arXiv subjects

Chang Feng

Publications and source records attributed to Chang Feng.

At least 19 recordsLinked to original sources

arXiv2026

Simultaneous inference of isotropic and anisotropic polarization rotation angles for next-generation cosmic microwave background experiments

The ultrahigh-sensitivity polarization imaging of the cosmic microwave background (CMB) is a treasure trove for new physics. Searching for a predicted polarization angle rotation known as the cosmic birefringence effect is a pursuit of the next-generation CMB experiments, and this new polarization signal would be important for testing fundamental physics theories. However, such a delicate rotation effect can be confused by different mechanisms including polarized Galactic foregrounds and instrumental calibration effects. Also, the cosmological rotation effects may arise from both the background evolution and spatial fluctuations of axion-like particles, leaving complicated imprints on CMB polarization fluctuations. In this work, we establish a comprehensive modeling of cosmological rotation effects, the instrumental miscalibration of polarization angles and complex foreground polarization with higher-order fluctuations, and perform a Bayesian analysis to infer both isotropic and anisotropic rotation angles simultaneously for foreground-mitigated polarization datasets from submillimeter to millimeter wavelengths. We find that such a Bayesian formalism can effectively extract the rotation effects for the next-generation CMB experiments and investigate the impact of the known sources including Galactic foregrounds and lensing on the inferred cosmological signals. The method in this work is well suited for future polarization data analyses, and the inferred rotation effects may shed light on the nature of the axion-like particles.

astro-ph.CO↗

arXiv2026

Unveiling dark energy properties with high-sensitivity cross-correlations of neutral hydrogen intensity mapping and galaxy surveys

The redshifted 21 cm line from the hyperfine structure of neutral hydrogen atoms is a promising tracer for the three-dimensional evolution of our universe. Its broad spatial and temporal coverage is crucial for understanding the complex nature of dark matter and dark energy. However, it is very challenging to directly detect the 21 cm signal due to the existence of radio foreground contaminants that are orders of magnitude brighter. Therefore, mitigating the foreground contamination becomes an indispensable task for detecting the 21 cm signal, which is also expected to be correlated with the dark-matter-dominated large-scale structure. The cross-correlations between the neutral hydrogen intensity mapping and galaxy surveys in the future can not only confirm a detection of the 21 cm signal but can also be a complementary probe for 21 cm cosmology. To meet the precision requirements for cosmological studies, it is important to investigate the complex features of the estimated cross-correlations using numerical simulations. In this work, we simulate the low-redshift HI observations and narrow-band optical surveys in the future and obtain the foreground- and bias-mitigated HI-galaxy cross-power spectra, with which we perform a Bayesian analysis to infer cosmological parameters of dynamical dark energy model. The method developed in this work will be important for cosmological studies with the 21 cm intensity mapping.

astro-ph.CO↗

arXiv2026

pespace: A new tool of GPU-accelerated and auto-differentiable response generation and likelihood evaluation for space-borne gravitational wave detectors

Space-borne gravitational wave detectors will expand the scope of gravitational wave astronomy to the milli-Hertz band in the near future. The development of data analysis software infrastructure at the current stage is crucial. In this paper, we introduce \texttt{pespace} which can be used for the full Bayesian parameter estimation of massive black hole binaries with detectors including LISA, Taiji, and Tianqin. The core computations are implemented using the high-performance parallel programming framework \texttt{taichi-lang} which enables automatic differentiation and hardware acceleration across different architectures. We also reimplement the waveform models \texttt{PhenomXAS} and \texttt{PhenomXHM} in the separate package \texttt{tiwave} to integrate waveform generation within the \texttt{taichi-lang} scope, making the entire computation accelerated and differentiable. To demonstrate the functionality of the tool, we use a typical signal from a massive black hole binary to perform the full Bayesian parameter estimation with the complete likelihood function for three scenarios: including a single detector using the waveform with only the dominant mode; a single detector using the waveform including higher modes; and a detector network with higher modes included. The results demonstrate that higher modes are essential in breaking degeneracies, and coincident observations by the detector network can significantly improve the measurement of source properties. Additionally, automatic differentiation provides an accurate way to obtain the Fisher matrix without manual fine-tuning of the finite difference step size. Using a subset of extrinsic parameters, we show that the approximated posteriors obtained by the Fisher matrix agree well with those derived from Bayesian parameter estimation.

gr-qc↗

arXiv2026

The BINGO project X. Cosmological parameter constraints from HI Intensity Mapping lognormal simulations

Context. Building on the transformative success of optical redshift surveys, the emerging technique of neutral hydrogen (HI) intensity mapping (IM) offers a novel probe of large-scale structure (LSS) growth and the late-time accelerated expansion of the universe. Aims. We present cosmological forecasts for the Baryon Acoustic Oscillations from Integrated Neutral Gas Observations (BINGO), a pioneering HI IM experiment, quantifying its potential to constrain the Planck-calibrated $\Lambda$CDM cosmology and extensions to the $w_0w_a$CDM dark energy model. Methods. For BINGO's Phase~1 configuration, we simulate the HI IM signal using a lognormal model and incorporate three dominant systematics: foreground residuals, thermal noise, and beam resolution effects. Using Bayesian inference, we derive joint constraints on six cosmological parameters ($\Omega_b h^2$, $\Omega_c h^2$, $100\theta_s$, $n_s$, $\ln 10^{10} A_s$, and $\tau_r$) alongside 60 HI parameters ($b_{\rm HI}^i$, $\Omega_{\rm HI}^i b_{\rm HI}^i$) across 30 frequency channels. Results. Our results demonstrate that combining BINGO with the Planck 2018 CMB dataset tightens the confidence regions of cosmological parameters to $\sim$40\% the size of those from Planck alone, significantly improving the precision of parameter estimation. Furthermore, BINGO constrains the redshift evolution of HI density and delivers competitive measurements of the dark energy equation of state parameters ($w_0$, $w_a$). Conclusions. These results demonstrate BINGO's potential to extract significant cosmological information from the HI distribution and provide constraints competitive with current and future cosmological surveys.

astro-ph.CO↗

arXiv2025

Inference of $B$-mode polarization in the presence of non-Gaussian foregrounds

The inflationary $B$-mode signals encode invaluable information about the origin of our Universe and searching for potential signatures of primordial gravitational waves (PGWs) is one of the major science goals for future precision observations of cosmic microwave background (CMB) polarization. However, dominant $B$-mode signals of both Galactic foreground contamination and gravitational lensing effects prevent direct measurements of the PGW $B$-mode signals. There are existing proposals which can effectively eliminate these two contaminants but issues remain for future high-sensitivity and multifrequency CMB polarization observations, such as spatially-varying spectral energy distribution (SED) of polarized foreground and cosmological $B$-mode signals due to primordial magnetic fields (PMFs). In this work, we investigate inference of PGW $B$-mode signals in the presence of both complexities. We employ a constrained moment internal linear combination (cMILC) method to remove polarization signals arising from spatially varying SEDs. Also, we employ a power-spectrum-based approach to extracting both the Galactic and cosmological $B$-mode components. Two methods have been validated by mock data and different consistency tests have been performed. We apply these two methods to end-to-end simulations for future high-sensitivity and multifrequency polarization observations and investigate the detectability of different $B$-mode signals in the presence of non-Gaussian polarized foregrounds under different scenarios. This study will be important for new physics studies with $B$-mode signatures.

astro-ph.CO↗

arXiv2025

Improved constraints on ultralight axions using latest observations of the early and late Universe

Ultralight axions (ULAs) are hypothetical particles which can behave like dark matter (DM) or dark energy (DE) depending on masses generated at the symmetry-breaking scale. It remains a mystery whether the ULAs can make up a fraction of DM or DE. Although theoretical predictions indicate that the ULAs may leave distinct imprints on cosmological signals, these signatures may exist in a broad spatial and temporal scales, and may be degenerate with the known effects of the standard model. The ULA signatures are extremely subtle and the observational evidence of the ULAs remain elusive. In this work, we infer the ULA properties using both the early and late universe observations from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO). We validate modeling of the ULA effects using the CMB and BAO mock data and perform different tests to cross-check the results. By analyzing the Planck 2018 CMB measurements and the BAO measurements from the Data Release 2 of Dark Energy Spectroscopic Instrument (DESI), we constrain the energy density fraction ratio of the ULAs to total dark matter $\Omega_a/\Omega_d$ and obtain a new upper bound of $\Omega_a/\Omega_d$. Future CMB and BAO measurements will achieve unprecedented precision and will be crucial for understanding the nature of the ULAs.

astro-ph.CO↗

arXiv2025

Sample Path Moderate Deviation Principle for Queues with Waiting-time Dependent Interarrival and Service Times

We consider a single-server queue where interarrival and service times depend linearly and randomly on customer waiting times, and establish a sample-path moderate deviation principle (MDP) for the waiting time process. The waiting times for the queue can be written as a modified Lindley recursion with a random weight coefficient. Under a natural scaling of the random coefficients, we analyze the fluid behavior of the workload process and derive the stable equilibrium point, which can be zero or a positive value. The moderate-deviation-scaled process is centered around the stable equilibrium point and then represented as a linear stochastic differential equation driven by two random walks together with additional asymptotically negligible error terms and possibly a reflection at zero. The rate functions of MDPs in the two scenarios can be characterized explicitly, and they differ in that the case with zero centering term involves the linearly generalized Skorokhod reflection mapping while the case with positive centering term does not (similar to the corresponding diffusion limits). Our analysis involves the MDP for the associated linearly recursive Markov chains, invoking a perturbation of two independent random walks, and employing martingale techniques to prove the asymptotically exponentially vanishing error terms.

math.PR↗

arXiv2025

Detectability of the 21 cm signal with BINGO through cross-correlation with photometric surveys

21 cm intensity mapping (HI IM) can efficiently map large cosmic volumes with good redshift resolution, but systematics and foreground contamination pose major challenges for extracting accurate cosmological information. Cross-correlation with galaxy surveys offers an efficient mitigation strategy, as both datasets have largely uncorrelated systematics. We evaluate the detectability of the 21 cm signal from the BINGO radio telescope by cross-correlating with the LSST photometric survey, given their strong overlap in area and redshift. Using lognormal simulations, we model the cosmological signal in the BINGO frequency range (980 - 1260 MHz), incorporating thermal noise, foregrounds, and cleanup. The LSST simulations include uncertainties in photometric redshift (photo-z) and galaxy number density in the first three redshift intervals (mean redshift approximately equal to 0.25, 0.35, 0.45), corresponding to the expected performance after 10 years of the survey. We show that photo-z errors significantly increase the noise in the cross-correlation, reducing its statistical significance to levels comparable to those of the autocorrelation. Still, the HI signal remains detectable through the cross-correlation, even with photo-z uncertainties similar to those of the LSST. Our results corroborate the feasibility of this approach under realistic conditions and motivate further refinement of the current analysis methods.

astro-ph.CO↗

arXiv2025

Cosmological Remapping for Efficient Generation of 21 cm Intensity Mapping Mocks

We present a novel application of cosmological rescaling, or "remapping," to generate 21 cm intensity mapping mocks for different cosmologies. The remapping method allows for computationally efficient generation of N-body catalogs by rescaling existing simulations. In this work, we employ the remapping method to construct dark matter halo catalogs, starting from the Horizon Run 4 simulation with WMAP5 cosmology, and apply it to different target cosmologies, including WMAP7, Planck18 and Chevallier-Polarski-Linder (CPL) models. These catalogs are then used to simulate 21 cm intensity maps. We use the halo occupation distribution (HOD) method to populate halos with neutral hydrogen (HI) and derive 21 cm brightness temperature maps. Our results demonstrate the effectiveness of the remapping approach in generating cosmological simulations for large-scale structure studies, offering an alternative for testing observational data pipelines and performing cosmological parameter forecasts without the need for computationally expensive full N-body simulations. We also analyze the precision and limitations of the remapping, in light of the rescaling parameters $s$ and $s_m$, as well as the effects of the halo mass and box size thresholds.

astro-ph.CO↗

arXiv2025

Unified and consistent structure growth measurements from joint ACT, SPT and \textit{Planck} CMB lensing

We present the tightest cosmic microwave background (CMB) lensing constraints to date on the growth of structure by combining CMB lensing measurements from the Atacama Cosmology Telescope (ACT), the South Pole Telescope (SPT) and \textit{Planck}. Each of these surveys individually provides lensing measurements with similarly high statistical power, achieving signal-to-noise ratios of approximately 40. The combined lensing bandpowers represent the most precise CMB lensing power spectrum measurement to date with a signal-to-noise ratio of 61 and an amplitude of $A_\mathrm{lens}^\mathrm{recon} = 1.025 \pm 0.017$ with respect to the theory prediction from the best-fit CMB \textit{Planck}-ACT cosmology. The bandpowers from all three lensing datasets, analyzed jointly, yield a $1.6\%$ measurement of the parameter combination $S_8^\mathrm{CMBL} \equiv \sigma_8\,(\Omega_m/0.3)^{0.25} = 0.825^{+0.015}_{-0.013}$. Including Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillation (BAO) data improves the constraint on the amplitude of matter fluctuations to $\sigma_8 = 0.829 \pm 0.009$ (a $1.1\%$ determination). When combining with uncalibrated supernovae from \texttt{Pantheon+}, we present a $4\%$ sound-horizon-independent estimate of $H_0=66.4\pm2.5\,\mathrm{km\,s^{-1}\,Mpc^{-1}} $. The joint lensing constraints on structure growth and present-day Hubble rate are fully consistent with a $\Lambda$CDM model fit to the primary CMB data from \textit{Planck} and ACT. While the precise upper limit is sensitive to the choice of data and underlying model assumptions, when varying the neutrino mass sum within the $\Lambda\mathrm{CDM}$ cosmological model, the combination of primary CMB, BAO and CMB lensing drives the probable upper limit for the mass sum towards lower values, comparable to the minimum mass prior required by neutrino oscillation experiments.

astro-ph.CO↗

arXiv2025

Investigating cross-correlations between cosmic microwave background lensing and 21 cm intensity mapping

The neutral hydrogen (HI) signal is a crucial probe for astrophysics and cosmology, but it is quite challenging to measure from raw data because of bright foreground contaminants at radio wavelengths. Cross-correlating the radio observations with large-scale structure tracers (LSS) could detect faint cosmological signals since they are not correlated with the foreground, but exquisite component separation procedures must be performed to reduce the variance induced by the foreground. In this work, we adopt the lensing of the cosmic microwave background (CMB) as the LSS tracer and investigate the cross-correlation of CMB lensing and HI observations at the post-reionization epoch. We use simulations to study lensing and HI cross-correlations in the context of next-generation CMB and intensity mapping experiments. We investigate the impact of the component separation based on linear combinations of the HI observations at different frequencies and estimate the signal-to-noise ratios for the cross-correlation measurements in different scenarios.

astro-ph.CO↗

arXiv2024

The BINGO/ABDUS Project: Forecast for cosmological parameters from a mock Fast Radio Bursts survey

There are various surveys that will provide excellent data to search for and localize Fast Radio Bursts (FRBs). The BINGO project will be one such survey, and this collaboration has already estimated a FRB detection rate that the project will yield. We present a forecast of the future constraints on our current cosmological model that the BINGO FRB detections and localizations will have when added to other current cosmological datasets. We quantify the dispersion measure (DM) as a function of redshift ($z$) for the BINGO FRB mock sample. Furthermore, we use current datasets (Supernovae, Baryonic Acoustic Oscillations, and Cosmic Microwave Background data) prior to assessing the efficacy of constraining dark energy models using Monte Carlo methods. Our results show that spatially localized BINGO FRB dataset will provide promising constraints on the population of host galaxies intrinsic DM and be able to measure the nuisance parameters present within a FRB cosmological analysis. They will also provide alternative estimates on other parameters such as the Hubble constant and the dark energy equation of state. In particular, we should see that BINGO FRB data can put constraints on the degenerate $w-H_0$ plane, which the CMB is incapable of measuring, allowing FRBs to be a viable alternative to BAO to constrain the dark energy equation of state. We conclude that FRBs remain a promising future probe for cosmology and that the FRBs localized by the BINGO project will contribute significantly to our knowledge of the current cosmological model.

astro-ph.CO↗

arXiv2024

Detecting ultralight axions from multifrequency observations of neutral hydrogen intensity mapping

We investigate the effects of ultralight axions (ULAs) on the differential brightness temperature fluctuations of neutral hydrogen at the post-reionization stage. Unique structure suppression features under the influence of ULAs are studied from angular correlations of the neutral hydrogen signals observed at different frequencies. Moreover, ULAs can behave like dark energy or dark matter at different mass regimes, implying that the fraction of the ULA energy density would be correlated with the sum of neutrino masses and the parameters of the dark energy equation of state for dark matter and dark energy like ULAs, respectively. We have explored the parameter space for the ULA physics and possible degeneracies among dark energy, neutrinos, and ULAs using the theoretical angular correlation functions expected from future intensity mapping surveys.

astro-ph.CO↗

arXiv2024

A measurement of atmospheric circular polarization with POLARBEAR

At millimeter wavelengths, the atmospheric emission is circularly polarized owing to the Zeeman splitting of molecular oxygen by the Earth's magnetic field. We report a measurement of the signal in the 150 GHz band using 3 years of observational data with the \textsc{Polarbear} project. Non-idealities of a continuously rotating half-wave plate (HWP) partially convert circularly polarized light to linearly polarized light. While \textsc{Polarbear} detectors are sensitive to linear polarization, this effect makes them sensitive to circular polarization. Although this was not the intended use, we utilized this conversion to measure circular polarization. We reconstruct the azimuthal gradient of the circular polarization signal and measure its dependency from the scanning direction and the detector bandpass. We compare the signal with a simulation based on atmospheric emission theory, the detector bandpass, and the HWP leakage spectrum model. We find the ratio of the observed azimuthal slope to the simulated slope is $0.92 \pm 0.01\rm{(stat)} \pm 0.07\rm{(sys)}$. This ratio corresponds to a brightness temperature of $3.8\,\mathrm{m K}$ at the effective band center of $121.8\,\mathrm{GHz}$ and bandwidth of $3.5\,\mathrm{GHz}$ estimated from representative detector bandpass and the spectrum of Zeeman emission. This result validates our understanding of the instrument and reinforces the feasibility of measuring the circular polarization using the imperfection of continuously rotating HWP. Continuously rotating HWP is popular in ongoing and future cosmic microwave background experiments to modulate the polarized signal. This work shows a method for signal extraction and leakage subtraction that can help measuring circular polarization in such experiments.

astro-ph.IM↗

arXiv2024

Constraints on large-scale polarization in northern hemisphere

Present cosmic microwave background (CMB) observations have significantly advanced our understanding of the universe's origin, especially with primordial gravitational waves (PGWs). Currently, ground-based CMB telescopes are mainly located in the southern hemisphere, leaving an untapped potential for observations in the northern hemisphere. In this work, we investigate the perspective of a northern hemisphere CMB polarization telescope (NHT) to detect PGWs and present mock data for such a project. We forecast the detection sensitivity on the tensor-to-scalar ratio r of NHT and compare it with the existed ground-based experiments, also search for optimal experimental configurations that can achieve the best sensitivity of r. Our results indicate that, considering realistic experimental conditions, the first year of NHT observations combined with Planck can achieve a precision of \sigma (r)= 0.015, reaching the level of BICEP2/Keck, with significant potential for improvement with subsequent instrumentation parameter enhancements.

astro-ph.CO↗

arXiv2024

Exploration of the polarization angle variability of the Crab Nebula with POLARBEAR and its application to the search for axion-like particles

The Crab Nebula, also known as Tau A, is a polarized astronomical source at millimeter wavelengths. It has been used as a stable light source for polarization angle calibration in millimeter-wave astronomy. However, it is known that its intensity and polarization vary as a function of time at a variety of wavelengths. Thus, it is of interest to verify the stability of the millimeter-wave polarization. If detected, polarization variability may be used to better understand the dynamics of Tau~A, and for understanding the validity of Tau~A as a calibrator. One intriguing application of such observation is to use it for the search of axion-like particles (ALPs). Ultralight ALPs couple to photons through a Chern-Simons term, and induce a temporal oscillation in the polarization angle of linearly polarized sources. After assessing a number of systematic errors and testing for internal consistency, we evaluate the variability of the polarization angle of the Crab Nebula using 2015 and 2016 observations with the 150 GHz POLARBEAR instrument. We place a median 95% upper bound of polarization oscillation amplitude $A < 0.065^\circ$ over the oscillation frequencies from $0.75~\mathrm{year}^{-1}$ to $0.66~\mathrm{hour}^{-1}$. Assuming that no sources other than ALP are causing Tau A's polarization angle variation, that the ALP constitutes all the dark matter, and that the ALP field is a stochastic Gaussian field, this bound translates into a median 95% upper bound of ALP-photon coupling $g_{a\gamma\gamma} < 2.16\times10^{-12}\,\mathrm{GeV}^{-1}\times(m_a/10^{-21} \mathrm{eV})$ in the mass range from $9.9\times10^{-23} \mathrm{eV}$ to $7.7\times10^{-19} \mathrm{eV}$. This demonstrates that this type of analysis using bright polarized sources is as competitive as those using the polarization of cosmic microwave background in constraining ALPs.

astro-ph.CO↗

arXiv2024

Forecast of foreground cleaning strategies for AliCPT-1

We report the test results of several independent foreground-cleaning pipelines used in the Ali CMB Polarization Telescope experiment (AliCPT-1), a high-altitude CMB imager in the Northern hemisphere with thousands of detectors dedicated to the search for a primordial CMB polarization $B$-mode signature. Based on simulated data from 4 detector modules and a single season of observation, which we refer to as Data Challenge 1 (DC1), we employ different and independent pipelines to examine the robustness and effectiveness of the estimates on foreground parameters and the primordial $B$-mode detection. The foreground-cleaning strategies used in the pipelines include the parametric method of template fitting (TF) and the non-parametric methods of the constrained internal linear combination (cILC), the analytical blind separation (ABS), and the generalized least squares (GLS). We examine the impact of possible foreground residuals on the estimate of the CMB tensor-to-scalar ratio ($r$) for each pipeline by changing the contamination components in the simulated maps and varying the foreground models and sky patches for various tests. According to the DC1 data with the simulation input value $r_{\rm true}=0.023$, the foreground residual contamination levels in the TF/ABS/cILC/GLS pipelines are well within the corresponding statistical errors at the $2\sigma$ level. Furthermore, by utilizing the tension estimator, which helps identify significant residual foreground contamination in the detection of the primordial $B$-mode signal by quantifying the discrepancy between various $r$ measurements, we conclude that the presence of small foreground residuals does not lead to any significant inconsistency in the estimation of $r$.

astro-ph.CO↗

arXiv2023

Multi-parameter Tests of General Relativity Using Bayesian Parameter Estimation with Principal Component Analysis for LISA

In the near future, space-borne gravitational wave (GW) detector LISA can open the window of low-frequency band of GW and provide new tools to test gravity theories. In this work, we consider multi-parameter tests of GW generation and propagation where the deformation coefficients are varied simultaneously in parameter estimation and the principal component analysis (PCA) method are used to transform posterior samples into new bases for extracting the most informative components. The dominant components can be more sensitive to potential departures from general relativity (GR). We extend previous works by employing Bayesian parameter estimation and performing both tests with injections of GR and injections of subtle GR-violated signals. We also apply multi-parameter tests with PCA in the phenomenological test of GW propagation. This work complements previous works and further demonstrates the enhancement provided by the PCA method. Considering a supermassive black hole binary system as the GW source, we show that subtle departures will be more obvious in posteriors of PCA parameters. The departures less than $1\sigma$ in original parameters can yield significant departures in first 5 dominant PCA parameters.

gr-qc↗