Chinese Physics C

Highlights

Physical parameter regression from black hole images using a multiscale adaptive neural network
Jialei Wei, Ao Liu, Dejiang Li, Cuihong Wen

2025, 49(12): 125105. doi: 10.1088/1674-1137/adf542

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High-precision regression of physical parameters from black hole images generated by General Relativistic Ray Tracing (GRRT) is essential for investigating spacetime curvature and advancing black hole astrophysics. However, owing to limitations in observational resolution, high observational costs, and imbalanced distributions of positive and negative samples, black hole images often suffer from data scarcity, sparse parameter spaces, and complex structural characteristics. These factors pose significant challenges to conventional regression methods based on simplified physical models. To overcome these challenges, this study introduces the Multiscale Adaptive Network (MANet), a novel regression framework grounded in deep learning. MANet integrates an Adaptive Channel Attention (ACA) module to selectively enhance features in physically informative regions. Meanwhile, a Multiscale Enhancement Feature Pyramid (MEFP) is employed to capture fine-grained spatial structures, such as photon rings and accretion disks, while alleviating information loss due to downsampling. Experimental evaluations on GRRT-simulated datasets demonstrate that MANet substantially improves parameter estimation accuracy and generalization capability in high-dimensional parameter spaces, outperforming existing baseline approaches. This framework presents a promising avenue for high-precision parameter regression in Event Horizon Telescope (EHT) data analysis and broader astrophysical imaging applications characterized by sparse and noisy data.
On the pole trajectory of the subthreshold negative parity nucleon with varying pion masses
Qu-Zhi Li, Zhiguang Xiao, Han-Qing Zheng

2025, 49(12): 123103. doi: 10.1088/1674-1137/adfa02

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We study the pole trajectory of the recently established subthreshold negative-parity nucleon pole, namely the $N^*(920)$, with varying pion masses in the scheme of linear σ model with nucleons, using the $N/D$ unitarization method. We find that, as the pion mass increases, the pole moves toward the real axis. For larger pion masses, at tree level, the pole falls to a specific point on u-channel cut and crosses to the adjacent Riemann sheet defined by the logarithmic u-channel cut. At the one-loop level, the pole does not meet the u-cut up to $m_\pi=0.36$ GeV. We also re-examined the σ pole trajectory and found it to be in good agreement with the Roy equation analysis result.
Feasibility study of measuring interaction cross sections of hypernuclei produced in projectile fragmentation reactions with WASA-FRS setup
Yiming Gao, Yoshiki K. Tanaka, Vasyl Drozd, Hiroyuki Ekawa, Samuel Escrig, Yan He, Ayumi Kasagi, Enqiang Liu, Manami Nakagawa, Christophe Rappold, Takehiko R. Saito, Ryohei Sekiya, He Wang, Ayari Yanai, Xiaohong Zhou

2025, 49(12): 124003. doi: 10.1088/1674-1137/adf4b2

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A novel method is proposed to measure the interaction cross sections of short-lived hypernuclei with the WASA-FRS experimental setup at GSI and FAIR. The interaction cross sections of hypernuclei, produced in projectile fragmentation reactions at relativistic energies, can be determined from their production point distribution within a target. The feasibility of such a measurement is evaluated through detailed Monte Carlo simulations. The results indicate that an aimed uncertainty on the order of 10% can be achieved for the case of a hypertriton, demonstrating the potential of this method for studying matter radii and the possible hyperon halo structure of hypernuclei.

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Further study on the lepton mass spectra and flavor mixing with S_3L × S_3R flavor symmetry
Chang-Qi Hu, Chun-Yuan Li, Xiao Liang, Xing-Hua Yang, Dai-Xing Zhang

Published: 2025-12-24

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Published: 2025-12-24

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The images of Brans-Dicke-Kerr type naked singularities
Fen Long, Weike Deng, Xin Qin, Songbai Chen, Jiliang Jing

Published: 2025-12-24

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Published: 2025-12-24

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Spatially covariant gravity with two degrees of freedom in the presence of an auxiliary scalar field: Hamiltonian analysis
Jun-Cheng Zhu, Shu-Yu Li, Xian Gao

Published: 2025-12-22

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Published: 2025-12-22

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Gravitational waves from equatorially eccentric extreme mass ratio inspirals around swirling-Kerr black holes
Yuhang Gu, Songbai Chen, Jiliang Jing

2026, 50(2): 025107-025107-11. doi: 10.1088/1674-1137/ae1afc

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The swirling-Kerr black hole is a novel solution of vacuum general relativity and has an extra swirling parameter characterizing the rotation of spacetime background. We study the gravitational waves generated by extreme mass ratio inspirals (EMRIs) along eccentric orbits on the equatorial plane in this novel swirling spacetime. Our findings indicate that this swirling parameter leads to a delayed phase shift in the gravitational waveforms. Furthermore, we investigate the effects of the swirling parameter on the potential issue of waveform confusion caused by the orbital eccentricity and semi-latus rectum parameters. As the swirling parameter increases, the relative variations in the eccentricity increase, whereas the variations in the semi-latus rectum rapidly decrease. The trends related to changes in the orbital eccentricity and semi-latus rectum with the swirling parameter resemble those observed with the MOG parameter in Scalar-Tensor-Vector-Gravity (STVG) theory but with different rates of change. Furthermore, our results also reveal that the effects of the background swirling parameter on the relative variations in the eccentricity and semi-latus rectum are distinct from those of the black hole spin parameter. These results provide deeper insights into the properties of EMRI gravitational waves and background swirling.

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Bayesian-optimized CatBoost for ground-state nuclear charge-radius prediction
Mudassar Ahmed, Abdul Kabir, Jameel-Un Nabi, Laiba Hamid, Manzoor Ahmad

2026, 50(2): 024109-024109-13. doi: 10.1088/1674-1137/ae19dc

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Understanding nuclear shape, behavior, and stability, as well as improving nuclear models, depends on the precise determination of ground-state nuclear charge radii. Existing experimental techniques are limited to extremely narrow regions of the nuclear chart; theoretical models, including relativistic Hartree-Bogoliubov (RHB) and Hartree-Fock-Bogoliubov (HFB), predict broad trends of nuclear properties but miss fine isotopic features such as odd-even staggering effects and shell-closure kinks. High computational time and cost are other obstacles to theoretical approaches. Although machine-learning algorithms have made significant progress in predicting charge radii, they are still hindered by a lack of balanced data and characteristics, primarily centered around $ A\ge40 $ and $ Z\ge20 $. In the present study, we present the first application of CatBoost regression to compute nuclear charge radii. We integrated two experimental datasets with RHB-calculated point-coupling interaction (PC-X) theoretical features and extended our study range to $ A\ge17 $, $ Z\ge8 $. We found the best hyperparameters using Optuna’s Tree-structured Parzen Estimator (TPE) sampler with 10-fold cross-validation (CV), achieving a CV root-mean-square error (RMSE) of 0.0106 fm and hold-out RMSE of 0.0102 fm, with only three features, i.e., neutron number (N), proton number (Z), and RHB theoretical binding energy (BE), outperforming nine other ML models: random forest (RF), quantile RF (QRF), Cubist, Gaussian process regression with polynomial kernel (GPPK), multivariate adaptive regression splines (MARS), SVR, ANN, convolutional neural network (CNN), and Brussels-Skyrme-on-a-grid 3 (BSkG3). SHapley Additive exPlanations (SHAP) analysis confirms the highest global influence of BE in the model's predictions, followed by proton number and neutron number. The proposed model can accurately reproduce the $ N=50 $ kink and odd-even staggering effects in krypton and strontium chains. These results establish CatBoost as a robust and notably promising model for charge-radius prediction and beyond, with the potential to impact r-process modeling and future theoretical development.

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Investigation of resonances in the Σ(1/2^–) system based on the chiral quark model
Yu Yao, Xuejie Liu, Xiaoyun Chen, Yuheng Wu, Jialun Ping, Yue Tan, Qi Huang

2026, 50(2): 023109-023109-11. doi: 10.1088/1674-1137/ae18af

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In this work, we investigate the resonance structures in the $ \Sigma(1/2^-) $ system from both three-quark and five-quark perspectives within the framework of the chiral quark model. An accurate few-body computational approach, the Gaussian expansion method, is employed to construct the orbital wave functions of multiquark states. To reduce the model dependence on parameters, we fit two sets of parameters to check the stability of the results. The calculations show that our results remain stable despite changes in the parameters. In the three-quark calculations, two $ \Sigma(1/2^-) $ states are obtained with energies around 1.8 GeV, which are good candidates for the experimentally observed $ \Sigma(1750) $ and $ \Sigma(1900) $. In the five-quark configuration, several stable resonance states are identified, including $ \Sigma \pi $, $ N \bar{K} $, and $ N \bar{K}^{*} $. These resonance states survive the channel-coupling calculations under the complex-scaling framework and manifest as stable structures. Our results support the existence of a two-pole structure for the $ \Sigma(1/2^-) $ system, predominantly composed of $ \Sigma \pi $ and $ N \bar{K} $ configurations, analogous to the well-known $ \Lambda(1380) $-$ \Lambda(1405) $ ($ \Sigma \pi $-$ N \bar{K} $) system. On the other hand, although the energy of the $ N \bar{K}^{*} $ configuration is close to that of $ \Sigma(1750) $ and $ \Sigma(1900) $, the obtained width is not consistent with the experimental values. This suggests that the $ N \bar{K}^{*} $ state needs to mix with three-quark components to better explain the experimental $ \Sigma(1750) $ and $ \Sigma(1900) $ states. According to our decay width calculations, the predicted two resonance states are primarily composed of $ \Sigma \pi $ and $ N \bar{K} $, with their main decay channel being $ \Lambda \pi $. Therefore, we encourage experimental groups to search for the predicted two-pole structure of the $ \Sigma(1/2^-) $ system in the invariant mass spectrum of $ \Lambda \pi $.

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Current Issued

2025 Vol. 49, No. 12
Published: 02 December 2025

Particles And Fields
Nuclear Physics
Particle And Nuclear Astrophysics And Cosmology