Medical Physics
High-spatial resolution, high-quality white matter tractography using DTI with dynamic slice-by-slice B0 shimming in a head-only high-gradient performance 3T MRI scanner
Jerome J. Maller, Patricia Lan, Sherry Huang et al. (+4 more)
Data from conventional
diffusion tensor imaging (DTI) using single-shot echo planar imaging (SS-EPI) acquisition are substantially influenced by
magnetic field inhomogeneities (delta B0), which result in image distortion and signal dephasing. Multi-shot EPI can mitigate the delta B0-induced artifacts but at the cost of increased scan time. Recent
brain tissue-selective, dynamic slice-by-slice B0 shimming techniques have demonstrated effective reduction of local delta B0 in the
brain. When combined with DTI utilizing an echo-planar imaging (EPI) read-out, image distortion and signal dephasing are significantly reduced. The purpose of our study was to assess the impact of DTI with dynamic slice-by-slice B0 shimming technique (DySiBo) on white matter (WM) tractography. We retrospectively analyzed DTI
datasets using SS-EPI and Multi-shot EPI with 2 shots (MS-2shot-EPI) readout at two spatial resolutions (1x1x2mm3 and 2x2x2mm3) with and without DySiBo. WM tractography was generated and inspected to examine the impact upon regions typically affected by delta B0-induced artefacts. We found more WM streamlines were generated in the DTI
datasets with DySiBo in regions conventionally impacted by delta B0-induced in EPI images, including the brainstem, temporal and frontal lobes. DySiBo substantially improved the generation of WM streamlines in DTI-based tractography at both in-plane resolutions. In conclusion, DySiBo in conjunction with DTI requiring 10
diffusion tensor directions is sufficient to generate data with high enough SNR and angular resolution to resolve crossing fibers and produce high quality WM tractography in
brain regions typically affected by susceptibility-induced artefacts. This has implications for quantitative WM microstructural indices and clinical evaluation of WM tracts in patients.
Read the full abstract ▾
All authors Jerome J. Maller, Patricia Lan, Sherry Huang, Chitresh Bhushan, Xinzeng Wang, Ante Zhu, Vincent A. Magnotta
High Energy Physics (Phenomenology)
LMC-Perturbed LZ Dark Matter Landscape
Nassim Bozorgnia, Samantha Contreras, Graciela B. Gelmini et al. (+3 more)
The local dark matter (DM) velocity distribution is significantly altered by the gravitational impact of the Large Magellanic Cloud (LMC), which creates a high-velocity tail. We evaluate how the LMC reshapes the DM landscape for a wide variety of theoretical models in light of the recent putative LZ DM event. We show that the LMC-induced velocity shifts substantially modify the parameter space for inelastic endothermic DM models across a broad range of possible interactions, driving the viable regions towards larger mass splittings, which are more susceptible to
collider and indirect detection constraints. By contrast, models for elastically colliding DM are less impacted, and some remain viable candidates – for example, the simple light Singlet-Doublet Majorana DM candidate at the
Higgs blind spot. Our work confirms that accurately accounting for LMC effects is essential when high-velocity DM is probed, rather than relying on the simplified Standard
Halo Model.
Read the full abstract ▾
All authors Nassim Bozorgnia, Samantha Contreras, Graciela B. Gelmini, Alvine C. Kamaha, Javier Reynoso-Cordova, Yongheng Xu
Plasma Physics
Applications of Poincaré Boundary Condition for 3D Ideal MHD Equilibrium and Optimization
Yigit Gunsur Elmacioglu, Dario Panici, Rory Conlin et al. (+2 more)
Stellarator ideal magnetohydrodynamic (MHD) codes that assume nested flux surfaces such as VMEC and DESC solve the
equilibrium problem by prescribing the total toroidal
magnetic flux,
plasma profiles and the last closed flux surface (LCFS), which analytically determines the unique field in
vacuum, whereas at finite $\beta$ bifurcations and distinct
equilibria sharing the same boundary have been reported in the literature. In this paper, we propose prescribing the Poincaré cross-section of the field at a single toroidal plane, and implement it in DESC, where the new condition enters only through the linear constraints and therefore costs no more than a fixed-LCFS solve. Fixing the geometry on one plane rather than on a full toroidal surface generally leaves more of the spectral coefficients free, and the ones it frees are those carrying the toroidal variation of the boundary flux surface, which a prescribed LCFS holds fixed at every toroidal angle; together these allow better-converged numerical solutions. We solve
equilibria with the cross-section held fixed, starting either from the axisymmetric shape obtained by revolving that cross-section toroidally, or from an existing fixed-LCFS solution. In the latter case, the volume-averaged normalized force error falls by an order of magnitude while the configuration stays close to the original one, and re-solving the resulting boundary with the conventional fixed-LCFS solver recovers the same
equilibrium. We further show that the Poincaré coefficients can be used directly as design variables by optimizing a quasi-helical configuration that maintains high-fidelity force balance throughout the process.
Read the full abstract ▾
All authors Yigit Gunsur Elmacioglu, Dario Panici, Rory Conlin, Daniel Dudt, Egemen Kolemen
High Energy Astrophysical Phenomena
What We Have Learned from NICER About Neutron Star Radii
M. C. Miller
The cores of
neutron stars have a combination of density, temperature, and
neutron-
proton asymmetry that cannot be replicated in laboratories or understood using first-principles
quantum chromodynamics. Thus, observations of
neutron stars are necessary to understand this regime. In particular, precise and accurate measurements of
neutron star radii are highly informative about cold, catalyzed matter at a few times
nuclear saturation density. X-ray observations with NASA's
Neutron star Interior Composition Explorer (NICER) have yielded radius measurements for a few nonaccreting
neutron stars, which have advanced substantially our understanding of dense matter. In this review we discuss the NICER radius measurements and their implications and demonstrate that the systematic errors thus far explored in NICER analyses have at most a minor effect on the inferred radii of
neutron stars.
Read the full abstract ▾
Materials Science
Fracture of Lattice Materials from Low to High Relative Density
Adam P. Taylor, Sage Fulco and Kevin T. Turner
Lattice materials have highly tunable mechanical properties that are controlled by their internal geometry and base material behavior. While fracture models for low-density
lattices are well-established, the fracture of
lattices at relative densities above 30% remains largely unexplored. Here, we present an analytical model that combines homogenization methods and blunt-crack fracture theory to predict the fracture toughness of triangular and hexagonal
lattices over a wide range of relative densities. Finite element modeling corroborates the analytical framework and demonstrates a shift in failure mechanisms between low and high relative density regimes. At high relative densities, failure is dominated by nodal stress concentrations, which are strongly influenced by the local crack-tip geometry and the macroscopic crack path. Significant stress redistribution is observed as the relative orientation and
lattice fillet radius are varied, resulting in increased fracture toughness relative to baseline geometries. Furthermore, quasi-brittle poly(methyl methacrylate) (PMMA)
lattices achieve about a 1.6x enhancement in fracture toughness relative to perfectly brittle
lattices as failure is delayed by localized plasticity. Notably, some quasi-brittle
lattices are found to exceed the fracture toughness of their base material – a feature only possible when the
cell size is large compared to the base material's plastic radius. Experiments on
lattice fracture specimens made from
laser-cut PMMA validate the finite element results, but highlight the
stochastic nature of failure in brittle
lattice materials, especially at higher relative densities.
Read the full abstract ▾
Instrumentation and Detectors
Non-Ionizing Radiation Measurements for Trajectography Radars
J. Marcos Leal Barbosa Filho, Millena M. de M. Campos, Daniel L. Flor et al. (+4 more)
This work presents a Non-Ionizing Radiation (NIR) measurement campaign and proposes a specific measurement method for trajectography radars. This kind of radar has a high gain narrow beam
antenna and emits a high power signal. Power density measurements from a C-band trajectography radar are carried out using bench equipment and a directional receiving
antenna, instead of the commonly used isotropic probe. The measured power density levels are assessed for compliance test via comparison with the occupational and general public exposure limit levels of both the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Brazilian National Telecommunication Agency (Anatel). The limit for the occupational public is respected everywhere, evidencing the safe operation of the studied radar. However, the limit for the general public is exceeded at a point next to the radar's
antenna, showing that preventive measures are needed.
Read the full abstract ▾
All authors J. Marcos Leal Barbosa Filho, Millena M. de M. Campos, Daniel L. Flor, William S. Alves, Adaildo G. D'Assunção, Marcio E. C. Rodrigues, Vicente A. de Sousa Jr
Quantum Physics
From Classical to Quantum Channels: Achieving Positive Covert Rates
Hassan ZivariFard, Xiaodong Wang and Alexei Ashikhmin
In this paper, we study the conditions under which covert communication at positive rates is feasible over discrete memoryless classical, classical-
quantum, and
quantum channels. For classical point-to-point channels, we show that if the dimension of the channel input probability simplex exceeds that of the channel output probability simplex, equivalently, if the input alphabet has larger cardinality than the output alphabet, then positive covert rates are achievable for certain classes of Discrete Memoryless Channels (DMCs). We further show that allowing the innocent symbol (i.e., the symbol transmitted in the no-communication mode) to be chosen appropriately can enlarge the class of DMCs for which positive covert rates are achievable. We also study covert communication over classical Multiple-Access Channels (MACs), where the additional transmitter effectively enlarges the set of available channel input pairs, and we show that the conditions required to satisfy the covertness constraint are less restrictive for MACs than for point-to-point channels. We extend these results to classical-
quantum DMCs by showing that if the dimension of the input probability simplex exceeds the affine dimension of the set of output states that can be induced at the channel output, then positive covert rates are achievable for certain classes of classical-
quantum DMCs. Finally, for
quantum channels, we show that if the innocent state (i.e., the state transmitted in the no-communication mode) is mixed, then the covertness constraint can always be satisfied by a non-trivial input ensemble. Consequently, positive covert rates are achievable whenever the legitimate receiver can distinguish at least two states in a suitable such ensemble.
Read the full abstract ▾
Solar and Stellar Astrophysics
PHAROS: Panchromatic spectral energy distributions of solar-like stars across evolutionary stages
Viktor Sumida, Raissa Estrela, Eric Mamajek et al. (+2 more)
Panchromatic
stellar spectral energy distributions (SEDs) provide the wavelength-dependent irradiation fields required for studies of
exoplanet atmospheres, photochemistry, atmospheric escape, and habitability. We present PHAROS, the Panchromatic Habitable-world Archive of Radiation from Observed
Solar-like
stars, a first release of fifteen component-traceable SEDs for nearby FGK
stars spanning adopted ages of 0.26–6.5\,Gyr. The catalogue covers 0.5–5000\,nm and combines archival XMM-Newton and Chandra high-energy constraints, semiempirical extreme-ultraviolet (EUV) reconstructions, HST and IUE ultraviolet spectra,
Gaia DR3 XP and ancillary optical spectrophotometry, and PHOENIX photospheric extensions. When X-ray data support spectral modelling, target-specific coronal
plasma models define the high-energy segment and anchor the EUV normalisation; otherwise, empirical high-energy templates are scaled to literature luminosity constraints. Each SED preserves segment-level provenance, distinguishing directly observed intervals from reconstructed components, empirical templates, bridges, and model-derived extensions. The largest diversity occurs at X-ray, EUV, and ultraviolet wavelengths. Younger age-context groups generally show stronger high-energy output relative to their photospheric continua, although the dispersion within each group shows that age alone does not uniquely determine the irradiation environment. PHAROS provides traceable panchromatic irradiation fields for studies of planetary atmospheres, photochemistry, atmospheric escape, forward modelling,
retrievals, and interpretation of future direct-imaging observations, including those anticipated for NASA's Habitable Worlds Observatory.
Read the full abstract ▾
All authors Viktor Sumida, Raissa Estrela, Eric Mamajek, Pin Chen, Adriana Valio
Materials Science
Facet- and thickness-dependent band-edge alignment at ZrSe\texorpdfstring{$_3$}{3} surfaces: hybrid-functional calculations with spin-orbit coupling
Sandro G Holanda, Bruno Ipaves, Astrid Campos-Mata et al. (+4 more)
Transition-metal trichalcogenides MX$_3$ are quasi-one-dimensional van der Waals materials whose layers form through lateral chain binding, giving them an interlayer cleavage plane and in-plane electronic anisotropy. Among them, ZrSe$_3$ is stable under ambient conditions and semiconducting. Exfoliated
crystals expose four crystallographic planes, and electrocatalytic measurements on an individual
crystal assigned the hydrogen
evolution activity to the high-energy (210) facet rather than to the basal plane. Those non-basal surfaces remain uncharacterized, since the available calculations treat either the bulk
crystal or the free-standing basal monolayer. Here, we compute the surface energies and the
equilibrium morphology of these four surfaces with a dispersion-corrected semilocal functional, and their band-edge
alignment with the HSE06 hybrid functional including
spin-orbit coupling. The surface energies span nearly an order of magnitude, from \SI{0.097}{\joule\per\meter\squared} for (001) to \SI{0.869}{\joule\per\meter\squared} for (010), and the Wulff shape exposes the four observed planes with area fractions of \SI{17.1}{\percent}, \SI{4.4}{\percent}, \SI{71.4}{\percent}, and \SI{7.0}{\percent}. The ionization potential varies by \SI{0.45}{\electronvolt} between facets and the electron affinity by \SI{0.80}{\electronvolt}, the gap of (210) falls from 1.43 to \SI{0.94}{\electronvolt} between 10 and \SI{23}{\angstrom}, and (010) remains metallic. The facets separate according to whether the cut preserves or distorts the Se-Se dimer, and the distorted dimers concentrate the frontier states. Because the same dimer governs the bulk electronic structure of the MX$_3$ family, the criterion transfers to the related trichalcogenides.
Read the full abstract ▾
All authors Sandro G Holanda, Bruno Ipaves, Astrid Campos-Mata, Shreyasi Chattopadhyay, Pulickel M Ajayan, Douglas S Galvao, Marcelo L Pereira Junior
Computational Physics
Moment hierarchy and exact steady-state solutions in a Callaway lattice Boltzmann model for phonon hydrodynamics
Shimpei Saito
We analyze the moment hierarchy of a Callaway
lattice Boltzmann model for
phonon hydrodynamics and derive exact steady-state solutions for a driven planar channel with diffuse walls. The collision operator decomposes the population space into conserved, heat-flux, and fast kinetic sectors, whose coupling through streaming determines the transport response. For the two-dimensional, eight-velocity (D2Q8)
lattice Boltzmann model, we derive a fully discrete closure that relates the heat flux to transverse kinetic moments. The higher-order transverse kinetic moment contains both a second-difference term and an explicit contribution from the imposed energy drop. Diffuse-wall population constraints then determine the heat-flux and kinetic-moment profiles without fitted parameters. The resulting solution reproduces the numerical bulk moment amplitudes and wall slip, while an exact wall relation separates the contribution of the higher-order moment from deviations from the leading gradient approximation. Finite-wave-number analysis further resolves the collision-sector mixing associated with longitudinal propagation. These results provide a unified description of collision relaxation, the moment hierarchy, and boundary response within the specified discrete model.
Read the full abstract ▾
Strongly Correlated Electrons
Magnetic excitations of the strongly-anisotropic triangular XXZ model: a projected spin-product state approach
Achille Mauri and Frédéric Mila
Recent experiments have sparked interest on the ground-state properties and on the excitation spectrum of the
spin-$1/2$ triangular XXZ model with strong Ising-like anisotropy. In this work, we introduce and analyze a “projected” coherent-state approximation to the model, constructed by projecting
spin-product states onto the low-energy configurations of the triangular Ising antiferromagnet. Within this approximation, we discuss the structure of the ground-state ordering and the magnetization curve under a longitudinal field. We then discuss the excitation spectrum by linearizing equations of motion deriving from a time-dependent variational principle. This leads to a natural description of
spin-wave-like excitations within the strongly constrained
Hilbert space. At zero field, the variational approximation leads to a very flat landscape of quasi-degenerate states, which results in a low-energy pseudo-Goldstone mode in the excitation spectrum. We compare our results to experimental measurements on the cobaltite K$_{2}$Co(SeO$_{3}$)$_{2}$ (KCSO). Our approximation leads to a dramatic improvement as compared to linear
spin-wave theory. However, there remain deviations in the value of the pseudo-Goldstone gap and in the dispersion near $M$ points at low field.
Read the full abstract ▾
Materials Science
Altermagnetism produces pair emission and absorption from dark excitons and magnons in La$_2$O$_3$Mn$_2$Se$_2$
Birender Singh, Xian Xu, Sabrina R. Hatt et al. (+21 more)
Altermagnets' (AMs) non-relativistic
spin splitting enables novel states, spintronic and magneto-optical devices, though their optical signatures remain elusive. Here, we report
exciton-
magnon emission and absorption: optical sidebands from a
spin-forbidden dark
exciton, a direct consequence of altermagnetic
symmetry. Combined optical spectroscopy and first-principles calculations reveal that La$_2$O$_3$Mn$_2$Se$_2$ is an altermagnetic
insulator, hosting a strongly bound,
spin-forbidden dark
exciton and a higher-energy bright
exciton. Photoluminescence (PL) and absorption reveal mirror-image sidebands, Stokes-shifted in emission and anti-Stokes-shifted in absorption, symmetric about the dark
exciton, whose energy shifts and spectral shapes match the
magnon energy scale and density of states measured independently by inelastic
neutron scattering. The PL intensity tracks the full equal-time
spin-
spin correlator, combining static and dynamical contributions, and rules out alternative processes. This directly couples PL to magnetism, with potential for magneto-optical devices. These results establish
exciton-
magnon spectroscopy as a new route for optically identifying and exploiting AMs.
Read the full abstract ▾
All authors Birender Singh, Xian Xu, Sabrina R. Hatt, Suvodeep Paul, Yu-Mi Wu, Chao-Chun Wei, Violet Williams, Kyung-Mo Kim, Yihao Zhang, Mohamed Shehabeldin, Cameron Grant, April Li, Michael Geiwitz, Xiaoyin Li, Garrett E. Granroth, Feng Liu, Qiong Ma, Benedetta Flebus, Judy J. Cha, Vinod M. Menon, Benjamin A. Frandsen, Diana Y. Qiu, Huiwen Ji, Kenneth S. Burch
Quantum Physics
Near-Optimal Parallel Unitary Process Tomography in Diamond Distance
Noam Scully and Sisi Zhou
Unitary process
tomography is the act of learning how an unknown
unitary gate acts on a
quantum system. It is an essential procedure for realizing a functioning
quantum computer. As
quantum technologies develop, it is important to understand the computational resources needed to conduct
unitary process
tomography using a variety of types of
circuits. In particular, when measuring error in diamond distance, it is known how to achieve optimal query complexity using a sequential
circuit architecture, but it had not been known whether a parallel
circuit architecture could achieve the same optimal query complexity. In this work, we prove that
unitary process
tomography with near-optimal query complexity is indeed possible using a parallel
circuit by introducing an explicit, novel parallel procedure. This closes the gap between sequential and parallel
circuits up to a logarithmic factor, showing that parallel and sequential strategies are nearly equally capable for this task.
Read the full abstract ▾
Cellular Automata and Lattice Gases · Cross-listed from cs.LG
Reasoning with Neural Cellular Automata
Mayalen Etcheverry, Pietro Miotti, Aidan Sirbu et al. (+7 more)
Modern AI architectures used to solve visual
reasoning tasks typically rely heavily on global connectivity and synchronization. As biological systems demonstrate, though, sophisticated computation can be performed in a more decentralized fashion. In this work, we test the
reasoning capabilities of Neural Cellular Automata (NCAs), networks of recurrent
cells that use strictly local connectivity and asynchronous updates. NCAs have been extensively studied in artificial life experiments, but it is unclear whether they can perform complex multi-step
reasoning. We show that NCAs produce spatio-temporal dynamics capable of solving challenging visual
reasoning tasks, including large mazes, Sudoku, and ARC-AGI-1. Furthermore, we provide evidence that NCAs generalize out-of-distribution when running with larger grids, longer rollouts, or parallel trials; and that the latter can be made more efficient via
pruning of redundant trajectories. We find that these generalization capabilities depend on training with sample replay and
stochastic perturbations, and that stochasticity remains beneficial at test time. Finally, we show that NCAs are robust reasoners capable of dynamically modulating compute to recover efficiently from damage, and that they can scale to solve
reasoning in raw pixel space.
Read the full abstract ▾
All authors Mayalen Etcheverry, Pietro Miotti, Aidan Sirbu, Konstantin Schürholt, Mariia Drozdova, Arna Ghosh, Blaise Agüera y Arcas, James Manyika, Blake Richards, Eyvind Niklasson
Materials Science
Far-field terahertz spectroscopy across the charge-density-wave transition in 2H-NbSe$_2$
Dmitriy Yavorskiy, Adil Rehman, Wojciech Brzezicki et al. (+7 more)
Charge-density-wave (CDW) formation in 2H-NbSe$_2$ modifies the low-energy electronic structure and gives rise to collective excitations coupled to the
lattice. Here, we investigate bulk 2H-NbSe$_2$ single
crystals using far-field terahertz time-domain spectroscopy (THz-TDS) in reflection geometry across the CDW transition at $T_{\mathrm{CDW}} \approx 33$~K. Below $T_{\mathrm{CDW}}$, the THz response shows a pronounced high-frequency feature near 1.5~THz together with longer-lived sub-THz oscillations. Both responses progressively weaken upon warming and are strongly suppressed across the CDW transition, supporting their association with the CDW state. Using time-dependent Ginzburg–Landau simulations, we reproduce the main features of the experimental THz response, associating the high-frequency response mainly with CDW amplitude dynamics and the sub-THz response with defect-pinned phase dynamics. The $\sim1.5$~THz feature lies close to the frequency range reported for the Raman CDW amplitude mode, while coupling to
lattice degrees of freedom may also influence its spectral position. We also performed complementary angle-resolved photoemission spectroscopy measurements, which reveal momentum-selective redistribution of near-
Fermi-level spectral weight across the transition. Together, these results show that far-field THz spectroscopy provides a sensitive probe of collective CDW dynamics in bulk 2H-NbSe$_2$.
Read the full abstract ▾
All authors Dmitriy Yavorskiy, Adil Rehman, Wojciech Brzezicki, Jan Skolimowski, Marcin Białek, Wojciech Knap, Dawid Wutke, Natalia Olszowska, Andrzej Wiśniewski, Ashutosh S. Wadge
Astrophysics of Galaxies
MEGATRON: The Physical Origins of Steep UV Slopes at High Redshift
Harley Katz, Nicholas Choustikov, Aayush Saxena et al. (+7 more)
The ultraviolet (UV) spectral slope, $\beta$, serves as a fundamental probe of
stellar population properties and interstellar medium conditions in
galaxies. At high
redshift, a small sample of
galaxies have been confirmed to have extremely blue spectral slopes of $\beta<-2.8$, as measured directly from spectroscopy. One explanation for such
galaxies is that they are leaking copious amounts of ionizing
photons such that these
photons are never processed into the nebular continuum and we are observing the bluer intrinsic slopes of the
stellar populations. Here, we use a detailed set of radiation hydrodynamics simulations with parsec-scale resolution and non-
equilibrium chemistry to elucidate the physical origin of extremely blue UV slopes at high
redshift. We show that, while some extremely blue
galaxies (EBGs) do indeed have high escape fractions, a second population of EBGs has $f_{\rm esc}<1\%$. In this second population, the ISM gas densities tend to be much lower, and the timescale for ionization fronts to reach their Strömgren radii can be longer than the main-sequence lifetime of massive
stars, leading to a lag in nebular emission. Our results demonstrate that extremely blue UV slopes do not uniquely imply high escape fractions, which highlights the importance of time-dependent (non-
equilibrium) nebular emission for interpreting the spectra of
galaxies in the early Universe.
Read the full abstract ▾
All authors Harley Katz, Nicholas Choustikov, Aayush Saxena, Corentin Cadiou, Martin P. Rey, Jeremy Blaizot, Alex J. Cameron, Fergus Cullen, Taysun Kimm, Kosei Matsumoto
Plasma Physics
Bayesian Active Learning of Ion Loss-Cone Boundaries in Tokamaks
Omar E. Lopez, Minglei Yang, Mark Cianciosa et al. (+1 more)
Loss-cone boundary determination in tokamaks is cast as an active learning problem in which a
Bayesian logistic regression model with radial basis function features acts as the learner and the guiding-center orbit integrator acts as the labeling method. The approach is applied to an analytic tokamak
equilibrium across a mesh of launch positions, producing a database of loss-probability models with approximate posterior uncertainty, each generated within a prescribed trajectory budget. Once generated, the database supports downstream applications, illustrated here with three examples. First, integrating the probability models against a Maxwellian distribution yields the lost-ion fraction and the energy and parallel momentum carried by lost ions, with posterior uncertainty propagated analytically to each integral. Second, a steady balance between the resulting orbit-loss torque and radial angular-momentum
diffusion gives co-current edge rotation whose amplitude is set mainly by the prescribed momentum diffusivity and loss-region renewal rate. Third, a neural network surrogate trained on the database learns the in-domain mapping from launch position to loss-probability image, and transport integrals computed from its predictions closely reproduce the
Bayesian reference values on held-out samples from the same mesh.
Read the full abstract ▾
All authors Omar E. Lopez, Minglei Yang, Mark Cianciosa, Gary M. Staebler
High Energy Astrophysical Phenomena
Fast Radio Bursts from Induced Upscattering. I. Magnetar Polar Fireballs
Rei Nishiura, Kunihito Ioka and Bing Zhang
The extreme brightness temperatures of fast
radio bursts (FRBs) demand a coherent process that converts magnetar burst energy into millisecond
radio emission. We propose that FRBs can be produced within magnetar magnetospheres by induced (stimulated) upscattering in a relativistic fireball
outflow. In this paper, we focus on induced Compton upscattering in an electron–positron fireball launched from the polar region of a magnetar. Radiation from the X-ray burst accelerates the polar fireball
outflow to Lorentz factors of $\Gamma\sim10$–$10^3$. Low-frequency seed waves, such as fast magnetosonic or Alfvén waves, entering the
outflow from the side or against its motion undergo induced scattering and are Lorentz-boosted by the relativistic bulk motion from $\nu_0\sim10\mathrm{kHz}$ to $\nu_{\rm obs}\sim\Gamma^2\nu_0\sim\mathrm{GHz}$. Combining the polar fireball dynamics with the linear growth and nonlinear saturation of the induced scattering instability, we derive the FRB luminosity $L_{\rm FRB}^{\rm iso}$ and fractional spectral bandwidth $\Delta\nu/\nu_{\rm c}$. By considering the possible range of pair densities and temperatures, we find that this polar channel can account for the luminosity of
Galactic FRB~20200428 and reach luminosities comparable to those of the brightest extragalactic FRBs. If the pair-loaded region is narrower than the relativistic beaming angle $1/\Gamma$, the model also produces a narrow spectrum and predicts $L_{\rm FRB}^{\rm iso}\propto(\Delta\nu/\nu_{\rm c})^2$, a trend consistent with observations of repeating FRBs. The induced upscattering model thus connects magnetar X-ray bursts to FRBs through a coherent emission process grounded in
plasma physics and makes observationally testable predictions.
Read the full abstract ▾
Quantum Physics
Donghoon Kim and Tomotaka Kuwahara
Understanding what limits many-body
quantum entanglement is a central problem in physics. Spatial locality has long provided a fundamental mechanism: correlations between a region and its complement must be mediated through a small spatial interface, thereby constraining their
entanglement. Here we show that universal constraints on
entanglement can persist even when interactions are strongly nonlocal, through collectivity: many weak interactions generate fluctuations controlled by their square-summed, rather than total, strength. We establish this mechanism rigorously for generic gapped
Hamiltonians with Kac-normalized power-law interactions $r^{-\alpha}$ on a $D$-dimensional
lattice. For arbitrary bipartitions, we prove that the ground-state
entanglement scales at most logarithmically with system size for $\alpha<D/2$ and subextensively for $D/2<\alpha<D$, due to suppressed collective fluctuations around individual sites. For spatially regular bipartitions with codimension-one boundaries, we use a renormalization-group construction to extend this suppression to larger length scales, yielding polylogarithmic scaling for $D/2 < \alpha < (D+1) / 2$ and parametrically stronger subvolume bounds for $(D+1)/2<\alpha<D$. We also establish the corresponding optimality results: for arbitrary bipartitions, the logarithmic scaling for $\alpha<D/2$ is optimal and $\alpha=D/2$ marks the optimal threshold for universal logarithmic bounds, while for regular bipartitions the threshold at $\alpha=(D+1)/2$ is likewise optimal for universal polylogarithmic bounds when $D\ge2$. Together, these results reveal collectivity as a fundamental mechanism for constraining many-body
entanglement alongside spatial locality.
Read the full abstract ▾
Earth and Planetary Astrophysics
Binary tidal evolution as a sculptor of circumbinary planet architectures
Mario Sucerquia, Nicolás Cuello and Gaspard Duchêne
Circumbinary
planets (CBPs) are expected to form in circumbinary discs and migrate towards the disc inner cavity, often near the binary stability boundary. Yet the observed population is not strictly marginally stable: excluding extreme systems, the typical offset is $\Delta \equiv a_{\rm p}/a_{\rm crit}=1.22^{+0.18}_{-0.07}$, suggesting post-formation
evolution may shape present-day architectures. We test whether secular
evolution of close binaries can contribute to this displacement. Using high-accuracy $N$-body simulations, we follow coplanar CBPs initially placed near $a_{\rm crit}$ while prescribing binary contraction and eccentricity damping along a track that approximately conserves orbital angular momentum. We quantify how the retreat of $a_{\rm crit}(t)$ affects planetary offsets and survival across binary mass ratios. The moving stability boundary filters the near-boundary population, adding a contraction-driven loss component dominated by ejections. Survivors remain quasi-fossilised, with median changes in $a_{\rm p}$ and $e_{\rm p}$ close to zero and semimajor-axis drifts of only a few per cent. For all valid synthetic survivors, the final offset has median $\Delta_f=1.86^{+0.18}{-0.26}$. Applying the same damping prescription to the observed sample shifts the median from $\Delta{\rm now}=1.22^{+0.18}{-0.07}$ to $\Delta{\rm damp}=1.44^{+0.32}_{-0.10}$. Near-equal-mass binaries undergo stronger filtering, with enhanced ejections and collisions. Binary
tidal evolution can therefore shape non-marginal circumbinary architectures. By removing
planets close to marginal stability while leaving survivors nearly fossilised, the retreat of $a_{\rm crit}$ can widen the inner gap and increase offsets from the present-day stability boundary. This links binary orbital
evolution, dynamical filtering, and transit detectability in a multi-channel interpretation of the CBP desert.
Read the full abstract ▾
Space Physics
Temporal Correlation between Ionospheric Storm-Enhanced Density Plume and Plasmaspheric Plume Occurrence
Xiangning Chu, Shunrong Zhang, Jacob Bortnik et al. (+5 more)
We present a statistical evidence of a temporal correlation between ionospheric storm-enhanced density (SED) and plasmaspheric plumes during
magnetic storms. We identified SED plumes in 75 storms between 2010-2024 with sufficient total electron content (TEC) coverage. We also identified plasmaspheric plumes during these storms using a plasmapause asymmetry (PPA) index derived from the machine-learning-based DEN3D model. We found that all SED plumes coincided with plasmaspheric plumes. The start and end times of both phenomena exhibit near-zero lag within a half-hour delay, confirming their synchronized
evolution. For the first time, superposed epoch analyses reveal that plume onsets align with
solar wind driving and geomagnetic activity, including peaks in the electric field, coupling function, auroral electrojet indices, and the asymmetric ring current index, all of which facilitate plume formation. This work provides timely new insights into magnetosphere-ionosphere coupling processes and demonstrates the utility of machine-learning-based diagnostics for space physics/weather.
Read the full abstract ▾
All authors Xiangning Chu, Shunrong Zhang, Jacob Bortnik, Naomi Maruyama, Jerry Goldstein, Kausik Chatterjee, David Malaspina, Phil Erickson
General Relativity and Quantum Cosmology
On the quasiblack-hole limit of rotating charged fluids
Marcos L. W. Basso and Vilson T. Zanchin
We investigate the extremal quasiblack-hole (QBH) limit of stationary, axisymmetric charged perfect fluids in rigid or differential rotation, with and without pressure. We emphasize Weyl-type configurations, whose
redshift factor is functionally related to the generalized electromagnetic potential. In this limit, the
redshift factor vanishes throughout the fluid interior and the boundary becomes a quasihorizon. We require regular matter and electromagnetic fields and smooth matching to the exterior. Under suitable convergence assumptions, electromagnetic regularity and the approach to uniform rotation imply a constant generalized electromagnetic potential throughout the connected fluid interior, independently of the Weyl ansatz. With additional integrability conditions, the mass formula reduces to the extremal Kerr-Newman Smarr relation. For rigid rotation, we examine charged
dust obeying a linear Weyl relation and fluids with pressure obeying the Kloster-Das or Guilfoyle relations. The linear Kloster-Das subclass becomes pressureless in the limit, whereas the general Guilfoyle case allows nonzero pressure. The Islam ansatz obstructs a regular limit when its coupling parameter, limiting potential, and limiting charge density are nonzero. For differential rotation, we analyze configurations with an identically vanishing Lorentz-force term and a linear Weyl subclass whose regularity requires control of angular-velocity gradients. Our results show that rotating Weyl-type systems admit extremal QBH limits much like their static counterparts, extending analyses of rotating
dust distributions and identifying conditions for more general rotating charged fluids to be compatible with this limit.
Read the full abstract ▾
Materials Science
Accelerating phase-field simulations on exascale computing systems for faster-than-real-time precipitate aging predictions
Stephen DeWitt, David J. Gardner, Philip Fackler et al. (+4 more)
Three-dimensional phase-field simulations are a gold-standard for microstructure prediction for materials, but their computational cost often limits application-relevant calculations to modest domain sizes and timescales. Here, we present a holistic approach for accelerating
Fourier pseudospectral phase-field simulations by combining performance-portable GPU computing, large-scale distributed-
memory parallelism, and high-order implicit-explicit time integration within the MEUMAPPS C++ framework. We demonstrate this approach with a 1.5-billion-grid-point simulation of the growth and coarsening of 1,920 gamma” precipitates in a Ni-Nb-Fe
alloy. The simulated seven-hour heat treatment is completed in 5.5 hours, making the calculation faster than real time and an estimated 217-501x faster than a CPU-only, first-order baseline. This performance makes three-dimensional simulations of thousands of interacting precipitates tractable, enabling quantitative studies ocollective microstructural phenomena, large simulation ensembles, and real-time integration into controlling and interpreting experiments. Benchmarking shows single-node GPU speedups of up to 17.5x relative to comparable CPU resources, near-ideal strong scaling to 4096 GPUs for a 12-billion-grid-point problem, and a further 2.6-2.9x acceleration from fourth-order time integration at scientifically relevant error tolerances. These results establish a performance-portable strategy for exploiting leadership-scale GPU systems that is applicable to a broad class of
Fourier pseudospectral simulations beyond phase-field models such as fluid dynamics and
crystal plasticity simulations.
Read the full abstract ▾
All authors Stephen DeWitt, David J. Gardner, Philip Fackler, Yonggil Song, Miroslav Stoyanov, Carol S. Woodward, Balasubramaniam Radhakrishnan
Instrumentation and Methods for Astrophysics
Comparing Active Anomaly Detection Frameworks: From Light Curves to Images
Sreevarsha Sreejith and Robert C. Nichol
The increasing volume and complexity of data from modern astronomical surveys are making comprehensive visual inspection increasingly impractical, motivating automated methods for identifying rare and unusual objects. Active anomaly detection (A-AD) combines unsupervised anomaly detection with iterative user feedback, allowing searches to adapt to scientific interests while retaining sensitivity to unexpected objects. We systematically compare three A-AD frameworks, Astronomaly, Protege, and PineForest, across Zwicky Transient Facility light curves and Euclid
galaxy images. In baseline experiments, Protege, PineForest, and Astronomaly recovered 83, 78, and 38 variable
stars, respectively, within the first 100 light-curve objects inspected, while PineForest recovered 70 merging or morphologically disturbed
galaxies within the first 100 Euclid images, compared with 29 and 19 for Astronomaly and Protege. Experiments using prior labels show that their effectiveness depends on the composition of the prior sample and varies between A-AD methods. Finally, we combine the complementary behaviour of Protege and PineForest in a hybrid search of 10,000 Euclid images, recovering 799 morphologically unusual objects. These include 29 retained strong lens systems and candidates, of which 9 candidates have no counterparts in the published Euclid Q1 strong lens catalogues searched, and 202 visually classified ring
galaxies. These results highlight the importance of selecting A-AD strategies according to both the scientific objective and
dataset properties, and demonstrate their potential for efficient, discovery-driven exploration of forthcoming astronomical surveys.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Constraining reionization with persistent homology: a novel summary statistic for wide-field Lyman-$\alpha$ emitter observations
Michael M. Wyatt, Nikolaos Triantafyllou, Steven R. Furlanetto et al. (+4 more)
The spatial clustering of Lyman-$\alpha$ emitters (LAEs) is one of the most promising observables for constraining reionization. In this work, we introduce persistent homology, a popular tool in topological data analysis, and specifically the Betti-0 curve as a summary statistic to characterize the clustering of LAEs. We compare the performance of the Betti-0 curve against the angular correlation function (ACF) and void probability function (VPF) by quantifying their ability to constrain the global neutral fraction $x_{\rm HI}$ during reionization using the Fisher information. We forward model observations of LAEs using 21cmFAST by including $\mathrm{Ly}\alpha$ emission as a post-processing step and account for
cosmic variance uncertainties. We focus our analysis within the framework of the SILVERRUSH. catalog at $z=5.7$ and 6.6, and find that the Betti-0 curve performs as well as or better than the ACF and VPF. We also find that the statistics are most sensitive to different physical scales and thus probe complementary information, and as a consequence that simultaneously constraining all three statistics improves constraints by a factor of $\sim 2$ compared with the ACF alone, with predicted minimum uncertainties of $\sigma_{\rm min} \sim$ 0.03 and 0.07 at $x_{\rm HI} = 0.05$ and $z=5.7$ and $x_{\rm HI} = 0.20$ and $z=6.6$, respectively. Our results show that the Betti-0 curve is a promising summary statistic to constrain reionization using LAE clustering and motivate further exploration of persistent homology for the same purpose in other wide-field surveys such as those made possible by the Nancy Grace Roman
Telescope.
Read the full abstract ▾
All authors Michael M. Wyatt, Nikolaos Triantafyllou, Steven R. Furlanetto, Hiroya Umeda, Samuel Gagnon-Hartman, Andrei Mesinger, Masami Ouchi
Plasma Physics
Electron Density Measurements from Stark Broadened Emission in a Sodium Plasma Produced by Laser Resonance Saturation
Mark A. Cappelli
Electron Stark broadening of the $4^2D$–$3^2P$ multiplet transition in a sodium
plasma produced by
laser resonance saturation has provided a means of undertaking the first spatial measurements of the free electron density across and along the
plasma channel created in sodium vapor of density $10^{15}$–$5\times10^{16}$~cm$^{-3}$. From these measurements and measurements of the neutral sodium density within a heat sandwich oven, we are able to deduce the corresponding electron temperature. These temperatures compare favourably with the electron temperature estimated from a Boltzmann analysis of line intensities and suggest that a highly ionized ($>$10%)
plasma of electron temperature $<$6000K can be produced within 100~ns of
laser excitation from a
laser of modest irradiance ($10^6$–$10^7$~Wcm$^{-2}$). The experimental results are in reasonable agreement with a recently developed 3-dimensional model which predicts a decrease in the degree of ionization along the path of the
laser beam as a result of significant depletion of
laser energy. These experimental results demonstrate that this LIBORS code is capable of predicting the 3-dimensional nature of this new mode of
laser ionization with reasonable accuracy, and may also explain the low electron temperatures and free electron densities observed by other research teams.
Read the full abstract ▾
Materials Science
Measuring trainable degrees of freedom in materials graph neural networks: a random-subspace intrinsic dimension analysis
Shehroz Ahmad Shoaib and Kangming Li
Final predictive accuracy is the standard basis for comparing graph neural networks (GNNs) in materials-property prediction, but it does not show how strongly performance depends on access to trainable parameter-space directions. Here, we introduce trainable-degree dependence as a complementary characterization of materials GNN learning. Using random-subspace intrinsic-dimension analysis, we train CGCNN, ALIGNN, and DimeNet++ in randomly oriented parameter subspaces across six prediction tasks and measure how performance recovers as independent trainable degrees of freedom are restored. The resulting recovery curves separate endpoint accuracy from the trainable-dimensional demand required to recover it. They reveal distinctions that final errors alone miss: metallic classification and log-bulk-modulus regression recover near-reference performance from small fractional subspaces, formation-energy and band-gap prediction show stronger architecture dependence, and
phonon prediction is most sensitive to dimensional restriction.
Dataset-size sweeps show that band-gap models require larger fractional subspaces as training data grows, whereas formation-energy and bulk-modulus responses are more stable. A width sweep shows that fractional thresholds can remain stable while absolute threshold dimensions increase with model size. Random-subspace analysis therefore provides a targeted stress test for how materials GNNs use their optimization space.
Read the full abstract ▾
Instrumentation and Detectors
Design and Analysis of a 2D Vernier Structure
Hüsna Yildiz and Rick Helmer
This paper presents the design and simulation of a 2D Vernier Time-to-Digital Converter (TDC) targeting less than 20 picosecond time resolution and 5-bit output resolution. The TDC comprises voltage-controlled delay buffers, NAND-based SR latches with reset functionality, and a calibration loop using a phase-frequency detector (PFD) and charge pump. The calibration loop dynamically adjusts delay mismatches to maintain consistent timing across process-voltage-temperature (PVT) corners, significantly improving linearity. Simulations show that the TDC achieves a resolution of 16.9 ps for tt corner and maintains DNL and INL below 0.5 LSB under all tested PVT conditions
Read the full abstract ▾
Quantum Physics
Witness-based quantification of non-Markovianity without complete Choi state reconstruction
Pritam Roy, Saheli Mukherjee and Bivas Mallick
Quantifying non-Markovianity is a fundamental problem in the theory of open
quantum systems, as it is essential for exploiting environmental
memory as a resource in
quantum technologies. Existing resource-theoretic and operational quantifiers, however, generally require complete knowledge of the intermediate dynamical map and are therefore experimentally demanding. Here, we develop a witness-based framework for the quantification of non-Markovianity that bypasses complete reconstruction of the Choi state associated with the intermediate dynamical map. We first show that every non-Markovianity witness provides a certifiable lower bound on the
geometric resource measure of non-Markovianity and identify the necessary and sufficient conditions under which this bound is tight. Motivated by the fact that non-positive-semidefinite witnesses are generally difficult to measure in real experimental scenario, we then focus on positive-semidefinite witnesses, which admit a natural implementation as positive operator valued measure (POVM) elements. We prove that every positive witness yields a certified lower bound on the Rivas–Huelga–Plenio (RHP) measure, thereby establishing a complete hierarchy connecting witness-based quantification, the RHP measure, and the
geometric distance measure. Applying our framework to amplitude-damping and general Pauli dynamics, we find that the optimal positive witnesses reduce to simple Bell-parity projectors. Furthermore, we show that the resulting witness values can be obtained directly from a small number of experimentally accessible correlation measurements, thereby eliminating the need for complete Choi-state reconstruction and providing an efficient and experimentally feasible approach for the quantification of non-Markovianity in open
quantum systems.
Read the full abstract ▾
Geophysics
Climate-informed cryospheric reanalysis via hierarchical Bayesian data assimilation
Kristoffer Aalstad, Esteban Alonso-González, Joel Fiddes et al. (+7 more)
The cryosphere regulates global cycles of water, energy, and carbon, affecting societies and ecosystems. By assimilating observations into models, we can infer the past trajectory of state variables, generating a cryospheric reanalysis. Existing cryospheric reanalyses typically treat each water year independently, with no pooling of information across years. With sparse and noisy observations, such '
climate-assumed' reanalyses perform poorly, reverting to an assumed yet uncalibrated background climatology. Conversely,
Bayesian calibration with static parameters completely pools information across water years, inferring climatological parameters without capturing inter-annual variability. Here, we propose a new hierarchical
Bayesian approach using partial pooling, which we coin '
climate-informed' cryospheric reanalysis. It jointly infers state trajectories, annual parameters, and local climatological hyperparameters using a nested hybrid particle smoothing workflow. We test the approach through three experiments by assimilating in situ snow water equivalent, satellite-based fractional snow-covered area, and glacier-wide mass balance data into a temperature index model at eight study areas, from the Swiss Alps to the High Arctic. Hierarchical reanalysis with partial pooling outperforms annually independent cryospheric reanalysis (no pooling) and static parameter calibration (complete pooling) for all experiments during calibration and for all but one during validation. Overall, it yields a 51% improvement in continuous ranked probability score relative to the prior, markedly exceeding that of annual reanalysis (38%) and static calibration (19%). Compared to a particle Markov chain Monte Carlo
benchmark, our workflow reduces computational cost by several orders of magnitude through recycling and expectation maximization, with comparable or improved skill.
Read the full abstract ▾
All authors Kristoffer Aalstad, Esteban Alonso-González, Joel Fiddes, Brian Groenke, Gregoire Guillet, Regine Hock, Bartłomiej Luks, Norbert Pirk, Sebastian Westermann, Yeliz A. Y{\i}lmaz