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Physics

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Monday 22 June

Nuclear Experiment

Measurements of Bremsstrahlung-Averaged Cross Sections for Reactions on Natural Nickel Targets at Eendpoint = 40MeV

O. Nusair, N. Solomon, M. Toro-Gonzalez et al. (+1 more)

Bremsstrahlung activation measurements were performed to study the production of $^{57}\mathrm{Ni}$, $^{56}\mathrm{Ni}$, $^{58}\mathrm{Co}$, $^{57}\mathrm{Co}$, $^{56}\mathrm{Co}$, and $^{55}\mathrm{Co}$ from natural nickel targets irradiated with photons generated by \SI{40}{MeV} electrons incident on a tantalum converter. Bremsstrahlung spectra were modeled using MCNP6.3\texttrademark{} and experimentally validated through activation of natural tin. Bremsstrahlung-averaged cross sections were extracted from end-of-irradiation activities, yielding $\langle\sigma\rangle = 8.983~\pm~0.028$~mb for $^{58}\mathrm{Ni}(\gamma,n)^{57}\mathrm{Ni}$, $0.248~\pm~0.025$~mb for $^{58}\mathrm{Ni}(\gamma,2n)^{56}\mathrm{Ni}$, $0.704~\pm~0.218$~mb for $^{nat}\mathrm{Ni}(\gamma,pxn)^{58}\mathrm{Co}$, $9.192~\pm~0.386$~mb for $^{58}\mathrm{Ni}(\gamma,p)^{57}\mathrm{Co}$, and $2.239~\pm~0.355$~mb for $^{58}\mathrm{Ni}(\gamma,pn)^{56}\mathrm{Co}$. A $90\%$ confidence-level upper limit of $\langle\sigma\rangle < 0.021$~mb is established for the $^{58}\mathrm{Ni}(\gamma,p2n)^{55}\mathrm{Co}$ channel. Comparison with JENDL-5 evaluations and prior studies indicates channel-dependent agreement, with residual discrepancies observed for selected charged-particle emission reactions. In particular, the measured $^{58}\mathrm{Ni}(\gamma,p)^{57}\mathrm{Co}$ cross section exceeds the JENDL-5 prediction by approximately a factor of two, whereas TALYS-2.2 calculations reproduce the experimental value, suggesting an underestimation of the $(\gamma,p)$ channel strength in JENDL-5 under bremsstrahlung conditions. For the $^{58}\mathrm{Ni}(\gamma,pn)^{56}\mathrm{Co}$ channel, both TALYS-2.2 and JENDL-5 predictions are in reasonable agreement, while the present measurement is higher by approximately a factor of two, though with larger associated uncertainty.
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All authors O. Nusair, N. Solomon, M. Toro-Gonzalez, D. DeVries

Optics

Single-Shot Realization of 10000-Mode Octave-Spanning Artificial Gauge Fields

Lida Xu, Apurva Padhye, Supratik Sarkar et al. (+6 more)

Artificial gauge fields (AGFs) enable photons and other bosons to emulate fermionic phenomena such as chiral edge transport and quantum Hall phases; however, existing theories and realizations remain confined to narrow bandwidths under single-mode approximation. We introduce a general theoretical framework for ultra-broadband, multi-modal dispersion-corrected AGFs in both linear and nonlinear regimes. Using integrated photonics, we realize over 100 distinct AGFs hosting more than 10,000 modes across nearly an optical octave – the first frequency-comb realization of the integer quantum Hall model for photons. Leveraging Kerr nonlinearity, we achieve single-shot AGF control beyond waveguide dispersion, robust to wafer-scale fabrication variations. Our results establish a new regime of ultra-broadband multimodal AGFs, opening pathways to exotic dispersion-corrected AGF dynamics and simulations, as well as volume-manufacturable device functionalities such as waveguide-dispersion-resilient photonic circuits, and AGF-enabled programmable nonlinear and quantum optics and optoelectrics.
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All authors Lida Xu, Apurva Padhye, Supratik Sarkar, Alireza Parhizkar, Christopher J. Flower, Gregory Moille, Kartik Srinivasan, Mohammad Hafezi, Mahmoud Jalali Mehrabad

Atomic Physics

Dual-isotope narrow-line MOT of dysprosium by phase modulation

M. Dürbeck, L. Reihs, J. Seifert et al. (+6 more)

We report on the characterization of a narrow-line magneto-optical trap (MOT), where two different isotopes of the dysprosium (Dy) atom can be simultaneously loaded and trapped. We rely on phase modulation via high-power, free-space electro-optic modulators (EOMs) to generate optical sidebands at the correct detuning for two different isotopes. This technique is applied on the slowing transition at 421 nm and the MOT transition at 626 nm. Using modular resonant electronic circuits, we match the sideband separation to the isotope shift among the two target isotopes, realizing mixtures of the bosonic isotopes 164Dy -162Dy and 162Dy -160Dy. We exploit the interplay between radiation forces and gravity in the narrow-line MOT to control the spatial position of the two isotopes with the EOM drive frequency. We demonstrate full control of the isotopic mixture with the EOM drive, offering new and cost-effective capabilities for controlling mixtures of atomic species that can be trapped in a narrow-line MOT.
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All authors M. Dürbeck, L. Reihs, J. Seifert, B. Choudhari, J.P. Marulanda-Serna, N. Werum, M. De Pas, G. Meijer, G. Valtolina

Mesoscale and Nanoscale Physics

Andreev exceptional points in Josephson junctions formed by minimal Kitaev chains

Jorge Cayao and Masatoshi Sato

We consider Josephson junctions formed by two minimal Kitaev chains and investigate how the interplay between non-Hermiticity and superconducting phase difference enables the realization of stable topological states that do not exist in the Hermitian realm. In particular, we focus on non-Hermiticity produced by coupling the minimal Kitaev chain Josephson junction to normal reservoirs, which renders the system open and characterized by a complex Andreev spectrum. Interestingly, we find that this complex spectrum hosts second order exceptional points, where a pair of eigenvalues and their respective eigenvectors coalesce, and are fully controlled by the superconducting phase difference. Depending on the spatial unequal distribution of non-Hermiticity, these Andreev exceptional points can appear at zero or finite energies connecting stable energy lines protected by non-Hermitian topology. Moreover, tuning the system parameters, such as onsite energies, non-Hermiticity, or electron cotunneling, the Andreev exceptional points give rise to Andreev exceptional lines enclosing protected two-dimensional zero real energy areas. We also discuss potential detection schemes of Andreev exceptional points by using local and nonlocal conductance signatures. Our results demonstrate the utility of non-Hermiticity from normal reservoirs as a useful resource for engineering non-Hermitian topological phases in minimal Kitaev chain Josephson junctions.
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Plasma Physics

Atmospheric carbon-14 production from neutron leakage in fusion energy systems

Brian James Albright and James Alastair Mercer-Smith

Neutron-producing fusion systems can generate atmospheric carbon-14 when neutrons leak into nitrogen-containing gas. We use MCNP6.2 neutron-transport calculations to estimate the probability that leaked neutrons produce $^{14}$C through $^{14}$N$(n,p)^{14}$C under representative near-ground conditions. For 14.1 MeV deuterium-tritium source neutrons, the conversion probability is 0.25-0.50 across the geometries studied; softer leakage spectra can give larger yields. Scaling this response to a 1 GWe fusion plant shows that percent-level neutron leakage into air would produce an atmospheric $^{14}$C source within a factor of a few of natural global production. At a 2500 GWe fleet scale, limiting fusion-derived radiocarbon to 10% of the natural source implies a mean atmospheric leakage fraction of order $10^{-6}$. These results provide a screening-level source-term estimate for atmospheric $^{14}$C production from terminal neutron leakage in neutron-producing fusion systems, with particular relevance to architectures containing open ports, beamlines, ducts, or other streaming paths.
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Quantum Physics

Biophysical EPR Using Superconducting Resonators

Austin R. Gamble Jarvi, Hamid R. Mohebbi, Ishit Raval et al. (+7 more)

We present innovations that enable the use of superconducting resonators for high sensitivity, high bandwidth pulsed electron paramagnetic resonance (EPR) measurements on biologically relevant samples with enhanced stability and throughput. A custom-built X-band pulsed EPR spectrometer with AWG and digital IF capability generated by an FPGA was used to control a novel patterned thin film planar superconducting microstrip resonator capable of generating Rabi fields sufficient to achieve 6 ns pi/2 Gaussian pulses using a 100 W solid-state HPA. The system allows automated sequential calibration, measurement, and analysis of five 3.5 uL samples contained in a sample cartridge. Performance was validated through measurements of double electron-electron resonance (DEER) distances in a variety of spin-labeled protein samples with biologically relevant concentrations, including measurements below 10 uM. The results enable broadening the scope of applications for both superconducting resonators and the use of EPR in biotechnology.
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All authors Austin R. Gamble Jarvi, Hamid R. Mohebbi, Ishit Raval, Omari Culzac, Jack Erickson, Sameh Hegazy, Don Carkner, Andrew Wiles, David G. Cory, Troy W. Borneman

Quantum Physics

Mølmer-Sørensen gates in trapped-ions chains in the presence of correlated noise

D. V. Donchenko, E. A. Anikin, O. Lakhmanskaya et al. (+1 more)

We analyze the impact of correlated laser frequency noise on Mølmer-Sørensen gates in qubit registers based on trapped-ion chains. Using perturbation theory, we calculate gate fidelities in the presence of noise with arbitrary power spectral density for different chain lengths and ion positions in the chain. With our approach, we account for simultaneous excitation of multiple phonon modes during gate operation. We find out that the impact of medium-frequency laser noise depends considerably on the positions of the ions in the chain. In contrast, low-frequency noise has similar effect for different chain lengths and ion positions.
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All authors D. V. Donchenko, E. A. Anikin, O. Lakhmanskaya, K. Lakhmanskiy

Plasma Physics

Design of a Doppler backscattering diagnostic for the Wisconsin HTS Axisymmetric Mirror (WHAM)

E. Wikarta, U. Kumar, V.H. Hall-Chen et al. (+5 more)

The Wisconsin HTS Axisymmetric Mirror (WHAM) is a compact high-field magnetic mirror. In such magnetic mirrors, cross-field transport is dominated by the flute instability (Endrizzi et al., 2023). To investigate density fluctuations associated with the flute instability, we designed a Doppler backscattering (DBS) diagnostic for WHAM, to be installed at the midplane port window. The diagnostic uses a two-channel tunable Ka-band (26.5–40 GHz) source and X-mode polarization. The azimuthal launch angle is set mechanically by rotating the external quasioptical assembly. As such, the system is reconfigurable during dedicated setup periods. Using the Scotty beam-tracing code (Hall-Chen et al., 2022), we show that the proposed DBS system can measure density fluctuations with perpendicular wavenumbers $1 \leq k_\perp \leq 3~\mathrm{cm}^{-1}$ over radial locations $0.7 \leq \rho \leq 0.9$, where $\rho$ is the normalized radial coordinate. This is achieved with probe frequencies between 28 and 38.5 GHz, an elevation launch angle of $0^\circ$, and azimuthal launch angles in the range $1^\circ$–$3^\circ$. The selected configurations have low mismatch angle at cutoff, $|\theta_{m,c}|<1^\circ$. The quasioptical system uses a Ka-band horn and a biconvex ultra-high molecular weight polyethylene lens, and satisfies the port-access constraints in WHAM. The planned microwave system has a monostatic, homodyne architecture based on two phase-coupled Ka-band microwave channels. These two channels will be for the transmitted signal and coherent local oscillator (LO) for IQ downconversion, respectively. As the two phase-coupled channels can be independently tuned or swept with a controlled frequency offset, the same microwave chain can also support profile-reflectometry measurements using cutoff-delay information.
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All authors E. Wikarta, U. Kumar, V.H. Hall-Chen, D. Endrizzi, S.J. Frank, C.M. Jacobson, X. Li, D.A. Sutherland

Instrumentation and Methods for Astrophysics

Stochastic Expectation Maximization for Robust State-Space Radio Interferometric Imaging

Nawel Arab, Mohammed Nabil El Korso, Isabelle Vin et al. (+1 more)

State–space models provide a flexible framework for analyzing dynamical systems, yet they often rely on Gaussian assumptions that fail to capture heavy-tailed or outlier-prone measurement noise. We propose a robust estimation scheme for linear state–space models subject to compound-Gaussian noise, as encountered for instance in radio interferometry affected by radio-frequency interference (RFI). The method relies on a Stochastic Approximation Expectation–Maximization (SAEM) algorithm in which the standard E-step is replaced by Monte Carlo sampling of the latent states and noise texture through closed-form Gibbs updates, enabling tractable inference despite the heavy-tailed likelihood. Numerical experiments show that the proposed method significantly improves reconstruction fidelity and robustness to RFI, outperforming a Gaussian EM algorithm and even an oracle RTS smoother. These results highlight the benefits of heavy-tailed state–space modeling and SAEM-based inference in interference-dominated imaging scenarios.
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All authors Nawel Arab, Mohammed Nabil El Korso, Isabelle Vin, Pascal Larzabal

Fluid Dynamics

Prediction of Viscoelastic Droplet Impact Dynamics Using a Vision Transformer-Based Approach

Diego A. de Aguiar and Cassio M. Oishi

Droplet impact on solid surfaces is a complex fluid dynamics problem with applications in spray cooling, inkjet printing, and pharmaceutical processing. Although numerical simulations are widely used to investigate these dynamics, their computational cost becomes significant when multiple parametric variations are considered. In this work, we investigate the use of a Video Vision Transformer (ViViT) architecture to predict the temporal evolution of viscoelastic droplets impacting solid surfaces using volume fraction fields obtained from the Volume of Fluid (VOF) method. In Newtonian fluids, impact dynamics are mainly characterized by the Reynolds number $Re$, representing the ratio of inertial to viscous forces, and the Weber number $We$, representing the ratio of inertial to surface tension forces. For viscoelastic fluids, additional parameters are required to account for elastic effects, namely the solvent viscosity ratio $\beta$ and the Weissenberg number $Wi$, increasing simulation complexity and cost. Instead of simulating the entire droplet dynamics, the proposed approach uses only the initial 10% to 20% of the simulation to predict the remaining evolution. Depending on the prediction configuration, this strategy reduces computational cost by approximately 80% to 90% compared to full numerical simulations. The ViViT produces physically consistent predictions across different parameters and prediction horizons, successfully capturing both spreading and bouncing regimes while preserving geometric features and structural similarity. Since volume fraction fields can also be extracted from experimental videos, the proposed framework could be extended to incorporate experimental data during training, potentially improving the physical fidelity of the predicted dynamics.
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Cosmology and Nongalactic Astrophysics

Cosmological constraints from the DESI DR1 Bispectrum Full-Shape and DR2 BAO

D. Forero-Sánchez, S. Novell-Masot, H. Gil-Marín et al. (+48 more)

We present cosmological constraints from DESI DR1 full-shape measurements, including the LRG bispectrum, combined with DESI DR2 BAO data. The analysis accounts for cross-covariance using mocks, while ShapeFit compression mitigates prior volume effects in beyond-$\Lambda$CDM analyses. In $\Lambda$CDM, the DESI1.5 (P+B) analysis yields $\sigma_8=0.868\pm0.026$ and $S_8=0.880\pm0.028$, compared with $\sigma_8=0.822\pm0.034$ and $S_8=0.827\pm0.036$ in the previous power-spectrum-only analysis. The marginalized uncertainties are reduced by 24% and 22%, respectively. For $w_0w_a$CDM, DESI-only analyses with the bispectrum shift dark energy parameters toward $\Lambda$CDM, consistent with a cosmological constant within $1\sigma$ in the $w_0$–$w_a$ plane. Adding CMB creates a preference for evolving dark energy: DESI+CMB (P+B) shows a $2.8\sigma$ deviation from $\Lambda$CDM. Including DES-Dovekie supernovae alone reduces this to $1.6\sigma$, while the full combination gives $3.1\sigma$. The bispectrum weakens evidence for time-varying dark energy relative to power-spectrum-only analyses. It also enhances sensitivity to massive neutrinos: in DESI-only data, the power-spectrum-only posterior for $\sum m_\nu$ is consistent with zero, whereas adding the bispectrum yields $0.26\pm0.18$ eV and a 95% upper limit of $0.59$ eV, shifting the peak into the positive region. For modified gravity, the bispectrum constrains $\mu_0 = 0.12\pm0.51$ from DESI-only data, consistent with general relativity.
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All authors D. Forero-Sánchez, S. Novell-Masot, H. Gil-Marín, L. Verde, J. Aguilar, S. Ahlen, D. Bianchi, A. Brodzeller, D. Brooks, F. J. Castander, S. Cole, A. de la Macorra, J. Della Costa, Biprateep Dey, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, Satya Gontcho A Gontcho, G. Gutierrez, C. Hahn, H. K. Herrera-Alcantar, K. Honscheid, D. Huterer, M. Ishak, D. Kirkby, A. Kremin, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, M. E. Levi, M. Manera, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, J. A. Newman, G. Niz, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, L. Samushia, E. Sanchez, D. Schlegel, M. Schubnell, J. Silber, G. Tarlé, B. A. Weaver

Quantum Physics

Augmenting Imaginary-Time Evolution with Local Geometric Information

Carlos L. Benavides-Riveros, Prachi Sharma, Pietropaolo Frisoni et al. (+1 more)

Imaginary-time evolution (ITE) underpins a broad family of algorithms for ground-state preparation in quantum simulation and quantum many-body physics. In these methods, convergence is governed by the energy variance of the instantaneous state, causing the flow to approach the ground state only asymptotically. We introduce an augmented imaginary-time evolution (AITE) framework that replaces the standard gradient flow on the energy landscape with a geometrically informed descent along locally optimal directions, which are identified by exploiting the higher-order statistical structure of the instantaneous energy distribution. The resulting flow strictly outperforms standard ITE throughout the entire evolution and exhibits two qualitatively distinct regimes: a superlinear convergence regime, followed by an extinction regime in which the energy error vanishes exactly at a finite value of the imaginary-time flow parameter, in contrast to the asymptotic exponential decay of ITE. Standard ITE is recovered in the zero-skewness limit of AITE, implying that the acceleration extends naturally across the broader ITE algorithmic family.
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All authors Carlos L. Benavides-Riveros, Prachi Sharma, Pietropaolo Frisoni, Fedor Šimkovic IV

Nuclear Theory

As above, so below: assessing extremeness of the neutron-star equation of state based on the unstable branch

Tyler Gorda, Oleg Komoltsev, Aleksi Kurkela et al. (+1 more)

Microscopic models of neutron-star matter have been widely used in astrophysical applications. The focus of attention has been on densities up to the maximal densities reached in stable neutron stars. The possibility that the underlying model assumptions may have important implications at higher densities has not been addressed. Here, we show that the behaviour at higher densities is strongly constrained by requiring a causal, stable, and thermodynamically consistent extension to the perturbative-QCD regime. We explicitly reveal what that behaviour must be and provide a tool for constructing and visualizing such extensions. We find that purely hadronic models trusted up to the maximal central density often require radically different behaviour at higher densities from that assumed in the original model, while models with additional degrees of freedom fare better. Our analysis disfavors purely nucleonic models for describing all stable neutron stars and supports the appearance of some type of additional degrees of freedom in stable massive neutron stars.
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All authors Tyler Gorda, Oleg Komoltsev, Aleksi Kurkela, Jürgen Schaffner-Bielich

Solar and Stellar Astrophysics

JWST NIRSpec Spectral Standards for M, L, and T Dwarfs and Subdwarfs

Evan Pritchard, Marylin Loritsch, Julia Haynes et al. (+3 more)

We present low resolution infrared spectral standards in the 0.76 to 5.0 {\mu}m range based on JWST NIRspec Prism data from deep sky surveys. Our standards encompass spectral types M, L, and T and dwarf and subdwarf metallicity classes. The standards extend ground based spectral templates and enable classification of low temperature stellar substellar discoveries from deep JWST NIRSpec data.
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All authors Evan Pritchard, Marylin Loritsch, Julia Haynes, Sara Morrissey, Emma Softich, Adam Burgasser

High Energy Astrophysical Phenomena

Detection of relativistic orbital deformation from improved timing of PSR J1757$-$1854

Jaikhomba Singha, Vivek Venkatraman Krishnan, Marisa Geyer et al. (+12 more)

PSR~J1757$-$1854, a 21.5\,ms pulsar, is a highly relativistic double neutron star (DNS) system in a tight eccentric ($e = 0.61$) 4.4\,hr orbit. With extremely large gravitational wave luminosity and one of the fastest orbital decay rates of any known DNS system, it is ideal for testing general relativity (GR) in the strong-field regime. Here we present results from a high-precision timing campaign combining archival data from the Murriyang telescope and Green Bank Telescope (GBT) with new high-sensitivity observations from the MeerKAT radio telescope and additional observations from the GBT. The extended baseline and superior sensitivity of MeerKAT have yielded substantial improvements to previously measured post-Keplerian parameters by a factor of around $\sim2$ or more. We report the first detection of the relativistic angular deformation, $\delta_\theta$ in this system, making PSR~J1757$-$1854 only the third DNS system for which $\delta_\theta$ has been measured, achieved here in just 9 yrs compared to the decades of timing required for both the double pulsar and the Hulse-Taylor binary. We demonstrate how $\delta_\theta$ can be used to constrain the spin-orbit geometry of the system, ruling out two of the four geometric solutions previously identified, while remaining consistent with GR. We also evaluate higher-order contributions to the periastron advance $\dot{\omega}$, including the second post-Newtonian correction and the Lense-Thirring term, and show that these have a measurable systematic effect on the inferred total system mass. The observed orbital period derivative, $\dot{P}_\mathrm{b}$ remains consistent with the GR prediction for gravitational-wave damping across a wide range of plausible distances.
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All authors Jaikhomba Singha, Vivek Venkatraman Krishnan, Marisa Geyer, Victoria Blackmon, Paulo Freire, Norbert Wex, Maura McLaughlin, Michael Kramer, Amanda Weltman, David Champion, Matthew Bailes, Sarah Buchner, Fernando Camilo, Andrea Possenti, Maciej Serylak

High Energy Physics (Phenomenology)

Event isotropy in perturbative QCD

Daniele Atzori, Matteo Cacciari, Simone Marzani et al. (+1 more)

It has recently been proposed that collider events can be equipped with a metric, the Energy Mover's Distance (EMD), which allows one to rephrase multiple aspects of collider physics in a geometric language. Further, the EMD can be exploited to define new observables. In this context, event isotropy quantifies the resemblance of an event to a uniform energy distribution. We present the first theoretical study of event isotropy within the framework of perturbative QCD. In particular, we first obtain the isotropy distribution in $e^+e^-$ collisions semi-analytically at $O(\alpha_s)$ (leading-order) and numerically at $O(\alpha_s^2)$ (next-to-leading order, NLO). Furthermore, we obtain all-order theoretical predictions by resumming the contributions of soft and collinear emissions, at next-to-leading logarithmic (NLL) accuracy. By matching resummed and fixed-order predictions we reach NLL+NLO accuracy.
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All authors Daniele Atzori, Matteo Cacciari, Simone Marzani, Gregory Soyez

Soft Condensed Matter

Stress-Boundary-Memory Feedback Drives Vortical-Polar Transitions in Softly Confined Active Matter

Haosheng Wen, P.B. Sunil Kumar and Mohamed Laradji

We computationally investigate how environmental sensitivity of active matter interacts with soft confinement to shape collective dynamics. In our model, the active constituents are represented as self-propelled particles (SPPs), implemented as nematic, disjoint ring polymers whose direction of motion can reverse without tumbling. Coarse-grained molecular dynamics simulations reveal that collective dynamics arise from a three-way feedback between active stresses, boundary elasticity, and particle-level memory. With increasing driving force, FD, this feedback generates a sequence of collective dynamical regimes. At low FD, SPP motion is dominated by thermal fluctuations. At intermediate FD, coherent vortical motion emerges with intermittent, noise-driven reversals. With further increase in FD, reversals are suppressed, yielding sustained unidirectional vortical motion. At sufficiently high FD, the system transitions to a polar state characterized by strong nematic ordering of the SPPs, symmetry breaking of the enclosure shape, and persistent polar collective motion. In this regime, the SPPs accumulate at the leading edge of the enclosure, driving sustained ballistic propulsion. These results demonstrate how environmental sensitivity and soft confinement jointly regulate emergent collective states and identify boundary elasticity as a control parameter governing the balance between vortical and ballistic dynamics.
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Soft Condensed Matter

Flexibility Controls Active-Filament Transport in Crowded Landscapes

Qingyi Di, Mohammad Fazelzadeh and Sara Jabbari-Farouji

Active filaments, ranging from motor-driven biopolymers to elongated bacteria and worms, are paradigmatic examples of deformable active matter. How filament flexibility interacts with environmental heterogeneity to control their transport in crowded environments, however, remains poorly understood. Here, we perform large-scale Brownian dynamics simulations of tangentially driven active polymers moving through ordered and disordered obstacle arrays to map the long-time diffusion as a function of obstacle density and filament flexibility. We find that flexibility can either enhance or hinder transport depending on the structure of the medium. In disordered environments, transport is optimized at intermediate filament flexibility, whereas both highly flexible and semiflexible filaments diffuse more slowly. In contrast, dense ordered arrays enhance the mobility of semiflexible filaments by promoting directed motion along periodic channels. We identify three distinct transport regimes: (i) tortuosity-controlled diffusion of highly flexible filaments, characterized by trapping-and-hopping dynamics; (ii) confinement-assisted transport of moderately flexible filaments, which enhances diffusion in dense media; and (iii) persistence-controlled transport of semiflexible filaments, which facilitates diffusion in dense ordered media, but suppresses it in disordered media. Combining theory and simulations, we show that long-time diffusion is governed by confinement-induced changes in filament conformation and reorientation dynamics. Our work uncovers general transport principles for deformable active agents in heterogeneous environments and provides a predictive framework for active-filament navigation in complex porous landscapes.
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Optics

Scalable reflective communication for microscopic electronics

Matthew F. Campbell, Kyle Skelil, Chaitanya Karimanasseri et al. (+6 more)

Untethered microscopic electronic circuits hold the potential for extraordinary advances in many fields such as neural transmitting and distributed sensing. However, establishing uplink communications from the microscale back to the macroscopic world remains challenging; existing micro-transmitters are difficult to integrate with semiconductor processing. Here we surmount this obstacle, introducing a strategy for modulating backscattered photons based on the electrochromic polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) that is scalable to micron-order sizes and manufacturable using standard parallelizable methods. Our devices, which we call SPOTs (submillimeter polymer optical transmitters), actuate at low voltages (< +/-1 V), switch in as fast as 10 {\mu}s, can run for millions of cycles, and operate seamlessly in electrolytes. We achieve this design by emphasizing architectural simplicity and mass-manufacturability rather than traditional metrics such as data rates or energy costs. As a demonstration, we develop SPOT-equipped temperature-sensitive photovoltaic-powered foundry-fabricated microchips and use them to wirelessly measure and transmit local temperatures. These results represent an important step toward fully-integrable, micron-scale bidirectional communication.
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All authors Matthew F. Campbell, Kyle Skelil, Chaitanya Karimanasseri, David Gonzalez-Medrano, Li Xu, Jungho Lee, David T. Blaauw, Igor Bargatin, and Marc Z. Miskin

Soft Condensed Matter

Yielding versus random organization: convex absorbing transitions in soft matter

Tristan Jocteur, Kirsten Martens, Eric Bertin et al. (+1 more)

We compare two different soft matter models, a generalized Random Organization Model (ROM) describing the stroboscopic dynamics of cyclically sheared suspensions, and an elastoplastic model describing the mesoscale dynamics of a yield-stress fluid under imposed stress. Both show absorbing phase transitions, sharing a peculiar mechanism: activity induces an internal noise which is transmitted over large distances by long-ranged mediated interactions, either hydrodynamic or elastic, which results in non-local creation of activity. They also both show convex transitions (i.e., the exponent $\beta >1$), in stark contrast with usual absorbing phase transitions, like (Conserved) Directed Percolation, which are concave ($\beta <1$). We further compare the dependence of the critical properties (activity mean value and fluctuations, avalanche statistics, low-wavenumber structure factor) on the decay exponent $\alpha$ of long-range interactions in both models, finding a qualitatively similar scenario. A smooth crossover is observed as a function of $\alpha$ between a concave transition regime for short-range interactions, with diverging fluctuations and compact avalanches, and a convex transition regime, with vanishing fluctuations and non-compact avalanches, for longer-range interactions. Although for a given range exponent $\alpha$, the values of critical exponents for both models differ, a good agreement between the models is found by parametrically plotting the different critical exponents as a function of the exponent $\beta$ of the mean activity. In this parametric representation, the concave regime is consistent with the behavior of the Long-Range Conserved Directed Percolation class, while the convex regime can be accounted for by a mean-field-type scenario with anomalous diffusion close to an absorbing boundary, inspired by the Hébraud-Lequeux model for the yielding transition.
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All authors Tristan Jocteur, Kirsten Martens, Eric Bertin, Romain Mari

General Relativity and Quantum Cosmology

Newtonian Shirokov Effect: Epicyclic Frequency Splitting from Mass Multipoles

Anuar Idrissov, Kuantay Boshkayev, Abylaikhan Tlemissov et al. (+1 more)

We analyze small oscillations of nearly circular orbits in an axisymmetric Newtonian potential expanded in mass multipoles, as the classical counterpart of the relativistic Shirokov effect. Computing the full Hessian of the effective potential at the true (possibly tilted) equilibrium and solving the coupled two-mode oscillator exactly, we obtain a complete picture. (i) A quadrupole splits the radial and vertical epicyclic frequencies, $\Omega_\theta^2-\Omega_r^2=-3GQ/r_0^5=6GMJ_2R^2/r_0^5$, at first order in $J_2$; the Newtonian analogue of the Shirokov splitting, equivalent to the classical statement that an oblate body's apsidal and nodal rates differ. (ii) A gravitational dipole produces no splitting: it equals $M r_{\rm CM}$, is removable by re-centering at the center of mass, and cannot appear in any coordinate independent frequency; the apparent first order coupling cancels at the true tilted equilibrium, any residual absorbed by the induced quadrupole of the shifted source, confirmed by direct orbit integration. (iii) A genuine octupole does split the frequencies, $\omega_+^2-\omega_-^2\approx6G|O|/r_0^6$. The selection rule is thus not even/odd parity: every multipole splits the frequencies except the dipole. These yield two complementary probes of an axisymmetric source: the frequency splitting measures the oblateness $J_2$, while the orbital plane tilt, $\delta\theta_0\simeq-r_{\rm CM}/r_0$, measures the center of mass offset $r_{\rm CM}$, an orbital geometry observable rather than a frequency one. We give solar system estimates for both. Carried through to Shirokov's original observable – the secular transverse drift after $n$ orbits – the quadrupole effect gives $\xi^\theta=\xi_0^{\theta}\,\pi n\,(6J_2R^2/r_0^2)$, of order $10^{-8}$ cm at $1$ au and $\sim10^{-6}$ cm near $0.1$ au, comparable to Shirokov's Schwarzschild estimate.
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All authors Anuar Idrissov, Kuantay Boshkayev, Abylaikhan Tlemissov, Hernando Quevedo

Earth and Planetary Astrophysics

Effects of Super-rotating Jets on Phase-Resolved Transmission Spectra at High Spectral Resolution

Hayley Beltz and Arjun B. Savel

Hot Jupiter atmospheric circulation can be shaped by a range of processes and planetary parameters, including rotation rate, irradiation gradients from tidal synchronization, magnetic effects, gravity, and clouds. Observations of exoplanetary spectral Doppler shifts as a function of phase, made possible with high-resolution spectrographs, can now probe the effects of exoplanetary winds at several points throughout transit. However, these measurements are difficult to interpret, given the variety of relevant atmospheric mechanisms. In this work, we generate high-resolution transmission spectra from two sets of circulation models: self-consistent dynamical models and idealized models that isolate circulation components. We identify how the strength of the jet — or the absence of one — alters the resultant net Doppler shifts. We find that the jet strength most prominently affects Doppler shifts during ingress and egress. During mid-transit, the strength of the jet linearly influences the Doppler shifts' slope; however, this effect is generally secondary to the overall blueshifting from planetary rotation. The slope induced by equatorial jets contrasts with the effect of pure day–night flows, which tend to add constant offsets to Doppler shifts during transit. Our modeling shows that jets also impact the cross-correlation function width; faster jets increase velocity dispersion across the limbs. We complement our simulations with semi-analytical arguments indicating that first-order changes of the cross-correlation function centroid and width (but not amplitude) probe thermal and velocity asymmetries. This work provides recommendations for interpreting net Doppler shifts in transmission and connecting these shifts with exoplanets' atmospheric circulation.
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Mesoscale and Nanoscale Physics

Generalized Fourier's law in mesoscopic systems

Luciano C. Lapas

Fourier's law fails when the mean free path of the energy carriers becomes comparable to the length and time scales over which the temperature field varies. We derive a thermodynamically consistent generalization in which the conductivity becomes a nonlocal memory operator $\mathbf{\kappa}_{\mathrm{eff}}(\mathbf{k},\omega)$, by combining mesoscopic nonequilibrium thermodynamics with the Mori–Kubo–Zwanzig projection-operator formalism. The Onsager kernel is a tensor sum over vibrational normal modes weighted by their Bose heat capacities and relaxation functions; it satisfies the second law for any closure consistent with the fluctuation–dissipation theorem and reduces, in the relaxation-time closure, to the nonlocal conductivity of the phonon Boltzmann equation. Two consequences follow. First, direction-dependent sampling of this tensor in a pump–probe experiment makes a nominally isotropic crystal exhibit apparent conductivities $\Lambda_z\neq\Lambda_r$. Second, the modulation frequency does not introduce temporal memory but sets the probed wavevector through the thermal penetration depth, so that the frequency-dependent suppression of the apparent conductivity measured by time-domain thermoreflectance on Ge and SiGe alloys is a spatial-nonlocality effect, with effective lengths of $0.25$–$0.4~\mu$m. With published mean-free-path spectra and no parameter adjusted to the thermoreflectance data, the kernel reproduces the spot-size dependence of Si, the frequency dependence of the apparent conductivity of Ge and Si$_{0.2}$Ge$_{0.8}$ and the rise of the apparent interface conductance of Al/Si$_{0.99}$Ge$_{0.01}$, and contains the two-channel ballistic/diffusive model as a two-sector projection.
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Atomic Physics

Analysis of the frequency shift in coherent population trapping resonance's dynamic continuous-wave spectroscopy at the phase-jump modulation and its comparison with the conventional approach

E. D. Chivilis and E. A. Tsygankov

We present the research of dynamic continuous-wave spectroscopy of the coherent population trapping resonance at the phase-jump modulation. {\Lambda} system of levels supplemented by a nonabsorbing state and bichromatic optical field, whose spectral components have different intensities, are considered. We demonstrate that the asymmetry leads to an additional nonlinear shift of the error-signal frequency under unisotropic relaxation of the ground-state density-matrix elements. We also investigate the conventional approach where the frequency difference of the optical field components is harmonically modulated to obtain the error signal. Comparison demonstrates that in the high-frequency modulation regime the corresponding frequency shift is more linear than at the phase-jump modulation for nonshort integration times.
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High Energy Astrophysical Phenomena

Deep Newtonian Afterglows: Theoretical Light Curves for Quasi-spherical Outflows

Nissim Fraija, Boris Betancourt-Kamenetskaia, Antonio Galván et al. (+1 more)

We investigate late-time gamma-ray burst (GRB) afterglows produced by quasi-spherical outflows propagating into a stratified circumburst medium during the deep Newtonian phase. Sub-relativistic ejecta generated in compact binary mergers or core-collapse explosions naturally develop velocity structures, while additional energy injection from a long-lived central engine, through spin-down luminosity and/or fallback accretion, can substantially modify the afterglow evolution. We develop an analytical framework for synchrotron emission from decelerated ejecta components undergoing energy injection in a stratified environment. The model provides multiwavelength light curves and corresponding closure relations for the deep Newtonian regime. We apply this framework to the late-time multiwavelength observations of GRB 171205A. In addition, we constrain the physical properties of quasi-spherical outflows using observations of short GRBs associated with kilonova candidates, together with long-term radio upper limits obtained years after the burst in a broader GRB sample. Our results show that late-time observations can place meaningful constraints on the dynamics, energetics, and energy-injection history of sub-relativistic quasi-spherical outflows from GRB progenitors.
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All authors Nissim Fraija, Boris Betancourt-Kamenetskaia, Antonio Galván, Maria G. Dainotti

High Energy Astrophysical Phenomena

Indication for Decreasing Dispersion Measure in the Population of Repeating Fast Radio Bursts and Connection to Young Supernova Remnant Expansion

Xiang-han Cui, Cheng-min Zhang, Di Li et al. (+8 more)

Fast Radio Bursts (FRBs) are millisecond-duration, highly energetic radio transients of uncertain origin. Repeating FRBs provide an excellent population for investigating their nature, particularly through studies of parameter evolution. Out of the 63 repeaters monitored by CHIME, we select the 19 sources with more than 10 detected bursts, and examine their long-term dispersion measure (DM) evolution. Seven sources show statistically significant DM evolution and are classified as the golden sample. Of these, five exhibit a decreasing DM trend and two show an increasing trend. We then perform a binomial test under the null hypothesis that decreasing and increasing DM variation trends have equal probabilities. The current combined sample, including our golden sample and additional repeaters with reported DM change rate from the literature, gives a p-value of 0.033, supporting that decreasing DM trends are more common in the repeating FRB population. This statistical result is consistent with scenarios in that the local electron density around repeaters generally decreases with time, for example, due to expansion of a young supernova remnant (SNR). Finally, within the SNR expansion model, we provide an illustrative estimate of the SNR contributions to the DM for different ejecta masses.
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All authors Xiang-han Cui, Cheng-min Zhang, Di Li, Pei Wang, Erbil Gügercinoğlu, Joeri van Leeuwen, Yi-dan Wang, Chao-wei Tsai, Xiang-lei Chen, Wen-qi Ma, Habtamu Menberu Tedila

Fluid Dynamics

On initiation of detonation in large fuel-air clouds

Leonid Kagan, Peter V. Gordon and Gregory Sivashinsky

The proposed study is motivated by experimental evidence, dating back to 1985, demonstrating the possibility of deflagration-to-detonation transition (DDT) in a fuel-air cloud. The detonation is initiated by a flame jet developed in a thin open-ended tube inserted into the cloud. Despite the experimental data, a first-principle understanding of the mechanism controlling the transition is still missing. The current research is aimed at resolution of this issue through a simple 2D formulation involving minimum physical ingredients.
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Earth and Planetary Astrophysics

Hydrogen airglow from an escaping ultrahot Jupiter atmosphere

Yapeng Zhang, Chenliang Huang, Aaron Householder et al. (+17 more)

Intense high-energy irradiation of close-in gaseous exoplanets drives the rapid escape of their atmospheres, fundamentally shaping planetary demographics. While atmospheric loss is routinely observed via transit absorption in atomic hydrogen, helium, and metal ions, the underlying physical properties, specifically the thermal structure, outflow dynamics, and mass-loss rate, remain poorly constrained due to inherent degeneracies in the transmission geometry. Here we report the first detection of atomic hydrogen emission from the escaping atmosphere of a gas giant. Using high-resolution spectroscopy of the ultrahot Jupiter KELT-9 b, we detect a hydrogen Balmer line (H{\alpha} 6564.6 Å) emission signature originating from the planetary dayside. The emission line profile features a distinctive double-peaked shape with 0.1-0.15% peak amplitudes at +/-30 km/s and central self-absorption. This profile breaks transmission degeneracies, providing direct observational constraints on the vertical thermal structure, excited-state hydrogen populations, and wind dynamics in the upper atmosphere of KELT-9 b. Initial modeling reveals a vigorous outflow with a mass-loss rate above 10^{13} g/s, among the highest measured to date for gaseous exoplanets. Our results establish hydrogen airglow emission as a powerful diagnostic of atmospheric escape, opening a new observational window into the evolution of worlds in extreme radiation environments.
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All authors Yapeng Zhang, Chenliang Huang, Aaron Householder, James E. Owen, Fei Dai, Aurora Y. Kesseli, Andrew W. Howard, Julie Inglis, Howard Isaacson, Heather A. Knutson, Dimitri Mawet, Nicole Wallack, Jerry W. Xuan, Michael Zhang, Theron W. Carmichael, Daniel Huber, Rena A. Lee, Nicholas Saunders, Lauren M. Weiss, Jingwen Zhang

Mesoscale and Nanoscale Physics

Fine structure of the cyclotron resonance in heterobilayers of proximitized graphene and transition metal dichalcogenides

M. A. Rakitskii, K. S. Denisov and N. S. Averkiev

A monolayer graphene and its Dirac electrons can be equipped with an enhanced spin-orbit coupling (SOC) when proximitized by other van der Waals (vdW) materials, such as transition metal dichalcogenides (TMDs). In this work we analyze the cyclotron resonance (CR) absorption of such heterobilayers at quantizing magnetic fields in the presence of proximity-induced spin interactions, including the spin-pseudospin Rashba coupling. We evaluate the spin-textured wave functions of the Landau levels and calculate the absorption spectrum paying special attention to its spin proximity induced modifications. We reveal the formation of a fine double-peak structure of the main interband CR transitions, as well as the presence of additional spin-flip absorption, the combined cyclotron resonance (CCR), centered at different resonant frequencies. The selection rules for CCRs are identified and complemented by the perturbation theory analysis. We also discuss the polarization dependence of the absorption and the proximity-induced emerging magneto-optical responses. Our theory explains the effect of proximity-induced spin interactions for Dirac electrons cyclotron resonance and points out at its experimental verifications.
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