Statistical Mechanics
Sokoban Random Walk: A Trapping Perspective
Prashant Singh, Eli Barkai and David A Kessler
We study caging/trapping in Sokoban-type models, featuring a random walker moving through a disordered medium of obstacles and capable of pushing some obstacles blocking its path. In one-dimension, we allow the walker to push up to an arbitrary $N_{\rm P}$ number of obstacles. For $N_{\rm P}\gg 1$, we use large-deviation theory to show that the survival probability to remain uncaged exhibits crossover from an exponential decay with time at intermediate times to a stretched-exponential decay at long times, with an exponent $1/3$ independent of $N_{\rm P}$. The long-time exponent matches the Balagurov–Vaks–Donsker–Varadhan (BVDV) theory of the classical trapping problem, while the exponential decay is qualitatively distinct from the Rosenstock's intermediate-time theory for classical trapping. Similarly, in two dimensions, numerical simulations reveal that both the Sokoban model and its generalized version exhibit long-time stretched-exponential relaxation with exponent $1/2$, again consistent with the BVDV theory. Finally, in two dimensions, we find that the mean trap size is nonmonotonic in $\rho$: it is small at both low and high densities, but reaches a peak at a characteristic density $\rho_*$. We estimate $\rho_* \approx 0.55$ for the Sokoban model and $\rho_* \approx 0.675$ for the generalized Sokoban model.
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Strongly Correlated Electrons
Disorder-driven stochastic dynamics in Mott resistive-switching systems
David J. Alspaugh, Lorenzo Fratino, Nareg Ghazikhanian et al. (+2 more)
Controlled disorder in correlated materials provides a new route to emergent
stochastic dynamics in neuromorphic hardware. Here we show that focused ion beam irradiation in VO$_{2}$- and V$_{2}$O$_{3}$-based resistive-switching oscillators induces a transition from regular periodic oscillations to strongly irregular
stochastic firing, while simultaneously reducing the required switching energy by orders of magnitude. Under an applied electric field, these materials undergo a volatile
insulator-to-metal transition characterized by the formation of percolating metallic filaments within an insulating bulk. Using numerical simulations based on the Mott resistor network, we demonstrate that defect-induced modifications to filament nucleation and stability drive these devices into
stochastic oscillatory regimes. These results are validated by experimental measurements on irradiated VO$_{2}$ and V$_{2}$O$_{3}$ devices.
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All authors David J. Alspaugh, Lorenzo Fratino, Nareg Ghazikhanian, Ivan K. Schuller, Marcelo Rozenberg
Materials Science
Stacking-Tunable Electronic Properties in Recently Synthesized Hydrogen-Substituted Graphdiyne
Guilherme S. L. Fabris, Raphael B. de Oliveira, Bruno Ipaves et al. (+2 more)
Recent progress in porous carbon materials has highlighted the importance of structural design in controlling emergent physicochemical properties. In this context, hydrogen-substituted graphdiyne (HsGDY), a three-dimensional framework derived from graphdiyne (GDY), has recently emerged as a promising architecture whose stacking-dependent behavior remains largely unexplored. Here, we present a comprehensive first-principles investigation of the structural, electronic, and optical properties of HsGDY across distinct stacking sequences. Our results identify the AA and ABC configurations as the most energetically favorable, with AA corresponding to the global minimum, consistent with recent experimental observations. Electronic-structure analysis reveals that HsGDY is an indirect
semiconductor with an electronic band gap of 0.89 eV (optB88-vdW), primarily governed by interlayer coupling and van der Waals interactions. The optical response exhibits pronounced absorption features spanning the visible to ultraviolet regions, highlighting strong potential for optoelectronic applications. Ab initio molecular dynamics (AIMD) simulations at 700 K confirm the thermal robustness of the framework, with negligible structural distortions. Collectively, these findings elucidate the stacking-dependent stability and semiconducting character of HsGDY, providing a solid theoretical foundation for its integration into next-generation nanoelectronic and energy-harvesting technologies.
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All authors Guilherme S. L. Fabris, Raphael B. de Oliveira, Bruno Ipaves, Marcelo L. Pereira Junior, Douglas S. Galvao
Materials Science
Magnetic skyrmion lattice disclinations in pentagon- and heptagon-shaped FeGe crystals
Thibaud Denneulin, Nikolai S. Kiselev, Vladyslav M. Kuchkin et al. (+1 more)
Magnetic skyrmions in
chiral magnets typically arrange into hexagonal
lattices, with their structural order influenced by factors such as temperature, external
magnetic fields and
geometric constraints. While translational defects in skyrmion
lattices such as dislocations have been extensively studied, individual angular defects, or disclinations, remain largely unexplored. Here, we report on the stabilization of five-fold and seven-fold disclinations in pentagon- and heptagon-shaped FeGe nanocrystals created using focused ion beam milling. The
magnetic and elastic structures of the disclinated
lattices are investigated using Fresnel imaging and off-axis electron holography in a transmission electron microscope. The results are supported by micromagnetic simulations and analytical models based on linear elasticity theory.
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All authors Thibaud Denneulin, Nikolai S. Kiselev, Vladyslav M. Kuchkin, Rafal E. Dunin-Borkowski
Strongly Correlated Electrons
Exchange interactions and finite-temperature magnetism in (111)-oriented (LaMnO$_3$)$_{2n}$|(SrMnO$_3$)$_n$ superlattices
Shivalika Sharma, Julio do Nascimento, Imran Ahamed et al. (+3 more)
We present a first-principles investigation of
magnetic exchange interactions and critical behavior in (111)-oriented (LaMnO$_3$)$_{2n}$|(SrMnO$_3$)$_n$ superlattices for $n=2,4,6$. For all superlattices under investigation, we find robust half-metallic ferromagnetism extending across all the layers of both component regions. Changing octahedral tilt patterns is found to have negligible effects on the
magnetic properties, despite determining the presence or absence of small Jahn-Teller distortions. The analysis of the response of the
magnetic coupling to a variation of the Coulomb interaction parameters demonstrates that ferromagnetism is driven by a double-exchange mechanism involving itinerant $e_g$ electrons, while its final strength is hampered by
antiferromagnetic contributions due to the superexchange of localized $t_{2g}$ electrons. Multi-scale simulations based on atomistic
spin dynamics show that the thinnest superlattices, $n=2,4$, possess an ordering temperature that is at least comparable to that of La$_{2/3}$Sr$_{1/3}$MnO$_3$. Conversely, as thickness increases, a two-phase behavior emerges, where the SrMnO$_3$ region loses long-range order faster than the LaMnO$_3$ region. While the global ordering temperature increases together with thickness, we argue that the high-temperature regime for the observed two-phase behavior is not representative of the real physical system, which will undergo a combined electronic,
magnetic and structural phase transition as soon as the long-range order is lost inside the SrMnO$_3$ region. This study provides insights into the emergent
magnetic phases and transition temperatures relevant to
oxide heterostructures.
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All authors Shivalika Sharma, Julio do Nascimento, Imran Ahamed, Fabrizio Cossu, Heung-Sik Kim, Igor Di Marco
Mesoscale and Nanoscale Physics
Nonlinear effects in a strongly coupled Nanoelectromechanical System
Narges Tarakameh Samani, Farhad Shahbazi and Mehdi Abdi
Controlling nonlinear effects in micro- and nano-electro-mechanical systems is essential for unlocking their full potential in sensing, signal processing, and frequency control. In this study, we develop a voltage-dependent
Hamiltonian framework for a nanoelectromechanical resonator with two strongly coupled vibrational modes, representative of a nanostring platform. The mode frequencies and couplings of the system are tuned electrostatically using a DC voltage, which also controls the strength of the interactions. Our theoretical model reproduces the experimentally observed avoided crossing in the absence of an AC drive and generates tunable frequency-comb spectra when a parametric drive is applied. By scanning the DC voltage, we generate a phase diagram that links comb formation and sharp regime boundaries to underlying bifurcations, multi-stability, and attractor switching. Phase-resolved diagnostics based on a Kuramoto order parameter, together with autocorrelation and Poincaré analyses, quantify coherence and critical slowing down near these transitions. We further explore the relationship between nonlinear coupling, parametric excitation, and stability transitions within a single device of experimental relevance and establish a dynamical framework for engineering nanoelectromechanical resonators that offer enhanced tunability, functionality, and a predictive link to experimental outcomes.
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Quantum Gases · Cross-listed from nucl-th
Quarkyonic matter and hadron-quark crossover from an ultracold atom perspective
Hiroyuki Tajima, Kei Iida, Toru Kojo et al. (+1 more)
The dense matter equation of state is of great interest due to the recent development of astrophysical observations for
neutron stars. A rapid increase in pressure indicates a continuous crossover from a
hadron phase to a
quark phase without any phase transitions, yet its microscopic mechanism remains elusive. Recently, a peak in the speed of sound and a
baryon momentum-shell structure, which are predicted from a quarkyonic matter picture, have been regarded as key features of the
hadron-
quark crossover. In this work, we explore a field-theoretical framework to describe the
hadron-
quark crossover, drawing an analogy with the Bose-Einstein condensate to Bardeen-Cooper-Schrieffer (BEC-BCS) crossover established in ultracold atomic experiments. Strikingly, a peak in the speed of sound and the
baryon momentum-shell structure can simultaneously be explained by the tripling fluctuation effect arising from a different context of
quantum many-body physics. We demonstrate these properties in a simplified model and provide a microscopic derivation of the quarkyonic matter model within our field-theoretical framework.
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All authors Hiroyuki Tajima, Kei Iida, Toru Kojo, Haozhao Liang
Materials Science
Delocalisation explains efficient transport and charge generation in neat Y6 organic photovoltaics
Daniel Balzer, Paul A. Hume, Geoffrey R. Weal et al. (+2 more)
Non-fullerene acceptors (NFA), such as Y6, have significantly improved the efficiency of organic photovoltaic devices (OPVs). However, the fundamental processes behind the high efficiencies of NFA devices have remained incompletely understood, with the high efficiencies persisting without the large energetic offsets often thought to be required for charge separation. Even more surprising has been the efficient charge generation in neat Y6 devices, where there is no energetic offset at all. Here, we simulate charge transport and separation in Y6 using delocalised kinetic Monte Carlo (dKMC) parameterised using atomistic calculations, thus taking into account the often-neglected ingredients of delocalisation, disorder, and polaron formation. Including delocalisation predicts higher carrier mobilities and
exciton diffusion coefficients than is possible with classical simulations, bringing them into agreement with experimental values. Delocalisation also predicts higher charge-generation efficiencies in neat Y6, in agreement with experimental measurements. Finally, this work establishes dKMC as a realistic, predictive tool for understanding next-generation OPVs.
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All authors Daniel Balzer, Paul A. Hume, Geoffrey R. Weal, Justin M. Hodgkiss, Ivan Kassal
Statistical Mechanics · Cross-listed from math-ph
Timescale for macroscopic equilibration in isolated quantum systems: a rigorous derivation for free fermions
Takashi Hara and Tatsuhiko Koike
For a class of translation-invariant free-
fermion systems (including those with uniform nearest neighbor hopping) on a $d$-dimensional $L \times \cdots \times L$ hypercubic
lattice, we prove that, starting from an arbitrary pure initial state, the system equilibrates with respect to the coarse-grained density within a timescale of order $L$. This scaling is optimal, since there exist initial states whose equilibration requires time of order $L$. Our result establishes $O(L)$ as the equilibration timescale, as is expected in normal macroscopic systems with a conserved quantity, such as total number of particles.
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Other Condensed Matter
Synergism in radiation effects in condensed matter. Fundamental and application aspects
Boris Oksengendler, Muhsin Ashurov, Sultan Suleymanov et al. (+4 more)
The impressive success achieved by condensed matter radiation physics over its 170-year development period is related to the solution of problems in three areas, the emergence of new materials, the development of new sources of radiation, and the formulation of new concepts with a wide range of applications. In the borderlands of the 20th and 21st centuries, significant changes occurred in each of these aspects (not-so-catastrophic disasters, R. Tom). A major role was played by the emergence of a new ideology - Complexity, which led to the birth of four paradigms, self-organization, dynamic chaos, self-organized criticality and nonadditivity (the first three are related to the concept of synergetics, the fourth - synergism). This article is devoted to radiation synergism, with an emphasis on combinations of radiation and other effects. It presents methods of graphical techniques to identify the specific issue of synergism effects, which is the non-additivity of the overall radiation effect. A parameter expression is proposed to account for the non-additivity of the radiation effect in the experiment, which can be compared to the q parameter introduced by Tsallis in the general science of Complexity, opening up new possibilities in condensed matter radiation physics for both living and non-living objects.
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All authors Boris Oksengendler, Muhsin Ashurov, Sultan Suleymanov, Nigora Turayeva, Farida Iskandarova, Gulnoza Akhmatova, Rahmatillo Ibrohimov
Materials Science
Dynamical screening effects on formation of swift heavy ions damage in GaN
S. V. Moskalets, R. A. Rymzhanov and A. E. Volkov
We used a multiscale model to study the damage caused by swift heavy ions in GaN. The model combines Monte Carlo and molecular dynamics simulations to analyze the material response to the excitation initiated by a projectile. We found that the most appropriate simulation approach couples the dynamical screening of charges of target atoms during the scattering of fast electrons with the Tersoff-Brenner interatomic potential describing atomic dynamics in the excited target. The simulations demonstrate the formation of damaged ion tracks with an amorphous core, containing voids filled with nitrogen. The core is surrounded by a damaged crystalline region containing edge dislocations, consistent with experimental observations.
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Statistical Mechanics
NMR study on equilateral triangular lattice antiferromagnet Ba2La2CoTe2O12
Keito Morioka, Takayuki Goto, Masari Watanabe et al. (+5 more)
We report a 139La-NMR study of Ba2La2CoTe2O12, S = 1/2 equilateral triangular-
lattice antiferromagnet with easy-plane anisotropy at low temperatures. This compound undergoes a
magnetic phase transition at TN = 3.26 K into an ordered state with the 120 degree
spin structure. Under
magnetic fields above 3T, TN splits into TN1 and TN2, which correspond to the transitions from the paramagnetic phase to the up-up-down (uud) phase and from the uud phase to the triangular coplanar phase, respectively. The NMR
spin-
lattice relaxation rate 1/T1 exhibits a critical divergence at TN1, indicating the onset of long-range
magnetic order. At TN2, the NMR-linewidth measured at 5.4 T exhibits an anomalous decrease, which we attribute to a change in the
spin structure from the uud to the triangular coplanar phase.
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All authors Keito Morioka, Takayuki Goto, Masari Watanabe, Yuki Kojima, Nobuyuki Kurita, Hidekazu Tanaka, Satoshi Iguchi, Takahiko Sasaki
Mesoscale and Nanoscale Physics
Interaction-Enabled Two- and Three-Fold Exceptional Points
Musashi Kato and Tsuneya Yoshida
We propose a novel type of exceptional points, dubbed interaction-enabled $n$-fold exceptional points [EP$n$s ($n=2,3$)] – EP$n$s protected by
topology that are prohibited at the non-interacting level. Specifically, we demonstrate that both bosonic and fermionic systems host such interaction-enabled EP$n$s ($n=2,3$) in parameter space that are protected by charge U(1), pseudo-
spin-parity, and $PT$
symmetries. The interaction-enabled EP2s are protected by zero-dimensional
topology and give rise to qualitative changes in the loss rate, an experimentally measurable quantity for cold atoms. Furthermore, we reveal that interactions enable EP3s protected by one-dimensional
topology beyond the point-gap topological classifications, suggesting the potential presence of a broader class of interaction-enabled non-Hermitian degeneracies.
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Materials Science
A Magnon-Based Electric Field Controlled Magnetoelectric Device for Energy-Efficient Logic-in-Memory
Rongqing Cong, Sajid Husain, Yumin Su et al. (+6 more)
We demonstrate a non-volatile magnetoelectric magnonic
memory (MEMM) that enables fully electrical write/read via direct
magnon-driven sensing in an insulating antiferromagnet. A fabricated SrIrO3/La-BiFeO3/SrIrO3 trilayer exhibits sub-100 ps switching, a remnant polarization of 20 uC/cm2, and a readout voltage contrast close to 1mV between high and low-resistance states. To connect device physics to
circuit behavior, we develop and experimentally validate a compact
circuit model that captures
spin Hall injection and
spin transport. Simulations with optimized material parameters predict output voltages > 100mV, enabling cascading without external amplification. Using this framework, we design MEMM-based
memory and logic blocks, including a 1T1R array, two inverter implementations (complementary two-device and single-device), and a three-input majority gate, and evaluate deep-pipelined operation. The model projects switching energies down to 1 aJ per operation and logic propagation delays of 30-60 ps, indicating MEMM as a promising platform for energy-constrained, high throughput computing.
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All authors Rongqing Cong, Sajid Husain, Yumin Su, Sasikanth Manipatruni, Naveed Ahmed, Dmitri E. Nikonov, Ramamoorthy Ramesh, Kaiyuan Yang, Zhi Jackie Yao
Disordered Systems and Neural Networks
Coexistence of topological Anderson insulator and multifractal critical phase in a non-Hermitian quasicrystal
Qi-Bo Zeng and Rong Lü
The interplay of
topology, disorder, and non-Hermiticity gives rise to phenomena beyond the conventional classification of
quantum phases. We propose a one-dimensional non-Hermitian Su-Schrieffer-Heeger model with quasiperiodically modulated nonreciprocal intracell hopping. We show that quasiperiodic modulation can substantially enhance the topological regime and, remarkably, induce a non-Hermitian topological Anderson
insulator (TAI) phase. Beyond the topological transition, increasing nonreciprocity drives a cascade of localization transitions in which all bulk eigenstates evolve from extended to multifractal critical and ultimately to localized states. Strikingly, the extended-to-critical transition coincides exactly with a real-complex spectral transition. We establish complete phase diagrams and derive exact analytical boundaries for both topological and localization transitions, uncovering an unanticipated coexistence of TAI and multifractal critical phases. Finally, we propose a feasible implementation in topolectrical
circuits. Our results reveal a new paradigm for studying the cooperative effects of
topology, quasiperiodicity, and non-Hermiticity.
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Mesoscale and Nanoscale Physics
Ion Concentration and Voltage Imaging with Fluorescent Nanodiamonds
Patrick Voorhoeve, Hiroshi Abe, Takeshi Ohshima et al. (+5 more)
The nitrogen-vacancy (NV) center in diamond exists in different charge states with distinct photoluminescence properties, which are sensitive to the nanoscale electrochemical environment. Hence, the NV charge state is emerging as a powerful all-optical platform for nanoscale sensing and imaging. Although significant progress has been made in engineering near-surface NV centers in bulk diamond, controlling the NV charge state in fluorescent nanodiamonds (FNDs) has proven challenging, limiting the sensitivity and reliability of FND-based charge state sensing. Here, we demonstrate reliable, reversible switching between the fluorescent NV$^0$ and non-fluorescent NV$^+$ charge states in sub-30 nm FNDs via surface oxidation and hydrogenation, respectively, for single particles and particle powder. In aqueous electrochemical
cells, we demonstrate voltage and ion concentration imaging based on the NV charge state in self-assembled FND layers on transparent substrates. Applied voltages reliably modulate the FND PL with a sensitivity of up to 16 mV Hz$^{-1/2}$. Importantly, FND PL is also modulated by local changes in salt concentration with a sensitivity of up to 1.8% per millimolar NaCl, enabling all-optical imaging of ion concentration gradients at the microscale. Our results represent a significant step toward realizing fast, stable, and scalable nanoscale charge- and voltage-imaging technologies with sub-micrometer spatial resolution.
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All authors Patrick Voorhoeve, Hiroshi Abe, Takeshi Ohshima, Qiang Sun, Anita Quigley, Rob Kapsa, Nikolai Dontschuk, Philipp Reineck
Soft Condensed Matter
Phason-Driven Diversity of Nucleation Pathways in Icosahedral Quasicrystals
Gang Cui, Lei Zhang, Pingwen Zhang et al. (+2 more)
The nucleation of quasicrystals remains a fundamental puzzle, primarily due to the absence of a periodic translational template. Here, we demonstrate that phasons - hidden degrees of freedom unique to quasiperiodic order - drive diverse nucleation pathways in icosahedral quasicrystals (IQCs). Combining a Landau free-energy model with the spring pair method, we compute distinct critical
nuclei and their corresponding minimum energy paths. At low temperatures, a direct,
symmetry-preserving pathway dominates. In contrast, higher temperatures promote a "
symmetry detour" that reduces the nucleation barrier via a lower-
symmetry critical
nucleus. Remarkably, while the resulting bulk IQCs exhibit distinct real-space
symmetries, they remain thermodynamically degenerate with identical diffraction patterns. We resolve this paradox within the high-dimensional projection framework, showing that phason shifts modulate real-space
symmetry without altering bulk thermodynamics. Our findings establish phasons as the structural origin of pathway diversity, offering a new physical picture for the emergence of quasiperiodic order.
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All authors Gang Cui, Lei Zhang, Pingwen Zhang, An-Chang Shi, Kai Jiang
Materials Science
Unified Phase-Field Framework for Antiferroelectric, Ferroelectric and Dielectric Phases: Application to HZO Thin Films
P. Pankaj, Sandeep Sugathan, Si Joon Kim et al. (+1 more)
Polycrystalline hafnia-based thin films exhibit mixed ferroelectric (FE), antiferroelectric (AFE), and dielectric (DE) behavior, with switching characteristics strongly influenced by microstructure and phase distribution. Here, we develop a unified grain-resolved three-dimensional phase-field framework for metal-
insulator-metal capacitors that simultaneously captures ferroic phase characteristics in realistic polycrystalline microstructures by explicitly incorporating grain
topology and crystallographic orientation. Antipolar sublattice kinetics are represented via the coupled
evolution of macroscopic and staggered polarization order parameters. All thermodynamic and kinetic parameters are calibrated to experimental P-E hysteresis loops and held fixed across all simulations. The results show that phase fractions primarily determine hysteresis character, while vertical segregation of AFE- and FE-rich regions systematically reduces the effective coercive field (Ec) under identical electrical loading. Grain-resolved analysis reveals that this reduction arises from microstructure-assisted switching pathways and electrostatic coupling between layers. These findings demonstrate that vertical phase arrangement provides a viable strategy to engineer switching behavior in hafnia-based ferroic capacitors and highlight the importance of explicit microstructural resolution for quantitative phase-field modeling.
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All authors P. Pankaj, Sandeep Sugathan, Si Joon Kim, Pil-Ryung Cha
Strongly Correlated Electrons · Cross-listed from math-ph
Anomalies in quantum spin systems and Nielsen-Ninomiya type Theorems
Ruizhi Liu
We provide an algebraic perspective on Nielsen–Ninomiya-type no-go
theorems arising from group cohomological anomalies, revisiting in particular the version proved by Kapustin and Sopenko. Departing from their analytic proof, our approach emphasizes the algebraic structure of
symmetry actions and the local computability of anomaly indices. We demonstrate that this no-go
theorem is due to a fundamental algebraic incompatibility between anomaly data and the dimension of local
Hilbert spaces. Specifically, when an anomaly index is locally computable via quasi-local
unitary operators, a suitable gauge fixing trivializes their (generalized) determinants, imposing unexpected and nontrivial constraints on
lattice regularizations.
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