosignatures from the extraterrestrial intelligence (ETI). The mitigation of radio frequency interference (RFI) is an important step, especially for the most sensitive Five-hundred-meter Aperture Spherical radio Telescope (FAST), which can detect more weak RFI. In this paper, we propose several new techniques for RFI mitigation, and use our procedure to search for ETI signals from the archival data of FAST's first SETI commensal survey. We detect the persistent narrowband RFI by setting a threshold of the signals' sky separation, and detect the drifting RFI (and potentially other types of RFI) using the Hough transform. We also use the clustering algorithms to remove more RFI and select candidates. The results of our procedure are compared to the earlier work on the same FAST data. We find that our methods, though relatively simpler in computation, remove more RFI (99.9912% compared to 99.9063% in the earlier work), but preserve the simulated ETI signals except those (5.1%) severely affected by the RFI. We also report more interesting candidate signals, about a dozen of which are new candidates that are not previously reported. In addition, we find that the proposed Hough transform method, with suitable parameters, also has the potential to remove the broadband RFI. We conclude that our methods can effectively remove the vast majority of the RFI while preserving and finding the candidate signals that we are interested in., Comment: 14 pages, 10 figures. AJ accepted

In this paper, we propose a novel method for distinguishing extraterrestrial intelligence (ETI) signals from radio frequency interference (RFI) by leveraging polarization features. We exploit the sinusoidal variation of the linearly polarized components of Stokes parameters with the parallactic angle as a characteristic signature of ETI signals, while such linearly polarized components remain relatively stable for terrestrial RFI. Typically, a minimum of 4-8 hours of observation time is required to detect these sinusoidal variations. The polarization approach in the search for extraterrestrial intelligence (SETI) also enables us to study the radio stellar bursts emitted by M-type stars as ancillary science, which is relevant to assessing the habitability of exoplanets. Compared to the frequency drift method, the polarization method effectively reduces the required observation time for signal identification while improving the signal identification process., Comment: 8 pages, 2 figures, published in The Astronomical Journal. Using polarization features as the criterion in SETI research

Cosmology constraints serve as a crucial criterion in discriminating cosmological models. The traditional combined method to constrain the cosmological parameters designates the corresponding theoretical value and observational data as functions of redshift, however, sometimes the redshift cannot be measured directly, or the measurement error is large, or the definition of redshift is controversial. In this paper, we propose a novel joint method to constrain parameters that eliminates the redshift $z$ and makes full use of the multiple observables $\left\lbrace \mathcal{F}_{1,\mathrm{obs}},\mathcal{F}_{2,\mathrm{obs}},\cdots,\mathcal{F}_{M,\mathrm{obs}}\right\rbrace$ spanning in $M$-dimensional joint observables space. Considering the generality of the mathematical form of the cosmological models and the guidance from low to high dimensions, we firstly validate our method in a three-dimensional joint observables space spanned by $H(z)$, $f\sigma_{8}(z)$ and $D_{A}(z)$, where the three coordinates can be considered redshift-free measurements of the same celestial body (or shared-redshift data reconstructed model independently). Our results are consistent with the traditional combined method but with lower errors, yielding $H_0=68.7\pm0.1\mathrm{~km} \mathrm{~s}^{-1}\mathrm{~Mpc}^{-1}$, $\Omega_{m0}=0.289\pm0.003$, $\sigma_{8}=0.82\pm0.01$ and showing alleviated parametric degeneracies to some extent. In principle, our joint constraint method allows an extended form keeping the redshift information as an independent coordinate and can also be readily degraded to the form of a traditional combined method to constrain parameters., Comment: 20 pages, 15 figures, 4 tables. Accepted for publication in ApJS. Corresponds to version published in ApJS. We propose a new approach to discriminate among concurring cosmological models by adopting classes of cosmological constraints that can maximize the use of the observable space and can allow to eliminate the redshift from the analysis

Dark energy is believed to be responsible for the acceleration of the universe. In this paper, we reconstruct the dark energy scalar field potential $V(\phi)$ using the Hubble parameter $H(z)$ through Gaussian Process analysis. Our goal is to investigate dark energy using various $H(z)$ datasets and priors. We find that the selection of prior and the $H(z)$ dataset significantly affects the reconstructed $V(\phi)$. And we compare two models, Power Law and Free Field, to the reconstructed $V(\phi)$ by computing the reduced chi-square. The results suggest that the models are generally in agreement with the reconstructed potential within a $3\sigma$ confidence interval, except in the case of Observational $H(z)$ data (OHD) with the Planck 18 (P18) prior. Additionally, we simulate $H(z)$ data to measure the effect of increasing the number of data points on the accuracy of reconstructed $V(\phi)$. We find that doubling the number of $H(z)$ data points can improve the accuracy rate of reconstructed $V(\phi)$ by 5$\%$ to 30$\%$., Comment: 17 pages, 12 figures, 4 tables, accepted by APJ on 05 July 2024

Gaussian Process (GP) has gained much attention in cosmology due to its ability to reconstruct cosmological data in a model-independent manner. In this study, we compare two methods for GP kernel selection: Approximate Bayesian Computation (ABC) Rejection and nested sampling. We analyze three types of data: cosmic Chronometer data (CC), Type Ia Supernovae (SNIa), and Gamma Ray Burst (GRB), using five kernel functions. To evaluate the differences between kernel functions, we assess the strength of evidence using Bayes factors. Our results show that, for ABC Rejection, the Mat\'ern kernel with $\nu$=5/2 (M52 kernel) outperformes the commonly used Radial Basis Function (RBF) kernel in approximating all three datasets. Bayes factors indicate that the M52 kernel typically supports the observed data better than the RBF kernel, but with no clear advantage over other alternatives. However, nested sampling gives different results, with the M52 kernel losing its advantage. Nevertheless, Bayes factors indicate no significant dependence of the data on each kernel., Comment: 15 pages, 4 tables, 6 figures, accepted for publication in ApJS. We draw a new conclusion which is different from the standard ABC-related methods(e.g. ABC-SMC) in kernel selection for Gaussian Process

The search for extraterrestrial intelligence (SETI) is to search for technosignatures associated with extraterrestrial life, such as engineered radio signals. In this paper, we apply the multibeam coincidence matching (MBCM) strategy, and propose a new search mode based on the MBCM which we call MBCM blind search mode. In our recent targeted SETI research, 33 exoplanet systems are observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). With this blind search mode, we search for narrowband drifting signals across $1.05-1.45$ GHz in two orthogonal linear polarization directions separately. There are two special signals, one of which can only be detected by the blind search mode while the other can be found by both blind and targeted search modes. This result reveals huge advantages of the new blind search mode. However, we eliminate the possibility of the special signals being ETI signals based on much evidence, such as the polarization, drift, frequency and beam coverage characteristics. Our observations achieve an unprecedented sensitivity and our work provides a deeper understanding to the polarization analysis of extraterrestrial signals., Comment: 15 pages, 1 table, 7 figures. Matches AJ published version. Based on MBCM strategy by Zhen-Zhao Tao et al (2022 AJ 164 160), we propose a new search mode: MBCM blind search mode for FAST SETI observations

In the procedure of constraining the cosmological parameters with the observational Hubble data and the type Ia supernova data, the combination of Masked Autoregressive Flow and Denoising Autoencoder can perform a good result. The above combination extracts the features from OHD with DAE, and estimates the posterior distribution of cosmological parameters with MAF. We ask whether we can find a better tool to compress large data in order to gain better results while constraining the cosmological parameters. Information maximising neural networks, a kind of simulation-based machine learning technique, was proposed at an earlier time. In a series of numerical examples, the results show that IMNN can find optimal, non-linear summaries robustly. In this work, we mainly compare the dimensionality reduction capabilities of IMNN and DAE. We use IMNN and DAE to compress the data into different dimensions and set different learning rates for MAF to calculate the posterior. Meanwhile, the training data and mock OHD are generated with a simple Gaussian likelihood, the spatially flat {\Lambda}CDM model and the real OHD data. To avoid the complex calculation in comparing the posterior directly, we set different criteria to compare IMNN and DAE., Comment: 13 pages, 1 tables, 19 figures

Damped Lyman-$\alpha$ Absorber (DLA), or HI 21cm Absorber (H21A), is an important probe to model-independently measure the acceleration of spectroscopic velocity ($v_\mathrm{S}$) via the Sandage-Loeb (SL) effect. Confined by the shortage of DLAs and Background Radio Sources (BRSs) with adequate information, the detectable amount of DLAs is ambiguous in the bulk of previous work. After differing the acceleration of scale factor ($\ddot{a}$) from the first order time derivative of spectroscopic velocity ($\dot{v}_\mathrm{S}$), we make a statistical investigation of the amount of potential DLAs in the most of this paper. Using Kernel Density Estimation (KDE) to depict general redshift distributions of BRSs, observed DLAs and a DLA detection rate with different limitations (1.4GHz flux, HI column density and spin temperature), we provide fitted multi-Gaussian expressions of the three components and their 1$\sigma$ regions by bootstrap, with a proportional constant of H21As in detected DLAs, leading to the measurable number predictions of H21As for FAST, ASKAP and SKA1-Mid in HI absorption blind survey. In our most optimistic condition ($F_\mathrm{1.4GHz}$>10mJy, $N_\mathrm{HI}>2\times10^{20}\mathrm{cm^{-2}}$ and $T_\mathrm{S}$>500K), the FAST, AKSAP and SKA1-Mid would probe about 80, 500 and 600 H21As respectively., Comment: 11 pages(without ref.), 20 figures, 6 tables. MNRAS 521, 3150-3161 (2023). Statistics of potential 21cm DLAs in Sandage-Loeb effect for FAST, ASKAP and SKA1-Mid. Comments welcome!

The $L-\sigma$ relation of HII galaxies (HIIGx) calibrated by a distance indicator is a reliable standard candle for measuring the Hubble constant $H_0$. The most straightforward calibration technique anchors them with the first tier of distance ladders from the same galaxies. Recently another promising method that uses the cosmological model-independent Cosmic Chronometers (CC) as a calibrator has been proposed. We promote this technique by removing the assumptions about the cosmic flatness and using a non-parametric Artificial Neural Network for the data reconstruction process. We observe a correlation between the cosmic curvature density parameter and the slope of the $L-\sigma$ relation, thereby improving the reliability of the calibration. Using the calibrated HIIGx Hubble diagram, we obtain a Type Ia Supernovae Hubble diagram free of the conventional assumption about $H_0$. Finally we get a value of $H_0=65.9_{-2.9}^{+3.0} \mathrm{km s^{-1} Mpc^{-1}}$, which is compatible with latest Planck18 measurement., Comment: 10 pages,4 figures,2 tables,V2: matches the published version

The Doppler shift of a radio signal is caused by the relative motion between the transmitter and receiver. The change in frequency of the signal over time is called drift rate. In the studies of radio SETI (Search for Extraterrestrial Intelligence), extraterrestrial narrowband signals are expected to appear "chirped" since both the exoplanet and the Earth are moving. Such planet rotation and orbital revolution around the central star can cause a non-zero drift rate. Other relative motions between the transmitter and receiver, such as the gravitational redshift and galactic potential, are negligible. In this paper, we mainly consider the common cases that the drift rate is contributed by the rotations and orbits of the Earth and exoplanet in celestial mechanics perspective, and briefly discuss other cases different from the Earth-exoplanet one. We can obtain the expected pseudosinusoidal drifting result with long-term observations, shorter orbital periods of exoplanets. Exoplanets with higher orbital eccentricities can cause asymmetric drifting. The expected result should be intermittent pseudosinusoidal curves in long-term observations. The characteristics of pseudo-sinusoidal curves, as another new criterion for extraterrestrial signals, can be applied to long-term SETI reobservations in future research., Comment: 18 pages, 12 figures, 3 tables , matches the published version

As a major approach to looking for life beyond the Earth, the search for extraterrestrial intelligence (SETI) is committed to detecting technosignatures such as engineered radio signals that are indicative of technologically capable life. In this paper, we report a targeted SETI campaign employing an observation strategy named multi-beam coincidence matching (MBCM) at the Five-hundred-meter Aperture Spherical radio Telescope (FAST) towards 33 known exoplanet systems, searching for ETI narrow-band drifting signals across 1.05-1.45 GHz in two orthogonal linear polarization directions separately. A signal at 1140.604 MHz detected from the observation towards Kepler-438 originally peaked our interest because its features are roughly consistent with assumed ETI technosignatures. However, evidences such as its polarization characteristics are almost able to eliminate the possibility of an extraterrestrial origin. Our observations achieve an unprecedented sensitivity since the minimum equivalent isotropic radiated power (EIRP) we are able to detect reaches 1.48 x10^9 W., Comment: 17 pages, 12 figures, matches the published version

In this work, we perform a full-spectrum fitting of 350 massive and passive galaxies selected as cosmic chronometers from the LEGA-C ESO public survey to derive their stellar ages, metallicities, and star-formation histories. We extensively test our results by assessing their dependence on the possible contribution of dust, calibration of noise and signal, and the use of photometric data in addition to spectral information; we as well identify indicators of the correct convergence of the results, including the shape of the posterior distributions, the analysis of specific spectral features, and the correct reproduction of the observed spectrum. We derive a clear age-redshift trend compatible with the aging in a standard cosmological model, showing a clear downsizing pattern, with more massive galaxies being formed at higher redshift ($z_f\sim2.5$) with respect to lower massive ones ($z_f\sim2$). From these data, we measure the differential aging of this population of cosmic chronometers to derive a new measurement of the Hubble parameter, obtaining $H(z=0.8) = 113.1 \pm 15.1 (\mathrm{stat.}) ^{+29.1}_{-11.3} (\mathrm{syst.})\ \mathrm{ km\ s^{-1}\ Mpc^{-1}}$. This analysis allows us for the first time to compare the differential ages of cosmic chronometers measured on the same sample with two completely different methods, the full-spectrum fit (this work) and the analysis of Lick indices, known to correlate with the age and metallicity of the stellar populations \citep{Borghi2022a}. Albeit an understood offset in the absolute ages, the differential ages have proven to be extremely compatible between the two methods, despite the very different data, assumptions, and models considered, demonstrating the robustness of the method., Comment: 21 pages, 1 table, 9 figures, published in ApJS. A new OHD supplement to 32 released data (including 4 OHD by Zhang et al. 2014. RAA, 14, 1221) is now available for cosmological model-independent studies

The measurements of expansion rate $H(z)$ and the growth rate $f\sigma_8(z)$ describe the evolution of the universe, and both of them can constrain the cosmological models through data analysis. Due to the lack of data points, these datasets are combined by the traditional combined method ($\chi^2$ method) to select a best-fitting cosmological model. In 2017, Linder proposed a joint method, which describes the evolution of the universe through $H(z)-f\sigma_8$ diagram instead of the redshift z. Compared to individual datasets, Linder demonstrated the advantages of the joint method to distinguish cosmologies. In this paper, we compare the significance between the traditional combined method and Linder's joint method by constraining the density parameter $\Omega_M$ using Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). The result shows that the joint method is more significant than the traditional combined method., Comment: 10 pages, 2 figures, 2 tables. Accepted by Physics of the Dark Universe

In large-scale online services, crucial metrics, a.k.a., key performance indicators (KPIs), are monitored periodically to check their running statuses. Generally, KPIs are aggregated along multiple dimensions and derived by complex calculations among fundamental metrics from the raw data. Once abnormal KPI values are observed, root cause analysis (RCA) can be applied to identify the reasons for anomalies, so that we can troubleshoot quickly. Recently, several automatic RCA techniques were proposed to localize the related dimensions (or a combination of dimensions) to explain the anomalies. However, their analyses are limited to the data on the abnormal metric and ignore the data of other metrics which may be also related to the anomalies, leading to imprecise or even incorrect root causes. To this end, we propose a cross-metric multi-dimensional root cause analysis method, named CMMD, which consists of two key components: 1) relationship modeling, which utilizes graph neural network (GNN) to model the unknown complex calculation among metrics and aggregation function among dimensions from historical data; 2) root cause localization, which adopts the genetic algorithm to efficiently and effectively dive into the raw data and localize the abnormal dimension(s) once the KPI anomalies are detected. Experiments on synthetic datasets, public datasets and online production environment demonstrate the superiority of our proposed CMMD method compared with baselines. Currently, CMMD is running as an online service in Microsoft Azure.

We present a model-independent method of reconstructing scale factor against lookback time from the Observational Hubble parameter Data (OHD). The reconstruction method is independent of dynamical models and is only based on the Friedmann-Robertson-Walker metric. We also calculate the propagation of error in the reconstruction process. The reconstruction data errors mainly come from trapezoidal rule approximation and the uncertainty from OHD. Furthermore, the model discrimination ability of original OHD and reconstructed a-t data is discussed under a dimensionless standard method. a-t data can present the differences between cosmology models more clearly than H-z data by comparing their coefficients of variations. Finally, we add fifty simulated H(z) data to estimate the influence of future observation. More Hubble measurements in the future will help constrain cosmological parameters more accurately., Comment: 9 pages, 8 figures, 3 tables. Accepted for publication in ApJ

Beginning with a brief review of the regular space-time with asymptotically Minkowski core, we can consider two copies of the space-time connected through a short-throat wormhole whose radius of mouth is equal to or larger than an extremal regular black hole with asymptotically Minkowski core's event horizon radius. If the wormhole is traversable and smooth, fluxes in these two space-times will interact with and flow into each other. On the cosmological scale, gravity is a candidate for the flux. As the gravitational field changes in one space-time, the behaviours of stars around the wormhole will be affected by the other space-time since we assume there exists enough exotic matter to keep the wormhole open. The changes in a gravitational field can be quantized through the gauge invariant perturbations. The variances in orbits of stars can be reflected by changes in the kinematic shifts of photon frequencies. Then, we use this to distinguish between the black hole and wormhole generated by the same space-time line element, since black hole can not connect two space-times and is unaffected by other space-time., Comment: 21 pages, 20 figures. Corresponds to version published in PRD (original version is arXiv:2111.14749v1)

Damped Lyman-$\alpha$ Absorber(DLA) of HI 21cm system is an ideal probe to directly measure cosmic acceleration in real-time cosmology via Sandage-Loeb(SL) test. During short observations toward two DLAs in the commissioning progress of FAST, we manage to exhibit an HI 21cm absorption feature from PKS1413+135 spectrum in one epoch with our highest resolution up to 100 Hz, preliminarily validating the frequency consistency under different resolutions and bandwidths. We make a Gaussian fitting to extract the spectral features, introduce two theoretical indicators to describe the fitted velocity uncertainty, and ultimately give a mean redshift and its constraint of $z_\mathrm{M}=0.24670045\pm0.00000036$ in accord with most literature. But our redshift error of the target is still three magnitudes higher than the level we can reach the drift signal. Though our first preparation has some flaws in time recording and diode settings, it still proves the correctness of our data process. Confined by limited observing time, we do not strech FAST's ability to obtain a better velocity constraint, so further researchs are needed and in schedule. With fine sensitivity and improving spectral resolution, such observations in FAST could have reasonable possibility to explore cosmic acceleration in late time universe practically., Comment: 19 pages(without ref.), 8 figures, 2 tables. Physics of the Dark Universe 37 (2022) 101088. The first measurement of Sandage-Loeb effect at FAST. Comments welcome!

We explore a possible time variation of the fine structure constant ($\alpha \equiv e^2/\hbar c$) using the Sunyaev-Zel'dovich effect measurements of galaxy clusters along with their X-ray observations. Specifically, the ratio of the integrated Compto-ionization parameter $Y_{SZ}D_A^2$ and its X-ray counterpart $Y_X$ is used as an observable to constrain the bounds on the variation of $\alpha$. Considering the violation of cosmic distance duality relation, this ratio depends on the fine structure constant as $\sim \alpha^3$. We use the quintessence model to provide the origin of $\alpha$ time variation. In order to give a robust test on $\alpha$ variation, two galaxy cluster samples, the 61 clusters provided by the Planck collaboration and the 58 clusters detected by the South Pole Telescope, are collected for analysis. Their X-ray observations are given by the XMM-Newton survey. Our results give $\zeta=-0.203^{+0.101}_{-0.099}$ for the Planck sample and $\zeta=-0.043^{+0.165}_{-0.148}$ for the SPT sample, indicating that $\alpha$ is constant with redshift within $3\sigma$ and $1\sigma$ for the two samples, respectively., Comment: 13 pages, 5 figures. Accepted by ApJ

Fast and accurate performance analysis techniques are essential in early design space exploration and pre-silicon evaluations, including software eco-system development. In particular, on-chip communication continues to play an increasingly important role as the many-core processors scale up. This paper presents the first performance analysis technique that targets networks-on-chip (NoCs) that employ weighted round-robin (WRR) arbitration. Besides fairness, WRR arbitration provides flexibility in allocating bandwidth proportionally to the importance of the traffic classes, unlike basic round-robin and priority-based arbitration. The proposed approach first estimates the effective service time of the packets in the queue due to WRR arbitration. Then, it uses the effective service time to compute the average waiting time of the packets. Next, we incorporate a decomposition technique to extend the analytical model to handle NoC of any size. The proposed approach achieves less than 5% error while executing real applications and 10% error under challenging synthetic traffic with different burstiness levels., Comment: This paper is accepted in International Conference on Computer Aided Design (ICCAD), 2021