arXiv subjects

X. Zhang

Publications and source records attributed to X. Zhang.

At least 19 recordsLinked to original sources

arXiv2026

The SRG/eROSITA All-Sky Survey: Early dark energy and Hubble constant from the cluster mass function

The evolution of the mass function of massive galaxy clusters is a well-established probe of cosmology. Using the eROSITA X-ray instrument on board the Spectrum Roentgen Gamma (SRG) mission, the western Galactic hemisphere of eROSITA's first All-Sky Survey (eRASS1) delivers a uniformly selected and securely confirmed sample of 5259 galaxy clusters spanning $0.1 < z < 0.8$. When combined with overlapping weak lensing data from DES Year 3, KiDS, and HSC for mass calibration, this dataset enables precise tests of the standard $\Lambda$CDM framework and beyond. In this work, we use the $0.1 < z < 0.45$ subsample of the eRASS1 cluster catalog to place constraints on an axion-like Early Dark Energy (EDE) scenario. Such models have been proposed as a possible mechanism to alleviate the tension between early- and late-Universe measurements of the Hubble constant. In this framework, a scalar field temporarily enhances the cosmic expansion rate around the epoch of recombination before rapidly diluting at later times, leaving distinct imprints on structure growth. We leverage these signatures to present the first constraints on EDE derived from galaxy cluster number counts. Using eRASS1 number counts alone, we obtain an upper limit on the maximum EDE fraction of $f_{\rm EDE} < 0.3$, consistent with primary CMB analyses. Combining our cluster analysis with primary CMB measurements, baryon acoustic oscillations, and CMB lensing, while notably excluding distance-ladder calibration data, yields results consistent with a nonzero EDE contribution and $H_0$ values compatible with late-Universe measurements. The most significant detection, at $\sim 3.2\sigma$, arises from the joint analysis of the eRASS1 sample with the full set of external datasets, yielding $f_{\rm EDE} = 0.10^{+0.04}_{-0.03}$ and $H_0 = 71.4 \pm 1.4$ km/s/Mpc. [ABRIDGED]

astro-ph.CO↗

arXiv2026

Electrostatic control of Li+ density and transport rate in double-gated van der Waals devices

Ion transport in crystalline hosts is controlled by an applied potential that simultaneously sets ionic distribution and transport rate, restricting operation to a one-dimensional control space. Here we show that the transport rate of Li+ ions in double-gated van der Waals devices can be modulated while the system occupies fixed ionic-density states. We measure the ionic current along the van der Waals interfaces between hexagonal boron nitride and graphene or MoS2 while simultaneously monitoring the in-plane electronic response. The ionic current exhibits pronounced hysteresis, with plateaus marking discrete ionic-density states balanced by electronic charge, while an independently tuneable electrochemical-potential drop controls the ionic transport rate. The devices sustain over 1,000 switching cycles and function as hybrid ionic-electronic transistors capable of logic operations and memory retention, with ON/OFF ratios exceeding two orders of magnitude. This work demonstrates a two-dimensional control space for ions intercalated in layered materials.

cond-mat.mes-hall↗

arXiv2026

Apodex 1.1: Scaling Agentic Intelligence for Complex Work

General-purpose language models can reason and synthesize knowledge, but complex work also requires sustained interaction with files, information sources, and executable code, together with state maintenance, failure recovery, and verifiable delivery. We call this \emph{working capability}: sustained, verifiable progress toward a real-world objective. Apodex 1.1 develops this capability along two complementary dimensions. \emph{Environment Scaling} expands the diversity and verifiability of executable file, search, and code environments, while \emph{Agentic Coordination Scaling} trains agents to decompose long-horizon tasks, delegate parallel work, integrate asynchronous results, and replan. A shared execution harness and AgentOS maintain task state and provenance across tools and agents, and training turns environment trajectories and coordination traces into reliable behavior. Across complex professional work, finance, scientific research, mathematics, coding, and search, Apodex 1.1 reaches the leading performance band despite using a substantially smaller model than many frontier systems. The 35B-parameter Apodex 1.1 Mini further retains strong working capability in a locally deployable form. These results ground agentic intelligence in useful, verifiable work completed over time and advance our goal of building a \emph{Heavy-Duty Solver} for ambitious, long-running tasks.

cs.AI↗

arXiv2026

Thermal or Non-thermal? Diffuse emission in the infall region of stacked galaxy groups

The faint infall regions surrounding the virial radius of galaxy groups remain largely unexplored due to their low X-ray surface brightness. Using the large statistical power of SRG/eROSITA survey observations, we present the first spectroscopic measurement of the intragroup medium (IGrM) in the infall regions of a large sample of low-mass galaxy groups ($M_{\rm tot}<1\times10^{14}\,M_{sun}$), extending to $\sim2\,R_{200m}$ (2.2 Mpc). Through spectral stacking of 827 nearby groups from the first eROSITA All-Sky Survey catalog, we detect diffuse emission and measure the thermodynamic properties of gas at densities previously inaccessible to X-ray observations. The stacked spectra are well described by a Gaussian differential emission measure model, yielding a temperature distribution with a mean temperature of $0.96_{-0.04}^{+0.05}$ keV and width of $0.28_{-0.10}^{+0.10}$ keV, and a metal abundance of $0.21_{-0.04}^{+0.06}$ A$_{sun}$, consistent with expectations for group outskirts. The inferred electron densities decrease from $(4.8\pm1.3)\times10^{-5}$cm$^{-3}$ at $(0.7-2)\,R_{500c}$ to $(5.5\pm2.0)\times10^{-6}$ cm$^{-3}$ at $(2-4)\,R_{500c}$, demonstrating eROSITA's ability to probe the low-density outskirts of galaxy groups. Residual emission in the spectra suggests the presence of an additional spectral component. While a secondary thermal interpretation requires an unexpectedly hot, metal-poor plasma, a non-thermal inverse Compton model provides an equally plausible explanation, contributing $\sim30\%$ of the thermal flux. Assuming that the additional component is produced by inverse Compton emission from a common population of relativistic electrons, the inferred magnetic field strength would be in the sub-$\mu$G regime.

astro-ph.HE↗

arXiv2026

Langmuir probe and infrared thermography measurements of wide and narrow heat flux profiles in the ST40 tokamak

Very narrow heat flux profiles have been observed on ST40 with decay lengths in the near scrape-off-layer (SOL) of $\lambda_{q,near}<$~1~mm in H-mode plasmas. Measurements from divertor Langmuir probes are compared with an infrared (IR) thermography system for upper-single null diverted plasmas in L-mode and ELM-free H-mode. SOL current to the grounded divertor targets is measured from the Langmuir probes with profiles exhibiting a similar exponential decay to $\lambda_{q,near}$ suggesting the near SOL heat flux is related to enhanced electron current to the divertor. Inclusion of electron current contributions to the heat flux transmission coefficient is crucial in capturing similar narrow profiles to those from the IR thermography system. Ongoing upgrades to ST40 will enable more investigations on SOL power decay lengths on inboard and outboard targets in double and single null configurations.

physics.plasm-ph↗

arXiv2026

Controllable localization and manipulation of optical hollow traps by means of optical-vortex diffraction

An optical vortex (OV) is coupled with the local intensity zero and is thus a field configuration suitable for "hollow" optical traps and optical tweezers. When an incident circular OV beam experiences diffraction at a rectilinear screen edge (SE), and the conditions of weak diffraction perturbation (the SE is far enough from the beam axis) are fulfilled, the main consequence is the OV-core displacement from its initial (axial) position. Based on the model of incident Laguerre-Gaussian (LG) beam, we investigate analytically and numerically the ways of controlling the OV-core position in the diffracted-field cross section by means of changing the SE position with respect to the incident-beam axis. The results show that regulating the SE position with ~1 mcm accuracy (which is available for existing mechanical tools), controllable OV-core motion with a sub-nanometer accuracy can be realized. Possible modifications of this motion depending on the incident beam topological charge, wavefront curvature, SE properties (semitransparent screen, phase-step screen) and the distance between the diffraction plane and the observation plane are analyzed. The conditions most favorable for the micro-object trapping and manipulation are specified and discussed.

physics.optics↗

arXiv2026

Sustainable Air-Ground Integrated Coverage Networks: ISCC Architecture, Technologies, and Testbed

The rapid emergence of sixth-generation (6G) networks and the low-altitude economy has accelerated the evolution of wireless infrastructures toward air-ground integrated coverage networks (AGICNs), which seamlessly fuse terrestrial and aerial communication resources. However, existing AGICN studies primarily focus on coverage enhancement, while ignoring sustainability. Pursuing sustainable AGICNs introduces new challenges due to the multidimensional resource coupling across heterogeneous air-ground segments. In view of this, this paper presents a comprehensive survey and tutorial on sustainable AGICNs, aiming to balance coverage capacity with carbon efficiency in low-altitude economies. An integrated sensing, communication, and computation (ISCC)-driven architecture, which enables dynamic resource orchestration through closed-loop control, is proposed. We thus introduce a multi-dimensional sustainability metric system, which covers operational efficiency, task-oriented performance, and full lifecycle carbon emissions, to quantify energy and carbon footprints. We review enabling technologies, including artificial intelligence, hybrid precoding, integrated sensing and communication, and simultaneous wireless information and power transfer, and discuss their integration into the ISCC framework to minimize energy consumption while maintaining robust coverage. Experimental results on a real-world testbed demonstrate a 20% reduction in power consumption while achieving over 90% coverage probability, highlighting the feasibility of sustainable AGICNs for future green networks.

cs.IT↗

arXiv2026

Gamma Backgrounds for Experiments at the High Flux Isotope Reactor

This article describes the deployment of a germanium detector at Oak Ridge National Lab's High Flux Isotope Reactor (HFIR) for the purpose of understanding the energy and spatial distribution of the gamma field in the experiment hall where the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT) took data and future neutrino experiments could be located. The sources from both the reactor and the neutron beamlines are described in detail, along with their temporal variations due to reactor power and their spatial variations due to the geometry of the beamlines and building materials in the vicinity. Additionally, a shielding study was performed to assess the amount that backgrounds in tens of keV range can be mitigated. This work helps inform backgrounds for future experiments at reactors such as IBD-based neutrino measurements and CEvNS measurements.

hep-ex↗

arXiv2026

Simulation-Based Inference for Cluster Cosmology with Set-Based Neural Network Architectures

The unprecedented statistical power of galaxy cluster catalogs from the SRG (Spectrum Roentgen Gamma)/eROSITA All-Sky Survey provides a unique opportunity to place stringent constraints on cosmological models through measurements of structure growth. Fully exploiting the potential of these large X-ray-selected cluster samples, however, requires robust statistical frameworks that accurately connect observable quantities to the underlying cosmological parameters. We develop and implement a simulation-based inference (SBI) framework for cosmological parameter estimation using a realistic mock-generation pipeline calibrated on eRASS1 simulations. Synthetic galaxy cluster catalogs are propagated through the survey selection function to produce mock eRASS1 observations that reproduce the data's statistical properties. At the core of the method lies a set-based neural network (GNN on sets) that encodes information from individual clusters and is coupled to a masked autoregressive flow for flexible posterior density estimation. This approach enables the use of the full cluster-level information content without compressing the observables into binned summary statistics. Our framework recovers the input cosmologies within the inferred uncertainties, and passes calibration tests, demonstrating robustness in the presence of realistic survey effects. We obtain mock constraints of 11.5% on $\Omega_m$ and 4.4% on $\sigma_8$ averaged over a suite of simulated cluster catalogs matching the effective sample size of the data set (3,259 clusters). We achieve a precision comparable to that obtained with traditional MCMC analyses based on substantially larger cluster samples. The framework is readily extensible to more complex forward models and additional observables. This work highlights the potential of SBI methods for next-generation large-scale structure analyses with forthcoming X-ray cluster surveys.

astro-ph.CO↗

arXiv2026

Probing Long-Lived Particle Production in Muon Decays at the SNS with a Highly Capable Hydrocarbon Detector

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) is a prolific muon producer, making it an ideal location for studying dark sector particles produced in muon decays at rest. In this paper, we explore sub-GeV dark particle detection possibilities in a tons-scale, highly capable hydrocarbon scintillator ($HC^2$) detector at the SNS. We consider a search for $e^+e^-$ final states produced by decays of long-lived, $O(10-100)$ MeV axion-like particles and heavy neutral leptons. The $HC^2$ technology space, exemplified by the PROSPECT and Mobile Antineutrino Demonstrator detectors, offers strong rejection capabilities for the cosmic ray backgrounds that would normally dominate this search. By benchmarking on-surface cosmic ray signatures with data from PROSPECT at ORNL, we generate robust predictions for a multi-year SNS deployment of a range of $HC^2$ detector implementations. Results indicate the potential for order-of-magnitude improvements in sensitivity to axion-like particles and heavy neutral leptons in the 10-100 MeV mass regime compared to current global limits. We also comment on the neutrino detection possibilities of a $HC^2$ deployment at the SNS.

hep-ex↗

arXiv2026

Constraints on axion-like particles from ultra-high-energy observations of M87 with the HAWC observatory

In this work, we perform an indirect search for axion-like particles (ALPs) through their hypothesized mixing with photons in the presence of magnetic fields. ALPs are a well-motivated dark-matter candidate class, and the photon-ALP conversion mechanism provides a unique channel to constrain their mass and coupling constant using very-high-energy gamma-ray observations. The photon-ALP mixing could alter the observed gamma-ray spectrum from extragalactic sources by effectively reducing the apparent attenuation due to extragalactic-background-light absorption. We analyze 7.5 years of data from the High Altitude Water Cherenkov (HAWC) Observatory, targeting the nearby radio galaxy M87. This source is located within the Virgo cluster and is an ideal environment for photon-ALP conversion due to its low redshift and the large-scale, strongly magnetized medium of the cluster. We find no evidence for a photon-ALP conversion signal and, consequently, set constraints on the ALP mass and photon-ALP coupling constant with emission from M87 which are consistent with previous results. Our analysis places competitive constraints on the ALP parameter space, defining an exclusion region in the mass range of approximately $10^{-8}$ to $10^{-6}$ eV for coupling constants above $5\times10^{-12}$ GeV$^{-1}$, complementing previous constraints from other gamma-ray observatories.

astro-ph.HE↗

arXiv2026

Neutrino monitoring of explosions for excluding fission yield

Nuclear fission produces neutrinos, so the absence of a neutrino signal can be used to set a limit on the fission content of an explosion. This capability could be employed on former nuclear test sites to assure regulators, international monitors, or other observers that activities involving chemical explosions do not exceed a designated limit for nuclear fission. This paper quantifies the neutrino detector masses that would be required to set fission yield limits at source-to-detector distances up to 100 km, assuming detection by inverse beta decay with realistic background levels. The analysis indicates that detectors with active mass in the ton- to tens-of-kiloton range can set potentially useful limits on the fission yield of large chemical explosions at the Nevada National Security Site. In contrast, inverse beta decay detectors are not well suited to excluding fission yield at longer range or in the subcritical nuclear experiments that have occurred at some test sites following the cessation of explosive nuclear testing.

physics.soc-ph↗

arXiv2026

Constraining the Photon Intensity of Extragalactic Background Light with the HAWC Observatory for the Blazar Mrk 421

The blazar Mrk 421 exhibits rapid variability over a wide range of timescales. Spectral differences have been observed during the different emission states of Mrk 421. During the high emission states, tests to constraint the Hubble constant and the photon intensity of Extragalactic Background Light (EBL) can be performed. The HAWC observatory provides an exceptionally long term monitoring of the source at TeV energies. We selected periods of high emission state and low emission state in data with total observation time of 2460 transits from the HAWC observatory using the All-sky Root around in an Unbiased way methodology. We report on evidence of a cutoff in the spectrum of Mrk 421 during high emission states. An Exponential Cutoff Power Law is preferred over a Simple Power Law at a $3.8\,\sigma$ level. In the Exponential Cutoff Power Law, the cutoff is found at $13\pm3~\text{TeV}$. Using this result, we provide upper limits on the specific intensity of EBL photons. Moreover, the value of the energy cutoff found in our analysis is different from the cutoff expected by the interaction of gamma-rays with EBL photons. This result indicates that the cutoff is intrinsic to the source.

astro-ph.HE↗

arXiv2026

The Ultrafast Superconducting Diode Effect

Nonreciprocal transport is generally observed in superconductors in which time reversal and inversion symmetries are simultaneously broken. This effect, which may become one of the backbones for future superconducting electronics, arises because of asymmetric vortex transport in a magnetic field. However, vortex transport is also intrinsically dissipative and limited in speed. Here, we report on the discovery of ultrafast non-reciprocal transport in centrosymmetric superconductors. For NbN films biased with a quasi-DC supercurrent, picosecond current pulses with the same sign as the bias experience resistive impedance, whereas pulses of opposite polarity encounter an inductive response. Strikingly, the effect is at least three orders of magnitude faster than in conventional superconducting diodes, limited only by ultrafast current-induced depairing. We demonstrate rectification of a 100 GHz signal, with dissipation levels of a few fJ per cycle. We foresee potential for superconducting logic elements, operating at THz bit rates with aJ energy dissipation per operation.

cond-mat.supr-con↗

arXiv2026

New Deep Learning Data Analysis Method for PROSPECT using GAPE: Genetic Algorithm Powered Evolution

We propose a genetic algorithm powered evolution (GAPE) method to create deep learning solutions for energy and position estimation for reactor antineutrino interactions in the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT) at the highly enriched High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. We also apply GAPE to create classification models to distinguish signatures of inverse beta decay (IBD) interactions of reactor antineutrinos from common background types. The GAPE method can also be adopted for optimization of other types of problems that utilize machine learning (ML) models for particle physics applications. When applied in the PROSPECT context, we find that the models selected by GAPE can, in some cases, outperform the traditional models previously used for PROSPECT data analysis. In particular, when benchmarked against conventional PROSPECT neutrino identification pathways using the same underlying information, the classifier offers the promise of improving the signal-to-background ratio by nearly 2.8 times. Performance biases uncovered during initial IBD classifier validation were primarily caused by differences in time-dependent response between background and signal training datasets. Biases were effectively mitigated through a data-period-specific training regimen, offering a pathway towards realizing an unbiased IBD signal classifier for future reactor neutrino datasets.

physics.data-an↗

arXiv2026

A high-resolution study of the double radio relic system in MACS J1752.0+4440

Radio relics are diffuse, extended synchrotron sources located at the outskirts of merging galaxy clusters. Their origin has been linked with shock waves injected into the intracluster medium, but the acceleration mechanism at the shock front is still under debate. Some clusters, like MACS J1752.0+4440, host a double relic system, with two relics found on opposite sides with respect to the cluster center. To investigate the acceleration mechanism that generates radio relics, we study the morphological and spectral properties of the double relic system in MACS J1752. We present new wideband radio continuum observations made with uGMRT and JVLA, and LOFAR data. We perform a detailed, high-resolution spectral analysis of the double relic system in MACS J1752, observing and characterizing substructures, particularly for the brighter relic. We find a double-peaked surface brightness and spectral index profile for the NE relic and identify a "bright bar" substructure. Moreover, we observed surprisingly flat integrated spectral indices for both relics, at $\alpha_{\mathrm{int}}^{\mathrm{NE}} = -0.91 \pm 0.06$ and $\alpha_{\mathrm{int}}^{\mathrm{SW}} = -0.83 \pm 0.05$. We study the spatial variation of the spectral index, observing a coherent trend with the observed substructures. We estimate an injection Mach number of $\mathcal{M}_{\mathrm{NE}} = 3.1^{+0.1}_{-0.1}$ and $\mathcal{M}_{\mathrm{SW}} = 3.2^{+0.1}_{-0.1}$. By performing a spectral curvature analysis for both relics, generating color-color plots and a spectral curvature maps, we observe two "concave" spectra represented by positive spectral curvature, in contrast with particle population ageing models. The observed properties of the NE relic are not consistent with a simple scenario with a single shock front. Multiple shock surfaces, re-acceleration, and projection effects likely play a role in shaping the morphology of the relic.

astro-ph.HE↗

arXiv2026

Simultaneous operation of an 18-qubit modular array in germanium

Utility-scale quantum computing requires the integration and operation of a large-scale qubit register. Semiconductor spin qubits are a primary candidate for this, due to the prospects of building integrated hybrid quantum-classical architectures. However, scaling spin-qubit systems while preserving performance and control has remained a challenge. Here, we demonstrate the operation of an 18-qubit array in germanium based on an extendable 2xN architecture. We achieve simultaneous initialization, control, and readout across the entire array, enabled by parallel operation of modular unit cells. Across the array, we achieve average and median single-qubit gate fidelities of 99.8% and 99.9%, respectively. Finally, we characterize the nearest-neighbor exchange couplings throughout the device and implement high-quality controlled-Z gates to generate a three-qubit Greenberger-Horne-Zeilinger (GHZ) state. These results demonstrate that spin-qubit arrays can be scaled while maintaining high-fidelity operation and establish a modular, extendable architecture for planar semiconductor quantum processors.

cond-mat.mes-hall↗

arXiv2026

Layer-selective hydrogenation and proton transport in twisted bilayer graphene

Recent work investigated graphene's hydrogenation with independent control of the electric field, E, and charge density, n, in the crystal and showed that the process is controlled by n. Here, we demonstrate layer-selective conductor-insulator transitions in twisted bilayer graphene, driven by hydrogenation at fixed n under strong E. This process is accompanied by proton transport through the bilayer, enabling several parallel and configurable logic gates in the devices. Selectivity arises because the large twist angle decouples the two layers' electronic systems, enabling independent control of their charge densities. Polarisation by the field then induces a charge imbalance at fixed total n, triggering hydrogenation when one of the layers' charge densities reaches the threshold for monolayer hydrogenation. Our results introduce a new type of electrode-electrolyte interface in which electrochemical processes are controlled with two decoupled 2D electron gases, opening new design opportunities for energy and information processing devices.

cond-mat.mes-hall↗