Mathematical Physics
Metric completion of the Bender–Brody–Müller Hamiltonian: dilation spectrum and missing eigenstates
Kejun Liu
The Bender–Brody–Müller (BBM)
Hamiltonian was proposed as a non-Hermitian
Hilbert–Pólya operator. We analyze the
Hilbert completion induced, on the standard half-line $L^2$ core, by BBM's candidate metric $\hat\eta=\sin^2(\hat p/2)=\Delta^\dagger\Delta/4$. The form $\eta_0=\Delta^\dagger\Delta$ is positive with trivial kernel but is not coercive. Completing $C_c^\infty(0,\infty)$ in the norm $\|\psi\|_{\eta_0}=\|\Delta\psi\|$ gives a
Hilbert space canonically unitarily equivalent to $L^2(\mathbb R_+)$. Its free self-adjoint realization is the dilation generator, with simple, purely absolutely continuous spectrum $\mathbb R$. The analysis yields two spectral statements of interest beyond the BBM problem. First, no bounded sandwich $\Delta^\dagger h(D)\Delta$ is boundedly invertible. Second, the transported symmetric operator has deficiency indices $(\infty,\infty)$ and an adjoint with every real point as an
eigenvalue of infinite multiplicity, while its free extension is purely continuous. The realization-independent BBM conclusion concerns the candidate eigenfunctions: $\Delta\psi_z=x^{-z}$, so for $\operatorname{Re}z=1/2$ they do not belong to the completed space. Thus the original BBM boundary-condition/eigenfunction mechanism cannot produce point-spectrum Riemann-zero states in this $L^2$-based metric completion.
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Instrumentation and Detectors
The Research and Development of New Electronics System and its Testing on the JNE-1ton Prototype Detector
Haoyan Yang, Yuzi Yang, Yapeng Wang et al. (+10 more)
The Jinping
Neutrino Experiment (JNE), a next-generation
neutrino observatory under construction at the China Jinping Underground Laboratory II (CJPL-II), requires high-precision waveform-based event reconstruction, imposing stringent demands on its readout electronics. To meet these requirements, we have developed a high-performance readout system featuring 1 GSa/s real-time sampling, 14-bit physical resolution with an effective number of bits (ENOB) of 10.6, a total data throughput of 64 Gbps, and a deterministic zero-delay clock distribution architecture. The new single-crate 64-channel system (PDS1500) was validated through bench tests and deployment on the upgraded JNE-1ton prototype detector. Its performance was further evaluated against a commercial reference system. The results demonstrate that all key metrics meet the JNE experimental requirements: zero data loss within a 1000 ns acquisition window, baseline noise reduced to one-third of the reference level, timing drift limited to 0.3 ns across power cycles, and an energy threshold as low as 0.1 MeV, enabling the detection of low-energy
solar neutrinos. While the 14-bit physical resolution provides significantly higher waveform fidelity, the overall energy resolution in this test remains dominated by the intrinsic limitations of the JNE-1ton detector, as expected. Furthermore, the modular architecture provides the throughput and scalability required to support the full-scale 3000-channel JNE detector. These results collectively demonstrate that the newly developed electronics system fully satisfies the technical requirements of the future JNE experiment.
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All authors Haoyan Yang, Yuzi Yang, Yapeng Wang, Changxu Wei, Haoyang Fu, Haozhe Sun, Juntao Liu, Zhiyi Liu, Tao Xue, Jianmin Li, Yinong Liu, Zhe Wang, Shaomin Chen
Soft Condensed Matter · Cross-listed from cs.LG
Deep learning-based prediction of time-resolved adhesive forces in viscoelastic Hertzian contacts
Ali Maghami, Merten Stender, Michele Ciavarella et al. (+1 more)
Fast prediction of the response of adhesive soft viscoelastic contacts represents a current challenge in soft robotics and for gripping and manipulation tasks. Determining the complete time-resolved force trajectory requires full numerical simulations, whose computational cost is strongly parameter-dependent, making them impractical for real-time application or design-optimization loops. In this work, we overcome this limitation by training a scalar-conditioned, stateful, sequence-to-sequence deep learning model to predict the full force
evolution from a prescribed displacement history for both short- and long-range adhesion regimes. The data set spans four orders of magnitude in loading and unloading rates and includes varied dwell times, with the Tabor parameter ranging from $0.2$ to $3.2$. To enable learning across these heterogeneous time scales, we introduce a fixed-measurement-step (FMS) representation that converts variable-length trajectories into fixed-length sequences while preserving their physical-time information. Different architectures were trained, including long short-term
memory (LSTM) networks, temporal convolutional neural (TCN) networks, and time-distributed dense layers with three different Tabor-conditioning mechanisms. The models were compared using global waveform and error metrics. We found that the best-performing model has an LSTM architecture with concatenated conditioning, which achieves a held-out mean-squared error of $5.0\times10^{-4}$, a median pull-off-force error of $\approx2.2\%$, and a median hysteresis error of $\approx1.1\%$. For the held-out protocols, the model predicts a complete force trajectory with a median inference time of $0.16$ s. The model is tested across unseen parameter combinations and against analytical limiting cases, providing a rapid surrogate for repeated numerical evaluations with potential use in control-oriented applications.
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All authors Ali Maghami, Merten Stender, Michele Ciavarella, Antonio Papangelo
Astrophysics of Galaxies
An (in)complete NIRSpec census of Balmer absorption in Type 1 AGN – radiation-driven outflows in little red dots, quasars and variable stars
Ignas Juodžbalis, Xihan Ji, Francesco D'Eugenio et al. (+17 more)
A notable achievement of the first generation of JWST surveys was the discovery of an abundance of faint high-
redshift ($z > 4$) broad-line active
galactic nuclei (AGN) in the $L_{\rm bol} < 10^{45}$~erg~s$^{-1}$ regime, previously only accessible at $z < 1$. The high prevalence of absorption features in their broad hydrogen lines is one of the peculiarities of a significant fraction of this new population. In this paper, we conduct a broad census of Balmer absorption in a sample of 47 Type-1 AGN spanning $2 < z < 7$. Accounting for incompleteness of JWST spectroscopic data, we estimate that $44_{-6}^{+21}$~% of Little Red Dots (LRDs) have absorption in \Has while the incidence rate is $< 25$~% (at 2$\sigma$) in Little Blue Dots (LBDs). Additionally, R1000 JWST/NIRSpec data is strongly resolution limited, implying an inability to disentangle Doppler broadening in the absorption from optical depth effects. This is alleviated with R2700 observations, although some degeneracies remain. We find a significant correlation between the velocity of the Balmer absorption and the [OIII]5007 narrow line luminosity, suggesting a common driving mechanism. We do not find any other significant correlations (and do not confirm previously claimed correlations) between Balmer absorption and other spectral properties of LRDs (except for the expected correlation between \Has and \Hbs absorption velocities). Comparing LRDs,
quasars and
stellar \Has absorbers, we establish that absorption in both LRDs and broad absorption line
quasars is consistent with radiatively driven
outflows, echoing the physics of variable
stars yet occurring at vastly different scales.
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All authors Ignas Juodžbalis, Xihan Ji, Francesco D'Eugenio, Jan Scholtz, Roberto Maiolino, Amanda Stoffers, Alessandro Marconi, Elena Bertola, Andrew J. Bunker, Stefano Carniani, Giovanni Cresci, Emma Curtis-Lake, Zheng Ma, Cosimo Marconcini, Eleonora Parlanti, Pierluigi Rinaldi, Brant Robertson, Hannah Übler, Giacomo Venturi, Junyu Zhang
High Energy Physics (Phenomenology)
Prospects for $K_{L}\to\pi^{0}\nu\bar{\nu}$, $K_S\to\mu^+\mu^-$, $K_L\to\pi^0 \ell^+\ell^-$ and $\varepsilon^{\prime}/\varepsilon$ after the new $K^{+}\to\pi^{+}\nu\bar{\nu}$ result from NA62
Monika Blanke, Andrzej J. Buras, Cristina Lazzeroni et al. (+1 more)
The recently announced NA62 measurement of the $K^{+}\to\pi^{+}\nu\bar{\nu}$ branching ratio, based on 2016–2024 data, is fully consistent with its very accurate Standard Model (SM) prediction. While it is not excluded that the final result based on 2016–2026 data will deviate from the SM prediction, the question arises whether a similar fate awaits the $K_{L}\to\pi^{0}\nu\bar{\nu}$ decay. This decay is currently being searched for by the KOTO experiment, with the present upper bound roughly two orders of magnitude above its very precise SM prediction. The proposed KOTO II experiment aims to provide the first discovery of the $K_{L}\to\pi^{0}\nu\bar{\nu}$ decay and measure its branching ratio. Building on the findings of several previous papers we demonstrate that in the presence of suitably chosen large new complex phases and of a small amount of new right-handed $\bar s d$ couplings, in addition to the left-handed ones, the $K_{L}\to\pi^{0}\nu\bar{\nu}$ branching ratio can still be enhanced by one order of magnitude with respect to the SM prediction while keeping both $K^{+}\to\pi^{+}\nu\bar{\nu}$ and $\varepsilon_K$ SM-like. Simultaneously the decays $K_S\to\mu^+\mu^-$, studied by LHCb, and $K_L\to\pi^0\ell^+\ell^-$, searched for by KOTO II, can be strongly enhanced and the anomaly in the ratio $\varepsilon^{\prime}/\varepsilon$, as claimed by Dual QCD, removed. We illustrate this with an example of a specific $Z^\prime$ scenario.
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All authors Monika Blanke, Andrzej J. Buras, Cristina Lazzeroni, Joel C. Swallow
Mesoscale and Nanoscale Physics
Electrostatic Control Enables Robust Helical Edge Channel Transport in III-V Quantum Spin Hall Insulators
Manuel Meyer, Tobias Fähndrich, Sebastian Schmid et al. (+12 more)
Quantum spin Hall transport in InAs/GaInSb-based two-dimensional topological
insulators can be limited by parasitic bulk and edge contributions. We demonstrate that these limitations are effectively mitigated through electrostatic control in dual-gated InAs/GaInSb/InAs trilayer
quantum wells grown on AlSb quasi-substrates. In macroscopic
Hall bars exceeding the phase coherence length, a multi-probe analysis reveals an insulating bulk and a constant edge resistance over a wide electric-field range. In microscopic devices with edge lengths below the phase coherence lengths, the edge resistance remains robust and quantized across a broad field range, revealing the intrinsic resilience of helical edge channels to electric-field perturbations. Only beyond a threshold value, parasitic edge contributions emerge. These results establish dual gating as a reliable strategy to suppress parasitic conduction while stabilizing helical edge transport, providing a versatile and reproducible platform for tunable topological transport in III-V
quantum spin Hall systems.
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All authors Manuel Meyer, Tobias Fähndrich, Sebastian Schmid, Justus Walter, Martin Kamp, Adriana Wolf, Sergey Krishtopenko, Guillaume Sigu, Jean-Baptiste Rodriguez, Eric Tournie, Gerald Bastard, Frederic Teppe, Fabian Hartmann, Sven Höfling, Benoit Jouault
Mathematical Physics · Cross-listed from math.PR
Semiclassical analysis for Yang–Mills random connections on compact surfaces
Nguyen Viet Dang and Elias Nohra
We introduce anisotropic
Banach spaces of distributional 1-forms on compact surfaces designed to capture the fine regularity properties of Morse gauge-fixed Yang–Mills random connections. Using singular connections supported on unstable curves of a Morse gradient flow, we provide a new description of the
moduli space of flat connections and of its canonical Atiyah–Bott–Goldman
symplectic form. When the group is the special
unitary group, we prove that in the zero-area limit, the Yang–Mills random connection converges, within these anisotropic spaces, to a random distributional 1-form whose law coincides with our Morse-theoretic representative of the Atiyah–Bott–Goldman measure. Our approach extends the works of Witten, Forman, Liu, and Sengupta by establishing the zero-area limit of the Yang–Mills measure at the level of random distributional connections, rather than only at the level of holonomies. This answers a question of Thierry Lévy on the semiclassical limits of Yang–Mills random connections.
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High Energy Physics (Experiment)
Analysis Preservation and Reproducibility in Collider Physics: An ADL/CutLang Implementation of ATLAS Open Data Analyses
Aytül Ad{\i}güzel, Ahmetcan Sansar, Kağan Şahan et al. (+1 more)
Analysis Description
Language (ADL) and the CutLang runtime interpreter offer an innovative and sustainable solution for describing, executing, and preserving the physics content of
collider data analyses. In this solution, all physics objects and event selection criteria are expressed in a human-readable form using ADL, a domain-specific
language designed for
collider physics. ADL descriptions are interpreted directly at runtime by CutLang without translation into a general-purpose programming
language, producing event selections that can be readily fed into statistical analysis tools. This approach addresses the long-standing challenge of analysis preservation and analysis reproducibility in high energy physics by decoupling the physics logic from experiment-specific software infrastructures. In this study, several
benchmark analyses within ATLAS Open Data C++ Framework are reimplemented in ADL and executed with CutLang using data provided by ATLAS Open Data at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 10 fb$^{-1}$. The reimplemented analyses yield results in good agreement with the original publications, validating the ADL/CutLang workflow as a reliable alternative to traditional analysis frameworks. The study also provides a detailed assessment of CutLang's current capabilities and identifies areas for further development, offering a roadmap toward broader adoption of ADL-based analysis preservation in the LHC community.
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All authors Aytül Ad{\i}güzel, Ahmetcan Sansar, Kağan Şahan, Kürşat Karaca
Soft Condensed Matter
Activity and Competing Length Scales in an Anomalous Core-Softened Fluid
Davi Felipe Kray Silva, Thiago Puccinelli, Walas Silva-Oliveira et al. (+2 more)
The interplay between activity and competing interaction length scales remains largely unexplored, despite its relevance to many soft and biological systems. Here, we study Active Brownian Particles interacting through a ramp-like core-softened potential that exhibits water-like anomalies in
equilibrium. By varying the activity over a broad range of densities along two representative isotherms, one within the anomalous region and the other above it, we examine how self-propulsion modifies the structure and dynamics of the fluid. To gain microscopic insight into these changes, we construct effective interactions from the steady-state pair correlations using iterative Boltzmann inversion. We find that activity progressively suppresses the anomalies of the passive fluid, although signatures of the underlying structural crossover remain visible in normalized quantities. The effective interactions reveal that self-propulsion lowers the distinction between the local environments and facilitates population transfer between the two characteristic length scales. These results indicate that activity primarily acts by facilitating population transfer between the two local environments, thereby reducing the structural competition responsible for the anomalous response.
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All authors Davi Felipe Kray Silva, Thiago Puccinelli, Walas Silva-Oliveira, Leandro B. Krott, José Rafael Bordin
Classical Physics
The Influence of Interior Noise on Just-Noticeable Speed Differences in Conventional and Electric Vehicles
Zhenxian Li, Etienne Parizet and Claudio Colangeli
Electric vehicles (EVs) and internal-combustion-engine vehicles (ICEVs) differ fundamentally in their in-cabin acoustics, notably the attenuation or absence of engine-order content. Prior work reports associations between reduced engine sound, speed underestimation, and poorer speed maintenance; however, research on how EVs' new sound affects speed perception and control is scarce, and most newer studies focus on comfort and subjective pleasantness rather than speed perception. Addressing this gap, the present study uses a two-interval, two-alternative forced-choice (2AFC) paradigm to directly measure just-noticeable differences (JNDs) in speed under ICEV, EV, and silent conditions. Thirty participants performed a 2AFC task in which, on each trial, they viewed two first-person highway clips (reference vs. comparison) and indicated which appeared faster. Results from ANOVA and post-hoc tests indicate that at the 40 km/h reference speed participants showed no clear differences across sound conditions, whereas at 100 km/h there were marked differences in JND: mean values were 1.93 km/h (ICEV), 3.48 km/h (EV), and 5.15 km/h (silence). A psychoacoustic parameter analysis suggests that this effect is not explained by speed-dependent changes in loudness or sharpness; we interpret that RPM-related, clearly audible frequency shifts in ICEV provide the primary contributory cue. For EV NVH or artificial sound design, enhancing speed-contingent, trackable spectral cues while respecting comfort may help maintain drivers' ability to discriminate speed differences.
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High Energy Physics (Theory)
3d SUSY enhancement with non-trivial Coulomb branch via 4d $\mathcal{N}=2$ SCFT
Ryo Hamachika, Takahiro Nishinaka, Shou Tanigawa et al. (+1 more)
In recent years, a variety of three-dimensional (3d) $\mathcal{N}=2$ Chern–Simons (CS) matter theories have been constructed that flow to 3d $\mathcal{N}=4$ superconformal field theories (SCFTs) obtained from $R$-twisted reductions of four-dimensional (4d) $\mathcal{N}=2$ SCFTs. In all previously studied examples, the resulting 3d $\mathcal{N}=4$ SCFTs have trivial Coulomb branches. In this paper, we construct a 3d $\mathcal{N}=2$ CS matter theory that flows to the $R$-twisted reduction of the $(A_2,D_4)$ Argyres–Douglas theory. This gives the first example in this class whose infrared 3d $\mathcal{N}=4$ SCFT has a non-trivial Coulomb branch, which we argue is given by the orbifold $\mathbb{C}^2/\mathbb{Z}_2$, while its
Higgs branch is trivial. We further identify the 4d $U(1)$ R-charge as a mixing of a 3d R-charge with an emergent 3d Coulomb branch
flavor charge that has no 4d origin.
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All authors Ryo Hamachika, Takahiro Nishinaka, Shou Tanigawa, Yutaka Yoshida
Optics
Free-form diamond refractive optics enable efficient high-energy X-ray nano-imaging
Aknur Karabay, Xianbo Shi, Frank Seiboth et al. (+4 more)
Full-field transmission X-ray microscopy (TXM) enables nondestructive three-dimensional imaging of thick and strongly absorbing materials with high spatial resolution. Such capabilities are essential for understanding structure-function relationships in hierarchical materials, with broad applications in biology, energy conversion, and energy storage. At high
photon energies, however, TXM performance is limited by the reduced efficiency of diffractive optics and by the challenge of matching the numerical aperture (NA) of the illumination to that of the objective optics. Here we harness freeform diamond refractive optics to overcome a key illumination-efficiency bottleneck in high-energy TXM, demonstrating full-field nano-imaging at 20 keV with a half-period resolution of 72 nm. The optical system combines a custom-designed diamond refractive beam shaper that produces a uniform near-flat-top illumination at the sample with a 94% efficiency, a moving diffuser placed near the sample to increase the effective illumination NA and improve image quality and resolution, and high-precision aberration-corrected diamond compound refractive lenses as the objective optics. These results establish free-form diamond optics as a powerful route to efficient high-energy TXM, expanding full-field nano-imaging to complex, evolving materials systems and enabling in situ, operando, and tomographic studies under experimentally realistic conditions. Furthermore, it opens new avenues for innovation of joint X-ray optical-digital design for a new generation of high-energy X-ray nano-imaging.
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All authors Aknur Karabay, Xianbo Shi, Frank Seiboth, Carlos S. Baraldi Dias, Azat Khadiev, Nazanin Samadi, Manuel Guizar-Sicairos
Mesoscale and Nanoscale Physics
Pure Spin Bulk Photovoltaic Effect in an Altermagnetic Higher-Order Topological Insulator
Sibgat Ulah, Ankan Bhattacharyya and Manisha Thakurathi
We investigate the bulk photovoltaic effect (BPVE) in a $PT$-symmetric two-dimensional
heterostructure consisting of a topological
insulator coupled to a $d$-wave altermagnet. To describe the
symmetry-enforced degenerate bands of this system, we develop a non-Abelian formulation of the
spin BPVE, extending the conventional theory from isolated nondegenerate bands to $PT$-degenerate
manifolds. We show that the orientation of the Néel vector controls both the topological phase and the character of the nonlinear optical response. When the Néel vector lies in the $xy$-plane, the
heterostructure realizes a second-order topological
insulator (SOTI) protected by $C_{4z}T$
symmetry. The system also retains $C_{2z}$
symmetry, which completely suppresses second-order charge photocurrents while allowing finite
spin photocurrents. As a result, the BPVE becomes an intrinsically pure
spin photovoltaic effect, generating a dc
spin current without an accompanying charge current. We find that linearly polarized light drives a
spin shift current, whereas circularly polarized light generates a
spin injection current. Both responses undergo a sign reversal whenever the local Dirac mass changes sign. As the Néel vector is rotated toward the $z$-axis, the SOTI phase transforms into a first-order topological insulating phase, leading to the coexistence of charge and
spin photocurrents. Our results establish $PT$-symmetric altermagnetic topological-
insulator heterostructures as a versatile platform for generating and controlling pure
spin photocurrents and reveal nonlinear
spin transport as a sensitive probe of
topology and
magnetic symmetry.
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Quantum Physics
Bound Entanglement Is Insufficient for an Exponential Quantum Learning Advantage
Hyeongu Kang, Sangwoo Jeon and Changhun Oh
While
entanglement is known to enable exponential improvements in the sample complexity of
quantum learning, it remains unclear which properties of entangled resources are responsible for such improvements. We address this question through the reduction criterion, a condition obeyed by all bound-entangled states. In $n$-
qubit Pauli-channel learning, we show that restricting either the input states or the measurement effects to satisfy this criterion rules out an exponential advantage for incoherent adaptive protocols. An exponential lower bound persists for the one-sided coherent adaptive protocols considered here, even when the unrestricted side retains
quantum correlations across channel uses. Using conditional min-
entropy, we further quantify how the sample-complexity lower bounds weaken as larger violations of the reduction criterion are allowed. Finally, we show that the same obstruction appears in conjugate-state learning: restricted joint measurements cannot reproduce the logarithmic-sample advantage of unrestricted joint measurements on $\rho\otimes\rho^*$. These results identify violation of the reduction criterion as a necessary condition for an exponential advantage in the learning tasks considered here.
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Optics
Dielectric-loaded guided-wave electro-optic modulator using bulk rubidium titanyl phosphate
David Trop and Boris Desiatov
Rubidium titanyl phosphate (RTP) is widely used in bulk Pockels
cells because it combines a useful linear electro-optic response with low dielectric permittivity, high electrical resistivity, negligible piezoelectric ringing, and high optical-damage tolerance. Its use in integrated or guided-wave modulators has been limited by the absence of a mature thin-film RTP platform. Here we propose a dielectric-loaded guided-wave modulator in which a silicon nitride strip on an unetched bulk RTP
crystal forms a near-surface optical mode that overlaps with side-electrode fields. The analysis focuses on full-vector optical modes, GSG electrostatic and RF response, tensor-aware electro-optic coupling, and device-level performance at 1064~nm.
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Lattice Field Theory
Resolving the $T_{cc}^+$ with $\pi$ Exchange from Lattice QCD
Nelson Pitanga Lachini and Raúl A. Briceño
We revisit the
lattice QCD description of the doubly charmed tetraquark $T_{cc}^+$ using a finite-volume scattering formalism that incorporates one-pion exchange nonperturbatively, thereby making the nearest left-hand cut explicit while respecting unitarity and analyticity. We simultaneously determine the $D D^\star \pi$ coupling and the isoscalar $DD^\star$ scattering amplitude by reanalyzing the previously computed finite-volume $DD^\star$ spectrum below the $D^\star D^\star$ threshold, on
lattices with pion mass $m_\pi\approx391~{\rm MeV}$. We find that the inclusion of pion exchange changes the $T_{cc}^+$ from a real-valued to a complex-valued pole in the second sheet of the $J^P=1^+$, $DD^\star$ amplitude below threshold. We further predict that the $T_{cc}^+$ pole will move closer to the real-energy axis as the pion mass approaches its physical value.
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Materials Science
Deciphering Mechanoluminescence: How the Nature of Mechanical Stress and Structural Dimensionality Shape Mechanisms and Responses
Alexis Duval, Xavier Rocquefelte, Yann Gueguen et al. (+2 more)
Mechanoluminescent materials exhibit a broad spectrum of controllable light-emission responses to mechanical stimuli of varying types and magnitudes. Yet progress toward high-performance systems remains constrained by an incomplete and often contradictory mechanistic understanding. Here, density functional theory (DFT) calculations optimized for the quantitative treatment of point defects are used to systematically investigate the interplay between stress type (hydrostatic vs. shear) and active-phase dimensionality (1D vs. 3D), using $SrAl_2O_4:Eu^{2+}, Dy^{3+}$ and $Ba_4Si_6O_{16}:Eu^{2+}, Ho^{3+}$ as representative model systems. Two distinct emission-driving mechanisms are identified: a piezoelectric contribution, and a second, apparently universal, mechanism arising from stress-induced structural reorganization at point defects sites. These results establish a design framework for mechanoluminescent materials in which
crystal dimensionality, stress type and stress-sensitive point defects are deliberately matched to tune emission behavior and overall performance.
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All authors Alexis Duval, Xavier Rocquefelte, Yann Gueguen, Patrick Houizot, Tanguy Rouxel
Solar and Stellar Astrophysics
Consistent Multi-Wavelength Spectral Modeling of Cool White Dwarfs with Carbon-Polluted Atmospheres
Jay Farihi, Piotr M. Kowalski, Sandy K. Leggett et al. (+3 more)
This work presents atmospheric modeling of multi-wavelength spectra for eight cool white
dwarfs with carbon-enriched atmospheres, with four each of spectral type DQ and DQp. The Deslanders-d'Azambuja bands of C2 are detected in all six DQ
stars that have data covering wavelengths shorter than 4000A. These bands are blue shifted in the DQp types, consistent with that observed for the Swan bands, and reproduced with the same pressure distortion model. The coolest
stars in the sample show significant near-infrared flux suppression, identified here as collision-induced absorption from dense helium, with trace hydrogen [H/He]<-6, estimated from the absence of CH features. Notably, the near-ultraviolet through near-infrared spectral energy distribution of WD0038-226 is correctly reproduced using an atmospheric model with [H/He]=-6.8; however, beyond 2um the predicted flux is too high, and a carbon-free atmosphere is able to reproduce the mid-infrared observations well. The multi-wavelength coverage permits accurate modeling characterization of these
stars, including constraining the ionization
equilibrium in fluid helium and the resulting density profiles. The densities found in this work are 2-3 times higher than determined in previous studies, approaching 2g/cm3 for the coolest
stars. Excluding the uncertain high masses obtained for the two coolest DQp
stars, the sample
stars have masses that are broadly consistent with those found for the wider white
dwarf population, with no difference across the DQ-DQp temperature boundary.
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All authors Jay Farihi, Piotr M. Kowalski, Sandy K. Leggett, Hania Azzam, Jackson Headon, John P. Subasavage
Mathematical Physics
Free energy and spectral edge of the SYK model
Yukun He
Consider the Sachdev-Ye-Kitaev model with $N$ Majorana
fermions and interaction order $q$. For even $4\leq q\ll \sqrt{N}$, we present a microscopic framework that determines the free energy limit at every fixed inverse temperature $\beta>0$. In particular, this gives the first rigorous derivation of the Schwinger-Dyson thermodynamics of the model. For all even $q\in \{4,6,...,N-4\}$, we further determine the asymptotic location of the largest
eigenvalue, which answers a question posed by Feng-Tian-Wei \cite{FengTianWei1}. Consequently, we obtained the free energy limit along every sequence $\beta\equiv \beta_N\to\infty$.
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Mathematical Physics
Topological Foundations of Multi-Field Instabilities in Continua: Part 1: Foundations Part 2:Analytical Formulation for 1-D Spin Chains Part 3: Numerical Upscaling
Klaus Regenauer-Lieb, Francois Nicot and Amir Saker
This three-part series establishes a parameter-free, topological classification of multi-field instability in granular continua, extending Maxwell's
rigidity count to dynamic, non-
equilibrium processes. Part 1 (Foundations): a discrete Volumetric-Mechanical-Configurational (VMC) contact formulation maps contact-scale
topology to macroscopic multiphysics coupling. A Parity
Theorem, $\det(\mathsf{L})=(-1)^N\det(\mathsf{L})$, forces a structural null-mode for every odd channel count $N$, creating "Gateway" layers of broken time-reversal
symmetry; once the basis-invariant Gateway number $\mathcal{G}_{\rm inv}\geq 1$, gyroscopic pumping drives non-modal transient amplification along the null direction. Part 2 (analytical, 1-D
spin chains): the minimal Gateway is the $N=3$ VMC contact, whose skew block $\mathsf{L}\in\mathfrak{so}(3)$ carries a persistent zero
eigenvalue and an unresisted configurational drift that operates even without friction. In an acyclic chain (first Betti number $\beta_1=0$) this isolates dilatancy; closed-form solutions give secular drift for $N=3$ and harmonic confinement for $N=4$. Part 3 (numerical upscaling): quad-precision integration of tridiagonal skew-symmetric Onsager chains ($N=3$ to $50$) confirms the contrast between odd-$N$ secular drift and even-$N$ confinement on invariant
tori, with even-chain frequencies scaling as $|\lambda_{\min}^{\rm even}|\sim\gamma\pi/N$. VMC channels map to measurable DEM observables, enabling parameter-free evaluation of $\mathcal{G}$ and four falsifiable oedometer protocols.
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Superconductivity
Annealing-enhanced spin-orbit effects in non-centrosymmetric superconducting NbRe films
Zahra Makhdoumi Kakhaki, Yuriy Yerin, Francesco Avitabile et al. (+5 more)
$\text{Nb}_{0.18}\text{Re}_{0.82}$ (NbRe) is a non-centrosymmetric
superconductor with a transition temperature $T_\mathrm{c}$ reaching $9\text{ K}$ in bulk form. While bulk and single-crystalline NbRe exhibit signatures of multigap superconductivity, thin films generally display a single-gap superconducting state due to structural disorder and reduced crystallite dimensions. Here, we investigate the impact of thermal annealing on the superconducting and normal-state magnetotransport properties of NbRe films. The temperature dependence of the upper critical field, $B_{\mathrm{c2}}(T)$, is analyzed within the microscopic Werthamer–Helfand–Hohenberg (WHH) framework, while the normal-state magnetoconductivity is described using the three-dimensional Kawabata weak-localization/weak-anti-localization model. Annealing drives a pronounced change in the electronic response, manifested by a strong weak anti-localization behavior in the normal state and an upper critical field that surpasses both the conventional orbital-limiting field and the Pauli paramagnetic limit. The microscopic analysis reveals a strong intrinsic increase in the relative
spin–orbit scattering strength, with the annealed film showing a significantly enhanced
spin–orbit-to-dephasing field ratio. These findings provide direct, independent evidence that thermal modification of the NbRe microstructure successfully amplifies
spin–orbit-mediated
quantum transport, which acts as the key mechanism protecting the non-centrosymmetric superconducting state against paramagnetic pair-breaking well beyond conventional theoretical boundaries.
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All authors Zahra Makhdoumi Kakhaki, Yuriy Yerin, Francesco Avitabile, Abhishek Kumar, Francesco Colangelo, Carla Cirillo, Oleksandr V. Dobrovolskiy, Carmine Attanasio
Fluid Dynamics
Preferential and differential diffusion in RANS simulation of lean hydrogen flames with tabulated chemistry
Alex M. Garcia, Emiliano M. Fortes, Eduardo J. Pérez-Sánchez et al. (+6 more)
Lean hydrogen flames are prone to thermo-diffusive instabilities due to preferential and differential
diffusion effects, posing significant challenges for their modeling in computational fluid dynamics simulations. This work extends a tabulated-chemistry (TC) model that includes preferential and differential
diffusion effects to a Reynolds-averaged Navier-Stokes (RANS) framework and assesses its performance for a lean premixed $\mathrm{H_2}$-air slot burner at two Reynolds numbers ($\mathrm{Re}=5500$ and $11000$) using direct numerical simulation (DNS) as a reference. The approach is based on transport equations for the progress variable and mixture fraction derived from the species mass transport equations considering mixture-averaged
diffusion and Soret effect, and incorporates
turbulence–chemistry interaction via a presumed probability density function (PDF) approach. RANS simulations including preferential-differential
diffusion are able to correctly reproduce the DNS flame length, heat-release distribution, and the characteristic equivalence-ratio and super-adiabatic temperature branches of the slot flame. Comparisons with (i) a unity-Lewis-number variant and (ii) a model including thermo-diffusive effects only in the flamelet table show the impact of preferential and differential
diffusion on the TC model at both the thermochemical and transport levels. Finally, the impact of the
turbulence closures for turbulent
diffusion, scalar dissipation rate, and Reynolds stresses is assessed. The results presented in this paper demonstrate the capability of the model to include preferential and differential
diffusion effects in cost-effective RANS simulations of lean hydrogen flames.
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All authors Alex M. Garcia, Emiliano M. Fortes, Eduardo J. Pérez-Sánchez, Daniel Mira, Marco Vivenzo, Michael Gauding, Heinz Pitsch, Nico Schmitz, Christian Wuppermann
Computational Physics
Random site percolation with complex neighborhoods in five dimension
Krzysztof Malarz and Maciej Wołoszyn
In this paper, the random site percolation problem in a five-dimensional space for complex neighborhoods is studied. The efficient C++ code (with ordinary work division) of the classical Newman–Ziff
algorithm is presented. The obtained speed-up of computations reduces 2170 years of single-core computations – necessary for obtaining the results presented in this paper – much below the typical half-decay time of the scientist. For complex neighborhoods, it is for neighborhoods composed with sites taken from several coordination zones (up to the seventh coordination zone), the 127 percolation thresholds are calculated (with 120 among them being estimated for the first time). For seven extended (compact) neighborhoods, the fractal dimensions are also calculated. The mean value of these fractal dimensions, averaged over these seven compact neighborhoods, is estimated as $\langle d_f\rangle\approx 3.5581(70)$. The percentage errors of the values obtained for the fractal dimensions for compact neighborhoods vary from 0.26% to 1.76% with respect to the theoretically predicted value based on scaling relations and the most recent estimates of critical exponents for five-dimensional space. The universality of the percolation threshold as dependent on the weighted coordination number $\zeta=\sum_i z_i r_i$ (where $z_i$ is the number of sites in the $i$-th coordination zone and $r_i$ is the Euclidean distance from the sites in the $i$-th coordination zone to the central site) is also verified. The latter manifests itself as the power law ($p_c\propto\zeta^{-g}$) with $g\approx 0.7913(43)$
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Materials Science
Mag4: An Automated First-Principles Workflow to Extract Magnetic Interactions, from Pair Couplings to Four-Spin Ring Exchange
Xavier Rocquefelte and Peter Blaha
Chemists design
magnetic materials through structure-property relationships built on pairwise exchange couplings $J$, now extracted routinely from first principles by energy-mapping. But wherever four
magnetic centers close a loop—as in cuprate CuO$_2$ planes or infinite-layer square nets—a four-
spin ring exchange $J_{\rm ring}$ can arise, reshaping ground states and corrupting the $J$ values used for design. Missing has been a direct, local way to obtain it, as the four-state method gives for $J$. We supply it by generalizing that method to a sixteen-state ($2^4$) scheme, automated in the open Mag4 package—the first automatic implementation of the four-state family. From one cif file, Mag4 proposes the supercell that isolates the couplings, generates DFT inputs in the user's chosen functional, extracts $J$ and $J_{\rm ring}$ with band-gap and local-moment diagnostics, and predicts the
magnetic order, propagation vector, and critical temperature.
Symmetry reduces the sixteen configurations to six or eight inequivalent energies, so the cost is modest. The derivation shows the conventional four-state $J$ is itself ring-renormalized by $\mp 2 J_{\rm ring} S^2$, the sign set by the reference state. T-La$_2$CuO$_4$ confirms this: three routes agree on $J_{\rm ring}$ to $0.2\%$, giving $J_{\rm ring}/J_1=0.25$, and a four-state $J_1$ quoted without its reference is wrong by $12\%$. The sixteen-state value is itself reference-dependent—Néel and
ferromagnetic baths bracket it—a fourth-order fingerprint of interactions beyond the pair-plus-ring model, resolved by further baths into a bare $J_{\rm ring}$ and a converging tower of six- and eight-
spin loop couplings. SrFeO$_2$ ($S=2$), same plaquette yet $J_{\rm ring}/J=0.006$, is the negative control: a plaquette is necessary for ring exchange but far from sufficient—a structure-property criterion for screening new multi-
spin magnets.
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Applied Physics
Ambient Pressure-Driven Actuators and Shape-Morphing Metamaterials
Benjamin Holdstock, Robert Trowbridge, Alexander W. Powell et al. (+1 more)
Actuators which change shape in response to ambient pressure have great potential for use in extreme environments, from space to the deep ocean. Bi-layer actuators have so far not been explored to this end, despite their lightness and mechanical simplicity (there is no requirement for a separate power source or pump, for example) making them ideal for applications where transport and maintenance are difficult. In this paper, foam-based
bilayer actuators powered by ambient pressure change have been constructed, modelled mathematically, characterised in terms of their actuating force, and built into deployable devices and metamaterial structures to showcase properties such as negative pressure expansivity. Actuators such as these are ideally suited for a range of applications, from deploying
solar panels and sensors in space and extra-terrestrial atmospheres, to under-sea expandable structures and sensing.
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All authors Benjamin Holdstock, Robert Trowbridge, Alexander W. Powell, Julian Monsalve Londono
High Energy Astrophysical Phenomena
Be/X-Ray Binaries: Phenomenology, Variability, and Accretion~Dynamics
Pablo Reig
Be/X-ray binaries constitute the largest and most diverse subgroup of
neutron star high-mass X-ray binaries. These systems feature a rapidly rotating Be
star surrounded by a circumstellar decretion disk that serves as the primary reservoir of accreted matter onto a strongly magnetized
neutron star. While a few Be/X-ray binaries remain persistently active, the majority manifest as hard X-ray transient sources, becoming detectable only during X-ray outbursts. This review synthesizes current understanding of their rich phenomenology across optical and X-ray wavelengths, focusing on variability ocurring over timescales that span from seconds to years.
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Physics and Society
Single-Snapshot Inference of Network Couplings from Universal Dynamics at Relative Equilibrium
Moritz Lampert, Dominic Grün and Ingo Scholtes
Many real-world systems can be modelled as complex networks whose collective behaviour is governed by hidden interactions between nodes. Existing methods for inferring these interactions typically require controlled perturbations, time-resolved observations or multiple independent snapshots, all of which are often unavailable in practice. Here we show that class-based coupling strengths can be inferred from a single snapshot of node states when the system is observed close to a relative
equilibrium. In this regime, all nodes share a common velocity, which can be absorbed into an effective class bias, transforming the inverse problem into a homogeneous linear system. The coefficients of this linear system are determined entirely by the observed local neighbourhoods and their coupling mechanism, enabling the application to arbitrary known coupling functions. We validate the approach on three different linear and nonlinear dynamical systems, recovering relative class-based couplings and, in special cases, absolute couplings. These results show that spatial heterogeneity can substitute for temporal sampling, enabling single-snapshot inference of hidden coupling strengths in networked dynamical systems.
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Astrophysics of Galaxies
Molecular gas hidden in plain sight in the early Universe
Pasquier Noterdaeme, Jens-Kristian Krogager and Sergei Balashev
We report the discovery of an extreme intervening molecular absorber at zabs = 4.1 towards the z = 4.7
quasar SDSS J080023.02+305101.22 revealed through strong H2 absorption that had remained unnoticed in archival data for about two decades. The system, which we analysed with new VLT/X-shooter observations, has a
metallicity of about one-fifth the
solar value, in line with the moderate
dust reddening AV~0.06 mag. More strikingly, it exhibits the highest molecular fraction, fH2 = 2N(H2)/(2N(H2) + N(HI))~=60%, measured at z>0 from direct determinations of both atomic and molecular hydrogen column densities. Notably, this fraction is comparable to the very highest values in the Local Group. The inferred fH2 still represents a conservative lower limit to the local molecular fraction since the H i absorption very likely includes atomic gas unrelated to the actual molecular component, as indicated by the wide (Delta v~500 km/s) multi-component low-ionisation metal profile. The detection of such a system at early
cosmic times is remarkable given the limited number of
quasar spectra probing z>4. It suggests an unexpectedly high incidence of H2, with important implications for the
evolution of molecular gas. This high incidence may be driven by high average densities and enhanced
turbulence at those
redshifts. At the same time, our results also highlight possible observational biases, both in
quasar selection and in recognising strong H2 absorption, suggesting that a significant fraction of molecular gas may remain undetected, in particular near the peak of
star formation. The present system offers a unique
benchmark for developing efficient detection
algorithms. Further progress will benefit from colour-independent
quasar surveys, while constraining the physical conditions and environments of such extreme absorbers will require observations on future extremely large
telescopes.
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High Energy Astrophysical Phenomena
A Type Ia Supernova Candidate at $z\sim4.3$: A Transient Interloper in the Search for $z\sim14$ Galaxies
Seiji Toshikage, Takahiro Morishita, Masaomi Tanaka et al. (+9 more)
The James Webb Space
Telescope (JWST) is opening a new window into the distant Universe by discovering
galaxies and transients in the early Universe. We investigate a high-
redshift transient candidate, beacon_1420-5253_4770. This object was initially identified as a high-
redshift galaxy candidate at $z\sim14$. However, the source was not detected in epochs before and after the detection epoch, suggesting that the object is a transient source rather than a persistent
galaxy. We classify the source by comparing the colors, magnitudes, light curves, and spectral energy distribution with various spectral templates of transients. Our analysis shows that the observed properties are consistent with a Type Ia
supernova at $z\sim4.3$. Strong absorption by Fe-group elements seen in Type Ia
supernova spectra can mimic the Lyman break used to detect high-
redshift galaxies. At $z \sim 4.3$, corresponding to a
cosmic age of only $\sim 1.5$ Gyr, our detection provides a direct probe of the delay time between
star formation and
supernova explosion. Our estimate of the event rate implies a minimum delay time shorter than 1 Gyr. We also discuss the implications of transient contamination for searches of
galaxies in the early Universe.
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All authors Seiji Toshikage, Takahiro Morishita, Masaomi Tanaka, Kazumi Kashiyama, Charlotte A. Mason, Andrew J. Bunker, Matthew J. Hayes, George Helou, Tadayuki Kodama, Kimi C. Kreilgaard, Massimo Stiavelli, Tommaso Treu
Solar and Stellar Astrophysics
Influence of local and global solar magnetic fields on medium-term forecasting of the number and parameters of coronal mass ejections
Irina A. Bilenko
It has been shown that both the frequency and parameters of coronal mass ejections (CMEs) increased as
solar cycles 23-25 approached their maxima and decreased toward their minima. However, significant differences were identified in the cyclic
evolution of strong versus weak CMEs. Unlike weak CMEs, powerful, high-speed CMEs, characterized by large angular widths and substantial mass and energy, follow the cyclic
evolution of active regions. During periods when the sector structure of the global
magnetic field (GMF) dominates, the latitudinal distribution of CMEs becomes more uniform, and their frequency and parameter values increase, particularly during the declining phase of
solar activity. A method based on combining GMF parameter data and Wolf numbers has been proposed for the medium-term
forecasting of the frequency and parameters of strong and weak CMEs in cycle 26. A comparison of predicted and observed CME parameters for cycle 25 shows good agreement.
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