arXiv subjects

Chen Tan

Publications and source records attributed to Chen Tan.

7 recordsLinked to original sources

arXiv2026

A Neutron Star Hidden Inside a Black Hole

We investigate dark matter admixed neutron stars in which the neutron star coexists with an anisotropic dark matter halo described by the Einasto density profile, a model recently shown to produce regular, singularity-free black hole solutions~[Phys. Rev. D \textbf{113}, 043011 (2026)]. Solving the modified Tolman--Oppenheimer--Volkoff equations with two different equations of state (BSk19 and SLy4), we find that the dark matter halo significantly alters the neutron star structure. Furthermore, for a specific range of halo parameters, $g_{rr}^{-1}$ changes sign outside the stellar surface, forming an event horizon with the neutron star persisting as a regular configuration inside it--- ``neutron stars in black holes''. This configuration appears in both equations of state and does not depend on a specific choice of the equation of state. The discovery of this configuration provides a new perspective and a concrete computable instance for the study of what lies inside a black hole.

gr-qc↗

arXiv2025

Frozen Neutron Stars in Four-Dimensional Non-polynomial Gravities

This paper investigates the structure and properties of neutron stars in four-dimensional non-polynomial gravities. Solving the modified Tolman-Oppenheimer-Volkoff equations for three different equations of state (BSk19, SLy4, AP4), we confirm that neutron star solutions remain in existence. As the modification parameter $\alpha$ increases, neutron stars grow in both radius and mass. We find that, when the parameter $\alpha$ is sufficiently large, a frozen state emerges at the end of the neutron-star sequence. In this state, the metric functions approach zero extremely close to the stellar surface, forming a critical horizon, making it nearly indistinguishable from a black hole to an external observer. Such a frozen neutron star constitutes a universal endpoint of the neutron-star sequence in this theory, independent of the choice of the equation of state. Based on our results and current observational constraints, we derive bounds on the modification parameter $\alpha$ and show that frozen neutron stars remain allowed in the bounds.

gr-qc↗

arXiv2025

Frozen Neutron Stars

We investigate neutron stars with nonlinear magnetic monopoles in the framework of the Einstein-nonlinear electrodynamics model, specifically within the Bardeen and Hayward models. Solving the modified Tolman-Oppenheimer-Volkoff equations for three different equations of state, we find that upon reaching the critical magnetic charge $q_{c}$, neutron stars enter frozen states characterized by the critical horizon. This extends the concept of frozen states to compact objects composed of ordinary matter (non-field matter), thereby offering a new perspective for related research.

gr-qc↗

arXiv2024

Gravitational Waves from Post-Collision of Fuzzy Dark Matter Solitons

According to the Schr\"odinger-Poisson (SP) equations, fuzzy dark matter (FDM) can form a stable equilibrium configuration, the so-called FDM soliton. The SP system can also determine the evolution of FDM solitons, such as head-on collision. In this paper, we first propose a new adimensional unit of length, time and mass. And then, we simulate the adimensional SP system with $\mathtt{PyUltraLight}$ to study the GWs from post-collision of FDM solitons when the linearized theory is valid and the GW back reaction on the evolution of FDM solitons is ignored. Finally, we find that the GWs from post-collisions have a frequency of (few ten-years)$^{-1}$ or (few years)$^{-1}$ when FDM mass is $m=10^{-18}\rm{eV}/c^2$ or $m=10^{-17}\rm{eV}/c^2$. Therefore, future detection of such GWs will constrain the property of FDM particle and solitons.

astro-ph.CO↗

arXiv2024

Diversity of Fuzzy Dark Matter Solitons

According to the Schr\"odinger-Poisson equations, fuzzy dark matter (FDM) can form a stable equilibrium configuration, the so-called FDM soliton. In principle, given the FDM particle mass, the profile of the FDM soliton is fixed. In practice, however, there is a great diversity of structures in the Universe. Possible causes of such diversity can lie in such sources as the gravitoelectric field due to a central supermassive black hole, the gravitomagnetic field due to the system angular momentum, an extra denser and compact FDM soliton and an ellipsoidal baryon background. We find that the effects of the gravitomagnetic field due to the soliton's self-angular momentum are very weak while those of the other sources are considerable.

hep-ph↗

arXiv2023

Forecasting constraints on the no-hair theorem from the stochastic gravitational wave background

Although the constraints on general relativity (GR) from each individual gravitational-wave (GW) event can be combined to form a cumulative estimate of the deviations from GR, the ever-increasing number of GW events used also leads to the ever-increasing computational cost during the parameter estimation. Therefore, in this paper, we will introduce the deviations from GR into GWs from all events in advance and then create a modified stochastic gravitational-wave background (SGWB) to perform tests of GR. More precisely, we use the $\mathtt{pSEOBNRv4HM\_PA}$ model to include the model-independent hairs and calculate the corresponding SGWB with a given merger rate. Then we turn to the Fisher information matrix to forecast the constraints on the no-hair theorem from SGWB at frequency $10[{\rm Hz}]\lesssim f\lesssim10^3[{\rm Hz}]$ detected by the third-generation ground-based GW detectors, such as the Cosmic Explorer. We find that the forecasting constraints on hairs at $68\%$ confidence range are $\delta\omega_{220}=0\pm0.1296$ and $\delta\tau_{220}=0\pm0.0678$ when the flat priors about the merger rate are added but $\delta\omega_{220}=0\pm0.0903$ and $\delta\tau_{220}=0\pm0.0608$ when the non-flat priors about the merger rate are added.

gr-qc↗

arXiv2023

Artificial Intelligence System for Detection and Screening of Cardiac Abnormalities using Electrocardiogram Images

The artificial intelligence (AI) system has achieved expert-level performance in electrocardiogram (ECG) signal analysis. However, in underdeveloped countries or regions where the healthcare information system is imperfect, only paper ECGs can be provided. Analysis of real-world ECG images (photos or scans of paper ECGs) remains challenging due to complex environments or interference. In this study, we present an AI system developed to detect and screen cardiac abnormalities (CAs) from real-world ECG images. The system was evaluated on a large dataset of 52,357 patients from multiple regions and populations across the world. On the detection task, the AI system obtained area under the receiver operating curve (AUC) of 0.996 (hold-out test), 0.994 (external test 1), 0.984 (external test 2), and 0.979 (external test 3), respectively. Meanwhile, the detection results of AI system showed a strong correlation with the diagnosis of cardiologists (cardiologist 1 (R=0.794, p<1e-3), cardiologist 2 (R=0.812, p<1e-3)). On the screening task, the AI system achieved AUCs of 0.894 (hold-out test) and 0.850 (external test). The screening performance of the AI system was better than that of the cardiologists (AI system (0.846) vs. cardiologist 1 (0.520) vs. cardiologist 2 (0.480)). Our study demonstrates the feasibility of an accurate, objective, easy-to-use, fast, and low-cost AI system for CA detection and screening. The system has the potential to be used by healthcare professionals, caregivers, and general users to assess CAs based on real-world ECG images.

cs.CV↗