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Physics

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Friday 18 September

Earth and Planetary Astrophysics

Comparative analysis of Neural Networks approaches for Initial Orbit Determination of Near-Earth Objects

Francesco Geroni, Roberto Paoli, Riccardo Massidda et al. (+1 more)

Initial Orbit Determination (IOD) from Very Short Arcs (VSAs) remains one of the most challenging open problems in asteroid surveillance and celestial mechanics. Classical methods require angular observations spanning a sufficient fraction of the orbit, and become ill-conditioned or fail outright when only a single observing night is available, as is the case for most newly discovered Near-Earth Objects (NEOs). We present a comparative analysis of two Neural Network (NN) models that attack the ranging problem directly: both ingest a triplet of time-tagged angular measurements $(t_i,\alpha_i,\delta_i)$, $i=1,2,3$, from a single VSA and predict the geocentric range and range-rate $(\rho,\dot\rho)$, thus completing the orbital state vector. The first is a Multi-Layer Perceptron trained on a purely data-driven objective; the second augments it with a physics-informed loss. Both are trained, under an object-disjoint partition, on a sample of the $568\,127$ VSAs of $39\,031$ real NEOs available in the NEODyS-2 catalogue. Each model returns an estimate on every arc by construction, so we assess instead whether that estimate is dynamically admissible: on a held-out test set of $56\,773$ arcs the physics-informed model places $85.1\%$ of its predictions inside the admissible region, against $76.5\%$ for the data-driven baseline, whereas Gauss's and Laplace's methods return a solution on only $45.0\%$ and $47.3\%$ of the same arcs and collapse onto the degenerate root in about nine of those cases out of ten. A stratified analysis over proper motion and true range shows that the physics-informed objective is not uniformly superior to the baseline: it trades a longer error tail for admissibility and for a marked advantage on the fast, nearby arcs that are operationally the most relevant.
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All authors Francesco Geroni, Roberto Paoli, Riccardo Massidda, Giacomo Tommei

Chemical Physics

ReaxKit: A Modular Python Toolkit for Preparing, Parsing, and Analyzing ReaxFF Molecular Dynamics Simulations

Ali Mohammadi Dinani, Alireza Sepehrinezhad, Anirban Phukan et al. (+7 more)

Empirical reactive force field (RFF) molecular dynamics enables atomistic simulation of bond breaking, bond formation, charge redistribution, and structural evolution in chemically complex systems. The ReaxFF method is arguably the most popular and transferable of the currently available RFF methods. However, routine use of ReaxFF often requires substantial manual effort to prepare inputs, interpret engine-specific outputs, organize simulation artifacts, and develop custom analysis scripts, limiting reproducibility and scalability. Here, we present ReaxKit, a modular Python toolkit for preparing, parsing, analyzing, and managing ReaxFF molecular dynamics simulations. ReaxKit uses a separation-of-concerns architecture that distinguishes engine-specific input/output handling, canonical domain data models, scientific analysis, workflow orchestration, presentation, storage, and graphical interaction. Engine adapters convert outputs from supported simulation environments into typed, engine-independent data structures, allowing analysis modules to operate independently of native file formats. User requests are executed through consistent command-line, functional Python, and browser-based graphical interfaces, while a dedicated workspace preserves raw data, normalized datasets, analysis settings, results, logs, caches, and provenance information. Representative applications demonstrate the breadth of the toolkit, including automated generation of elastic and equation-of-state training data from Materials Project structures and mechanical properties, characterization of active sites and local structural environments, and execution of simulation campaigns through YAML-defined study workflows. These capabilities show that ReaxKit supports all essential stages of the ReaxFF workflow.
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All authors Ali Mohammadi Dinani, Alireza Sepehrinezhad, Anirban Phukan, Asma Ul Hosna, Jupjeet Dhingra, Mozhdeh Mirakhory, Seyed Mahmoud Mortazavi, Yun Kyung Shin, Swarit Dwivedi, Adri C.T. van Duin

Optics

Optical Mode Sorting with a Programmable Diffractive Neural Network

Qian Zhang, Shiyue Chen and Juergen W Czarske

Programmable diffractive optical processors are particularly attractive for spatial light manipulation because their optical transformations can be dynamically reconfigured and adapted without modifying the physical hardware. However, their practical performance is often limited by the gap between simulation and experiment caused by optical aberrations, alignment errors, and nonideal phase responses. In this paper, we introduce a hybrid optimization framework that combines high-dimensional numerical design with low-dimensional hardware-in-the-loop calibration, enabling programmable diffractive optical networks to compensate experimentally for mismatch without retraining their underlying optical transformations. We demonstrate a programmable optical diffractive neural network (ODNN) designed by back-propagation to spatially sort six linearly polarized modes supported by a multimode fiber. The experimental distortions are represented using a truncated Zernike basis with only 19 correction coefficients per layer. These coefficients are optimized directly on the physical system using stochastic parallel gradient descent, avoiding re-optimization of the full pixelated phase masks. Experimentally, the proposed calibration yields an SNR improvement of approximately 3.26 dB, and a decrease in amplitude error of 0.04. This separation of high-dimensional optical-function design from low-dimensional physical calibration provides a scalable route towards adaptive and reconfigurable spatial-mode processors for optical router on spatial modes and wavelengths, programmable photonic computer systems and quantum information processing.
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High Energy Physics (Phenomenology)

Charged lepton flavor violating decays and $(g-2)_{e_a}$ in an extended standard model with singlet and triplet leptoquarks

L.T. Hue, N.V. Hop, Vo Quoc Phong et al. (+1 more)

We study the anomalous magnetic moments of charged leptons and their lepton flavor-violating decays in a Standard Model extension containing one $SU(2)_L$singlet and one $SU(2)_L$ triplet scalar leptoquark. Our results reveal significant correlations among $\Delta a_{e,\mu}$ and the decay rates of $e_b\to e_a\gamma$, and $h,Z\to e_b e_a$. In particular, the branching ratios $\mathrm{Br}(e_b\to e_a\gamma)$ and $\mathrm{Br}(h,Z\to e_b e_a)$ exhibit significant correlations. The model cannot simultaneously accommodate sizable values of $|\Delta a_e|=\mathcal{O}(10^{-13})$ and $|\Delta a_\mu|=\mathcal{O}(10^{-10})$. For $|\Delta a_\mu|=\mathcal{O}(10^{-10})$ and $\mathrm{Br}(\mu \to e\gamma)>10^{-15}$, the decay rates are suppressed to $\mathrm{Br}(\tau \to e\gamma)<\mathcal{O}(10^{-12})$ and $\mathrm{Br}(h\to \tau e)<\mathcal{O}(10^{-6})$, while the remaining ones can reach the forthcoming experimental sensitivities. Conversely, for $|\Delta a_e|=\mathcal{O}(10^{-13})$, one obtains the suppressed decay rates $\mathrm{Br}(\tau \to \mu \gamma)<\mathcal{O}(10^{-11})$ and $\mathrm{Br}(h\to \tau \mu)<\mathcal{O}(10^{-7})$.
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All authors L.T. Hue, N.V. Hop, Vo Quoc Phong, N.H.T. Nha

Quantum Physics

Selection rules for pinned and quasipinned occupation numbers with degeneracy

Robin Reuvers

When the natural occupation numbers of a fermionic state saturate a generalized Pauli constraint, the state obeys a selection rule: only those configurations of natural orbitals that saturate the constraint themselves contribute. Pinning thus singles out an active space. The selection rule was proved for non-degenerate occupation numbers; for degenerate ones it was conjectured, and proved for one saturated constraint under an assumption checked only for the constraints known at the time. Here, it is proved for every generalized Pauli constraint, with no assumption, and also in the spin-adapted setting. The rule can only fail for the ordering constraints $\lambda_j\ge\lambda_{j+1}$. Several saturated constraints are served by one basis whenever their common zero face contains a non-degenerate point. In practice, occupation numbers are quasipinned rather than pinned, and the rule survives with an explicit error bound.
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Materials Science

Insights into the long-standing controversy over sound velocities in lizardite

Chenxing Luo, Timothy Liao, Hongjin Wang et al. (+1 more)

Serpentine minerals are abundant H-bearing phases in the upper mantle and play a central role in water transport in subduction zones. Lizardite is the low-temperature polymorph expected in cold slabs and shallow serpentinized mantle. Using an ab initio thermoelastic framework combining density-functional theory with the r2SCAN meta-GGA and the quasiharmonic approximation, we calculate its compression curve, elastic tensor, and acoustic velocities at 300 K. r2SCAN reproduces the measured compression curve and equilibrium volume to within 0.2%. Weak interlayer hydrogen bonding gives rise to pronounced axial softening, with $C_{33} \simeq 0.21C_{11}$ and $C_{44} \simeq 0.13C_{66}$ at 0 GPa. Solving the Christoffel equation over all propagation directions, we construct the velocity density of states (VelDOS), which reveals a high density of slow acoustic modes and other directional features obscured by Voigt-Reuss-Hill (VRH) aggregate averages. Reported experimental velocities preferentially sample the slower portion of this distribution rather than clustering near the VRH values, a correspondence consistent with subtle crystallographic texture or preferential orientation not resolved experimentally. Thus, the appropriate seismic-velocity endmember for lizardite depends on its orientational state, and reliance on VRH velocities alone may lead to overestimation of the degree of serpentinization when seismic observations preferentially sample slow crystallographic directions. Direction-resolved single-crystal measurements and aggregate measurements with independently quantified texture would provide direct tests of this interpretation.
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All authors Chenxing Luo, Timothy Liao, Hongjin Wang, Renata M. Wentzcovitch

Optics

All-Optical Control over Nonlocality for Ultrafast Image Processing with an Excitonic Metasurface

Bernardo S. Dias, Romain Tirole, Michele Guizzardi et al. (+4 more)

Image processing lies at the foundation of many modern technologies, such as augmented reality and autonomous driving, yet conventional digital approaches remain energy-intensive and limited in speed. Nonlocal metasurfaces - 2D structures engineered at the nanoscale to support delocalized, dispersion engineered resonances - provide a fast, energy-efficient and ultrathin platform to perform image processing directly on the light path. Introducing tunability in this platform is an outstanding challenge, and would enable dynamic real-time control over the implemented processing operation, facilitating flexible integration into adaptive and multifunctional photonic architectures. Here, we demonstrate optically tunable edge detection at ultrafast speeds by integrating a dielectric nonlocal metasurface with multilayer WS2, whose strong exciton-driven optical response enables dynamic control of the metasurface nonlocality at sub-ps speeds. Using resonant optical pumping of the A-exciton in WS2, the metasurface transfer function is rapidly switched from edge detection to bright-field imaging by tuning its spatial nonlocality. Operating in the visible spectral range at a wavelength around 700 nm, the device shows ultrafast switching times and reaches an amplitude modulation depth of 11.5 dB for normal incident light. This approach provides a reconfigurable, ultrathin, all-optical platform for adaptive optical computing systems and highlights the potential of the highly nonlinear properties of 2D materials for active metasurfaces at ultrafast speeds.
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All authors Bernardo S. Dias, Romain Tirole, Michele Guizzardi, Andrea Cordaro, Albert Polman, Andrea Alù, Jorik van de Groep

Quantum Physics

Microwave dielectric properties of LiNbO$_{\mathbf{3}}$ and AlN at millikelvin temperatures and single-photon power

Alessandro Reineri, Francesco Crisa, Maithlee Shinde et al. (+8 more)

Efficient bidirectional microwave-optical photon conversion is a key capability for scaling superconducting quantum processors into distributed networks. However, achieving the necessary conversion efficiency requires filling a critical knowledge gap in understanding the loss mechanisms of electro-optic materials. Here, we characterize the microwave properties of single-crystal bulk LiNbO3 and AlN over a broad range of powers, down to single-photon levels, and spanning from millikelvin temperatures to above 1 K. We demonstrate that both materials exhibit two-level systems (TLS) behavior, while piezoelectric-related losses are excluded. We show that TLS-induced dissipation is predominantly localized on the surface rather than being an intrinsic bulk property, a result further corroborated by room-temperature 3D XPS and time-of-flight SIMS analyses. These findings provide useful insights to engineer hybrid architectures that integrate bulk electro-optic crystals within superconducting cavities, proving that microwave quality factors compatible with high-efficiency microwave-optical transduction are within reach.
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All authors Alessandro Reineri, Francesco Crisa, Maithlee Shinde, Daniel Bafia, Akshay Murthy, Changqing Wang, Tanay Roy, Alexander Romanenko, John Zasadzinski, Anna Grassellino, Silvia Zorzetti

Mesoscale and Nanoscale Physics

Photogalvanic effect in monolayers of transition metal dichalcogenides

G.V. Budkin and E.L. Ivchenko

We present a theoretical study of photocurrents generated by direct optical transitions induced by linearly polarized radiation in monolayers of transition metal dichalcogenides. A microscopic theory of both the ballistic and shift contributions to the photocurrent is developed that accounts for Coulomb attraction between photoexcited electrons and holes. It is demonstrated that, in typical 2D semiconductors, the Coulomb correlation causes the ballistic contribution to dominate over the shift photocurrent.
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Soft Condensed Matter

Merons Mediate Re-Ordering of Curved Rods Under Shear Flow

Nicholas W. Hackney, Joel T. Clemmer, Thomas O'Connor et al. (+1 more)

Bent-core liquid crystals are a canonical example of a soft matter system whose behavior is controlled by a local preference for order that cannot be universally achieved. This geometric frustration, arising from the rod's curved shape, has been shown to stabilize a variety of equilibrium phases, such as the helically ordered nematic twist-bend phase ($N_{\rm TB}$). Unlike a traditional nematic, the twist-bend state has 1D translational order arising from a periodic rotation of bend orientation along the helical axis. Here, we use molecular dynamics simulations to study the effect of shearing the $N_{\rm TB}$ phase along directions parallel and perpendicular to the helical axis. In the case of shear perpendicular to the helical axis, the nematic twist-bend phase is stable and flows without disordering. Conversely, shear along the helical axis disrupts order and leads to the emergence of fractionally charged Skyrmion defects, i.e. merons. These defects act as topological machines, locally rotating rods into a re-ordered and stable orientation of the $N_{\rm TB}$ phase. These findings reveal a new mechanism to create and control merons and highlight the potential application of bent-core liquid crystals in designing functional material with specific optical and computational properties.
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All authors Nicholas W. Hackney, Joel T. Clemmer, Thomas O'Connor, Gary S. Grest

High Energy Physics (Phenomenology)

Searching for Axions from Atmospheric Kaon Decays

Tousif Raza

Cosmic-ray interactions in the Earth's atmosphere produce copious secondary mesons, providing a natural laboratory for searches for new physics. We investigate the atmospheric production of axions through the rare kaon decay $K^{+}\rightarrow\pi^{+}a$. If sufficiently long-lived, these axions can reach large underground detectors such as Super-Kamiokande and IceCube and decay through the diphoton channel, $a\rightarrow\gamma\gamma$. Using data from Super-Kamiokande and IceCube, we derive constraints on the axion decay constant $f_a$ for masses up to $m_a\sim 350~\mathrm{MeV}$. We demonstrate that atmospheric kaon decays provide a novel probe of axion parameter space, yielding constraints complementary to existing bounds.
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General Relativity and Quantum Cosmology

Light bending and observational bounds in dyonic Kalb-Ramond gravity

A. A. Araújo Filho

We investigate the weak and strong gravitational lensing of a dyonic black hole in Kalb-Ramond gravity. After fixing the asymptotic normalization, we distinguish the effective charge governing the local null trajectories from the global angular identification associated with Lorentz-symmetry breaking. In the weak-deflection regime, we evaluate the Gaussian curvature explicitly and apply the Gauss-Bonnet theorem with a perturbed ray boundary, recovering the complete second order mass contribution. Independent calculations based on the orbit equation, the turning point integral, and Fermat's principle reproduce the same bending angle. In the strong-deflection regime, Tsukamoto's method yields closed expressions for both strong-deflection coefficients, with exact charge dependence. We derive finite-distance lens equations and the associated image positions, magnifications, flux ratios, and differential arrival times, retaining the physical winding condition. Shadow sizes inferred from observations of Sgr~A$^*$ and M87$^*$ yield conditional charge bounds, complemented by an estimate from S2 precession. We further construct combinations of strong-lensing observables that separate the effective charge from the conical parameter within the model: angular separation and relative brightness remove the explicit winding dependence, while a timing ratio incorporating an independent distance estimate isolates the conical deformation.
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Materials Science

PAOFLOW: an automated suite for ab initio electronic, transport, and topological properties of materials

Anooja Jayaraj, Sergio Alvarruiz, Mia Falatko et al. (+10 more)

High-throughput first-principles property calculations are often constrained by costly post-processing and dense Brillouin-zone sampling, impeding the creation of large, internally consistent materials-property datasets and limiting AI-driven discovery workflows. Pseudo-atomic-orbital (PAO) Hamiltonians provide an exact tight-binding representation of first-principles electronic structure that enables the calculation of a wide range of electronic, optical, topological, and transport properties at negligible cost, thereby supporting scalable generation of training-quality data and AI-ready data infrastructures. In this work, we present PAOFLOW 3.0 – an open-source Python suite that automates the construction and analysis of PAO Hamiltonians from plane-wave density functional theory calculations performed with either Quantum ESPRESSO or VASP. The resulting Hamiltonians enable efficient electronic structure interpolation, Fermi surface analysis, optical and dielectric response, transport coefficients, Berry phase and topological quantities, quantum transport, and other materials properties. Compared with previous releases, PAOFLOW 3.0 substantially extends the scope of the package through the introduction of internal projections enabling support for VASP calculations, self-consistent Hubbard U and V corrections obtained using ACBN0 and eACBN0 methods, generation of environment-dependent Slater-Koster tight-binding models, Landauer–BÃŒttiker quantum transport, and calculation of quantum oscillations using the integrated PySKEAF module. The theoretical foundations and the software architecture are presented together with representative calculations illustrating the current capabilities of the package.
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All authors Anooja Jayaraj, Sergio Alvarruiz, Mia Falatko, Zhiren He, Jonathan Red, Caua F. Schuch, Karma Tenzin, Chao Chen Ye, Davide Ceresoli, Marcio Costa, Stefano Curtarolo, Jagoda Slawinska, Marco Buongiorno Nardelli

Astrophysics of Galaxies

Stochastic black hole growth tracks stellar mass in ultramassive galaxies

Michele Cappellari, Dieu D. Nguyen and Susan A. Kassin

Over the past three decades, it has been established that galaxy spheroids contain supermassive black holes (BHs) whose masses correlate tightly with the properties of their host galaxies. The most predictive of these correlations is between BH mass and stellar velocity dispersion (the $M_{\rm BH}-\sigma$ relation), alongside a relation with bulge luminosity or stellar mass (the $M_{\rm BH}-M_\star$ relation). Theoretical models of galaxy evolution predict that for the most massive galaxies, whose late-time growth proceeds mainly via gas-poor `dry' mergers, $M_\star$ should become a better predictor of BH mass than $\sigma$. However, genuine deviations from the $M_{\rm BH}-\sigma$ relation have remained difficult to observe due to the extreme rarity and low central surface brightness of such galaxies. Here we report James Webb Space Telescope (JWST) measurements of central BHs in a sample of eight ultramassive galaxies. We find the largest deviations from the $M_{\rm BH}-\sigma$ relation ever reported, with most BH masses exceeding $10^{10}$ solar masses. In this extreme mass regime, the galaxies tightly follow the $M_{\rm BH}-M_\star$ relation with minimal scatter, successfully confirming theoretical predictions. Furthermore, we observe significant stochasticity: For one ultramassive galaxy, the central dispersion drops rather than peaks, revealing no evidence for a central mass; while we can formally only place an upper limit, the data are entirely consistent with no BH at all. Crucially, this physical dichotomy is already evident directly in the raw kinematic maps prior to any fitting, and is robustly confirmed by our dynamical modelling. This unexpected diversity suggests that extreme multi-body dynamical processes, such as gravitational recoil or three-body ejections, significantly disrupt BH growth in the Universe's most massive galaxies.
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Astrophysics of Galaxies

The JWST Ultramassive Galaxy Sample – II. Supermassive Black Hole Masses for 8 Extreme Early-Type Galaxies via Jeans Anisotropic Modelling of High-Resolution Integral-Field NIRSpec Stellar Kinematics

Michele Cappellari, Dieu D. Nguyen and Susan A. Kassin

We present central supermassive black hole (BH) mass measurements for the JWST Ultramassive Galaxy Sample, comprising 8 galaxies selected from a complete sample of the most massive early-type galaxies in the nearby Universe ($M_\star \gtrsim 2\times10^{12} M_\odot$). Building on the MGE photometric profiles and JWST/NIRSpec stellar kinematics from Paper I, we use the Jeans Anisotropic Modelling (JAM) framework to reconstruct the nuclear dynamics. Given the unique structural properties of these dry-merger-dominated systems, our Bayesian MCMC analysis explicitly tests both oblate and prolate intrinsic geometries. By marginalizing over classical dynamical degeneracies (including orbital velocity anisotropy, mass-to-light ratios, and inclination), we extract robust BH masses. We demonstrate that JWST's exceptional resolution allows JAM to tightly constrain the central potential using nuclear kinematics alone. Crucially, not all ultramassive galaxies host ultramassive BHs: while most display a classic central velocity dispersion peak, notable exceptions emerge, including a clear central dispersion drop in one galaxy and a subdued peak in another. These kinematic differences yield distinct BH masses, suggesting BH growth at extreme mass scales is highly stochastic. This stochasticity may be driven by three-body ejections during hierarchical mergers or gravitational recoil kicks from coalescing binaries. In the latter case, the kicked BH may be displaced and wandering outside the compact NIRSpec field of view. Our derived BH masses populate the historically sparse upper envelope of the galaxy mass hierarchy, providing the critical foundation for Paper III to investigate extreme-mass BH scaling relations and test models of galaxy-BH co-evolution.
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Astrophysics of Galaxies

The JWST Ultramassive Galaxy Sample – I. Overview, Photometry, and Stellar Kinematics: Selecting Optimal Template Subsets via Non-Negative Matrix Factorization

Michele Cappellari, Dieu D. Nguyen and Susan A. Kassin

We introduce the JWST Ultramassive Galaxy Sample, comprising 8 extreme early-type galaxies ($M_\star \gtrsim 2\times10^{12}\,\mathrm{M}_\odot$) drawn as a representative subset from a comprehensive full-sky census of over 100 such objects. This program aims to dynamically measure their central supermassive black holes (BHs) to probe the extreme high-mass end of BH–galaxy scaling relations, a critical regime where the physical mechanisms governing BH growth and host-galaxy co-evolution are expected to fundamentally change. In this first paper, we present the foundational data products: detailed photometric models and spatially resolved nuclear stellar kinematics. To accurately map the stellar mass distribution from the BH sphere of influence out to the extended halo, we combine diffraction-limited JWST/NIRCam imaging with wide-field DESI Legacy Surveys data, parametrizing the surface brightness using Multi-Gaussian Expansion (MGE). We extract stellar kinematics from JWST/NIRSpec integral-field observations using the penalized pixel-fitting (pPXF) method. To fully exploit the continuous $1.66-3.17\,\mu\mathrm{m}$ wavelength coverage—avoiding the telluric gaps of ground-based empirical libraries and the computational burden of massive theoretical grids—we introduce the use of near-separable Non-Negative Matrix Factorization (NMF). This algorithm identifies an optimal, highly compressed subset of synthetic spectra from the updated BOSZ library, perfectly capturing its spanning power at a fraction of the computational cost. The resulting kinematic maps reveal that these ultramassive systems are overwhelmingly slow rotators, frequently harboring kinematically decoupled cores. These high-quality photometric and kinematic data provide the inputs required for the robust Jeans Anisotropic Modelling (JAM) of the central BH masses in Paper II.
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Strongly Correlated Electrons

Unified Field Bosonization Technique for strongly inhomogenous Luttinger Liquids

Soundarya P, Venkata Suryanarayana M and Joy Prakash Das

We introduce the Unified Field Bosonization Technique (UFBT), a direct bosonization framework for strongly inhomogeneous one-dimensional Luttinger liquids (LLs) containing static impurities. UFBT incorporates impurity scattering through a symmetrized combination of bosonic phase fields and yields closed-form expressions for arbitrary N-point correlation functions for a broad class of static impurity potentials, including delta barriers, finite barriers and finite wells. The formalism requires neither renormalization-group analysis nor perturbative expansions, providing an analytical description of the inhomogeneous system at the bosonized level. The resulting correlation functions capture the leading singular contributions relevant to the present analysis. The technique is validated by recovering known limiting cases, showing agreement with the first-order perturbative expansion in the interaction strength, and demonstrating consistency with the Schwinger-Dyson equations. A key result is that the correlation function exponents remain independent of the impurity strength, while the impurity dependence is captured by the spatial structure and amplitudes of the correlation functions. The resulting correlation functions establish a foundation for analytical studies of transport, Friedel oscillations, and the local and dynamical density of states in strongly inhomogeneous Luttinger liquids.
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Mathematical Physics · Cross-listed from math.PR

A variational approach for the 2D Abelian Yang-Mills-Higgs measure

Nikolay Barashkov, Ajay Chandra, Ilya Chevyrev et al. (+2 more)

We use the Boué-Dupuis variational method to construct the Abelian Yang-Mills-Higgs measure on the two-dimensional torus with polynomial Higgs potentials, giving, to our knowledge, the first rigorous construction of an interacting gauge theory by this approach. We first use the variational method to construct the Higgs field conditioned on the gauge field, with a covariant Gaussian free field as the reference measure. Integrating out the Higgs field produces a weight on the gauge field, which we control through a second application of the variational method. We also prove new exponential integrability estimates for the joint gauge-Higgs field and establish gauge covariance. Finally, we prove convergence of the Laplace transforms of the regularised measures and establish a new large-deviation principle for gauge-invariant observables in the semiclassical limit.
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All authors Nikolay Barashkov, Ajay Chandra, Ilya Chevyrev, Andreas Koller, Abdulwahab Mohamed

Chemical Physics

Development of a Non-Empirical Exchange-Hole Dipole Moment Dispersion Model

Alastair J. A. Price and Alberto Otero-de-la-Roza

The inclusion of dispersion effects is important in density-functional theory (DFT) to model non-covalent interactions correctly, a task that is essential in many applications of the theory. Many dispersion functionals have been proposed in the past. The exchange-hole dipole moment (XDM) model combines the simplicity of a damped pairwise asymptotic expression for the dispersion energy with a theory-grounded approach to calculate the dispersion coefficients. XDM is, arguably, the most accurate dispersion correction for the description of molecular crystals and it has been thoroughly tested for other applications across a wide range of chemistries. Here, we address the two main shortcomings of XDM. First, XDM relies on the use of experimentally determined free-atom polarizabilities. Second, because the XDM atom-in-molecule properties (volumes, polarizabilities, exchange-hole dipole moments) use the Hirshfeld partition method, XDM describes systems with large atomic partial charges, like alkali cations or halide anions, poorly. We propose neXDM, a non-empirical variant of XDM that removes the experimental parameters by using the Kirkwood polarizability formula, thereby making neXDM a pure meta-GGA dispersion functional. In addition, following previous work by Bučko et al. on the similar Tkatchenko–Scheffler (TS) method, we replace the Hirshfeld partitioning with its iterative counterpart. The performance of neXDM is shown to be on par with XDM in standard molecular and crystal benchmark sets, and greatly improves the modeling of ionic systems. The new neXDM method sets a new record for the best dispersion-corrected generalized-gradient approximation (GGA) functional for molecular crystal lattice energies in the X23 set (0.700~kcal/mol).
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Strongly Correlated Electrons

Machine learning magnetic interactions from neutron powder diffraction data

Adit S. Desai, Yongqiang Cheng and Joseph A. M. Paddison

Neutron diffraction is a versatile experimental technique capable of probing a material's magnetic properties. While diffraction is typically used to determine the magnetic structure of a material, magnetic diffuse scattering data from a diffraction experiment are also sensitive to the magnetic interactions in its Hamiltonian. However, accurately determining magnetic interaction parameters from neutron-scattering data involves an inverse scattering problem that is challenging to solve in general. Here, we investigate the effectiveness of a machine learning approach to predict the interaction parameters given magnetic diffuse-scattering data measured on powder samples, for a comprehensive survey of isotropic interactions on eight high-symmetry lattices. Across all lattices we considered, the machine-learning approach estimates the interaction parameters with high (~2%) accuracy, while avoiding the issue of false minima that is encountered with non-linear least squares refinement. Our results highlight that powder diffuse-scattering data can provide a compact "fingerprint" of the magnetic interactions for many materials.
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Mathematical Physics · Cross-listed from math.AP

2D Torus defocusing NLSE with a potential and random initial data

Nicolas Lindstrom

We consider the non-linear cubic defocusing Schrödinger equation on the 2D Torus ($T^2$) with a potential $V(x)\in H^{2^+}(T^2)$. The initial data, $u_0$,is given by a centered gaussian variable with covariance $(-\Delta+V)^{-1}$, and thus is almost surely in $H^{0^-}(T^2)$. We show that it is almost surely well-possed for all time in the weak sense, and that $u-e^{it(\Delta -V)}u_0$ is in $H^{s}(T^2)$ for some $s>0$, and that the solution is the limit of the solutions to the truncated equation. This result is a generalization of the results first given by Bourgain in Invariant Measures for the {2D}-Defocusing Nonlinear {Schrödinger} Equation.
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Soft Condensed Matter

Active colloidal rafts perform swimming strokes that propel their host droplets

Airi N. Kato, Julien Brémont, Etienne Harté et al. (+3 more)

Active particles confined in droplets can set their host droplet into motion. This phenomenon is usually attributed to direct hydrodynamic forcing by the enclosed particles. Here we reveal a different mechanism: we show that a self-propelled raft of active colloids confined in a thin oil droplet at the surface of water typically follows an off-centered orbit, thus periodically deforming the droplet's contact line in an anisotropic way. This non-reciprocal deformation acts as a swimming stroke and propels the droplet according to the principles of low-Reynolds-number swimming. The effect is absent for a single colloid and arises from the intrinsically many-body dynamics of the raft, which we capture with a dynamical model coupling viscous hydrodynamics and many-body active dynamics. Our results show how collective internal activity can be converted into locomotion through deformation of a soft confining boundary.
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All authors Airi N. Kato, Julien Brémont, Etienne Harté, Jean-Michel Rampnoux, Jean-François Joanny, Hamid Kellay

Quantum Physics

Single-atom-based asynchronous photonic interconnect for scalable modular quantum computing

Jérémy Raskop, Nadav Kandel, Geva Arwas et al. (+6 more)

Scaling quantum computation beyond the capacity of a single quantum processing unit requires quantum interconnects between modular processors. Optical photons are natural carriers for distributing entanglement between these processors. Most loss-resilient protocols use photonic Bell-state measurements based on the linear-optics type-II fusion gate. The resulting entanglement rate scales quadratically with each processor's typically low photon-delivery probability. Here we analyze a memory-assisted quantum interconnect using a near-deterministic, robust photon–atom controlled-$Z$ gate via a single atom trapped in a high-finesse cavity. Detecting and measuring a photon from one processor heralds entanglement between that processor and the atom. This entanglement is preserved while the process repeats with the second processor until the second photon is detected and measured. Reading out the atomic qubit finalizes the entanglement between the processors. As the entanglement is mediated by the atom, the photons from both processors do not need to be indistinguishable, removing a major source of infidelity. Furthermore, by removing the simultaneous photon-arrival requirement, the protocol allows the entanglement rate to scale linearly rather than quadratically with photon-arrival probability over a wide parameter range. We derive entanglement rates under realistic parameters, accounting for decay of the atom's entanglement with the first processor and for decoherence caused by unheralded photon interactions. The nanosecond-scale of the gate and read-out operations leads to orders-of-magnitude entanglement-rate gain over linear optics, removing a key bottleneck in modular quantum computing.
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All authors Jérémy Raskop, Nadav Kandel, Geva Arwas, Yaniv Amichy, Yaron Jarach, Tal Kanonich, Andrei Militaru, Johannes Fink, Barak Dayan

Optics

Momentum microscopy of a holey nanostructure

Kerstin Harland, Julia Altenburg, Xiaofei Wu et al. (+10 more)

Momentum microscopy records the three-dimensional momentum distribution of photoelectrons emitted from a solid sample and, by utilizing sufficiently high photon energies in the ultraviolet spectral range, offers direct access to the electronic band structure of a material. By employing a pump-probe scheme, this method provides a femtosecond view of light-matter interaction and the subsequent relaxation and transport dynamics in a broad range of material systems. However, momentum microscopy has so far been mostly limited to flat and spatially extended surfaces. Photoelectron emission from different three-dimensional facets, in combination with inhomogeneous electric fields around these structures, makes the analysis of the momentum distribution significantly more challenging. Here, we extend the state-of-the-art to a substantially more complex structure and show that a careful analysis of the electron distribution recorded with a momentum microscope provides rich information about both the spatial and momentum distributions on a few-nm and few-mÅ$^{-1}$ scale, respectively. Combined with prior knowledge of the three-dimensional structure, momentum-resolved photoelectrons can be assigned to nano-localized emission spots, permitting a new level of insight into spatio-temporal charge carrier dynamics.
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All authors Kerstin Harland, Julia Altenburg, Xiaofei Wu, Zsuzsanna Pápa, Leon David Schwarz, Lina Hansen, Katrin Meier, Arvid Klösgen, Bert Hecht, Germann Hergert, Péter Dombi, Jer-Shing Huang, Jan Vogelsang

Plasma Physics

Azimuthal mode decomposition Particle in Cell algorithm for cylindrical plasma sources

Matteo Ripoli, Eduardo Ahedo and Mario Merino

An efficient Particle-in-Cell numerical approach to perform full-dimensional kinetic simulations of low temperature plasmas is presented. Taking advantage of the cylindrical geometry of most plasma sources, a Fourier mode decomposition of the fields is carried out in the azimuthal ($\theta$) direction up to a chosen maximum number of modes $N_m$. Macroparticles are pushed in all $D$ dimensions and weighed, for each mode $m$, onto a $(D-1)$ dimensional grid. The computation of the electric field for each mode is independent and reduces to solving $(N_m+1)$ $(D-1)$ dimensional Poisson problems. The approach brings spectral accuracy in the azimuthal direction, while the computational cost is comparable to that of a simulation with $(D-1)$ dimensions. We verify this approach against a planar test case based on a Penning discharge, widely used for benchmarking and validation purposes in the low-temperature plasma community. Our approach allows us to reduce the 2D problem into a collection of coupled 1D problems and to naturally perform spectral analysis of the different azimuthal modes, recovering the contribution of each mode to radial transport, with a computational time saving of one order of magnitude with respect to state of the art 2D particle-in-cell codes.
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High Energy Physics (Experiment)

Test of lepton flavor universality with $\bar{B} \rightarrow D^{(*)} \tau^{-} \bar{\nu}_{\tau}$ and $\bar{B} \rightarrow D^{(*)} \ell^{-} \bar{\nu}_{\ell}$ decays at Belle II

Belle II Collaboration: M. Abumusabh, I. Adachi, K. Adamczyk et al. (+494 more)

We test lepton flavor universality with a measurement of the branching-fraction ratios $R(D^{(*)}) \equiv \mathcal{B}(\bar{B} \rightarrow D^{(*)} \tau^{-} \bar{\nu}_{\tau})/\mathcal{B}(\bar{B} \rightarrow D^{(*)} \ell^{-} \bar{\nu}_{\ell})$, where $\ell$ denotes an electron or muon. The analysis uses $387\times 10^6$ $\Upsilon(\mathrm{4S})$ decays collected with the Belle II detector in energy-asymmetric $e^+e^-$ collisions. One $B$ meson is fully reconstructed in a hadronic decay mode, while the other is reconstructed either in $\bar{B}\rightarrow D^{(*)}\tau^{-}\bar{\nu}_{\tau}$, with $\tau^- \rightarrow \ell^- \bar{\nu}_{\ell}\nu_{\tau}$, or in $\bar{B}\rightarrow D^{(*)}\ell^{-}\bar{\nu}_{\ell}$. We extract the signal from the distributions of the residual calorimeter energy and the squared mass of the undetected particles, obtaining $R(D^{*}) = 0.242 \pm0.019(\mathrm{stat}) \pm0.016(\mathrm{syst})$ and $R(D) = 0.439 \pm 0.055(\mathrm{stat}) \pm 0.046(\mathrm{syst})$. These results are consistent with both the standard model predictions and previous measurements, and constitute the most precise determination of $R(D^{(*)})$ with hadronic tagging.
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All authors Belle II Collaboration: M. Abumusabh, I. Adachi, K. Adamczyk, A. Aggarwal, L. Aggarwal, H. Ahmed, Y. Ahn, H. Aihara, M. Akdag, N. Akopov, A. Akram, S. Alghamdi, M. Alhakami, A. Aloisio, N. Althubiti, K. Amos, M. Angelsmark, N. Anh Ky, C. Antonioli, K. Arai, D. M. Asner, H. Atmacan, T. Aushev, V. Aushev, R. Ayad, V. Babu, H. Bae, N. K. Baghel, S. Bahinipati, P. Bambade, Sw. Banerjee, S. Bansal, M. Barrett, M. Bartl, J. Baudot, A. Baur, A. Beaubien, F. Becherer, J. Becker, J. V. Bennett, F. U. Bernlochner, V. Bertacchi, M. Bertemes, E. Bertholet, M. Bessner, S. Bettarini, V. Bhardwaj, B. Bhuyan, F. Bianchi, T. Bilka, A. Biswas, D. Biswas, A. Bobrov, D. Bodrov, A. Bondar, G. Bonvicini, J. Borah, A. Boschetti, A. Bozek, M. Bračko, P. Branchini, R. A. Briere, T. E. Browder, A. Budano, S. Bussino, F. Callet, Q. Campagna, M. Campajola, L. Cao, M. Carminati, G. Casarosa, C. Cecchi, M.-C. Chang, P. Chang, P. Cheema, L. Chen, B. G. Cheon, C. Cheshta, H. Chetri, K. Chilikin, K. Chirapatpimol, H.-E. Cho, K. Cho, S.-J. Cho, S.-K. Choi, S. Choudhury, S. Chutia, J. Cochran, J. A. Colorado-Caicedo, I. Consigny, L. Corona, H. Crotte Ledesma, S. Cuccuini, J. X. Cui, L. Damer, E. De La Cruz-Burelo, S. A. De La Motte, G. de Marino, G. De Nardo, G. De Pietro, R. de Sangro, M. Destefanis, S. Dey, R. Dhayal, A. Di Canto, J. Dingfelder, Z. Doležal, I. Domínguez Jiménez, T. V. Dong, X. Dong, M. Dorigo, K. Dugic, G. Dujany, P. Ecker, D. Epifanov, J. Eppelt, R. Farkas, P. Feichtinger, T. Ferber, T. Fillinger, C. Finck, G. Finocchiaro, F. Forti, A. Frey, B. G. Fulsom, A. Gabrielli, P. Gagneja, A. Gale, E. Ganiev, M. Garcia-Hernandez, R. Garg, A. Garmash, L. Gärtner, G. Gaudino, V. Gaur, V. Gautam, A. Gaz, P. Gebeline, A. Gellrich, G. Ghevondyan, D. Ghosh, H. Ghumaryan, G. Giakoustidis, R. Giordano, A. Giri, P. Gironella Gironell, A. Glazov, B. Gobbo, R. Godang, O. Gogota, P. Goldenzweig, W. Gradl, E. Graziani, D. Greenwald, Y. Guan, K. Gudkova, I. Haide, H. Haigh, Y. Han, K. Hara, K. Hayasaka, H. Hayashii, S. Hazra, C. Hearty, M. T. Hedges, A. Heidelbach, G. Heine, I. Heredia de la Cruz, M. Hernández Villanueva, T. Higuchi, M. Hoek, M. Hohmann, R. Hoppe, P. Horak, X. T. Hou, C.-L. Hsu, A. Huang, T. Humair, T. Iijima, K. Inami, G. Inguglia, N. Ipsita, A. Ishikawa, R. Itoh, M. Iwasaki, P. Jackson, D. Jacobi, W. W. Jacobs, E.-J. Jang, Q. P. Ji, S. Jia, Y. Jin, A. Johnson, K. K. Joo, H. Kakuno, M. Kaleta, J. Kandra, K. H. Kang, S. Kang, G. Karyan, T. Kawasaki, F. Keil, C. Ketter, M. Khan, C. Kiesling, C. Kim, D. Y. Kim, H. Kim, J.-Y. Kim, K.-H. Kim, H. Kindo, K. Kinoshita, P. Kodyš, T. Koga, S. Kohani, K. Kojima, H. Korandla, A. Korobov, S. Korpar, E. Kovalenko, R. Kowalewski, M. Krein, P. Križan, P. Krokovny, T. Kuhr, Y. Kulii, D. Kumar, J. Kumar, R. Kumar, K. Kumara, T. Kunigo, S. Kurokawa, B. Kutsenko, A. Kuzmin, Y.-J. Kwon, S. Lacaprara, T. Lam, L. Lanceri, J. S. Lange, T. S. Lau, M. Laurenza, R. Leboucher, F. R. Le Diberder, H. Lee, M. J. Lee, C. Lemettais, P. Leo, P. M. Lewis, C. Li, H.-J. Li, L. K. Li, Q. M. Li, S. X. Li, W. Z. Li, Y. Li, Y. B. Li, Y. P. Liao, J. Libby, J. Lin, S. Lin, Z. Liptak, V. Lisovskyi, A. Little, G. Liu, M. H. Liu, Q. Y. Liu, Y. Liu, Z. Q. Liu, D. Liventsev, S. Longo, A. Lozar, T. Lueck, C. Lyu, J. L. Ma, Y. Ma, M. Maggiora, S. P. Maharana, R. Maiti, G. Mancinelli, R. Manfredi, E. Manoni, M. Mantovano, D. Marcantonio, S. Marcello, M. Marfoli, C. Marinas, C. Martellini, A. Martens, T. Martinov, L. Massaccesi, M. Masuda, J. Materne, T. Matsuda, K. Matsuoka, D. Matvienko, S. K. Maurya, M. Maushart, F. Mawas, J. A. McKenna, Z. Mediankin Gruberová, R. Mehta, F. Meier, D. Meleshko, M. Merola, C. Miller, M. Mirra, K. Miyabayashi, H. Miyake, R. Mizuk, G. B. Mohanty, S. Moneta, A. L. Moreira de Carvalho, H.-G. Moser, N. Mudgal, Th. Muller, H. Murakami, R. Mussa, I. Nakamura, K. R. Nakamura, M. Nakao, H. Nakayama, Y. Nakazawa, M. Naruki, Z. Natkaniec, A. Natochii, M. Nayak, M. Neu, M. Niiyama, S. Nishida, R. Nomaru, A. Novosel, S. Ogawa, R. Okubo, H. Ono, Y. Onuki, I. Ostrowski, F. Otani, P. Pakhlov, G. Pakhlova, A. Panta, S. Pardi, K. Parham, J. Park, K. Park, S.-H. Park, A. Passeri, S. Patra, S. Paul, T. K. Pedlar, R. Pestotnik, M. Piccolo, L. E. Piilonen, P. L. M. Podesta-Lerma, T. Podobnik, L. Polat, A. Prakash, V. Prasad, C. Praz, S. Prell, E. Prencipe, M. T. Prim, S. Privalov, I. Prudiiev, H. Purwar, P. Rados, S. Raiz, V. Raj, K. Ravindran, J. U. Rehman, M. Reif, S. Reiter, M. Remnev, L. Reuter, D. Ricalde Herrmann, I. Ripp-Baudot, G. Rizzo, S. H. Robertson, J. M. Roney, A. Rostomyan, N. Rout, G. Russo, S. Saha, L. Salutari, D. A. Sanders, S. Sandilya, L. Santelj, C. Santos, V. Savinov, B. Scavino, C. Schmitt, J. Schmitz, S. Schneider, G. Schnell, M. Schnepf, K. Schoenning, C. Schwanda, A. J. Schwartz, Y. Seino, K. Senyo, J. Serrano, M. E. Sevior, C. Sfienti, W. Shan, G. Sharma, C. P. Shen, X. D. Shi, T. Shillington, T. Shimasaki, J.-G. Shiu, D. Shtol, A. Sibidanov, F. Simon, J. B. Singh, J. Skorupa, R. J. Sobie, M. Sobotzik, A. Soffer, A. Sokolov, E. Solovieva, W. Song, S. Spataro, K. Špenko, B. Spruck, M. Starič, P. Stavroulakis, S. Stefkova, R. Stroili, M. Sumihama, K. Sumisawa, N. Suwonjandee, M. Takahashi, M. Takizawa, U. Tamponi, S. Tanaka, S. S. Tang, K. Tanida, F. Tenchini, F. Testa, A. Thaller, T. Tien Manh, O. Tittel, R. Tiwary, E. Torassa, K. Trabelsi, F. F. Trantou, I. Tsaklidis, M. Uchida, I. Ueda, E. Uenlue, T. Uglov, K. Unger, Y. Unno, K. Uno, S. Uno, P. Urquijo, Y. Ushiroda, S. E. Vahsen, R. van Tonder, K. E. Varvell, M. Veronesi, A. Vinokurova, V. S. Vismaya, L. Vitale, V. Vobbilisetti, R. Volk, R. Volpe, M. Wakai, S. Wallner, M.-Z. Wang, X. L. Wang, A. Warburton, M. Watanabe, S. Watanuki, C. Wessel, J. Wiechczynski, E. Won, X. P. Xu, B. D. Yabsley, S. Yamada, W. Yan, W. Yan, J. Yelton, K. Yi, J. H. Yin, K. Yoshihara, C. Z. Yuan, J. Yuan, L. Zani, F. Zeng, B. Zhang, X. Zhao, V. Zhilich, J. S. Zhou, Q. D. Zhou, X. Y. Zhou, L. Zhu, R. Žlebčík

Quantum Physics

Guiding Agents of Quantum Games to Equilibrium using Matrix Exponential Fixed-Point Iteration

Alireza Habibi, Luis F. Abanto Leon and Setareh Maghsudi

In recent years, quantum game theory has gained significant attention as a framework for studying decision-making in multi-agent systems using quantum principles. However, computing equilibrium strategies is challenging because the dimension of the joint Hilbert space grows as the product of the players' local dimensions. In this paper, we consider an extended Gutoski-Watrous (EGW) game in which each player's quantum strategy is represented by a local density matrix. We derive tensor-contraction expressions for the payoff functions and their gradients, thereby avoiding the explicit construction of the full joint density matrix and its computationally expensive multiplication by the payoff operators. Building on the resulting effective Hamiltonians, we propose the Matrix Exponential Fixed-Point Iteration with Annealing (MEFPIA) algorithm to search for equilibrium points in EGW games. We compare MEFPIA with the Matrix Multiplicative Weights Update (MMWU) algorithm in terms of convergence. For the tested instances and parameter settings, both algorithms approach the same strategy profiles and payoffs, while MEFPIA achieves lower relative error in fewer iterations. These results indicate that MEFPIA is a promising numerical method for equilibrium search in multi-agent quantum games. Our findings provide important insights into the quantum game theory's potential for addressing complex decision-making processes, as well as opening up new paths for future research and exploration in multi-agent quantum systems.
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Astrophysics of Galaxies

Stellar Yields of Rapidly Rotating Population III Stars for the High Redshift Universe

Devesh Nandal, Konstantinos Topalakis, Vasilisa Sergienko et al. (+6 more)

JWST has revealed rapid nitrogen enrichment in high redshift galaxies, renewing the need for stellar yields that follow metal free stars beyond the main sequence and across their final fates. We present Geneva stellar evolution models of rapidly rotating Pop~III stars with $5 \leq M_{\rm ini}/M_\odot \leq 200$ and $\upsilon_{\rm ini}/\upsilon_{\rm crit}=0.7$, evolved to the end of core O-burning. We calculate gross adopted ejecta masses using fate dependent remnant prescriptions spanning core collapse, pulsational pair instability, and complete pair instability. Our quantitative results focus on hydrostatically produced CNO material, while heavier species are treated as final-model reservoirs. Rotation produces primary CNO material by mixing newly synthesized C and O into H-burning layers, where CNO cycling generates nitrogen. The resulting abundance signature depends strongly on which stellar layers escape. Models leaving compact remnants can reach $\log({\rm N/O})=-0.49$ while remaining poor in Si/S/Ar/Ca-rich material. PISN models eject the largest nitrogen masses, $M_{\rm N}=1.8$–$2.5,M_\odot$, but also release $57$–$65,M_\odot$ of oxygen, lowering $\log({\rm N/O})$ to $-1.44$ to $-1.29$. Thus, high nitrogen yields do not imply high N/O ratios. This trend persists after IMF weighting, as increasingly top-heavy populations add oxygen and deep alpha material faster than they build a nitrogen dominated mixture. Our grid provides a new CNO-focused prompt-enrichment dataset for interpreting nitrogen-rich systems including GN-z11, CEERS-1019, and GS~3073.
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All authors Devesh Nandal, Konstantinos Topalakis, Vasilisa Sergienko, Doga Eker, Efe K. Celep, Danielle A. Berg, Daniel J. Whalen, Sophie Tsiatsiou, Raphael Hirschi

Mathematical Physics · Cross-listed from math.PR

Independence Threshold for Collision Times of Many Planar Random Walks

Ziyang Liu

We study collision times of many independent simple random walks on $\mathbb Z^2$ through the joint moment generating function of their pairwise collision local times. For a fixed number of walks, these collision times are known to be asymptotically independent after a suitable logarithmic normalisation. We investigate the extent to which this independence persists when the number of walks grows. For $N$ being the walk length, our results identify a threshold $\asymp (\log N)^{\frac{1}{3}}$, on which the transition from independence to dependence happens. The proofs combine chaos expansion techniques and a correlation inequality, which is the result of a local limit theorem.
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Chemical Physics

fix uvt and fix pimd/uvt: A Unified LAMMPS Framework for Constant-Potential Constant-Temperature Molecular Dynamics

Li Fu, Yifan Li and Shenzhen Xu

Accurate simulations of electrochemical interfaces require the simultaneous treatment of constant-potential conditions, nuclear quantum effects, and sufficient configurational sampling. Integrating these capabilities within a general and efficient molecular dynamics (MD) framework remains challenging. In this work, we implement fix uvt and fix pimd/uvt in LAMMPS for constant-potential classical MD and path integral molecular dynamics (PIMD), respectively. We organize the class hierarchy to reuse LAMMPS's existing Nosé–Hoover chain thermostat routines and share nuclear propagation routines across PIMD integrators. A common interface connects these integrators to models that provide the electron-number derivative of the potential energy. We present three examples with accompanying input commands to guide users through constant-potential classical MD, thermostatted PIMD, and constant-potential PIMD, covering analytical models, liquid water, and electrochemical interfaces described by machine learning potentials. This work provides practical tools and guidance for large-scale constant-potential simulations incorporating nuclear quantum effects.
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