arXiv subjects

Y. Liu

Publications and source records attributed to Y. Liu.

At least 19 recordsLinked to original sources

arXiv2026

The beamformed trigger of RNO-G: its design and in-field performance

The Radio Neutrino Observatory in Greenland (RNO-G) is a neutrino detector under construction at Summit Station, with 8 out of a planned 35 stations currently deployed. We have designed and deployed a new phased array (PA) trigger based on delay-and-sum beamforming and power integration. This trigger improves detector performance by suppressing thermal noise and better targeting neutrino-induced Askaryan signals. The new PA trigger has been deployed since the 2025 season. The trigger performance has been characterized using test pulses and calibration pulsers both in the lab and in-situ, and we find across these tests a 25% average reduction in the signal-to-noise ratio (SNR) needed to trigger on signals. Simulations are shown to be representative of the detector, and simulated trigger efficiencies are within 10% of measured data. Following the in-situ trigger validation, we use data-driven trigger performance to inform simulations of the detector effective volumes. The PA trigger increases our effective volume significantly, by over a factor of 2 below 0.1 EeV and at least a factor of 1.3 at the highest energies of 100 EeV.

astro-ph.IM↗

arXiv2026

EP-FXT Observations of Abell 1795: X-ray Properties and Structure out to $R_{200}$

We present deep X-ray observations of the nearby, X-ray luminous galaxy cluster Abell 1795 obtained with the Einstein Probe Follow-up X-ray Telescope (EP-FXT), with a total exposure time of 480 ks. Exploiting the large field of view and low particle background of EP-FXT, we directly measure the radial temperature profile of A1795 out to $R_{200}$ with full azimuthal coverage, which increases with radius within 6 arcmin and then gradually declines toward larger radii. The surface-brightness residual map and 2D thermodynamic maps reveal a clockwise spiral structure extending from the cluster core toward the southeast, which traces low-temperature, low-entropy gas and is consistent with sloshing-induced cold fronts. In the northwest, the surface-brightness-enhanced region exhibits an arc-like high-temperature feature, and both the temperature-derived and density-derived Mach numbers support that it is a weak shock. These substructures can be explained by a binary merger scenario: the perturbing subcluster induces sloshing during its first passage past the primary core, and its subsequent return passage through the ICM may drive the shock toward the northwest. Our results indicate that relaxed galaxy clusters such as A1795 can still retain signatures of dynamical activity.

astro-ph.HE↗

arXiv2026

SKA$-$VLBI view of AGN jets in the early Universe

Active Galactic Nuclei (AGN) are among the brightest sources in the Universe, and those that are also jetted are uniquely valuable at the earliest epochs, because their relativistic outflows can regulate the gas supply of their host galaxies, potentially affecting both early star formation and the rapid growth of supermassive black holes (SMBHs). Their compact, high-brightness-temperature radio cores provide the sharpest beacons for very long baseline interferometry (VLBI), enabling direct constraints on Doppler boosting, jet duty cycles, and jet$-$environment coupling at extreme redshifts. In this White Paper, we discuss how the SKA-VLBI will provide sub-$\mu$Jy sensitivity together with milliarcsecond (mas) angular resolution to image and characterise jetted AGN at $z>6$ across SKA-Mid and SKA-Low frequencies. These observations can directly test SMBHs ($>10^6$ M$_{\odot}$) formation/evolution models (including jet-assisted super-Eddington phases) and infer the geometry of the Universe, directly probing the cosmological framework at high precision. Synergies with current and next-generation multi-band facilities will also be crucial to fully understand their host galaxies and their environment, providing an unprecedented panchromatic knowledge of the first jetted AGN.

astro-ph.GA↗

arXiv2026

Calibration and Performance of Germanium High Voltage Detectors for SuperCDMS SNOLAB

As SuperCDMS SNOLAB is getting ready to search for low mass dark matter particles, using cryogenic Ge and Si detectors, a set of six of the new SuperCDMS High Voltage (HV) detectors (four Ge and two Si) were tested in the Cryogenic Underground TEst facility (CUTE) at SNOLAB. This provided the first opportunity to gain experience with this new detector type and assess their performance thoroughly under low background conditions. Here we describe the SuperCDMS HV detector concept and discuss some of the newly developed analysis methods and approaches. Focusing on the Ge detectors, we investigate the detector performance under voltage bias (up to 90 V), exercise the low energy (keV to sub-keV range) calibration based on the electron capture peaks generated by the decay of $^{71}$Ge, assess the detector resolution, and demonstrate the unexpected (and encouraging) ability of these detectors to also measure high energy interactions in the hundreds of keV range with good resolution (better than 3% at 356 keV).

physics.ins-det↗

arXiv2026

A rare sextuple-merging brightest cluster galaxy system in a disturbed galaxy cluster observed with the Einstein Probe Follow-up X-ray Telescope

The evolutionary processes of galaxy clusters influence the properties of their member galaxies. We present a joint X-ray--optical analysis of the galaxy cluster WHY J050106.2+013714 at $z_{\rm c}=0.151$. X-ray observations with the Einstein Probe Follow-up X-ray Telescope indicate that the cluster is dynamically young. The cluster displays an average X-ray temperature of $2.8^{+0.4}_{-0.3}$ keV and a total luminosity of 9.4$\pm0.3\times10^{43}$ erg s$^{-1}$, consistent with the scaling relation of typical disturbed clusters. Remarkably, the cluster hosts a multi-merging brightest cluster galaxy (BCG) system composed of six massive galaxies, with a total stellar mass of $1.16\times10^{12}M_{\odot}$. We detected a well-defined intracluster light component extending to a size of 310 kpc. A systematic search for merging BCGs in the DESI Legacy Surveys reveals that this sextuple-merging BCG is extremely rare in the local Universe. Additionally, other merging BCGs are also likely to form in moderately disturbed clusters, which provides valuable insights into the formation of BCGs.

astro-ph.CO↗

arXiv2026

Complexity of the Laughlin wave function from the Dyson-orbital perspective

The Fermi sea is a simple and common concept in physics. However, a related and equally simple concept -- the Dyson orbital -- is far less discussed in physics, especially in textbooks. Yet, Dyson orbitals offer a valuable tool for characterizing the complexity of a fermionic wave functions, particularly in distinguishing between Fermi-sea-like and non-Fermi-sea-like states. As a preliminary application, we examine the Laughlin wave function and find the fortunate fact that the Dyson orbitals can be determined analytically. Further numerical data provides \emph{quantitative} evidence that the Laughlin wave function describes a strongly correlated, non-Fermi liquid state.

cond-mat.str-el↗

arXiv2026

The SVOM mission, its profile and its system

The SVOM (Space-based Variable Objects Monitor) mission, launched into low Earth orbit on 22 June 2024, is a French-Chinese multi-wavelength observatory dedicated to the study of the transient sky. Inspired by the Neil Gehrels Swift Observatory, it consists of an autonomous rapid-slewing satellite, linked in real time to several ground-based telescopes. The space segment comprises two X-ray/gamma-ray wide-field instruments (ECLAIRs and GRM) with real-time triggering capabilities combined with two narrow-field telescopes in X-ray (MXT) and in visible (VT). In addition, the SVOM collaboration has also developed a unique visible and NIR ground-based follow-up system to promptly respond to the gamma-ray transients detected on board. The core program of SVOM will provide new insights into the Gamma-Ray Burst physics by providing a homogeneous dataset covering both the prompt and afterglow emissions, as well as better studying the low luminosity and soft Gamma-Ray Burst populations. As a versatile satellite platform with fast slewing capabilities, SVOM also comprises a Target of Opportunity program and a General Program consisting in pointed observations scheduled over the year that will both significantly contribute to the multi-messenger and time-domain astronomy.

astro-ph.HE↗

arXiv2026

Inverse design of exceptional points in a single-resonance two-port network

Exceptional points (EPs) in non-Hermitian photonic systems enable unconventional control of wave amplitude and phase. However, identifying the EPs in a multidimensional parameter space of a system can be nontrivial and, in some cases, even infeasible. Here we propose an inverse-design method to efficiently locate the scattering EPs for a two-port resonant system supporting a single mode. The proposed method provides a direct way for tuning of geometric parameters to realize scattering EPs, as confirmed by both full-wave simulation and equivalent circuit model. In principle, our method is compatible with multi-mode system and applicable to a broad class of resonant systems.

physics.optics↗

arXiv2026

Detection of Spin-Spatial-Coupling-Induced Dynamical Phase Transitions in Real Time

We demonstrate the real-time detection of dynamical phase transitions (DPTs) in lattice-confined spinor gases subject to a priori unknown time-variant interactions, via the temporal behaviors of both the system energy and spinor phases extracted from the observed spin dynamics. Using this technique, we describe the observed nonequilibrium spin dynamics, governed by intricate spin-spatial couplings, across a range of conditions. This work also introduces an observable that can quickly identify DPTs at holding times when commonly-used order parameters still exhibit transient, nonuniversal behavior. Our approach can naturally extend to other complex systems subject to time-dependent parameters, such as Floquet systems under driven magnetic fields, driven interactions, or spin-flopping fields, with potential applications in the study of DPTs in nonintegrable models.

cond-mat.quant-gas↗

arXiv2026

An energetic dirty fireball detected in soft X-rays

The collapse of massive stars drives explosions that power relativistic fireballs. If only a small amount of matter is entrained, such clean fireballs can expand with Lorentz factors $\Gamma> 100$, accounting for gamma-ray bursts (GRBs). It has been hypothesized that energetic explosions with more baryon contamination, dubbed ``dirty fireballs'', may exist in nature, but they have not been observed. Here we report the observation of an extragalactic fast X-ray transient, EP241113a, detected by Einstein Probe. Compared to GRBs, it has a similar isotropic energy of $1.4\times 10^{51}$ erg, but significantly lower spectral peak energy. Theoretical modeling of its early X-ray afterglow suggests a relativistic jet with a low Lorentz factor of $\Gamma \sim 20$ aligned close to the line-of-sight, signifying the prototype of a dirty fireball.

astro-ph.HE↗

arXiv2026

The dipole strength distribution of $^8$He and decay characteristics

The weak binding and spatially extended neutron densities characteristic of drip-line nuclei give rise to a distinctive low-energy dipole response. The drip-line nucleus $^8$He is the most neutron-rich bound nucleus with a mass-to-charge ratio of $A/Z=4$. We measure the dipole response of $^8$He, including for the first time the four-neutron decay channel. A total dipole strength of $\sum B(E1)(E^*<15$~MeV$)=0.95(16)~e^2$fm$^2$ and a dipole polarizability of $\alpha_D = 0.61(1)$~fm$^3$ are extracted from the differential Coulomb-excitation cross section and compared to state-of-the-art theoretical calculations employing coupled cluster and three-body approaches. We find that the dipole continuum is dominated, even at high excitation energies well above the $4n$ decay threshold, by two-neutron emission, pointing to a $^6$He$+2n$ structure of the excited dipole mode. No indication was found for a $4n$ final-state correlation, while pronounced $nn$ and $^6$He-$n$ final-state correlations are apparent.

nucl-ex↗

arXiv2026

Anisotropic non-Hermitian skin effect in a two-dimensional Lieb photonic crystal

In this contribution paper, we construct a two-dimensional non-Hermitian (NH) photonic crystal (PhC) to prototype its anisotropic non-Hermitian skin effect (NHSE) for experimental proposal. Based on the tight-binding model for Lieb lattice with NH coupling, a nontrivial spectral winding number is pinpointed for certain eigenstates, which translates to geometry-dependent skin modes with tilt boundaries. For ease of implementation, complex refractive indices are employed for the Lieb unit cell of PhC to emulate the NH coupling. Validated by full wave simulation, our work underscores the boundary dependence of skin effect, and provides a concrete prototype design of NHSE implementable by state-of-the-art of topological metamaterial platforms.

physics.optics↗

arXiv2026

Direct observation of three-neutron emission from $^7$He$^*$ and the search for the trineutron

Three-neutron emission from $^7$He has been directly measured for the first time, following neutron knockout from a $^8$He beam at 156 MeV/nucleon. A resonance-like structure at $2.08(4)$ MeV above the $^4$He+$3n$ threshold [$E_x=2.68(4)$ MeV] with a width of $3.9(2)$ MeV was observed and deduced to arise predominately from the predicted $J^{\pi}=3/2^{-}_2$ level. The three-neutron invariant-mass spectrum was reconstructed and found to peak at around 1 MeV and could, through complete simulations incorporating neutron-neutron correlations, be very well described by the sequential decay of $^7$He$^*$ via the $2_1^+$ excited state of $^6$He. No evidence was found for any significant three-neutron correlations beyond those expected from well-established two-body interactions, including a trineutron resonance.

nucl-ex↗

arXiv2026

Search for Light-Mass Fractionally Charged Particles in Space with DAMPE Experiment

Free Fractionally Charged Particles (FCPs) are predicted by some theories beyond or extended to the standard model. FCPs have been widely searched for by underground and space-based experiments based on the assumption of heavy lepton-like particles. However, there is a paucity of research focusing on light-mass FCPs (LFCPs) in the sub-MeV mass range. In this work, we report the LFCPs in primary high energy cosmic rays, based on observational data from the Dark Matter Particle Explorer (DAMPE) satellite. This study utilized ten years on-orbit data of DAMPE to search for LFCPs with a charge of $\frac{2}{3}~e$. No LFCP candidate was observed. Upper flux limit of LFCPs with a mass of 0.511 MeV$/c^{2}$ and a charge of $\frac{2}{3}~e$ is determined to be $\rm 5.0 \times 10^{-11}\,cm^{-2}sr^{-1}s^{-1}$ at the $\rm 90\%$ confidence level.

astro-ph.HE↗

arXiv2026

Diverse properties of electron Forbush decreases revealed by the Dark Matter Particle Explorer

The Forbush decrease (FD) of cosmic rays is an important probe of the interplanetary environment disturbed by solar activities. In this work, we study the properties of 8 FDs electrons (including positrons) between 2 GeV and 20 GeV from January, 2016 to March, 2024, with the Dark Matter Particle Explorer. The maximum decrease amplitudes of these events are about 30% - 15%, and the amplitudes reduce with energy. The recovery time of these events shows diverse behaviors of their energy-dependence. Some of them show strong energy-dependence, while some have a nearly constant recovery time. It has been shown that such diverse behaviors could be related with the geometry of the disturbed regions of the interplanetary space by coronal mass ejections (CME), represented by the combined effect of the CME velocity, angular spread, and ejection direction.

astro-ph.HE↗

arXiv2026

Optofluidic light routing via analytically configuring streamlines of micro-flow

Transformation optics (TO) is a new method to design metamaterials that can manipulate electromagnetic fields. Inspired by the traditional TO techniques which is mostly based on the solid metamaterials with a limited range of tunability, a novel streamline tracing-based transformation optofluidics (STTOF) method is proposed to manipulate the light path by analytically designating the light-carrying streamlines of the flow in a two-dimensional circular bounded domain. A dipole flow model is built to analytically calculate the streamlines of the flow field inside the domain which allocates the optical/fluidic source and sink pairs at arbitrary positions. Liquid core/liquid cladding (L2) configuration is used in the experiment to trace the light via a specific streamline. Experimental results verify that the light paths agree well with the theoretical predictions, and demonstrate that a good range of tunability can be achieved by adjusting the flow rates and the source-sink positions of optical/fluidic source and sink pairs.

physics.optics↗

arXiv2026

The high speed analog optical readout system designed for low temperature experiments

For low-temperature experiments such as liquid xenon dark matter detectors, it is crucial to read out detector signals from cryostats. Traditionally, photoelectrical signals are transmitted from the cryogenic region to the outside using coaxial cables through vacuum feedthroughs on the cryostats. In this paper, we investigate an analog optical transmission method in which the raw electrical signals are converted into optical signals with light intensity linearly proportional to the electrical amplitude, transmitted out of the cryogenic environment through optical fiber, and subsequently converted back into electrical signals by photoelectric devices while preserving the signal waveform. This new approach offers advantages, including low attenuation over long-distance transmission and reduced crosstalk across the feedthroughs. Additionally, the low-temperature optical wavelength multiplexing scheme has been investigated and applied, increasing the transmission capability of a single fiber. At -100 degree Celsius, the proposed analog optical readout system achieves a -3dB bandwidth of larger than 150MHz, a dynamic range of up to 500mV, and a low cryogenic-region power consumption of 70mW per channel, demonstrating its strong potential for low-temperature experiments.

physics.ins-det↗

arXiv2026

Non-Hermitian curved space via inverted wave equation

Directly solving graded materials from amplitude and phase was a method developed following transformation optics (TO), which provided reflectionless media for an incidence wave. However, this inverting method gives Hermitian media thus not applicable to non-Hermitian (NH) photonics. In this Letter we then design NH media offering more freedom to manipulate waves of no reflection. Our picture of curved-space powered with gain and loss, is exemplified by three types: amplitude controlling, phase conversion, and direction shunting. These examples showcase precise wave manipulation in a surprisingly simple manner, which is implementable in photonic platform similar to TO.

physics.optics↗