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Physics

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Tuesday 11 August

Mathematical Physics

Nonlinear systems of PDEs admitting infinite-dimensional Lie algebras and their connection with Ricci flows. II: The two-dimensional space case

Roman Cherniha and John R. King

The work is a natural continuation of that published in Stud Appl Math. 2024; 153:e12737. All possible two-components evolutions systems of (1+2)-dimensional second-order PDEs admitting an infinite-dimensional Lie algebra are constructed. It is shown that a natural generalisation of this Lie algebra to the higher-dimensional case does not lead to a more general result because the infinite-dimensional symmetry is broken. The recently derived system, which is related to Ricci flows, is identified as a very particular case among the evolution systems obtained. All possible stationary solutions of this system in the radially symmetric case are constructed using the surprisingly rich Lie algebra of the reduced system of ODEs. Moreover, it is proved that this Lie algebra is reducible to the fifteen-dimensional algebra of the simplest system of two second-order ODEs. Several time-dependent exact solutions in the radially symmetric case are constructed as well. It is shown that the solutions obtained are bounded and smooth provided arbitrary parameters are correctly specified.
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High Energy Physics (Experiment)

An improved direct limit on the muon electric dipole moment

The Muon g-2 Collaboration: D. P. Aguillard, T. Albahri, D. Allspach et al. (+191 more)

A limit on the permanent electric dipole moment (EDM) of the positive muon is presented based on data from the Fermilab Muon g-2 Experiment taken between 2019 and 2020. The tracking detectors measure the average vertical decay angle of positrons from muon decays, enabling a search for an interaction between a possible muon EDM $d_\mu$ and the lab-frame magnetic field. The result, $d_\mu = (-0.35 \pm 0.19_{\mathrm{stat}} \pm 0.34_{\mathrm{sys}}) \times10^{-19}~e\cdot$cm, is consistent with zero and sets a new direct limit on the muon EDM of $|d_\mu|<1.10\times10^{-19}~e\cdot$cm at the 95 percent confidence level.
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All authors The Muon g-2 Collaboration: D. P. Aguillard, T. Albahri, D. Allspach, J. Annala, K. Badgley, S. Baeßler, L. Bailey, E. Barlas-Yucel, T. Barrett, E. Barzi, F. Bedeschi, M. Berz, M. Bhattacharya, H. P. Binney, P. Bloom, J. Bono, E. Bottalico, T. Bowcock, S. Braun, M. Bressler, G. Cantatore, R. M. Carey, B. C. K. Casey, D. Cauz, R. Chakraborty, A. Chapelain, S. Chappa, S. Charity, C. Chen, M. Cheng, R. Chislett, Z. Chu, T. E. Chupp, C. Claessens, F. Confortini, M. E. Convery, S. Corrodi, L. Cotrozzi, J. D. Crnkovic, S. Dabagov, P. T. Debevec, S. Di Falco, G. Di Sciascio, S. Donati, B. Drendel, A. Driutti, M. Eads, A. Edmonds, J. Esquivel, M. Farooq, R. Fatemi, K. Ferraby, C. Ferrari, M. Fertl, A. T. Fienberg, A. Fioretti, D. Flay, S. B. Foster, H. Friedsam, N. S. Froemming, C. Gabbanini, I. Gaines, S. Ganguly, J. George, L. K. Gibbons, A. Gioiosa, K. L. Giovanetti, P. Girotti, W. Gohn, L. Goodenough, T. Gorringe, J. Grange, S. Grant, F. Gray, S. Haciomeroglu, T. Halewood-Leagas, D. Hampai, F. Han, J. Hempstead, D. W. Hertzog, G. Hesketh, E. Hess, A. Hibbert, Z. Hodge, S. Y. Hoh, K. W. Hong, R. Hong, T. Hu, Y. Hu, M. Iacovacci, M. Incagli, S. Israel, P. Kammel, M. Kargiantoulakis, M. Karuza, J. Kaspar, D. Kawall, L. Kelton, A. Keshavarzi, D. S. Kessler, K. S. Khaw, Z. Khechadoorian, B. Kiburg, M. Kiburg, O. Kim, N. Kinnaird, E. Kraegeloh, J. LaBounty, K. R. Labe, M. Lancaster, S. Lee, B. Li, D. Li, L. Li, I. Logashenko, A. Lorente Campos, Z. Lu, A. Lucà, G. Lukicov, A. Lusiani, A. L. Lyon, B. MacCoy, R. Madrak, K. Makino, S. Mastroianni, R. McCarthy, J. P. Miller, S. Miozzi, B. Mitra, J. P. Morgan, W. M. Morse, J. Mott, A. Nath, J. K. Ng, H. Nguyen, Y. Oksuzian, Z. Omarov, W. Osar, R. Osofsky, S. Park, G. Pauletta, J. Peck, G. M. Piacentino, R. N. Pilato, K. T. Pitts, B. Plaster, N. Pohlman, C. C. Polly, D. Počanić, J. Price, B. Quinn, M. U. H. Qureshi, G. Rakness, S. Ramachandran, E. Ramberg, R. Reimann, B. L. Roberts, D. L. Rubin, M. Sakurai, L. Santi, C. Schlesier, A. Schreckenberger, Y. K. Semertzidis, A. K. Soha, M. Sorbara, J. Stapleton, D. Still, C. Stoughton, D. Stratakis, D. Stöckinger, H. E. Swanson, G. Sweetmore, D. A. Sweigart, M. J. Syphers, Y. Takeuchi, D. A. Tarazona, T. Teubner, A. E. Tewsley-Booth, V. Tishchenko, N. H. Tran, W. Turner, E. Valetov, D. Vasilkova, G. Venanzoni, T. Walton, A. Weisskopf, L. Welty-Rieger, P. Winter, Y. Wu, B. Yu, M. Yucel, E. Zaid, Y. Zeng, C. Zhang

Quantum Physics

Robust CHSH Self-Testing with Finite-Energy GKP States

Farzin Salek and Masahito Hayashi

We present a full-oscillator analysis of a finite-energy GKP CHSH test whose observed score yields robust Bell-pair self-testing. Periodically binned position and momentum give the Pauli settings, while a fixed binary coarse-graining of photon number modulo four and its displaced conjugate realize the tilted settings. For a number-filtered GKP source, we retain the finite codeword overlap, define the measurements on all photon-number sectors, and compute the physical correlations without logical post-corrections. With the canonical ideal-logical displacement \(d=\sqrt{\pi}\), the CHSH value exceeds the local bound above \(4.56\) dB of per-peak squeezing, and Kaniewski's extractability bound becomes nontrivial above \(5.02\) dB. Calibrating only \(d\) using an independently characterized finite-energy parameter lowers these model thresholds to \(4.21\) dB and \(4.58\) dB, respectively; at \(12\) dB, it raises the score from \(2.69486\) to \(2.78858\) and the corresponding target-state overlap bound from \(0.90758\) to \(0.97243\). This calibration is fixed before Bell-test data are collected. The displacement activates the odd modulo-four sectors, so their fixed a priori assignments are a genuine finite-energy component. The large gain is specific to the deterministic phase-bit coarse-graining; independently calibrating the one-bit POVM with randomized odd-sector outcomes gives only a much smaller improvement. These are honest-model predictions, not loss, detection-efficiency, or finite-sample thresholds. In an experiment, a device-independent guarantee for an extracted Bell pair follows by inserting a confidence lower bound on the observed CHSH score into the self-testing theorem.
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General Relativity and Quantum Cosmology

All You Need is not $\Omega_\mathrm{gw}$: Beyond the Mean of the Cross-Correlation Estimator when Searching for an Astrophysical Gravitational-Wave Background

Haowen Zhong, Francesco Iacovelli, Vuk Mandic et al. (+1 more)

Searches for the stochastic gravitational-wave background (SGWB) using ground-based detectors rely heavily on the cross-correlation estimator $\bar C_f$, whose statistical properties determine the theoretical foundation for inference frameworks built on it. Past analyses usually assume Gaussianity of $\bar C_f$, but this assumption has not been systematically tested for a background of astrophysical origin like the one produced by compact binary coalescences. In this work, we decompose $\bar C_f$ into three physically motivated components: (1) the mean intensity, (2) the geometrical shot noise, and (3) the polarization leakage, and we compute 90% credible intervals for its cumulants up to fourth order for the binary black hole, binary neutron star, and neutron star-black hole populations by propagating local merger rate uncertainties. We find that for the upcoming LIGO O5 sensitivity, $\bar C_f$ remains effectively Gaussian for all three populations, validating current Gaussian likelihood frameworks. For Cosmic Explorer (CE), however, the $\bar C_f$ produced by binary black holes becomes non-Gaussian, with skewness and excess kurtosis of $0.31^{+0.04}_{-0.03}$ and $1.3^{+0.4}_{-0.3}$, respectively, in the most sensitive band over a one-year observation period. For binary neutron star and neutron star - black hole mergers, $\bar C_f$ remains largely Gaussian even at CE. These results indicate that the Edgeworth expansion provides an adequate leading-order description of the non-Gaussianity expected in the next-generation era, while also motivating the development of more sophisticated statistical methods for a more accurate treatment.
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All authors Haowen Zhong, Francesco Iacovelli, Vuk Mandic, Emanuele Berti

High Energy Physics (Phenomenology)

Hilbert Series of Pseudoscalar Mesons: Operators and Sum Rules

Joydeep Chakrabortty, Sabyasachi Chakraborty and Siddhartha Karmakar

We construct the complete non-redundant basis of operators built from pseudoscalar mesons using the Hilbert series method, subject to the global flavor symmetry $SU(3)_L \times SU(3)_R \times SU(2)_{L_H} \times SU(2)_{R_H}$, together with the underlying shift symmetry. The SM weak interactions are incorporated systematically by promoting the CKM matrix elements to spurion fields transforming under the global symmetry. The resulting operator basis provides a model-independent parametrization of two- and three-body weak decay amplitudes of heavy mesons, with the corresponding Wilson coefficients serving as reduced hadronic amplitudes. We demonstrate that all amplitude sum rules follow directly from the structure of the operator basis and propose an unfolding procedure that connects the effective operators to their possible ultraviolet origins. Our framework reproduces the known flavor relations while predicting additional identities arising from the symmetry-constrained operator basis.
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Medical Physics

T1, T2, and complex permittivities of hydrogels, paramagnetic salt solutions, and oils at 0.35, 1.5, and 3 Tesla

H Michael Gach, Kerri Prinos and Hannah Sechaga

Approach: The T1, T2, and complex permittivities of candidate MRI phantom constituents (hydrogels, paramagnetic electrolytes, and oils) were measured at different magnetic field strengths and concentrations. Data: T1 decreased with increasing concentration except for PEG. The T1 and T2 relaxivities of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), sodium polyacrylate, and deionized water did not significantly vary with field strength. The T2 relaxivities of gelatin and sodium alginate did not significantly vary with field strength. All of the hydrogels and paramagnetic electrolyte solutions had high static dielectrics (e.g., {\epsilon}s~70) similar to water. The static electrical conductivities of Miller's LB agar, gelatin, PVA, sodium alginate, sodium polyacrylate, xanthan gum, CuSO4, NiCl2, and Mn(NO3)2 rose with concentration. However, the conductivities of PEG and PVP did not rise with concentration. Conclusions: Sodium polyacrylate, PVP, and PEG hydrogels are challenging for generating consistent phantoms. Sodium alginate, Miller's LB agar, and xanthan gum were good hydrogel candidates. Mn(NO3)2 had the highest relaxivities of the tested samples. All three oils (canola, castor, and grapeseed) are good candidates for low dielectric ({\epsilon}s<10) phantoms for high field applications) but with low conductivities.
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Instrumentation and Methods for Astrophysics

High-temperature photovoltaics for solar-electric Oberth maneuvers: ton-class payload feasibility for interstellar-precursor missions

Nadim Maraqten, Willem van Lynden, Carlos Gómez de Olea Ballester et al. (+1 more)

In-situ exploration beyond the giant planets remains rare because timely Solar System escape demands very high specific orbital energy, which existing concepts typically achieve only with small payloads, super-heavy launchers, or nuclear-powered propulsion. Motivated by laboratory demonstrations of high-intensity, high-temperature (HIHT) solar cells operating near $400\,^{\circ}\mathrm{C}$, we assess a solar-electric Oberth maneuver that concentrates thrust near a $0.3\,\mathrm{AU}$ perihelion. Evolutionary steering optimisation indicates that an expendable Falcon Heavy could deliver ton-class payloads to $200\,\mathrm{AU}$ within 25 years if HIHT power systems reach specific powers about $10\%$ above present-day conventional levels with a Jupiter gravity assist, or about twice those levels on a direct trajectory, under the stated assumptions. The gain stems from a threefold increase in specific orbital energy for the same $\Delta v$ compared with a $1\,\mathrm{AU}$ spiral. These results suggest HIHT photovoltaics could shift from survival hardware to propulsion-enabling technology for high-energy deep-space missions.
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All authors Nadim Maraqten, Willem van Lynden, Carlos Gómez de Olea Ballester, Andreas M. Hein

Mathematical Physics

The Renormalization Group as a Stochastic Exploration Process

Denis Bernard

The Renormalization Group (RG) is a powerful and versatile framework for analyzing complex physical systems. Here, we reinterpret it as a stochastic process that explores physical phase spaces, scale by scale, progressively revealing finer details of small-scale structures. This perspective establishes a natural connection to other random exploration processes, such as the Schramm-Loewner evolution, and is more suited for a probabilist audience. It links RG concepts such as RG transformations, effective actions, etc, to usual probabilistic tools such as conditional expectation values, martingales, etc, but also makes contact with stochastic quantization.
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Statistical Mechanics

Exact Expressions of Entropy for Classical Non-interacting Many-body Systems

Yuheng Wu, Henrik Heelweg and Rigel Galgana

In the thermodynamic limit, the equilibrium state of a many-body system can be characterized by three pairs of conjugate thermodynamic variables: $E/T,V/P,N/\mu$. In this limit, the thermodynamic properties in all ensembles are equivalent up to the leading order of $E,V,N$. However, for systems of finite size, this ensemble equivalence is no longer exact, and the thermodynamic properties may differ substantially among ensembles. To quantify these finite-size effects rigorously, it is desirable to develop a universal ensemble theory applicable to systems of arbitrary size, providing exact expressions for entropy and, thereby, giving rise to the precise value of all equilibrium thermodynamic quantities. In this work, we propose a theory that determines the exact entropy expressions for classical non-interacting many-body systems of arbitrary size across all statistical ensembles, based on only two postulates: stationarity, requiring that the physical laws be invariant under time translation, and unbiasedness, requiring that the equilibrium mixed state maximize the entropy subject to the prescribed constraints. Moreover, we show that the entropy expressions obtained in different ensembles converge to the common asymptotic form $S \asymp \ln\!\left( \left( \frac{4\pi m e E}{3N} \right)^{3N/2} \cdot \left(\frac{V}{N}\right)^N \right)+N$, consistent with the predictions of the large deviation theory.
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Materials Science

Stable Glasses of Organic Semiconductor Resist Crystallization

Kushal Bagchi, Marie E. Fiori, Camille Bishop et al. (+2 more)

The instability of glassy solids poses a key limitation to their use in several technological applications. Well-packed organic glasses, prepared by physical vapor deposition (PVD), have drawn attention recently because they can exhibit significantly higher thermal and chemical stability than glasses prepared from more traditional routes. We show here that PVD glasses can also show enhanced resistance to crystallization. By controlling the deposition temperature, resistance towards crystallization can be enhanced by at least a factor of ten in PVD glasses of the model organic semiconductor Alq3 (Tris(8-hydroxyquinolinato) aluminum). PVD glasses of Alq3 first transform into a supercooled liquid before crystallizing. By controlling the deposition temperature, we increase the glass to liquid transformation time thereby also increasing the overall time for crystallization. We thus demonstrate a new strategy to stabilize glasses of organic semiconductors against crystallization, which is a common failure mechanism in OLED (organic light emitting diode) devices.
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All authors Kushal Bagchi, Marie E. Fiori, Camille Bishop, M.F. Toney, M.D. Ediger

Optics

High-dimensional Supermode Photonics Enabled by Hierarchical Supersymmetric Transformation

Yuan Zhong, Kaile Chen, Qi Lu et al. (+8 more)

Modes provide a fundamental degree of freedom for photonic information processing, yet conventional multimode waveguides exhibit non-equidistant effective-index distributions, making closely spaced modes vulnerable to intermodal crosstalk. Supermode photonics can overcome this limitation by geometrically engineering coupled waveguide arrays to realize large and equidistant effective-index spacing, but precise supermode excitation and detection remain challenging at the subwavelength scale. Here, we report a hierarchical second-order discrete supersymmetric (DSUSY) transformation method that enables high-purity excitation and extraction of arbitrary target supermodes in a compact and scalable architecture. We experimentally demonstrate six-supermode multiplexing systems on silicon-on-insulator and silicon nitride platforms. Benefiting from the large supermode index spacing and the isospectrality of DSUSY transformations, the fabricated devices exhibit low insertion losses (<2.6 dB) and intermodal crosstalk (<-11.1 dB) for all channels over a 100-nm wavelength range. A high-speed transmission experiment on the silicon device achieves an aggregate data rate of 1.2 Tbit/s, with all channel bit error rates below the 7% hard-decision forward-error-correction threshold. The method can further support polarization-insensitive architectures, enabling compact polarization-supermode hybrid multiplexing. This work provides a scalable route toward high-dimensional supermode photonics for high-capacity optical interconnects, highly parallel AI optical computing, and high-dimensional quantum information processing.
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All authors Yuan Zhong, Kaile Chen, Qi Lu, Chunxue Wang, Jingchi Li, Yuru Li, Zhaohui Li, Chao Lu, Xinchen Ji, Yikai Su, Lu Sun

Quantum Physics

Physics-Constrained Compressed Sensing for Quantum Sensing in the Data-Starved Regime

Amir Kalev

Quantum sensors promise measurement sensitivities that can scale at the Heisenberg limit, but in practice their performance is often degraded by noise, finite sampling, and implementation imperfections. In this work we present a general framework for improving parameter estimation in such settings by exploiting intrinsic structural constraints of time-domain correlation functions. Our approach builds on the observation of Kemper et al. [PRL 132, 160403 (2024)] that two-time correlation functions of Hermitian observables generate Gram matrices that are positive semidefinite, a property that can be violated in experimentally acquired data. We formulate signal reconstruction as a convex optimization problem that enforces positive semidefiniteness, Toeplitz structure, and low-rank priors motivated by the underlying dynamics. We show analytically that, under suitable conditions, the ground-truth signal can be uniquely identified in the noiseless case and recovered stably in the presence of noise. We further demonstrate numerically, in a GHZ-based magnetometry protocol, that enforcing these physical constraints can significantly improve frequency estimation from sparse and noisy data. In particular, we observe a clear advantage in the data-starved regime, where only a small number of time samples are available and standard spectral estimation methods, including matrix pencil techniques, provide limited or unstable improvement over direct fitting. While the reconstructed signals do not in general reach the shot-noise-limited performance, the proposed approach consistently reduces estimation error and recovers much of the underlying structure of the signal. These results indicate that incorporating universal physical constraints into data analysis can enhance the practical performance of quantum sensing protocols without requiring additional hardware resources or calibration.
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Materials Science

Competition between local magnetic disorder and altermagnetism in doped FeSb$_2$

Enrico Di Lucente and Michele Simoncelli

Recent experimental reports suggest that the narrow-gap nonmagnetic semiconductor FeSb$_2$ can be transformed into an altermagnetic metal through Co doping (Co$_{0.15}$Fe$_{0.85}$Sb$_2$), or into a magnetically disordered or short-range-ordered state through Cr doping (Cr$_{0.15}$Fe$_{0.85}$Sb$_2$). Here we explore the energy landscape and magnetic states of these doped systems from first principles, relying on Hubbard-augmented density-functional theory (DFT+U) combined with the Romeo ground-state search algorithm. Within the established virtual-crystal approximation (VCA), we show that Romeo finds several non-trivial magnetic states, which inform targeted explicit simulations of doping in supercells. We rely on these findings to discuss strengths and limitations of the VCA-Romeo approach versus the explicit-doping supercell approach, and how they can be used in synergy. Overall, our simulations suggest that the ground state of the Cr-doped system is a Locally Disordered Spin-Compensated (LDSC) configuration, formally compatible with Néel's L-type fully compensated ferrimagnetism, whereas the ground state of the Co-doped system is found to be altermagnetic (AFMo). This work shows how approximate and explicit simulations of magnetic alloys can be mutually informative, and establishes a protocol for studying candidate metallic altermagnets.
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General Relativity and Quantum Cosmology

Quasinormal modes in effective loop quantum gravity and consequences for isospectrality

Alejandro García-Quismondo, Guillermo A. Mena Marugán and Alvaro Torres-Caballeros

We investigate the quasinormal mode spectra of axial and polar perturbations about the effective Ashtekar, Olmedo, and Singh black hole geometry within the hybrid approach to loop quantum gravity. We also compare our results with those previously obtained by del-Corral and Olmedo for the dressed metric approach. Starting from mode equations that are straightforward effective counterparts of the classical equations, we compute these spectra by means of a high-order WKB method with Padé resummation. The violation of isospectrality between axial and polar perturbations that was claimed to exist in the dressed metric approach persists with the hybrid quantization, with deviations of the same order of magnitude as in the former effective case, although slightly larger for the hybrid prescription. In both situations, the isospectrality breaking decreases with the cubic root of the squared black hole mass in Planck units, consistently recovering the classical Schwarzschild limit. In addition, we perform a careful assessment of the applicability of the WKB approximation to the present effective analysis, confirming the parameter regions where the method remains reliable and highlighting specific mode cases for which the approximation breaks down.
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Solar and Stellar Astrophysics

Intense but Harmless: Exo-Space Weather Around an M Dwarf with a Single-Hemisphere Dynamo

Zheng Sun, Julián D. Alvarado-Gómez, Hui Tian et al. (+4 more)

M dwarfs are among the most promising host stars in the search for habitable exoplanets. However, their active atmospheres drive intense magnetic activity, including energetic flares and possibly coronal mass ejections (CMEs), which may pose serious threats to planetary habitability. In this study, we perform three-dimensional magnetohydrodynamic (MHD) simulations of CMEs on a fully convective M dwarf with a rotation period of 30 days, corresponding to the moderate-rotation regime. The magnetic topology driving our simulations is adopted from an exploratory global dynamo simulation of a fully convective low-mass star exhibiting a single-hemisphere magnetic configuration, which is not yet observationally confirmed. The large-scale magnetic field is mostly restricted to a single hemisphere and characterized by high-latitude polarity inversion lines (PILs), with the implication that most CMEs should originate from high latitudes. We find that these high-latitude CMEs propagate radially and away from the equatorial plane, producing only weak and spatially limited disturbances along the equatorial orbits of exoplanets. Moreover, low-latitude CMEs experience stronger drag within the dense and slow stellar wind near the equator, which significantly reduces both their propagation speeds and their overall impact on exoplanets. The resulting dynamic pressure enhancements on equatorial exoplanets caused by these CMEs are within two orders of magnitude above the quiescent conditions, much lower than those reported in previous M-dwarf CME simulations. These results indicate that, if such magnetic topologies indeed exist on M dwarfs, they may produce a relatively benign CME environment, which could be favorable for planetary habitability at face value.
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All authors Zheng Sun, Julián D. Alvarado-Gómez, Hui Tian, Ofer Cohen, Jeremy J. Drake, Katja Poppenhäger, Yue-Hong Chen

High Energy Physics (Theory)

Distance-Higuchi Bounds on Inflationary Field Ranges and Lifetimes

Luis A. Anchordoqui, Ignatios Antoniadis and Alek Bedroya

We show that quasi-de Sitter inflation driven by a nearly flat scalar potential has a finite polynomial lifespan dictated by the interplay between the swampland Distance Conjecture and the generalized Higuchi bound. By analyzing classical scalar rolling and quantum stochastic diffusion, we demonstrate that for any arbitrarily high but fixed statistical confidence, a universe cannot live longer than $\sim \min\left\{\ln(\frac{1}{H})\frac{\sqrt V}{V'},V^{-\frac{d-1}{2}}\ln^2(\frac{1}{H})\right\}$ in reduced Planck units while remaining Higuchi-consistent, where $H$ is the Hubble parameter, $V$ is the scalar potential, $d$ is the number of spacetime dimensions, and prime denotes derivative with respect to the scalar field. This bound despite being weaker than the Trans-Planckian Censorship Conjecture, which has been argued for classical cosmologies that flow to the asymptotic of the field space without tunneling, is powerful given its minimal quantum gravity input and applicability to all points in the moduli space.
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Earth and Planetary Astrophysics

Opposition effect of comet 28P/Neujmin observed with Subaru Hyper Suprime-Cam

Takafumi Ootsubo, Hideyo Kawakita, Tadafumi Takata et al. (+8 more)

We present an observational study of the nucleus of comet 28P/Neujmin at a heliocentric distance exceeding 10 au, where coma contamination is effectively minimized. Observations were conducted in the $g$, $r$, and $y$ bands with the Hyper Suprime-Cam (HSC) on the 8.2-m Subaru Telescope. The measured colors, $g - r = 0.67\pm0.17$ and $r - y = 0.41\pm0.19$, yield a spectral index of $S' = 8.8\pm4.2\%/100$ nm, comparable to that of D-type asteroids. By incorporating new observational data at a phase angle $\alpha = 0.334^{\circ}$ with previous observations, we determined the phase function for the nucleus of 28P and confirmed an opposition surge at small phase angles. The derived opposition effect amplitude depends on the adopted phase coefficient, which is uncertain due to potential systematic effects in multi-apparition phase curves. Nevertheless, even under conservative assumptions, the opposition effect of 28P suggests a larger coherent backscattering contribution than is typical for C- and D-type asteroids. The Subaru HSC observations suggest that, although the nucleus color resembles that of D-type asteroids, the surface microstructure of comet 28P's nucleus likely differs from those of C- and D-type asteroids. Future single-apparition observations covering a wide phase angle range from near-opposition to larger angles, combined with polarimetric measurements, will be essential to definitively establish the physical mechanisms responsible for the opposition effects of cometary nuclei.
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All authors Takafumi Ootsubo, Hideyo Kawakita, Tadafumi Takata, Junko Furusawa, Hisanori Furusawa, Tsuyoshi Terai, Toshihiro Kasuga, Akira Keida, Yoshiharu Shinnaka, Fumi Yoshida, Seitaro Urakawa

Soft Condensed Matter

Using Deposition Rate and Substrate Temperature to Manipulate Liquid Crystal-like Order in a Vapor-deposited Hexagonal Columnar Glass

Camille Bishop, Zhenxuan Chen, Michael F. Toney et al. (+3 more)

We investigate vapor-deposited glasses of a phenanthroperylene-ester, known to form an equilibrium hexagonal columnar phase, and show that liquid crystal-like order can be manipulated by the choice of deposition rate and substrate temperature during deposition. We find that rate-temperature superposition (RTS), the equivalence of lowering deposition rate and raising substrate temperature, can be used to predict and control the molecular orientation in vapor-deposited glasses over a wide range of substrate temperatures (0.75Tg to 1.0Tg). This work extends RTS to a new structural motif, hexagonal columnar liquid crystal order, which is being explored for organic electronics applications. By several metrics, including the apparent average face-to-face nearest-neighbor distance, PVD glasses of the phenanthroperylene-ester are as ordered as the glass prepared by cooling the equilibrium liquid crystal. By other measures, the PVD glasses are less ordered than the cooled liquid crystal. We explain the difference in the maximum attainable order with the existence of a gradient in molecular mobility at the free surface of a liquid crystal, and its impact upon different mechanisms of structural rearrangement. This free surface equilibration mechanism explains the success of the RTS principle and provides guidance regarding the types of order most readily enhanced by vapor deposition. This work extends the applicability of RTS to include molecular systems with a diverse range of higher-order liquid crystalline morphologies that could be useful for new organic electronic applications.
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All authors Camille Bishop, Zhenxuan Chen, Michael F. Toney, Harald Bock, Lian Yu, M.D. Ediger

Soft Condensed Matter

A Dynamical Mechanism for Irreversibility in Cyclically Driven Amorphous Solids

Sauvik Chatterjee, Asaf Szulc and Ido Regev

Amorphous solids subjected to athermal quasistatic oscillatory shear undergo a transition from periodic reversible dynamics to irreversible diffusive dynamics at yielding. How irreversibility arises in such deterministic, strongly dissipative systems remains unclear. Here we directly test the proposal that post-yield irreversibility originates from chaotic dynamics and exponential sensitivity to initial conditions. Contrary to this interpretation, perturbations initially contract rather than grow, even in the irreversible regime, with nearby trajectories remaining close for extended periods. Separation occurs only through rare branching events, after which the distance grows diffusively at the rate expected for independent trajectories. The waiting times to branching are exponentially distributed, defining a steady-state branching rate that vanishes in trained reversible limit cycles and becomes finite above yielding. A mean-field soft-spot model reproduces these branching statistics and reveals their microscopic origin: a small perturbation can reverse the activation order of two nearly degenerate plastic instabilities, altering the subsequent sequence of plastic events. These results show how local stability and global irreversibility can coexist in a dissipative many-body system and identify instability-selection-induced branching as a distinct dynamical route to irreversibility in driven amorphous solids.
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Mesoscale and Nanoscale Physics

Assessing fidelity-limiting factors and achieving single-qubit gate fidelity beyond 99.999% in driven silicon spin qubits

Kenta Takeda, Akito Noiri, Takashi Nakajima et al. (+4 more)

In semiconductor single-spin qubits, high-fidelity quantum gates have been demonstrated; however, achieving consistent performance remains challenging due to variations in driven qubit coherence, which is less explored than free-evolution coherence such as $T_2^*$. Here, we report single-qubit gate fidelities above 99.999%, achieved by dramatically extending the driven-spin coherence time and suppressing off-resonant driving effects that are detrimental to accurate fidelity benchmarking. We demonstrate that removing proximal reservoirs significantly enhances the spin-locking coherence time ($T_{1\rho}$), a critical metric for qubits under microwave driving. Furthermore, we reveal that in typical spin qubit setups using parity readout and rectangular pulses, off-resonant excitation of neighboring qubits causes substantial benchmarking artifacts. By optimizing device conditions to mitigate microwave-induced degradation and implementing spectrally tailored pulse shaping, we achieve a ${\pi}/2$ gate fidelity of 99.99920(2)%, with remaining errors primarily limited by incoherent noise. These results showcase the mechanisms that bound fidelity benchmarking in state-of-the-art silicon spin qubits and provide practical guidelines for achieving and verifying high fidelities in these systems.
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All authors Kenta Takeda, Akito Noiri, Takashi Nakajima, Leon C. Camenzind, Takashi Kobayashi, Giordano Scappucci, Seigo Tarucha

Strongly Correlated Electrons

Competing collinear and non-collinear spin textures imaged by spatially-resolved REXS in Eu(Al0.4Ga0.6)4

Fellipe B. Carneiro, Zéetény Bacsó, Kevin Allen et al. (+6 more)

Here, we use resonant elastic x-ray scattering (REXS) to investigate the inhomogeneity of the zero-field magnetic spin texture of Eu(Al$_{0.4}$Ga$_{0.6}$)$_4$. By using spatially-resolved REXS, we show that the two magnetic transitions at T$_{N1}$ = 17 K and T$_{N2}$ = 14 K originate from two nearly degenerate, yet distinct, orthogonal pairs of q-vectors. The corresponding phases are segregated spatially, such that one fraction of the sample comprises coexisting orthogonal spin-density-wave domains, while another fraction hosts coexisting orthogonal helical domains. Additionally, the helical state forms inversion domains indicating that the inversion symmetry is not broken prior the magnetic transition. Our results suggest that the magnetic state is single-q and revealed a large variation of spin textures across a 0.8 - 1 mm area of the sample surface. These results demonstrate clear differences between the locally and globally probed magnetic textures, typically assumed to be representative of the system as a whole, highlighting the importance of spatially-resolved probes for accurately describing the magnetic behavior of this class of materials.
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All authors Fellipe B. Carneiro, Zéetény Bacsó, Kevin Allen, Aly H. Abdeldaim, Rebecca Scatena, Jaime M. Moya, Roger D. Johnson, Emilia Morosan, Alessandro Bombardi

Soft Condensed Matter

Multi-step deformation experiment and development of a model for the mechanical behavior of polymeric glasses

Grigori A Medvedev, Enran Xing, Mark D Ediger et al. (+1 more)

Traditional models for stress-strain behavior of glassy polymers are based on the assumption that the critical features of the stress-strain response can be explained by changes in the molecular mobility. The four-step deformation experiments consisting of (i) an initial constant strain rate loading, (ii) unloading to specified stress, (iii) creep under that stress and (iv) second constant strain rate loading, challenges that assumption. Specifically, existing models fail to predict the experimentally observed large second stress overshoot in case of a slight unloading. Until now there has remained a possibility that the mobility was actually lower in case of a partial rather than complete unloading, which would preserve the main assumption, if not particular details, of these specific constitutive models. By performing direct optical experiments using the photobleaching technique simultaneously with the mechanical four-step experiments it is shown that a lower molecular mobility upon partial unloading does not take place. As traditional models cannot account for these experimental results, a new model has been developed where the changes of molecular structure manifest not in the relaxation time, but in the shear modulus, which is function of an internal variable that is the fraction of the efficiently packed material. This fraction obeys a population balance equation, where the steady-state fraction is controlled by the applied stress. In the absence of deformation, the efficiently packed fraction increases, which explains the increase in the modulus in the course of physical aging below Tg. The model qualitatively describes the four-step experiment as well as single step loading experiments.
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All authors Grigori A Medvedev, Enran Xing, Mark D Ediger, James M Caruthers

Soft Condensed Matter

Patterned states in the nematic phase of flexible-core phenyl benzoate dimers

K. S. Krishnamurthy, S. Y. Khatavi, C. V. Yelamaggad et al. (+1 more)

This study deals with both spontaneously-formed and electrically-induced structures observed in the nematic phase of two dielectrically negative twist-bend nematogens. In planar cells, the nematic layers are inhomogeneous, existing in a quasiperiodic ground state that involves essentially azimuthal director deviations. This phenomenon is understood using a simple model based on the relative flexoelectric and elastic contributions to free-energy. In an external electric field, a variety of instabilities are obtained. In an increasing static field, for example, the initial periodic surface electroconvective instability is followed by the volume periodic flexoelectric instability. Uncommonly, the growth of the latter takes place via nucleation and front propagation. Due to the low bend elastic deformation cost, flexoelectric bands progressively distort as they narrow (mediated by edge dislocations) under an increasing field to eventually form fanlike objects. In the megahertz region, in each half cycle following 0 V, the electroconvective and flexoelectric instabilities appear transiently with the latter setting in at a higher voltage. Above a few hertz, flexoelectric instability ceases; the sequence of patterned states then is oblique roll to bimodal-grid to normal-roll to chevron. Above 100 kHz, periodic wide bands oriented normal to the rubbing axis are obtained at a threshold voltage that decreases with increasing frequency. Our measurement of threshold voltage corresponding to different frequencies (or electrical conductivity and permittivity values) in this regime agrees well with the earlier theoretical predictions relating to the inertial conduction instability.
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All authors K. S. Krishnamurthy, S. Y. Khatavi, C. V. Yelamaggad, N. V. Madhusudana

Quantum Physics

Quantum Coordination Advantages in AI State-Tracking Tasks: Semantic Compilation and Latent Memory

Ming Yang

We prove inference-time quantum coordination advantages for specified AI state-tracking tasks. A solver compresses semantic history into a future-accessible boundary state and later answers a query. We count communication $B$, persistent instance-dependent memory $M$, and local work $D$; classical recurrence, caches, tools, and recomputation are allowed and charged. The central result is a boundary-preserving semantic-compilation theorem. It maps a finite one-way, streaming, or adaptive causal task into a semantic AI interface while preserving event order and access to past input. Classical boundary-state lower bounds and quantum-memory upper bounds transfer up to explicit compiler overhead, independently of the finite-precision recurrent architecture. Two applications have classical semantics. Matched-entity synopsis QA inherits the hidden-matching separation between $O(\log N)$ qubits and $\Omega(\sqrt{N})$ classical boundary bits. Continual requirements auditing inherits a Max-$k$SAT streaming separation: a recurrent solver uses $O(\log^5 n\log(1/\delta))$ qubits and polylogarithmic classical workspace to obtain a $0.7172$-approximation, whereas every classical one-pass finite-information solver attaining that ratio requires $\Omega(\sqrt{n})$ coordination width. As a quantum-native compiler test, a stabilizer latent-state dialogue uses $n$ qubits, while every exact finite-state classical causal online realization satisfies $B+M \ge \frac{1}{2}n^2+(\frac{3}{2}-\log_2 3)n+O(1)$. The source protocols, streaming algorithms, and stabilizer witness are imported; the new result is their architecture-independent semantic transfer. These are memory and coordination separations, not runtime or empirical advantages for present-day language models. The stabilizer result assumes exact simulation and ideal noiseless quantum memory.
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High Energy Physics (Phenomenology)

Tricritical dynamics in $\mathrm{^3He}$-$\mathrm{^4He}$ mixtures and QCD

Maneesha Pradeep, Johannes V. Roth and Lorenz von Smekal

In this paper we study the universal critical dynamics near the tricritical points in $\mathrm{^3He}$-$\mathrm{^4He}$ mixtures and QCD with two massless quark flavors. In particular, we use the real-time formulation of the functional renormalization group to understand how the tricritical region connects the $O(4)$ Model G dynamics of the two-flavor chiral phase transition to that of Model H for the QCD critical point with explicitly broken chiral symmetry. We show that in presence of an additional subdiffusive energy-like density, the tricritical dynamics inherits the strong dynamic scaling of Model G, where the critical fluctuations of order parameter and conserved $O(N)$ charges relax at identical rates. The strong scaling in the planar $O(2)$ case relevant for the $\lambda$-line and the tricritical point in the liquid $\mathrm{^3He}$-$\mathrm{^4He}$ mixtures arises as an interesting limiting case. Including the explicit symmetry breaking by the finite light-quark masses in QCD, the energy-like density of the tricritical dynamics mixes linearly with the $Z_2$ order parameter to eventually produce the characteristic slow fluctuations of the entropy per baryon near the QCD critical point.
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Materials Science

Accelerated Discovery of Materials with Extreme Work Functions through Uncertainty-Aware Multi-Fidelity Screening

Jun Meng, Ryan Jacobs, Rehan Kapadia et al. (+1 more)

Work function plays a pivotal role in technologies ranging from energy conversion and electronics to catalysis. In this work, we integrated machine learning (ML) with multi-fidelity screening to develop a data-driven framework for accelerating the discovery of materials with extreme work functions. We augmented a previously published Random Forest (RF) model for work function to include prediction uncertainty calibration and domain of applicability assessment to enhance prediction robustness. By combining the augmented RF model with universal ML interatomic potential simulations and targeted ab initio calculations, we screened 5.5 million compounds from the GNoME and Alexandria databases. This workflow identified 209 surfaces with extreme low work functions below 2.0 eV and 227 surfaces with extreme high work functions above 6.0 eV, corresponding to 136 and 172 unique materials, respectively. The resulting candidates revealed trends consistent with established chemical principles, including the tendency of alkali- and alkaline-earth-terminated surfaces to exhibit low work functions. While it also uncovered less conventional motifs: lanthanide-rich surface terminations were strongly associated with extremely low work functions, whereas surfaces containing metalloids or phosphorus at the top layer were correlated with exceptionally high work functions. This work demonstrates a scalable strategy that leverages ML models and multi-fidelity computational efforts to accelerate the discovery of materials with extreme work functions for advanced electronic, energy-conversion, and catalytic applications.
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All authors Jun Meng, Ryan Jacobs, Rehan Kapadia, John Booske

Soft Condensed Matter

Singularities in Soft Matter Systems

Vatsal Sanjay

When a liquid thread pinches off, its neck thins as it separates into two unconnected regions. Using continuum mechanics, we can predict that the neck reaches zero radius in finite time while its curvature grows without bound. Together, the vanishing neck and diverging curvature form a finite-time singularity. However, a real fluid does not realise these mathematical limits as molecular or material physics takes over once the neck becomes sufficiently small. Similar singularities arise throughout soft matter whenever a smooth continuum description is used at vanishing length scales. This review asks what the shrinking region forgets, what it retains, and which material length, time, or stress cuts off the apparent divergence. The dynamics near a singularity often become self-similar, with profiles at different times collapsing onto one shape when rescaled by the shrinking local length. Sometimes that collapse is universal enough that the surrounding geometry and forcing no longer determine the local dynamics. Nonetheless, the measured output could still depend on how the shrinking region is fed by the surrounding flow and on the small-scale physics that finally replaces the ideal divergence. Complex fluids and active matter change the same local balance by bringing their own timescales into the shrinking region. Beyond interfaces, the same logic applies when the localised object is a stress concentration or a defect in geometry or order rather than a moving surface. Singularities matter because they show where continuum theory stops being the relevant description and how the small-scale cutoff sets the outputs that count in printing, coating, aerosols, and stretchable solids.
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Plasma Physics

Machine-learning surrogate models for nonlinear energetic-particle transport predictions in ITER

Yashika Ghai, Donald A. Spong, Jacobo Varela et al. (+1 more)

Fast and accurate prediction of energetic-particle transport driven by Alfvén eigenmode (AE) instabilities is essential for integrated modeling workflows used in the design and optimization of burning plasma fusion reactors. In this work, we develop machine-learning-based surrogate models for rapid prediction of energetic beam and alpha-particle transport fluxes, together with predictive uncertainty estimates, for an ITER steady-state scenario. Two complementary surrogate methodologies, Gaussian process (GP) regression and hierarchical neural networks (NNs), are trained using nonlinear FAR3d gyrofluid simulations of energetic-particle transport. A flux-variability analysis demonstrates that the selected plasma-state representation provides a sufficiently unique parameterization of the nonlinear transport response over most of the sampled feature space, thereby justifying the surrogate formulation. Both surrogate models reproduce the nonlinear transport fluxes with high predictive accuracy while reducing the computational cost of transport evaluation by approximately five to six orders of magnitude relative to direct nonlinear FAR3d simulations. Although the two approaches achieve comparable predictive accuracy, they exhibit distinct uncertainty characteristics: the GP provides more consistent global uncertainty estimates, whereas the NN more clearly distinguishes between different transport regimes. This work establishes a proof of concept for developing machine-learning surrogate models of energetic-particle transport that are sufficiently accurate and computationally efficient to be incorporated into future integrated modeling workflows.
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All authors Yashika Ghai, Donald A. Spong, Jacobo Varela, Luis Garcia

General Relativity and Quantum Cosmology

Periodic orbits and gravitational wave signatures from magnetic dipoles around magnetized Kerr black holes

Shokhzod Jumaniyozov, Javlon Rayimbaev, Chengxun Yuan et al. (+3 more)

We study periodic orbits and the associated gravitational radiation of a magnetized (uncharged) test particle carrying a magnetic dipole moment with coupling constant beta, moving in the equatorial plane of a rotating, magnetized Kerr black hole immersed in an external asymptotically uniform magnetic field, starting from the effective potential derived for such particles. We compute the marginally bound orbit (MBO) and the innermost stable circular orbit (ISCO) as functions of the black hole spin a and the magnetic coupling beta, and map out the allowed region of the orbital energy-angular momentum (L, E) plane for bound motion. We then classify periodic orbits using the topological zoom-whirl scheme of Levin and Perez-Giz, characterized by three integers (z,w,v) through the rational rotation number q=w+v/z, and construct a family of closed rosette orbits at fixed angular momentum. Using the numerical-kludge, restricted-quadrupole approximation for an extreme-mass-ratio inspiral consisting of a stellar-mass magnetized secondary orbiting a supermassive magnetized Kerr black hole, we compute the time-domain gravitational waveforms h_+(t), h_\times(t) produced by these periodic orbits and their frequency-domain characteristic strain, and compare the latter with the anticipated instrumental sensitivity curves of LISA, Taiji and TianQin. We find that the magnetic coupling \beta systematically shifts the MBO and ISCO outward and lowers their orbital energy and angular momentum, that the zoom-whirl structure of the periodic orbits is imprinted directly on the burst-like morphology of the emitted waveform, and that the resulting gravitational-wave signals fall within the sensitivity band of upcoming space-based detectors for suitably close and massive sources.
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All authors Shokhzod Jumaniyozov, Javlon Rayimbaev, Chengxun Yuan, Satimbay Palvanov, Khurshida Khaknazarova, Faisal Javed

Quantum Physics

Entanglement depth and ancilla efficiency in quantum channel estimation

Javid Naikoo

We study the role of ancillary entanglement in quantum channel parameter estimation and investigate the minimal ancilla dimension required to achieve the maximum Fisher information. We introduce the $k$-ancilla Fisher information, which quantifies the optimal estimation precision achievable with input states of rank at most $k$, and derive a variational characterization in terms of a rank-constrained optimization problem. This formulation leads to a simple characterization of the minimum ancilla dimension $k^*$ required for optimal estimation, given by the minimum rank among the maximizers of the associated variational problem. We further identify sufficient conditions under which ancillary entanglement provides no advantage, including channel families admitting a fixed measure-and-prepare representation and channels satisfying a natural horizontality condition. In addition, we derive a bound on the incremental gain in Fisher information obtained by increasing the ancilla dimension under suitable structural assumptions on the optimal input states. The general results are illustrated through explicit examples, including unitary channels, qubit depolarizing and amplitude damping channels. These results provide a systematic framework for understanding and quantifying the entanglement resources required for optimal quantum channel estimation.
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