arXiv subjects

Zhen-Zhao Tao

Publications and source records attributed to Zhen-Zhao Tao.

At least 19 recordsLinked to original sources

arXiv2026

A Wavelet-Integrated Search Pipeline for Narrowband Technosignatures in FAST Observations of 33 Exoplanet Systems

Building on prior FAST targeted and blind SETI campaigns toward 33 exoplanet systems, we introduce a wavelet-integrated search pipeline for narrowband technosignature candidates in radio dynamic spectra. At its core, the pipeline uses a Multi-Scale Wavelet Net (MSWNet) to produce an interpretable multi-resolution representation, followed by a lightweight parameter estimator for endpoint localization. Rather than relying solely on hard-threshold drift searches, the pipeline reframes narrowband detection as wavelet-guided feature extraction followed by endpoint regression, morphology-aware filtering, raw-data S/N validation, and multi-beam anticoincidence veto. Applied to real FAST data, the pipeline recovers representative events from prior analyses and produces a compact set of veto-ready candidates for downstream inspection. The resulting workflow preserves interpretability, low regression complexity, and auditable threshold control, making it readily transferable to other radio surveys and large-scale technosignature searches.

astro-ph.IM↗

arXiv2026

Periodic Radio Technosignature Search toward 3I/ATLAS with FAST

3I/ATLAS, the third confirmed interstellar object discovered in the Solar System, provides a unique opportunity for targeted technosignature searches. We report a periodic radio technosignature search toward 3I/ATLAS using the Five-hundred-meter Aperture Spherical Telescope (FAST) L-band multibeam receiver. To search for periodically modulated signals and distinguish center-beam-dominated candidates from multibeam radio-frequency interference, we apply canonical polyadic decomposition (CPD) to the multibeam dynamic spectra. CPD factorizes the multibeam data tensor into a set of separable components, with associated time, frequency, and beam signatures. Candidate components are then selected through periodogram and autocorrelation diagnostics. We find no credible artificial periodic radio technosignature above 0.146 W is detected from the direction of 3I/ATLAS. This search expands the range of signal types explored for this target by including periodic modulated signal, and illustrates that CPD is a promising framework for multibeam periodic technosignature searches.

astro-ph.IM↗

arXiv2026

Gaia DR3 Limits on Stellar Engine Technosignatures in Nearby Stars

An operating stellar engine that transfers momentum to its host star could produce an approximately persistent transverse acceleration during the Gaia Data Release 3 (DR3) observing epoch. We search for such accelerations among 406,984 quality-selected Gaia DR3 stars with nominal distances below 200 pc (about 650 light-years), using 8,890 published Acceleration7 solutions. Because long-period binaries and astrometric systematics can produce similar sky-plane curvature, we model these conventional explanations together with a broad component that can absorb any remaining persistent acceleration or model mismatch. At $a_0 = 2.60 \times 10^{-4}$ m s$^{-2}$, where essentially the entire parent sample is searchable, mapping the residual weights evaluated at the one-sided 95% profile-limit point gives a parent-population fraction limit of $1.21 \times 10^{-5}$. Multiplying this fraction by the parent-sample size gives a summed upper-limit weight of about five star-equivalents above the threshold. Toward the lowest acceleration thresholds, the searchable fraction declines rapidly, so the corresponding bounds primarily describe the reach of the search. No individual source is interpreted as a technological signal.

astro-ph.GA↗

arXiv2026

Narrowband Radio Technosignature Search toward 3I/ATLAS with FAST

3I/ATLAS is the third confirmed interstellar object passing through the Solar System. In this work, we conduct narrowband radio technosignature search toward 3I/ATLAS using the Five-hundred-meter Aperture Spherical Telescope (FAST) L-band multibeam receiver from October 2025 to January 2026 on 4 separate dates (i.e. Mars closest, perihelion, Earth closest and a post-Earth-closest epoch, respectively). We carry out frequency-drifting signal searching with signal-to-noise ratio (SNR) over 10 within 1.05-1.45 GHz via \texttt{bliss} pipeline. These signal hits are grouped into event by beam, frequency and drift rate matching. The events are then filtered by cluster analysis and drift rate cut-off. We also characterized the events by their significance in SNR, structure tensor as well as principal component analysis (PCA). No credible narrowband radio technosignature are detected from 3I/ATLAS after visual inspections. The null results place constraints on the presence of transmitters above $2.862\times 10^{-3}$ W. We further introduce a Bayesian inference framework to assess the occurrence probability of hypothetical transmitters while accounting for uncertainty in their characteristic transmitter power through physically motivated priors.

astro-ph.IM↗

arXiv2026

Phase-Space Crystallization in Galactic Globular Clusters: A Gaia-Based Metric and Implications for Technosignature Searches

We develop a model-independent framework to quantify phase-space "crystallization", the degree of ordered radial and kinematic substructure, in 79 Galactic globular clusters using the Gaia EDR3-based membership catalogue of E. Vasiliev & H. Baumgardt (2021a). We construct a scalar crystallization index, C_index, by combining a radial inhomogeneity metric (z_rad) and a local, cluster-centric tangential-velocity metric (z_vel) standardized against empirical nulls. The population distribution is strongly non-Gaussian: most clusters are consistent with smooth, equilibrium expectations, while a small high-C tail (C_index >= 2) identifies dynamically complex systems, including NGC 5139 (ωCen) and NGC 104 (47 Tuc). Correlation and fixed-N tests show that sample size affects detectability, but does not by itself explain all high-rank objects. Through synthetic injection tests in dynamically "quiet" control clusters, we demonstrate sensitivity to ultra-cold, shell-confined kinematic components, ruling out single-shell structures comprising more than a few to ~ 10-20% of core stars in the best-sampled control clusters. We find no evidence, within the sensitivity of the adopted diagnostics, for phase-space structures that require explanations beyond known dynamical processes. However, C_index provides a useful tool for ranking clusters by dynamical extremeness, serving both as a diagnostic for internal complexity and as a quantitative metric for prioritizing follow-up dynamical or technosignature-oriented observations.

astro-ph.GA↗

arXiv2026

A Deep SETI Search for Technosignatures in the TRAPPIST-1 System with FAST

The Five-hundred-meter Aperture Spherical Telescope (FAST) is the world's largest single-dish radio telescope, and the search for extraterrestrial intelligence (SETI) is one of its five key science objectives. We conducted a targeted narrowband search toward the TRAPPIST-1 system using FAST. The observations consisted of five independent L-band pointings, each with a 20-minute integration, for a total on-source time of 1.67h. The frequency coverage spanned 1.05--1.45GHz with a spectral resolution of ~7.5Hz. We searched for narrowband drifting signals with Doppler drift rates within +_4Hz/s and a signal-to-noise ratio threshold of S/N>10 in two orthogonal linear polarizations separately.Based on the system parameters adopted in this work, we estimate a minimum detectable equivalent isotropic radiated power of 2.04x10^10W, placing one of the most stringent constraints to date on persistent or high-duty-cycle narrowband transmitters in this system. No credible technosignature candidates were identified within the searched parameter space. Nevertheless,TRAPPIST-1 remains a compelling target for future SETI efforts. We plan to extend our search to other signal types, such as periodic or transient transmitters, and to carry out broader surveys of nearby exoplanetary systems with FAST.

astro-ph.IM↗

arXiv2026

A Calibrated Bayesian Search for Potential Chemical Technosignatures in Polluted White Dwarf

We present a meteorite-calibrated Bayesian framework for searching archival abundance records for chemical technosignatures--operationally, compositional patterns better explained by an idealised "processed" template (endmember) than by the empirical distribution of natural rocks. We fit a multi-modal natural-composition reference using 3,493 whole-rock meteorite analyses, and for each of 697 star-paper abundance sets--spanning at least 397 distinct objects once Gaia-designated repeats are consolidated--we compare the Bayesian evidence for (i) natural material and (ii) a mixture of natural material with a fixed siderophile-enriched template, parameterised by a Ca-normalized mixing fraction alpha. Strong support for the processed template is uncommon: in the photospheric compilation (atm) 8/697 records have BF > 10 (4/697 have BF > 100), and in the diffusion-adjusted steady-state subset (acc ss; 148 records spanning at least 94 objects) 6/148 have BF > 10. We report the highest-evidence candidate records and infer the fraction of records detectably favoring the mixture model, with posterior medians pi-tilde = 0.011 (atm) and pi-tilde = 0.041 (acc ss). We calibrate the analysis with end-to-end injection-recovery experiments matched to each record's coverage and censoring. The calibration shows that discrimination is driven mainly by chemical information, typically requires greater-than-or-similar-to 5 detected elements for decisive support, and--for the siderophile template--is strongest for exact five-element panels that include Fe, Mg, Cr, and Ti together with Ni, Si, or Na. These results constrain the detectable incidence of the tested processed-composition class in current data and set observational requirements for future multi-element surveys and expanded template families.

astro-ph.EP↗

arXiv2026

First Lunar Farside SETI Observations for Periodic Signals with the Low-frequency Radio Spectrometer of Chang'E-4 Mission

Chang'E-4 (CE4), the first mission to soft-land on the lunar farside, provides a unique opportunity for astronomical observations from an environment shielded from terrestrial radio interference, and thus serves as pathfinder for lunar farside radio search for extraterrestrial intelligence (SETI) studies. We present a search for periodic technosignatures using low-frequency radio observations from the CE-4 mission, the first radio SETI study based on data from on the observation in lunar farside. We analyze the CE4 dynamic spectra with a component-level framework that combines principal component analysis (PCA), cross-antenna basis alignment, as well as temporal periodicity and frequency comb structure diagnostics. No final periodic candidate signal is found after the selection procedure, and we therefore find no evidence in the present CE4 sample for a credible periodic artificial signal. This study serves as a pathfinder and provides a practical framework for lunar radio SETI analysis. As more future lunar missions begin to incorporate radio instrumentation, lunar farside may become a promising site for expanding radio SETI research.

astro-ph.IM↗

arXiv2026

WISE/CatWISE Constraints on Dysonian Waste-Heat Technosignatures in Nearby Galaxies

We search for galaxy-scale (Dysonian) waste heat in the mid-infrared using WISE. Starting from the 2MASS Redshift Survey (2MRS), we cross-match to CatWISE2020 and AllWISE, apply standard MIR AGN/starburst vetoes (Stern, Assef R90, Jarrett), and treat W1 and W2 as stellar baselines and W3 and W4 as constraining bands. For each galaxy and for blackbody waste heat temperatures T=150-600 K, we convert W3/W4 photometry into conservative 3-sigma per-galaxy upper limits on the bolometric waste heat luminosity using the WISE bandpass (RSR) color correction. The resulting distributions have median caps of ~(5-9) x 10^8 L_sun across T=150-600 K. Aggregated at the population level, the one-sided 95% upper bound on the fraction of nearby galaxies that could host waste heat above a given threshold monotonically decreases with threshold and asymptotes to ~1/6500 at high thresholds (set by the sample size). Sensitivity transitions from W4 at T <= 200K to W3 at T >= 300K. Interpreted with the AGENT formalism, a fiducial Milky Way like stellar luminosity L_=3 x 10^10 L_sun implies typical per galaxy caps of alpha = L_wh/L_ <= 1.7-2.9% over T=150-600 K (e.g., alpha <= 1.8% at T=300 K). At T ~= 300K, no more than f_95 ~= 1.61 x 10^-4 (~= 0.0161%) of nearby galaxies can host KIII-scale systems reprocessing >= 21% of a Milky Way-like stellar luminosity into ~ 300K waste heat.

astro-ph.GA↗

arXiv2026

SETI Observations of k-Hz Periodic Radio Signals from Five Nearby Stars with FAST at L Band

We report a radio SETI search for periodic, kHz-wide signals from five of the nearest stars observable with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Using the 19-beam L-band receiver (1.05-1.45 GHz), we obtained 1200 s tracking observations of Groombridge 34 A/B, Ross 248, 61 Cygni B, and Ross 128. Dynamic spectra from all beams and both linear polarisations were searched channel by channel with a fast-folding algorithm sensitive to periods between 1.1 and 300 s. A multi-layer RFI-mitigation pipeline exploits multi-beam occupancy, cross-target bad-channel statistics, XX/YY polarisation coincidence, broad frequency masks, and narrow site-specific RFI exclusion zones, followed by clustering in period-frequency space. The pipeline is validated on FAST observations of PSR B0329+54, where we recover the known 0.714 s spin period and harmonic structure in the expected beam. For the stellar sample, successive cuts reduce the raw FFA hit lists (> 10^6 hits per target) to a small number of cluster-level candidates, all of which exhibit clear radio-frequency interference signatures in phase-time and phase-frequency diagnostics. We therefore report no convincing detections of periodic transmitters in our searched parameter space. Using the radiometer equation with our adopted detection threshold (S/N = 25) and assuming a duty cycle delta = 0.1, we obtain upper limits of approximately (7-9) x 10^9 W on the isotropic-equivalent EIRP of kHz-wide periodic beacons at these stars, among the most stringent constraints to date on periodic radio emission from nearby stellar systems.

astro-ph.SR↗

arXiv2026

The FAST-SETI Milky Way Globular Cluster Survey I: A Pilot Multibeam On-the-Fly Search of Five Globular Clusters at L-Band

We report a narrowband technosignature search toward five Milky Way globular clusters (NGC 6171, NGC 6218, NGC 6254, NGC 6838, and IC 1276) using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) 19-beam L-band receiver (1.05-1.45 GHz). We adapt the MultiBeam Point-source Scanning (MBPS) strategy to extended targets by gating detections to generalized on-target windows (gOTWs), i.e. the time intervals when a beam main lobe intersects a buffered cluster mask, and by enforcing the deterministic multibeam illumination sequence as a geometry test. Dynamic spectra with frequency resolution about 7.5 Hz and time resolution about 10 s are searched with turboSETI over drift rates |nu_dot| <= 4 Hz s^-1 at signal-to-noise ratio S/N >= 10. From about 2.75e5 raw hits across both linear polarizations, none survive the gOTW gating, array-wide simultaneity veto, in-stripe ordering, and single-drift coherence checks, yielding a robust null result. With system equivalent flux density SEFD about 1.5 Jy and an effective 60 s per illuminated crossing, our per-crossing flux density threshold is S_min about 0.50 Jy, corresponding to minimum isotropic-equivalent radiated power EIRP_min in the range (0.72-1.8)e16 W for cluster distances 4-6.5 kpc; when multiple illuminated crossings occur, non-coherent stacking improves sensitivity by up to sqrt(N). To our knowledge this is the first FAST technosignature survey dedicated to globular clusters and the first to use MBPS as the primary observing strategy. These limits disfavor bright, persistent, isotropic L-band beacons above the stated thresholds during our epochs and establish a scalable blueprint, based on geometry-aware gating and verification, for multi-epoch MBPS campaigns that expand signal morphologies and combine passes to deepen constraints on transmitters in dense stellar systems.

astro-ph.GA↗

arXiv2026

An Improved Machine Learning Approach for Radio Frequency Interference Mitigation in FAST-SETI Survey Archival Data

The search for extraterrestrial intelligence (SETI) commensal surveys aim to scan the sky to detect technosignatures from extraterrestrial life. A major challenge in SETI is the effective mitigation of radio frequency interference (RFI), a critical step that is particularly vital for the highly sensitive Five-hundred-meter Aperture Spherical radio Telescope (FAST). While initial RFI mitigation (e.g., removal of persistent and drifting narrowband RFI) are essential, residual RFI often persists, posing significant challenges due to its complex and various nature. In this paper, we propose and apply an improved machine learning approach, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, to identify and mitigate residual RFI in FAST-SETI commensal survey archival data from July 2019. After initial RFI mitigation, we successfully identify and remove 36977 residual RFIs (accounting for $\sim$ 77.87\%) within approximately 1.678 seconds using the DBSCAN algorithm. This result shows that we have achieved a 7.44\% higher removal rate than previous machine learning methods, along with a 24.85\% reduction in execution time. We finally find interesting candidate signals consistent with previous studies, and retain one candidate signal following further analysis. Therefore, DBSCAN algorithm can mitigate more residual RFI with higher computational efficiency while preserving the candidate signals that we are interested in.

astro-ph.IM↗

arXiv2026

Dual-Backend Multibeam Position Switching Targeted SETI Observations toward Nearby Active Planet-Hosting Systems with FAST

The Five-hundred-meter Aperture Spherical Telescope (FAST), the world's largest single-dish radio telescope, lists the search for extraterrestrial intelligence (SETI) as one of its key scientific objectives. In this work, we present a targeted SETI observation for 7 nearby active stars utilizing the FAST L-band multibeam receiver, employing a observational strategy that combines position switching with multibeam tracking to balance on-source integration time with the accuracy of the beam response. Using both pulsar and SETI backends, we perform a comprehensive search for narrowband drifting signals with Doppler drift rates within diversified drift rate ranges and channel-width periodic signal with periods between 0.12 and 100 s and duty cycles between 10% and 50%. No credible radio technosignatures were detected from any of the target systems. Based on this null result, we place constraints on the presence of transmitters at a 95% confidence level, ruling out narrowband transmitters with with EIRP above $3.98\times10^8 \,\mathrm{W}$ and periodic transmitter with EIRP above $1.80\times10^{10} \,\mathrm{W}$,respectively, within the observation band.

astro-ph.IM↗

arXiv2025

Theoretical Radio Signals from Radio-Band Gravitational Waves Converted from the Neutron Star Magnetic Field

Gravitational waves (GWs) can convert into electromagnetic waves in the presence of a magnetic field via the Gertsenshtein-Zeldovich (GZ) effect. The characteristics of the magnetic field substantially affect this conversion probability. This paper confirms that strong magnetic fields in neutron stars significantly enhance the conversion probability, facilitating detectable radio signatures of very high-frequency (VHF, $\left(10^6-10^{11}\mathrm{~Hz}\right)$) gravitational waves. We theoretically identify two distinct signatures using single-dish telescopes (FAST, TMRT, QTT, GBT) and interferometers (SKA1/2-MID): transient signals from burst-like gravitational wave sources and persistent signals from cosmological background gravitational wave sources. These signatures are mapped to graviton spectral lines derived from quantum field theory by incorporating spin-2 and mass constraints, resulting in smooth, featureless profiles that are critical for distinguishing gravitational wave signals from astrophysical foregrounds. FAST attains a characteristic strain bound of $h_c<10^{-23}$, approaching $10^{-24}$ in the frequency range of $1-3\mathrm{~GHz}$ with a 6-hour observation period. This performance exceeds the $5 σ$ detection thresholds for GWs originating from primordial black holes (PBHs) and nears the limits set by Big Bang nucleosynthesis. Additionally, projections for SKA2-MID indicate even greater sensitivity. Detecting such gravitational waves would improve our comprehension of cosmological models, refine the parameter spaces for primordial black holes, and function as a test for quantum field theory. This approach addresses significant deficiencies in VHF GW research, improving detection sensitivity and facilitating the advancement of next-generation radio telescopes such as FASTA and SKA, which feature larger fields of view and enhanced gain.

astro-ph.HE↗

arXiv2025

Multibeam SETI Observations toward Nearby M dwarfs with FAST

The search for extraterrestrial intelligence (SETI) targeted searches aim to observe specific areas and objects to find possible technosignatures. Many SETI researches have focused on nearby stars and their planets in recent years. In this paper, we report a targeted SETI observations using the most sensitive L-band Five-hundred-meter Aperture Spherical radio Telescope (FAST) toward three nearby M dwarfs, all of which have been discovered exoplanet candidates. The minimum equivalent isotropic radiant power of the lower limit from the three sources we can detect is $6.19 \times 10^{8}$ W, which is well within the reach of current human technology. Applying the multibeam coincidence matching (MBCM) blind search mode, we search for narrowband drifting signals across 1.05-1.45 GHz in each of the two orthogonal linear polarization directions. An unusual signal at 1312.50 MHz detected from the observation toward AD Leo originally piqued our interest. However, we finally eliminate the possibility of an extraterrestrial origin based on much evidence, such as the polarization, frequency, and beam coverage characteristics.

astro-ph.IM↗

arXiv2023

SETI at FAST in China

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.

astro-ph.EP↗

arXiv2023

Polarization Criterion in Targeted SETI Observation

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.

astro-ph.IM↗

arXiv2023

A solution to continuous RFI in narrowband radio SETI with FAST: The MultiBeam Point-source Scanning strategy

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.

astro-ph.IM↗