arXiv subjects

Y. J. Li

Publications and source records attributed to Y. J. Li.

At least 19 recordsLinked to original sources

arXiv2026

Effect of Strong Field Space-time Features on Vacuum Pair

The relativistic dynamics of bound states across inertial reference frames are investigated using the computational quantum field theory (CQFT). The results reveal that the spatiotemporal properties of bound states within a given potential well are strictly frame-dependent. Crucially, this spatiotemporal modulation of the external field enables a reduction in the laser intensity threshold required for vacuum electron-positron pair creation. Analytical and numerical calculations demonstrate that this threshold reduction originates from the Lorentz transformation of the four-momentum, which reshapes the vacuum excitation pathways in phase space. By developing CQFT, we establish a comprehensive framework in which relativistic effects intrinsically govern the quantum vacuum decay process

quant-ph↗

arXiv2026

Phase control of multi-photon electron-positron pair creation from vacuum

We investigate the creation of electron-positron pairs by two spatiotemporally inhomogeneous electric fields with a relative phase, employing computational quantum field theory. We find that, when the two fields are closely spaced, the pair yield exhibits a cosine-like dependence on the relative phase. This suggests that the relative phase provides an effective way to enhance multi-photon transition channels. Furthermore, our analysis reveals that the response of pair-creation channels to the relative phase changes substantially with the photon order of the transition. For one-photon transitions, the rate exhibits a $2π$ periodicity, whereas a reduced periodicity of $π$ is observed for two-photon transitions. To clarify the underlying mechanism, we map the quantum field-theoretical framework onto a time-dependent perturbation approach. By extending this approach to $n$-photon processes, we show that the transition probability is periodic in the relative phase with period $2π/n$. This observation suggests that the relative phase offers an effective means of identifying the order of multi-photon transitions.

physics.plasm-ph↗

arXiv2026

Compact Objects Revealed by SKA and SKA-VLBI

Compact objects represent a crucial interdisciplinary frontier between astronomy and fundamental physics.The SKA/SKA-VLBI, with exceptional sensitivity (at $μ$Jy levels) and ultrahigh positional precision (at $μ$as levels), will enable direct, precise measurements of orbital dynamics in compact objects including black holes and neutron stars. This facility is expected to achieve at least three breakthroughs: (1) Developing effective methodologies for detecting and identifying black hole-neutron star binaries to construct observational catalogues, thus advancing investigations into the equation of state of ultra-dense nuclear matter and strong-field relativistic effects; (2) Determining critical parameters such as orbital elements and component masses in compact binaries, yielding insights into stellar structures and evolutionary mechanisms under extreme conditions; (3) Identifying intermediate-mass black holes and measuring their masses to deepen understanding of black hole formation and evolution.

astro-ph.HE↗

arXiv2026

Gravitational Light Deflection with SKA-VLBI and Its Application to Precision Tests of General Relativity

Experimental test of general relativity remains an ongoing endeavour. Radio astrometry provides a vital tool for precisely measuring the light deflection caused by the Sun, testing general relativity, and discriminating between gravitational theories. The best accuracy for the post-Newtonian relativistic parameter, $γ$, achieved with very long baseline interferometry is $9 \times 10^{-5}$. With 300-sec integration, SKA-VLBI can achieve a sensitivity of $\sim$15 $μ$Jy at 15 GHz over a bandwidth of 0.256 GHz. This enables detection of $\sim$36 extragalactic radio sources per square degree with flux densities of $\sim$1.5 mJy, and potentially detecting in-beam radio sources. Single-epoch SKA-VLBI observations may achieve an astrometric precision of $\sim$2 $μ$as. Utilising the Sun as a gravitational lens, 10-epoch positional tracking of extragalactic sources could improve $γ$ accuracy to $\sim$10$^{-7}$. Even with Jupiter as a lens, SKA-VLBI can measure $γ$ to $\sim$10$^{-4}$. Critically, it may conduct the first measurement of quadrupolar deflection of light caused by Jupiter, determining the physical oblateness of Jupiter, $J_{\mathrm{2, J}}$, to within $\sim${}$10^{-3}$. These advances are expected to rigorously test and improve gravitational theories or high-order parameterized post-Newtonian formalisms, while laying the foundations for (sub)$μ$as astrometry.

astro-ph.IM↗

arXiv2026

Constraints on ultraheavy dark matter from the CDEX-10 experiment at the China Jinping Underground Laboratory

We report a search for ultraheavy dark matter (UHDM) with the CDEX-10 experiment at the China Jinping Underground Laboratory. Using a Monte Carlo framework that incorporates Earth shielding effects, we simulated UHDM propagation and energy deposition in p-type point-contact germanium detectors. Analysis of 205.4 kg$\cdot$day exposure in the 0.16--4.16 keVee range showed no excess above background. Our results exclude the spin-independent UHDM-nucleon scattering with two cross section scales, with the UHDM mass from $10^6$ to $10^{11}$ GeV, and provide the most stringent constraints with solid-state detectors below $10^8$ GeV.

hep-ex↗

arXiv2026

Angular momentum transfer in multiphoton pair production

We propose a method to accurately calculate the momentum distributions and the phase distributions of the probability amplitude for both boson and fermion pair production in a spatially homogeneous and time-dependent electric field. Applying this method to multiphoton pair production in a circularly polarized electric field rotating around the $z$-axis, we clarify that the topological charge appearing in the phase distribution of the probability amplitude for pair production reflects the orbital angular momentum (OAM) of the produced pairs rather than that of individual particles. On this basis, we demonstrate that, within the semiclassical framework, the $z$-component of the total angular momentum of the field and the particles is conserved, whereas the conservation of total angular momentum cannot be verified. The results also reveal that the pair production is also constrained by $C$-parity conservation, and that pairs with smaller OAM are produced more favorably. These findings provide deeper insight into angular momentum transfer in pair production.

hep-ph↗

arXiv2026

First search for light fermionic dark matter absorption on electrons using germanium detector in CDEX-10 experiment

We present the first results of the search for sub-MeV fermionic dark matter absorbed by electron targets of germanium using the 205.4~kg$\cdot$day data collected by the CDEX-10 experiment, with the analysis threshold of 160~eVee. No significant dark matter (DM) signals over the background are observed. Results are presented as limits on the cross section of DM--electron interaction. We present new constraints of cross section in the DM range of 0.1--10 keV/$c^2$ for vector and axial-vector interaction. The upper limit on the cross section is set to be $\rm 6.8\times10^{-46}~cm^2$ for vector interaction, and $\rm 2.3\times10^{-46}~cm^2$ for axial-vector interaction at DM mass of 5 keV/$c^2$.

hep-ex↗

arXiv2026

Search for Cosmic Ray Electron Boosted Dark Matter with the CDEX-10 Experiment

We present new constraints on the cosmic ray electron boosted light dark matter (CReDM) using the 205.4 kg$\cdot$day data of the CDEX-10 experiment located at the China Jinping Underground Laboratory. The cosmic ray electron spectrum and distribution in the Galaxy are generated by the $\tt GALPROP$ code package. In the calculation process of DM-electron scattering process in the Galaxy, we consider the energy-dependency of the DM-electron scattering cross section. The constraints on CReDM are set for both heavy and light mediator scenarios using the CDEX-10 dataset. The result exceeds previous Standard Halo Model (SHM) limits for DM mass lower than 0.6 MeV in heavy mediator case and corresponds to the best sensitivity among all direct detection experiments from 1 keV to 0.5 MeV in the light mediator scenario.

hep-ex↗

arXiv2025

Constraints on inelastic dark matter from the CDEX-1B experiment

We present limits on spin-independent inelastic weakly interacting massive particles (WIMP)-nucleus scattering using the 737.1 kg$\cdot$day dataset from the CDEX-1B experiment. Expected nuclear recoil spectra for various inelastic WIMP masses $m_χ$ and mass splittings $δ$ are calculated under the standard halo model. An accurate background model of CDEX-1B is constructed by simulating all major background sources. The model parameters are then determined through maximum likelihood estimation and Markov chain Monte Carlo fitting. The resulting 90\% confidence level upper limits on the WIMP-nucleon cross section $σ_{\mathrm{n}}$ exclude certain DAMA/LIBRA allowed regions: the $χ^2 < 4$ regions for $δ< 30$ keV at $m_χ= 250$ GeV and the $χ^2 < 9$ region for $δ< 50$ keV at $m_χ= 500$ GeV. The method is applicable to other inelastic dark matter scenarios, and the upcoming CDEX-50 experiment is expected to improve sensitivity by four orders of magnitude.

hep-ex↗

arXiv2025

Constraints on dark matter boosted by supernova shock within the effective field theory framework from the CDEX-10 experiment

Supernova shocks can boost dark matter (DM) particles to high, yet nonrelativistic, velocities, providing a suitable mechanism for analysis within the framework of the nonrelativistic effective field theory (NREFT). These accelerated DM sources extend the experimental ability to scan the parameter space of light DM into the sub-GeV region. In this study, we specifically analyze DM accelerated by the Monogem Ring supernova remnant, whose age ($\sim 68000$ yr) and distance to Earth ($\sim 300$ parsec) are strategically matched to enable detection with current terrestrial detectors. Utilizing the 205.4 kg$\cdot$day data obtained from the CDEX-10 experiment at the China Jinping Underground Laboratory, we derive new constraints on boosted DM within the NREFT framework. The NREFT coupling constant exclusion regions now penetrate the sub-GeV mass range, with optimal sensitivity achieved for operators $\mathcal{O}_{3}$, $\mathcal{O}_{6}$, $\mathcal{O}_{15}$ in the 0.4--0.6 GeV mass range.

hep-ph↗

arXiv2025

Electron-positron pair creation in a supercritical static asymmetric potential well

The electron-positron pair creation in a supercritical static asymmetric potential well, which is composed of a subcritical and a supercritical potential separated by a fixed distance, is investigated using computational quantum field theory. To explain the discrete peaks in the positron energy spectrum, an analytical formula for determining the positions of bound states in a subcritical asymmetric potential well is derived and extended to the supercritical asymmetric potential well in two ways. One of the two methods can not only predict the positions of bound states, but also offer the pair creation rate. This study also reveals that the subcritical potential height can optimize the energy spread of created electrons, providing a new way to produce high-energy electron beams with concentrated energy in experiments. Moreover, it is found that the pair creation rate in a supercritical asymmetric potential well, composed of a subcritical symmetric potential well and a supercritical Sauter potential, exceeds the sum of the pair creation rates produced by each potential individually. This finding suggests a potential method for enhancing pair yield.

quant-ph↗

arXiv2025

Enhancing pair production with optimized chirped laser fields

The optimal chirped field for enhancing electron-positron (EP) pair production is explored using a quantum kinetic approach. First, the momentum spectrum and number density of EP pairs produced by Gaussian chirped fields are investigated. The results show that the momentum spectrum exhibits distinct interference patterns, while the number density grows monotonically with chirp parameters but oscillates with the carrier angular frequency. Moreover, the number density increases by four orders of magnitude compared to chirp-free fields. The results are further compared with those from four other chirped fields: frequency-modulated, linear, quadratic, and sinusoidal chirp. The analysis reveals that the maximum number density for sinusoidally chirped fields is the highest, followed by Gaussian, frequency-modulated, quadratically, and linearly chirped fields. This ranking also applies to the maximum enhancement factors for these chirped fields. Notably, the number density for sinusoidally chirped fields improves nine orders of magnitude compared to chirp-free fields. These results not only deepen our understanding of pair production in chirped fields but also provide significant optimization strategies for future vacuum pair production experiments.

hep-ph↗

arXiv2025

Study of spin states in vacuum pair production via the Dirac-Heisenberg-Wigner formalism

A general spin-resolved momentum distribution of electron-positron pairs produced in strong external fields is derived by combining the covariant spin projection operator and the Dirac-Heisenberg-Wigner (DHW) formalism. The result shows that the spin-resolved and helicity-resolved momentum distributions given in previous literature are actually two special cases of it. For any spin-direction unit vector, numerical investigations demonstrate that when the $z$-component of the unit vector vanishes, the number density of produced spin-up and spin-down particles is equal, while their momentum distributions have some asymmetry. For a nonzero $z$-component of the unit vector, there is a difference of $1-3$ orders of magnitude in the number density of spin-up and spin-down particles induced by angular momentum transfer in multiphoton absorption. Moreover, as the electric field strength increases and/or the field frequency decreases, the asymmetry between the spin-up and spin-down particle number density decreases rapidly. These results offer an approach to study general spin states in vacuum pair production, and enhance our understanding of angular momentum transfer from fields to matter in extreme environments.

hep-ph↗

arXiv2025

Transition signatures for electron-positron pair creation in space-time inhomogeneous electric field

The process of electron-positron pair creation through multi-photon absorption in a space-time dependent electric field is analyzed using computational quantum field theory. Our findings reveal two distinct pair creation channels: the symmetric and asymmetric transition channels. We propose that the asymmetric transition channel arises from the inherent spatial inhomogeneity of intense laser pulses. By mapping the field-theoretical model of laser-assisted multi-photon pair creation onto a quantum-mechanical time-dependent framework, a semi-analytical solution that captures the asymmetric transition signatures of vacuum decay is derived. Additionally, it is demonstrated that neglecting spatial inhomogeneity leads to erroneous transition amplitudes and incorrect identification of pair creation channels. Furthermore, we have established that asymmetric transition channels substantially enhance the creation of electron-positron pairs for a given laser pulse energy.

hep-ph↗

arXiv2025

Nonadiabatic quantum kinetic equations and Dirac-Heisenberg-Wigner formalism for Schwinger pair production in time-varying electric fields with multiple components

The nonadiabatic quantum kinetic equations and Dirac-Heisenberg-Wigner formalism for Schwinger pair production in a spatially uniform and time-varying electric field with multiple components are derived and proven to be equivalent. The relation between nonadiabatic and adiabatic quantum kinetic equations is also established. By analyzing the time evolution of the distribution functions of particles created in a circularly polarized Gaussian pulse field with a subcycle structure, it is found that the nonadiabatic and adiabatic distribution functions are the same after the field, with a sufficient number of oscillation cycles, fades away. However, during the presence of the field, the two distribution functions typically differ. Nonetheless, the time evolution characteristics of the nonadiabatic and adiabatic momentum distributions are similar. For instance, the number of spirals is one less than the number of photons absorbed in both cases. Furthermore, for a rapidly oscillating electric field, the nonadiabatic quantum kinetic approaches may provide a more meaningful description of pair production at intermediate times. These findings deepen our understanding of the nonadiabatic quantum kinetic approaches and their application in pair production.

hep-th↗

arXiv2024

Electron-hole pair production in graphene for two arbitrarily polarized electric fields with a time delay

The momentum distributions of electron-hole (EH) pair production in graphene for two arbitrarily polarized electric fields with a time delay are investigated employing a massless quantum kinetic equation and compared with the results obtained in electron-positron (EP) pair production from vacuum. For a single elliptically polarized electric field, the momentum distributions of created EH and EP pairs are similar in multiphoton absorption region. However, for two co-directional linearly polarized electric fields with a time delay and no field frequency, the momentum distribution of created EH pairs exhibits ring patterns, which is not present in EP pair production. For two circularly polarized fields with identical or opposite handedness, the momentum distributions of created EH pairs also show Ramsey interference and spiral structures, respectively. Different from EP pair production, the spiral structures are insensitive to the number of oscillation cycles in electric field pulses. For two elliptically polarized fields with same-sign or opposite-sign ellipticity, the momentum distributions of EH pairs are much more insensitive to ellipticity than those in EP pair production. These results provide further theoretical reference for simulating the EP pair production from vacuum in solid-state systems.

cond-mat.mes-hall↗

arXiv2024

Probing Dark Matter Particles from Evaporating Primordial Black Holes via Electron Scattering in the CDEX-10 Experiment

Dark matter (DM) is a major constituent of the Universe. However, no definite evidence of DM particles (denoted as ``$χ$") has been found in DM direct detection (DD) experiments to date. There is a novel concept of detecting $χ$ from evaporating primordial black holes (PBHs). We search for $χ$ emitted from PBHs by investigating their interaction with target electrons. The examined PBH masses range from 1$\times$10$^{15}$ to 7$\times$10$^{16}$ g under the current limits of PBH abundance $f_{PBH}$. Using 205.4 kg$\cdot$day data obtained from the CDEX-10 experiment conducted in the China Jinping Underground Laboratory, we exclude the $χ$--electron ($χ$--$e$) elastic-scattering cross section $σ_{χe} \sim 5\times10^{-29}$ cm$^2$ for $χ$ with a mass $m_χ\lesssim$ 0.1 keV from our results. With the higher radiation background but lower energy threshold (160 eV), CDEX-10 fill a part of the gap in the previous work. If ($m_χ$, $σ_{χe}$) can be determined in the future, DD experiments are expected to impose strong constraints on $f_{PBH}$ for large $M_{PBH}$s.

hep-ex↗

arXiv2024

Searching for $^{76}$Ge neutrinoless double beta decay with the CDEX-1B experiment

We operated a p-type point contact high purity germanium (PPCGe) detector (CDEX-1B, 1.008 kg) in the China Jinping Underground Laboratory (CJPL) for 500.3 days to search for neutrinoless double beta ($0νββ$) decay of $^{76}$Ge. A total of 504.3 kg$\cdot$day effective exposure data was accumulated. The anti-coincidence and the multi/single-site event (MSE/SSE) discrimination methods were used to suppress the background in the energy region of interest (ROI, 1989$-$2089 keV for this work) with a factor of 23. A background level of 0.33 counts/(keV$\cdot$kg$\cdot$yr) was realized. The lower limit on the half life of $^{76}$Ge $0νββ$ decay was constrained as $T_{1/2}^{0ν}\ > \ {1.0}\times 10^{23}\ \rm yr\ (90\% \ C.L.)$, corresponding to the upper limits on the effective Majorana neutrino mass: $\langle m_{ββ}\rangle < $3.2$-$7.5$\ \mathrm{eV}$.

nucl-ex↗