arXiv subjects

Xiangyan An

Publications and source records attributed to Xiangyan An.

8 recordsLinked to original sources

arXiv2026

$X$-dispersionless solver for electromagnetic and axion fields in a cylindrical particle-in-cell code

We develop a quasi-cylindrical direction-splitting (QDS) dispersionless Maxwell solver for the open-source EPOCH particle-in-cell framework. The method preserves the exact axial phase velocity for every retained azimuthal mode by advecting transverse transport variables with the $c\Delta t=\Delta x$ shift. Building on the same transport viewpoint, we formulate an axion solver that advances the Klein--Gordon equation and the axion-regenerated electromagnetic fields within the QDS solver, so that axion--photon coupling is handled self-consistently. Benchmarks demonstrate that the cylindrical QDS solver reproduces the standard Yee wakefield structure while removing the axial group-velocity error and reducing computational cost by orders of magnitude. In the resonant axion generation test via two-color laser mixing, the QDS solver eliminates the spurious vacuum source term and maintains phase matching, whereas the Yee solver suffers from rapid dephasing due to numerical dispersion. The proposed algorithm therefore enables quasi-3D simulations of axion--photon physics in laser-plasma interaction with dispersion-free laser transport.

physics.plasm-ph↗

arXiv2026

Vacuum-Triggered Instability in Paired Superradiance

Paired superradiance (PSR) is a macro-coherent two-photon process capable of very large gain, making it promising for detecting ultra-weak signals induced by neutrinos or dark matter. A major goal has been to increase the system volume $V$ and density $n$, since the signal intensity scales as $(nV)^2$. We recast finite PSR as a parametric amplifier driven by the electromagnetic vacuum. The usual zero-field semiclassical initial condition is replaced by vacuum inputs fixed by the quantum two-point function. Combining this formulation with Maxwell--Bloch evolution and finite-length stability analysis, we find that PSR produces an irreducible vacuum background that can develop into macroscopic bursts once the gain-length product exceeds $\Gamma L=\pi/2$ for a sufficient coherence time. These results, together with a closed-form formula for estimating the vacuum-seeded photon yield, establish a previously overlooked constraint for high-gain PSR, with direct implications for proposed neutrino and dark-matter studies.

physics.optics↗

arXiv2025

Acceleration of Ultrahigh Energy Particles from Fast Radio Bursts

Two extreme events in the universe, fast radio bursts (FRBs) and cosmic rays (CRs), could be correlated, where FRBs with extreme field strength near their sources may contribute to CRs. This study investigates localized particle acceleration driven by FRB-like ultra-relativistic electromagnetic pulses in an electron--positron--ion plasma system. It is found ultra-high energy neutral plasma sheets form constantly via the front erosion of an FRB pulse. There are two regimes of ion acceleration depending upon the field strength and the plasma density: the piston regime driven by the Lorentz force of the pulse, and the wakefield regime dominated by charge separation field. The predicted energy scalings align well with particle-in-cell simulations. A power-law energy spectrum with an index close to the CRs naturally emerges during FRBs expansion outward. Detecting high-energy particles possibly produced by FRBs enables deeper insights into their origins and promotes the development of multi-messenger astronomy.

astro-ph.HE↗

arXiv2025

Coherently Enhanced Axion-Photon Conversion via Seeded Photons for Short-Pulse Axion Detection

We propose a seeded axion-photon conversion scheme to enhance the sensitivity of light-shining-through-a-wall (LSW) experiments for axion detection, where the axions are generated from short pulse lasers and the usual resonant cavity is not applicable. By injecting a weak, coherent seed electromagnetic (EM) field into the axion-photon conversion region, the axion-induced EM field can constructively interfere with the seed field, amplifying the number of regenerated photons to a level exceeding that of the unseeded scenario. We evaluate the expected signal enhancement, statistical limits from Poisson counting with seed fluctuations and background, and the potential improvement in coupling sensitivity. Compared to a standard LSW setup, the seeded scheme can achieve orders-of-magnitude higher photon yield per axion, potentially surpassing resonance-enhanced experiments in certain parameter regimes. This approach presents a promising pathway to extend the reach of laboratory axion searches, particularly in scenarios where the resonant cavities are impractical.

hep-ph↗

arXiv2025

Axion generation and detection in laser-plasma wakefields

The axions are compelling candidates for cold dark matter, but their extremely weak interaction with photons makes laboratory searches challenging. We show that the quasi-static electromagnetic fields of a laser-plasma wakefield, which can exceed $10^{11}$\,V/m, enable axion generation without an external production magnet and enhance the conversion rate by two orders of magnitude over a conventional magnetic production region. Self-consistent particle-in-cell simulations reveal two complementary routes to detection. In the first route, axions are reconverted into photons within the wakefield and laser fields, eliminating the need for a separate regeneration magnet but requiring to suppress the intense laser-plasma background. The regenerated photons have polarization, harmonic-frequency, and Laguerre-Gaussian transverse-mode signatures that are largely absent from the driving fields, allowing successive filters to isolate the signal. In the second route, axions traverse a wall and undergo reconversion in a downstream magnet, providing a much lower background at the cost of requiring both the magnet and a seed pulse for coherent amplification. For axion masses below $0.1$\,meV, meter-scale wakefield guiding under our stated assumptions yields a projected coupling sensitivity down to $3.9\times10^{-12}\,\mathrm{GeV}^{-1}$, surpassing the projected constraint of next-generation laboratory searches. These results establish ultra-strong plasma wakefields as a magnet-free axion source with two experimentally distinct and complementary detection strategies.

physics.plasm-ph↗

arXiv2024

Coherent Axion Production through Laser Crystal Interaction

We investigate the interaction between an optical laser and an ionic crystal and reveal coherent emission of axions through phase-match between laser and axion fields. Such emission is further enhanced by stacking thin crystal layers of half-wavelength thickness. Based on these findings, we propose a novel method for generating and detecting axions in terrestrial experiments, achieving up to a two-order-of-magnitude increase in transition probability compared to light-shining-through-wall (LSW) experiments with the same interaction region size. For an experimental length of 10 meters, this setup could lower the exclusion limit to $g_{a\gamma\gamma}\gtrsim1.32\times10^{-11}\textrm{GeV}^{-1}$ with currently available laser technologies.

hep-ph↗

arXiv2024

Modeling of axion and electromagnetic fields coupling in a particle-in-cell code

Axions have aroused widespread research interest because they can solve the strong CP problem and serve as a possible candidate for dark matter. Currently, people have explored a lot of axion detection experiments, including passively detecting the existing axions in the universe, and actively generating axions in the laboratory. Recently, axion-coupled laser-plasma interactions have been discussed as a novel method to detect axions. Petawatt (PW) lasers are considered as a powerful tool to study not only the vacuum polarization but also the axion coupling, due to their extreme fields. However, particle-in-cell (PIC) simulation is still missed in current studies, which limits the understanding of axion-coupled laser-plasma interactions. In this paper, we proposed the method to include the axion field and the coupling with electromagnetic (EM) fields in PIC codes. The axion wave equation and modified Maxwell's equations are numerically solved, while the EM field modulation from axions is considered as a first-order perturbation. Meanwhile, different axion field boundary conditions are considered to satisfy different simulation scenarios. The processes of conversions between axions and photons, and weak laser pulse propagation with axion effects are checked as benchmarks of the code. Such an extended PIC code may help researchers develop novel axion detection schemes based on laser-plasma interactions and provide a better understanding of axion-coupled astrophysical processes.

hep-ph↗

arXiv2022

Modeling of bound electron effects in particle-in-cell simulation

To include the bound electron effects in particle-in-cell (PIC) simulation, we propose a model in which the response of the dipole components of partially ionized ions to external electromagnetic fields can be included. Instead of treating the macro-ion particle as a single particle without an internal structure, the ions are considered to have a structure composed of a central nucleus and a bounded electron cloud in our model. The two parts experience the interactions of both the external electromagnetic fields and the internal Coulomb fields. In this way, the laser scattering effects by a partially ionized medium can be modeled properly in the PIC simulation. The laser propagation in a neutral medium and the Bragg scattering of the laser in crystal structure have been simulated with a PIC code modified based on our model as the benchmark. Our model may find applications to study some interesting problems, such as the x-ray laser-driven wakefield acceleration in crystals, the x-ray laser-driven high energy density physics, and intense laser propagation in partially ionized nonlinear optical materials, etc.

physics.plasm-ph↗