arXiv subjects

Xiao-Jun Bi

Publications and source records attributed to Xiao-Jun Bi.

At least 37 records · Page 2Linked to original sources

arXiv2025

Constraints on Lorentz-invariance violation in the neutrino sector from the ultrahigh-energy event KM3-230213A

Lorentz invariance is a fundamental symmetry of spacetime and serves as the cornerstone of modern physics, supporting the constancy of the speed of light. A crucial implication of this principle is that no particle can propagate faster than this universal speed limit. In this study, we present a stringent neutrino-based test of Lorentz invariance, utilizing the highest-energy neutrino ever detected, known as event KM3-230213A. The detection of this neutrino, with measured energy of approximately 220 PeV, allows us to establish a lower bound on the scale of second-order Lorentz invariance violation, quantified as $Λ_2>5.0\times 10^{19}$ GeV at 90 \% confidence level.

hep-ph↗

arXiv2025

Construction of fuzzy dark matter halos with arbitrary initial velocities

Cosmological simulations of fuzzy dark matter (FDM) are computationally expensive, and the resulting halos lack flexibility in parameter adjustments, such as virial mass, density profile, and global velocity. Previous studies have introduced a method for constructing FDM halos with predefined density profiles. In this study, we investigate the initial global velocity of these constructed halos and find that it is nonzero. We provide the theoretical formula for this velocity and illustrate that it arises from the interference between states of odd and even parity. Our calculated results closely match simulation outcomes. Additionally, we showcase how to counteract this velocity and create a halo with a customizable initial global velocity. Our study presents a practical method for adjusting the initial global velocity of halos in controlled FDM simulations, facilitating investigations into tidal effects, galaxy collisions, and other scenarios.

astro-ph.CO↗

arXiv2025

Interpreting the Extremely Diffuse Stellar Distribution of the Nube Galaxy through Fuzzy Dark Matter

Recent observations have uncovered a remarkably flat and extremely diffuse stellar distribution within the almost dark dwarf galaxy Nube, posing a challenge to the standard cold dark matter scenario. In this study, we employ numerical simulations to explore the possibility that this anomalous stellar distribution can be attributed to the dynamical heating effect of fuzzy dark matter (FDM). The relatively isolated location and low baryon fraction of Nube make it an ideal system for investigating this effect. Our findings indicate that by adopting a halo profile consistent with the dynamical mass estimation of Nube and an FDM particle mass on the order of $10^{-23}$ eV, the final 2D stellar distribution derived from simulation closely matches observational data. These results suggest that FDM could provide an explanation for the extremely diffuse stellar distribution of Nube.

astro-ph.GA↗

arXiv2025

Exploring Axion-Like Particle from observation of FSRQ Ton 599 by Fermi-LAT

High energy photons traveling through astrophysical magnetic fields have the potential to undergo oscillations with axion-like particles (ALPs), resulting in modifications to the observed photon spectrum. High energy $γ-$ray sources with significant magnetic field strengths provide an ideal setting to investigate this phenomenon. Ton 599, a flat spectrum radio quasar with a magnetic field strength on the order of Gauss in its emission region, presents a promising opportunity for studying ALP-photon oscillations. In this study, we analyze the effects of ALP-photon oscillations on the $γ$-ray spectrum of Ton 599 as observed by Fermi-LAT. Our investigation considers the potential influences of the broad-line region and dusty torus on the $γ-$ray spectrum of Ton 599. We set the constraints on the ALP parameters at the $95\%$ confidence level, and find that the constraints on $g_{aγ}$ can reach approximately $2 \times 10^{-12}~\mathrm{GeV}^{-1}$ for $m_a \sim 10^{9}~\mathrm{eV}$.

astro-ph.HE↗

arXiv2025

Prediction of lithium isotope fluxes using data-driven production cross sections

Galactic cosmic rays (CRs) generally share common propagation features, leading to consistent spectral observations of secondary nuclei such as Li, Be, and B. However, the Li spectrum predicted by the CR diffusion coefficient inferred from B/C is significantly lower than the latest measurement of AMS-02. This anomaly may be attributed to the missing contributions from the heavy nuclei components in cosmic rays. By including these missing contributions the excess of the Li spectrum disappears. However, another inconsistency still exists since the calculated Li spectrum is now overestimated compared to the data. In this work, we update the cross-section model used to calculate the Li production according to more cross-section measurements. We find that the cross sections of these added reactions are systematically overestimated, and should be renormalized to the interpolations of available data. As a result, our prediction of the total Li spectrum is consistent with the measurement without discrepancy, and our prediction of the $\rm^6Li$ and $\rm^7Li$ spectra are consistent with the preliminary measurements of AMS-02 within the cross-section uncertainties.

astro-ph.HE↗

arXiv2025

Deciphering the spectral bumps of Galactic cosmic rays through gamma-ray observations of nearby molecular clouds

The observed spectral bump in cosmic-ray (CR) proton and helium spectra, along with the phase and amplitude evolution of CR dipole anisotropy, provide plausible yet indirect evidence for the presence of a nearby CR source. This study investigates the potential of giant molecular clouds (GMCs) located near the solar system to act as natural probes of CRs from the nearby source, with their gamma-ray emissions serving as indicators of spatial variations in CR flux within the solar neighborhood resulting from this source. We show that a nearby source, accounting for the CR data, could imprint distinct features on the $γ$-ray spectra of different GMCs. We expect that these features are detectable by LHAASO and upcoming high-energy $γ$-ray observatories, providing a powerful test for the hypothesized nearby source. Notably, we find that determining the energy dependence of the $γ$-ray spectral index offers a promising approach to investigate the nearby source and constrain its distance. Conversely, if the spectral bump is a widespread Galactic phenomenon, the energy dependence would exhibit uniformity across all GMCs, distinguishing the underlying mechanism accounting for the spectral bump from the scenario involving a nearby source.

astro-ph.HE↗

arXiv2024

Cosmic-ray deuteron excess from a primary component

The recent AMS-02 measurements of cosmic-ray (CR) deuteron fluxes suggest the presence of primary deuterons in quantities far exceeding predictions from Big Bang nucleosynthesis. This poses a significant challenge to modern astrophysics, as no known processes can account for such large amounts of deuterons without violating existing constraints~\cite{Epstein:1976hq}. In contrast, it is recently proposed that the AMS-02 measurements can be explained by a purely secondary origin when contributions from heavier nuclei are considered. In this study, we recalculate the secondary deuteron flux using production cross sections updated with the latest collider data. We find that some of the deuteron production cross sections are overestimated in the widely-used calculation tools for CR propagation, and a primary deuteron component is still necessary. We then propose a novel process for generating primary deuterons at CR sources through a fusion mechanism, which is naturally unique to deuterons. This model could explain the observed deuteron excess while maintaining consistency with other CR measurements.

astro-ph.HE↗

arXiv2024

Constraining the Thickness of the Galactic Halo through Cosmic-Ray Anisotropy Using the Spatial-Dependent-Propagation Model

The spatial-dependent-propagation (SDP) model with a nearby source works well to reproduce the coevolving features of both cosmic-ray (CR)-nuclei spectra and anisotropy. However, it is well known that the Sun is actually deviating from the galactic disk. This will lead to a dominating anisotropy in the direction perpendicular to the galactic disk, which is discrepant with current observations. Thus, it is necessary to further investigate the effect of the solar offset on anisotropy. In this work, to the best of our knowledge, this is the first time that the combined studies of the solar offset, nuclei spectra, and anisotropy have been performed based on the SDP model. As a result, to reproduce CR spectra and anisotropy, the thickness of the inner halo $ (Z_{IH})$ needs to increase linearly with the displacement of the Sun. We also know that the PeV anisotropy could be used to estimate the value of the diffusion coefficient, thus breaking the degeneracy between the diffusion coefficient and halo thickness. Therefore, it is a good approach to constrain the halo thickness. Moreover, the anisotropy in the PeV energy region, as a new probe, might also shed new light on constraining the solar offset. It is hoped that the anisotropy of the energies from $\rm \sim$TeV to $\rm PeV$ can be finely measured with the LHAASO experiment, leading to a better understanding of the thick halo.

astro-ph.HE↗

arXiv2024

A rigorous solution to the superluminal issue in the diffusion equation

Superluminal propagation is an intrinsic problem in the diffusion equation and has not been effectively addressed for a long time. In this work, a rigorous solution to this issue is obtained under the assumption that particles undergo a random flight process, where they move isotropically at a constant speed while experiencing random scatterings. We validate this solution by comparing it with comprehensive simulations of the random flight process and find that it significantly deviates from the solution derived from the Jüttner propagator. This solution is broadly applicable to various diffusion phenomena, such as cosmic-ray propagation. We emphasize that our rigorous solution is particularly crucial in scenarios involving burst-like particle injection, where previous phenomenological approaches to the superluminal diffusion problem may not yield accurate results.

astro-ph.HE↗

arXiv2024

SKA Sensitivity to Potential Radio Emission from Dark Matter Annihilation in Ursa Major III

The recently discovered stellar system, Ursa Major III/UNIONS 1, may be the faintest and densest dwarf spheroidal satellite galaxy of the Milky Way. Owing to its close proximity and substantial dark matter (DM) component, Ursa Major III emerges as a highly promising target for DM indirect detection. It is known that electrons and positrons originating from DM annihilation can generate a broad radio spectrum through the processes of synchrotron radiation and inverse Compton scattering within galaxies. In this study, we investigate the potential of the Square Kilometre Array (SKA) in detecting radio signatures arising from DM annihilation in Ursa Major III over a 100 hour observation period. Our analysis indicates that the SKA has strong capabilities in detecting these signatures. For instance, the SKA sensitivity to the DM annihilation cross section is estimated to reach $\mathcal{O}(10^{-30})-\mathcal{O}(10^{-28})\; \rm cm^{3} s^{-1}$ in the DM mass range from several GeV to $\sim100$ GeV for the $e^+e^-$ and $μ^+μ^-$ annihilation channels. The precise results are significantly influenced by various astrophysical factors, such as the strength of magnetic field, the diffusion coefficient, and the DM density profile in the dwarf galaxy. We discuss the impact of the uncertainties associated with these factors, and find that the SKA sensitivities have the potential to surpass the current constraints, even when considering these uncertainties.

hep-ph↗

arXiv2024

Determination of dark matter distribution in Ursa Major III and constraints on dark matter annihilation

The recently discovered satellite dwarf galaxy Ursa Major III provides a promising opportunity to explore the signatures resulting from dark matter (DM) annihilation, due to its proximity and large J-factor. Owing to the absence of an excess of $γ$-ray signatures originating from Ursa Major III, observations of $γ$-rays, such as those from Fermi-LAT, can be utilized to set constraints on the DM annihilation cross section. In this study, we determine the DM density profile, and consider the relationship between DM density and velocity dispersion at different locations within Ursa Major III through Jeans analysis. We calculate the J-factor of Ursa Major III for s-wave annihilation, along with the effective J-factors for p-wave and Sommerfeld enhanced annihilation scenarios. Utilizing these derived J-factors, we set stringent constraints on DM annihilation cross sections in three scenarios. Given the substantial impact of member star identification on the J-factor of Ursa Major III, we further calculate J-factors with the condition of excluding the largest velocity outlier. Our analysis reveals a notable reduction in the median value and an increase in the deviation of J-factors, thereby leading to considerably weaker constraints.

astro-ph.HE↗

arXiv2024

A theoretical perspective on the almost dark galaxy Nube: exploring the fuzzy dark matter model

In recent astronomical observations, an almost dark galaxy, designated as Nube, has unveiled an intriguing anomaly in its stellar distribution. Specifically, Nube exhibits an exceptionally low central brightness, with the 2D half-light radius of its stars far exceeding the typical values found in dwarf galaxies, and even surpassing those observed in ultra-diffuse galaxies (UDGs). This phenomenon is difficult to explain within the framework of cold dark matter (CDM). Meanwhile, due to its ultralight particle mass, fuzzy dark matter (FDM) exhibits a de Broglie wavelength on the order of kiloparsecs under the typical velocities of galaxies. The interference between different modes of the FDM wave gives rise to fluctuations in the gravitational field, which can lead to the dynamical heating of stars within galaxies, resulting in an expansion of their spatial distribution. In this paper, we aim to interpret the anomalous stellar distribution observed in Nube as a consequence of the dynamical heating effect induced by FDM. Our findings suggest that a FDM particle mass around $1-2\times 10^{-23}$ eV can effectively account for this anomaly. And we propose that the FDM dynamical heating effect provides a new insight into understanding the formation of field UDGs.

astro-ph.CO↗

arXiv2024

Tidal Formation of dark matter deficit diffuse galaxy NGC1052-DF2 by SIDM

Observations have revealed a significant dark matter deficit in the ultra-diffuse galaxy NGC1052-DF2 (DF2). It is widely accepted that the formation of this unique galaxy can be attributed to the tidal stripping of its host galaxy, NGC1052. In this study, we simulate the evolution of a satellite system containing globular clusters (GCs) within an accreting host halo in the framework of self-interacting dark matter (SIDM). Our simulation results suggest that the heightened tidal stripping resulting from DM self-interactions can give rise to the transformation of a conventional dwarf galaxy into a dark matter deficit galaxy resembling DF2. By comparing the simulation results with identical initial conditions in both the standard cold dark matter (CDM) and SIDM models, we find that the latter is more likely to replicate the properties of DF2. Furthermore, we demonstrate that a DF2 analog can also be produced on an orbit with a greater pericenter distance by increasing the strength of DM self-interactions. This suggests that the issue of extreme orbital parameters can be mitigated by implementing the SIDM model. The distributions of the GC population derived in our SIDM simulation are consistent with the observed characteristics of DF2. For comparison, we also explored the potential for achieving GC distributions in the context of CDM.

astro-ph.CO↗

arXiv2024

Reproduction of NGC1052-DF4 by self-interacting dark matter: dark matter deficiency and tidal features

Observations of the velocity dispersion indicate a severe dark matter (DM) deficit in the ultra-diffuse galaxy, NGC1052-DF4 (DF4). The ultra-deep images obtained with the Gemini telescope, which has the deepest imaging data till now, confirm the presence of tidal tails in DF4, suggesting its tidal formation. To enhance tidal effects, we consider the self-interaction among DM particles. Using an N-body simulation in the scenario of self-interacting dark matter (SIDM), we reproduce a DM-deficient galaxy that is consistent with all observational data of DF4. Specifically, our simulation result yields an extremely low DM-to-star mass ratio and a radial surface brightness profile very similar to that from deep images, showing accurate tidal features. By performing simulations with similar tidal effects and various cross-sections of SIDM, we show a significant impact of SIDM on the DM-to-star mass ratio in the central region of the galaxy. Our work confirms the tidal formation of DF4 in theory.

astro-ph.CO↗

arXiv2024

Impact of Parameters in the Blazar Jet Magnetic Field Model on Axion-Like Particle Constraints

The interaction between axion-like particles (ALPs) and photons induces ALP-photon oscillations in astrophysical magnetic fields, leading to spectral distortions in the $γ$-ray spectrum of blazars. The primary uncertainty of this phenomenon may originate from the magnetic field within the jet of the blazar. While many studies have explored the effects of ALP-photon oscillations using typical values for jet magnetic field parameters, it is important to recognize that these parameters can be constrained by multi-wavelength observations. In this study, we utilize the high energy $γ$-ray spectrum of Mrk 421 obtained from MAGIC and Fermi-LAT observations. By employing multi-wavelength fitting with a one-zone synchrotron self-Compton model, we derive the parameters characterizing the magnetic field model within the jet, and investigate their impacts on the ALP constraints.

astro-ph.HE↗

arXiv2024

Possible spectral irregularities in the AMS-02 positron spectrum

The excesses in the electron and positron spectra observed by many experiments, such as PAMELA and AMS-02, have sparked significant theoretical investigation. It is not easy to distinguish the two primary hypotheses dark matter annihilation/decay and pulsars from the spectral features. Should pulsars be the source of this excess, the expected variability in their distribution may introduce distinct irregularities in the positron energy spectrum. In this study, we use an irregularity estimator to detect these potential features in the positron energy spectrum of AMS-02. Our analysis of the current AMS-02 data reveals these spectral irregularities with a statistical significance of $1.75σ$. However, our projection indicates that, with AMS-02 data collected over a period of 20 years, such irregularities could be identified with a confidence level of $3σ$ level in 71\% of our simulations.

astro-ph.HE↗

arXiv2024

Constraints on Lorentz invariance violation from the LHAASO observation of GRB 221009A

In some quantum gravity (QG) theories, Lorentz symmetry may be broken above the Planck scale. The Lorentz invariance violation (LIV) may induce observable effects at low energies and be detected at high energy astrophysical measurements. The Large High Altitude Air Shower Observatory(LHAASO) has detected the onset, rise, and decay phases of the afterglow of GRB 221009A, covering a wide energy range of photons approximately from $0.2$ to $18$ TeV. This observation provides an excellent opportunity to study the Lorentz invariance violation effect. In this study, we simultaneously utilize the data from the KM2A and WCDA detectors of LHAASO, and apply two event by event methods, namely the pair view method and maximum likelihood method, to investigate LIV. We obtain stringent constraints on the QG energy scale. For instance, through the maximum likelihood method, we determine the 95$\%$ confidence level lower limits to be $E_{QG,1} > 14.7 (6.5)\times 10^{19}$GeV for the subluminal (superluminal) scenario of $n = 1$, and $E_{QG,2} > 12.0 (7.2)\times 10^{11}$GeV for the subluminal (superluminal) scenario of $n = 2$. We find that the rapid rise and slow decay behaviors of the afterglow can impose strong constraints on the subluminal scenario, while the constraints are weaker for the superluminal scenario.

astro-ph.HE↗

arXiv2024

Precise measurement of the cosmic-ray spectrum and $\left \langle \ln A \right \rangle$ by LHAASO -- connecting the Galactic to the extragalactic components

Recently LHAASO Collaboration gives precise measurements of cosmic rays (CR) all particle energy spectrum and mean logarithmic mass $\left \langle \ln A \right \rangle$ from 0.3 PeV to 30 PeV. Combining the CR measurements by AMS-02 and DAMPE in space and that by LHAASO and Auger on the ground we construct a model to recover all these measurements from tens of GeV to tens of EeV. We find the LHAASO measurement is crucial in the model construction by connecting the Galactic component to the extragalactic component. The precise measurements of CR spectra for individual species by AMS-02 and DAMPE together with the newest LHAASO results clearly indicates three Galactic CR components, that is, a soft low energy background, a hard high energy component, and a local source contribution. However, the LHAASO data show that above $\sim 10^{16}$ eV a nonnegligible extragalactic component must be included. Combining the Auger results and the LHAASO results we figure out the extragalactic CRs which need at least two components at lower and higher energies. Thanks to the precise measurements by LHAASO the constraints on the model parameters are quite stringent. The spectra features and mass measurements in all energy range are all well reproduced in the model.

astro-ph.HE↗