Statistical Mechanics
Random-matrix and transport frequencies in eigenstate spectral functions
Kadir Çeven, Rohit Patil, Marcos Rigol et al. (+1 more)
The fact that generic isolated many-body
quantum systems thermalize is understood using the eigenstate thermalization hypothesis (ETH). In recent years, there has been much interest in the behavior of the ETH spectral functions, which characterize the smooth dependence of the variance of the off-diagonal
matrix elements of observables on the associated energy and frequency, and whose low-frequency part contains information about the long-time dynamics. In finite systems described by the ETH, the spectral functions are expected to exhibit plateaus below a characteristic frequency $\omega^{}_{\mathrm{ETH}}$. In this regime, the statistics of the
matrix elements of observables are expected to be described by random
matrix theory. Related frequencies that have been studied in the literature are $\omega^{}_{\mathrm{SFF}}$, which controls the onset of random-
matrix behavior in the spectral form factor, and the transport frequencies $\omega^{}_{\mathrm{tr}}$, which are derived from transport coefficients. However, a direct quantitative comparison of these frequencies is lacking. Using exact diagonalization, we conduct such a comparison for the spectral functions of current operators in clean and disordered
quantum spin ladders with diffusive energy and
spin transport. We find clear evidence for the expected low-frequency plateaus in the ETH spectral functions. For the accessible system sizes, $\omega^{}_{\mathrm{SFF}}$ is consistent with the extent of the plateaus, while the transport frequencies are systematically larger and lie in the nonuniversal regime of the spectral functions. Our findings highlight the need to better understand the origin of these quantitative differences.
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All authors Kadir Çeven, Rohit Patil, Marcos Rigol, Fabian Heidrich-Meisner
Chemical Physics
Composition-Dependent Self-Diffusion Coefficients in Liquid Mixtures from Hybrid Machine Learning
Jens Wagner, Thomas Specht, Hans Hasse et al. (+1 more)
Self-
diffusion coefficients are key descriptors of molecular mobility, yet experimental data remain scarce, highlighting the need for reliable prediction methods. In previous work, we introduced the hybrid Enhanced Stokes-Einstein (ESE) model, which advanced the state of the art in the physically consistent prediction of self-
diffusion coefficients of solutes at infinite dilution in pure solvents by integrating the Stokes-Einstein equation with machine learning (ML). Here, we extend this approach to concentration-dependent self-
diffusion coefficients and multicomponent solvents with HADES. This hybrid architecture leverages a deep-set neural network to connect pure-component and mixture prediction within a single framework. HADES predicts self-
diffusion coefficients in
liquid mixtures with any number of components at any composition and temperature. The only required inputs are SMILES-encoded molecular structures of the components and the pure-component viscosities, making the method broadly applicable. Trained and evaluated on a comprehensive
dataset of 2526 data points for 600 systems, HADES significantly outperforms
benchmark prediction methods. The trained model and its source code are fully disclosed, and the application is available via an interactive website https://ml-prop.mv.rptu.de/.
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All authors Jens Wagner, Thomas Specht, Hans Hasse, Fabian Jirasek
Atomic Physics
Vector Measurements Using Integrated Radio Frequency Atomic Magnetometers
Ayse Marasli, Thomas W. Kornack, D. Casey Oware et al. (+1 more)
We demonstrate reconstruction of three-dimensional
radio-frequency (RF)
magnetic-field vectors using a pair of integrated RF atomic magnetometers operated with orthogonal bias-field orientations. A theoretical and experimental analysis identifies a phase-ambiguity dead band that limits reconstruction when the two sensor responses become nearly identical. Measurements performed in an unshielded laboratory environment demonstrate accurate reconstruction of RF
magnetic-field orientations and validate the predicted dependence of reconstruction accuracy on signal imbalance. These results establish integrated RF atomic magnetometers as a compact and sensitive platform for directional RF
magnetic-field sensing, particularly at low frequencies, and provide a foundation for portable source-localization and field-mapping applications.
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All authors Ayse Marasli, Thomas W. Kornack, D. Casey Oware, Karen L. Sauer
Astrophysics of Galaxies
LATED: JWST integral field spectroscopy of a galaxy caught in chemical infancy at $z=4.8$ behind Abell 2744
Mingyu Li, Roberto Maiolino, Zheng Cai et al. (+26 more)
When Population III (Pop III)
star formation ended remains an open question. LATED-1 is an intrinsically faint ($M_\mathrm{UV}=-16.15$) Ly$\alpha$ emitter at $z=4.80$ revealed by VLT/MUSE behind the
lensing cluster Abell 2744 ($z=0.308$). Before any spectroscopic
metallicity constraints, it was identified as an extremely metal-poor or metal-free
galaxy candidate from JWST imaging by LATED, our novel photometric selection framework. Here we present serendipitous JWST/NIRSpec PRISM integral-field spectroscopy of this target. The spectrum reveals Ly$\alpha$, H$\beta$, and H$\alpha$ at 7.0, 5.6, and 17.7$\sigma$, as well as tentative detections of [O III]$\lambda\lambda4959,5007$ at 2.9$\sigma$, and yields $R3=\mathrm{[O\,III]\lambda5007/H\beta}=0.59^{+0.27}_{-0.21}$, upholding the earlier LATED photometric prediction of $R3<1.54$ ($2\sigma$ limit). The canonical JWST-based strong-line calibration, extrapolated to low
metallicity, implies $\log (O/H)=6.45^{+0.17}_{-0.19}$, or $Z/Z_\odot=0.58_{-0.20}^{+0.28}\%$, placing LATED-1 among the most metal-poor
galaxies known. Its modest magnification ($\mu=2.80$) leaves the intrinsic properties insensitive to the lens model. LATED-1 is therefore a
dwarf galaxy caught in the earliest state of chemical enrichment, and a compelling target for testing whether Pop III
star formation can persist to $z<5$. The result demonstrates that photometric selection, especially through the LATED methodology, can reach below one per cent
solar metallicity to identify Pop III
galaxy candidates for spectroscopic follow-up.
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All authors Mingyu Li, Roberto Maiolino, Zheng Cai, Hannah Übler, Boyuan Liu, Qiao Duan, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Eiichi Egami, Bjorn H. C. Emonts, Xiaohui Fan, Yuki Isobe, Lucy R. Ivey, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, J. Xavier Prochaska, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Yunjing Wu, Fujiang Yu, Zijian Zhang
Astrophysics of Galaxies
LATED: Ly$\alpha$-anchored photometric selection of candidate metal-free and extremely metal-poor star formation from the end of reionisation to cosmic noon
Mingyu Li, Zheng Cai, Roberto Maiolino et al. (+24 more)
Cosmological simulations allow a low-level tail of Population III (Pop III)
star formation to persist to $z=2-6$. Spectroscopic confirmation is expensive, so an efficient photometric pre-selection is needed. We present LATED (Lyman-Alpha
Tomography of Extremely Metal-poor Domains), which selects metal-free and extremely metal-poor candidates from a Ly$\alpha$-emitter parent sample using strong-line diagnostics. The method requires three bands and two colours, $x=m_{\rm OIII}-m_{{\rm H}\alpha}$ and $y=m_{{\rm H}\alpha}-m_{\rm cont}$, which trace oxygen abundance and the H$\alpha$ equivalent width, respectively. Requiring that the filters simultaneously contain [O III]+H$\beta$ and H$\alpha$, together with a Ly$\alpha$ parent selection, defines five windows spanning $z=1.92-6.60$ (four JWST/NIRCam, one Roman/WFI). The criteria, $x\geq x_{\rm min}(z)$ and $y\leq y_{\rm max}(z)$, are set by the per-
redshift extrema of a forward-modelled Pop III template locus. Ordinary metal-enriched
star-forming and AGN templates fall outside the selection region, and possible contaminants such as little red dots are flagged by their multi-band colours. To check contamination empirically, we apply LATED to 1126 JADES spectroscopic
galaxies, and no source is selected in the four NIRCam windows. We release a Python package which converts the same photometry into R3=[O III]/H$\beta$ as a measurement or upper limit, reproducing JADES spectroscopy with small 0.12 dex scatter. Applied to 85 archival MUSE Ly$\alpha$ emitters in Abell 2744, LATED recovers the confirmed extremely metal-poor
galaxy AMORE6 and reveals three new candidates at $z=3-5$. Photometry alone cannot establish a metal-free nature. LATED delivers prioritised candidates for spectroscopic follow-up, providing a scalable route toward a systematic census of late-time Pop III
star formation.
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All authors Mingyu Li, Zheng Cai, Roberto Maiolino, Fuyan Bian, Sijia Cai, Francesco D'Eugenio, Qiao Duan, Eiichi Egami, Xiaohui Fan, Yuki Isobe, Xihan Ji, Gareth C. Jones, Maria Koller, Xiaojing Lin, Boyuan Liu, Christopher C. Lovell, Kimihiko Nakajima, Masami Ouchi, Robert G. Pascalau, Zijin Su, Jan Scholtz, Fengwu Sun, Sandro Tacchella, Hannah Übler, Yunjing Wu, Fujiang Yu, Zijian Zhang
Mesoscale and Nanoscale Physics
Corbino-Enhanced Supersonic Acoustic-Emission Threshold in a GaAs Two-Dimensional Electron System
A. D. Levin, A. S. Jaroshevich, Z. D. Kvon et al. (+5 more)
We report nonlinear differential-resistance measurements in a high-mobility GaAs/AlGaAs two-dimensional electron system patterned in a Corbino geometry. At zero
magnetic field, $R_{\mathrm{diff}}(I_{dc})$ exhibits a pronounced polarity-selective threshold peak on the negative-current branch, gradually suppressed by a perpendicular
magnetic field. We interpret the Corbino anomaly as a local Cherenkov-like threshold for acoustic
phonon emission, enabled by the radial current concentration $j_r(r)=I/(2\pi r)$, which drives the local electron velocity above the sound velocity in a region adjacent to the inner contact. The polarity selectivity is attributed to Peltier heating and cooling, which modify the local thermal and boundary conditions near the contact, rather than to the kinematic threshold itself. Our results identify the Corbino geometry as a sensitive platform for probing local nonequilibrium electron–
phonon processes in a high-mobility electron system within an independently established hydrodynamic-crossover regime and suggest that the inner Corbino contact can act as a geometry-defined source for supersonic acoustic emission.
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All authors A. D. Levin, A. S. Jaroshevich, Z. D. Kvon, V. A. Chitta, M. S. Aksenov, D. V. Dmitriev, A. K. Bakarov, G. M. Gusev
High Energy Physics (Theory)
The Gaiotto-Kim Trace Formula and Line Defects
Sungjoon Kim and Spencer Stubbs
We study the insertion of 4d half-BPS line defects into the trace formula proposed by Gaiotto and Kim, which computes the ellipsoid partition function of the 3d topological
quantum field theory (TQFT) arising from a 4d $\mathcal{N}=2$ superconformal field theory. This yields a homomorphism to 3d Wilson loops, preserving the fusion
algebra of the 4d defects. We also present a systematic
algorithm for determining the simple objects of a 3d TQFT in terms of Wilson loops in the UV 3d $\mathcal{N}=2$ abelian Chern-Simons-matter theory. Utilizing supersymmetric localization, we characterize the modular $S$- and $T$-
matrices of the TQFT. We apply our
algorithm to various 3d TQFTs arising from the trace formula with higher-power monodromy of the $(A_1,G)$ Argyres-Douglas theories.
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Mesoscale and Nanoscale Physics
The Superconducting Talbot Effect in Phased-Array Josephson Junctions
Hechen Ren and Ziying Li
We introduce the superconducting Talbot effect—a macroscopic
quantum self-imaging phenomenon occurring when proximitized Cooper pairs propagate through a ballistic two-dimensional electron gas. By configuring periodic superconducting leads into a phased-array Josephson junction with programmable phase differences, we demonstrate active steering of the resulting superconducting Talbot carpet. To overcome transport resolution limits, we design a Vernier-scale collector array that performs sub-wavelength sampling of the fractional Talbot pattern. This approach maps real-space
quantum interference with high robustness to disorder, enabling direct extraction of
Fermi wavelengths across helical,
spin-degenerate, and
spin-orbit-split
Fermi surfaces. Tight-binding numerical calculations on a square
lattice validate the real-space interference patterns. Our results establish a versatile framework for coherent wavefront engineering and
quantum materials diagnostics in superconducting optics.
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Instrumentation and Methods for Astrophysics
Pushing high angular resolution and high contrast observations on the VLTI from Y to L band with the Asgard instrumental suite: integration status and plans
Marc-Antoine Martinod, Michael J. Ireland, Denis Defrère et al. (+39 more)
ESO's VLTI has a history of record-breaking discoveries in astrophysics using high-angular resolution instrumentation. Its latest visitor instrument, the Asgard instrumental suite, is one key to further enhance the potential of the facility, particularly in the very near-infrared. It comprises four natively collaborating instruments: HEIMDALLR, a K-band fringe tracker, wavefront corrector and
stellar interferometer in K band, with the same optics; Baldr, an H-band Zernike wavefront sensor; BIFROST, an Y-J-H-band photonic combiner whose main science case is studying the formation processes and properties of
stellar and planetary systems; and NOTT, an L-band nulling interferometer for imaging young planetary systems. Each of these instruments promise significant advances in their respective science goals that scale with their technical challenges and technology innovations. The integration of Asgard is planned in three phases. The first one (integration, commissioning of HEIMDALLR and Baldr) is successfully done. In this paper, we show an overview of the current progress of the integration of Asgard, the first results of the on-sky commissioning of HEIMDALLR and the future steps and observing policies for Asgard to serve the broader community.
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All authors Marc-Antoine Martinod, Michael J. Ireland, Denis Defrère, Stefan Kraus, Frantz Martinache, Peter G. Tuthill, Emilie Bouzerand, Julia Bryant, Sorabh Chhabra, Peter Chingaipe, Benjamin Courtney-Barrer, Fred Crous, Nick Cvetojevic, Daniel S. Dahl, Colin Dandumont, Steve Ertel, Germain Garreau, Adrian M. Glauser, Xavier Haubois, Lucas Labadie, Stéphane Lagarde, Daniel Lancaster, Romain Laugier, Roxanne Ligi, Nathan Long, Alexandra Mazzoli, Thomas Mattheussen, György Medgyesi, Kwinten Missiaen, Sébastien Morel, Daniel J. Ahrer, Barnaby Norris, Jyotirmay Paul, Romain Petrov, Gert Raskin, Sylvie Robbe-Dubois, Gordon Robertson, Muhammad Salman, Ahmed Sanny, Nicolas Schuhler, Owain Snaith, Adam K. Taras
High Energy Physics (Phenomenology)
Probing axion-like particle couplings to leptons via the $\gamma\gamma jj$ signal at the FCC-ee
Hua-Ying Zhang and Chong-Xing Yue
We study the sensitivity of the Future Circular
Collider in electron-positron mode (FCC-ee) to the
axion-like particle (ALP) couplings with
leptons via the process $e^{+}e^{-} \rightarrow \gamma\gamma jj$ at the center-of-mass energy $\sqrt{s}=91$ GeV with the integrated luminosity $\mathcal{L}=150~\text{ab}^{-1}$. We analyze three scenarios, $\mathbf{c}_R=0$, $\mathbf{c}_L=0$ and $\mathbf{c}_R=\mathbf{c}_L$, for both unpolarized and polarized beams with $(P_{e^-}, P_{e^+}) = (+80\%, -80\%)$, and derive projected lower limits on the effective coupling strengths. The polarized case provides higher sensitivity than the unpolarized case. Specifically, for the $\mathbf{c}_R=0$ scenario (probing the ALP-
neutrino coupling $\text{Tr}(g_{a\nu\nu})/f_a$), the projected sensitivity in the polarized case reaches approximately $0.0105~\text{GeV}^{-1}$ for the ALP mass in the range $10$–$24$ GeV; for $\mathbf{c}_L=0$ (probing the ALP-charged
lepton coupling $\text{Tr}(g_{a\ell\ell})/f_a$), it reaches $0.0174~\text{GeV}^{-1}$ in the $10$–$27$ GeV range; and for $\mathbf{c}_R=\mathbf{c}_L$ (probing the ALP-
neutrino coupling $\text{Tr}(g_{a\nu\nu})/f_a$), it reaches $0.00394~\text{GeV}^{-1}$ in the $45$–$80$ GeV range. In these ALP mass ranges, our projected sensitivities are complementary to the projected sensitivities from other search channels at future
colliders.
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Quantum Physics
A Reconfigurable Multilayer Quantum Key Distribution Network over Existing Metropolitan Fibre
Mariella Minder, Andreas Siakolas, Elizabeth Pasatembou et al. (+4 more)
Scaling
quantum networks requires architectures extending end-to-end service reachability despite constrained fibre and equipment. Critically, in brownfield deployments, the
quantum network must be engineered around classical telecommunications infrastructure and the operating capabilities of
quantum key distribution (QKD) technology. To address this, we demonstrate a seven-node, multilayer QKD network deployed over existing metropolitan fibre. The implementation compares spectral management techniques to accommodate inherited constraints across its layers. It combines a trusted-node ring with a three-node subnetwork interconnected through reconfigurable optical switching, extending physical connectivity and service reachability without an additional transmitter. A meshed key management layer maps endpoint requests onto trusted-relay paths and supplies Layer 1, Layer 3, and one-time-pad applications. Over 73 days, eight link configurations generated 119.4 Gbit of secret key material with 99.1% link availability. Randomised end-to-end requests revealed indirect cross-layer coupling between key consumption, stored-key state and
quantum-layer reconfiguration, demonstrating resource sharing through reconfigurability, spectral multiplexing and logical key-management abstraction.
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All authors Mariella Minder, Andreas Siakolas, Elizabeth Pasatembou, Stylianos Mavrikos, Stephanos Yerolatsitis, Konstantinos Katzis, Kyriacos Kalli
Quantum Physics
Collective advantage from a minimal record in a quantum information engine
Kangqiao Liu, Jie Gu and Deyou Chen
For a single particle, a
quantum information engine can turn measurement fluctuations into transport by raising a barrier behind the particle each time its position is measured. When many particles are present, the barrier still depends on just one number, the position of the leftmost particle, so we let the demon measure that order statistic and nothing else. A demon that resolves every position instead pays a record
entropy that grows with particle number, even though the extra distinctions never change where the barrier is placed. We show that the coarser measurement supplies an energy that is bounded independently of particle number, and that this bound yields a ceiling on the record
entropy that falls as the filling increases. At the same tilt, the collective engine then delivers $44\%$ more work per recorded nat than independent single-particle engines, each with its own optimized cycle time and each running at equal or greater power per particle. Pauli blocking ends this advantage once the accessible region just above the wall fills. We also evaluate the coherence that the coarse measurement leaves behind, and the cost of placing the barrier imprecisely.
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High Energy Physics (Theory)
Takamasa Kanai
We investigate the relation between de Sitter
entropy and
holographic entanglement entropy in higher-
curvature gravity and its braneworld realization. Using the canonical formulation of the gravitational action and the Euclidean gravitational path integral, we derive the de Sitter
entropy, including contributions from higher-
curvature surface terms, and compare it with the
holographic entanglement entropy obtained from the corresponding
entropy functional. We first consider Gauss-Bonnet
gravity and show that the two
entropies coincide for static asymptotically de Sitter braneworld spacetimes on the RS II model, while they generally differ for stationary spacetimes. The mismatch in the stationary case arises from an extrinsic-
curvature contribution associated with the constant-time surface, which vanishes for static configurations but is generally nonzero for stationary geometries. We then extend the analysis to general Lovelock
gravity and show that the agreement between the de Sitter
entropy and
holographic entanglement entropy persists for static asymptotically de Sitter braneworld spacetimes in the RS II model beyond the Gauss-Bonnet case. We also comment that the same distinction between static and stationary configurations applies to braneworld black holes: the black hole
entropy agrees with the
holographic entanglement entropy in the static case, while the two generally differ for stationary braneworld black holes. Our results clarify the relation between gravitational and
holographic entropies in higher-
curvature gravity and provide a broader perspective on
holographic correspondence in Lovelock theories and their braneworld realizations.
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Mathematical Physics · Cross-listed from math.DG
Dirac-harmonic maps from manifolds with boundary via index theory
Volker Branding and Nicolas Ginoux
Dirac-harmonic maps are a mathematical version of the supersymmetric non-linear sigma model of
quantum field theory. Since they arise as critical points of an unbounded energy functional, it is a challenging task to establish general existence results. Within this manuscript we mainly prove a general existence result based on index theory for
manifolds with boundary and apply it in various situations. Due to the presence of a boundary there are additional contributions in the Atiyah-Patodi-Singer index formula allowing for a non-vanishing index, which is the key argument in our proofs. Further explicit examples based on twistor spinors on surfaces are also presented.
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Physics and Society
Unused power surge compromises U.S. road vehicles sustainability
Hugues Perraut, Joseph Le Bihan, Eric Herbert et al. (+1 more)
Material and energy flows underpin sociotechnical metabolism. However, despite growing sustainability concerns over expanding material stocks and declining stock productivity, the link between material use and energy consumption remains poorly understood. This gap reflects a limited distinction between structures and the activity they enable, and the lack of quantification of the installed power of energy consuming structures. Here we reconstruct the long-term growth dynamics of U.S. road vehicles, distinguishing professional and consumer assets. We show that installed power, mass, and fuel energy use follow divergent patterns within and across vehicle categories. By introducing the usage factor as a metric linking structure to activity, we quantify decoupling mechanisms such as engine oversizing and fleet redundancy, which drive up material immobilization. As electrification requires large-scale fleet replacement, our findings highlight that avoiding power oversized vehicles could reduce material demand, emphasizing the need to account for structure-activity decoupling in energy transition policies.
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All authors Hugues Perraut, Joseph Le Bihan, Eric Herbert, Petros Chatzimpiros
Instrumentation and Methods for Astrophysics
Silencing the stellar glare with kernel-nulling and active phase control on photonic chips
Marc-Antoine Martinod, Vincent Foriel, Nick Cvetojevic et al. (+4 more)
Characterizing
exoplanets and finding biosignatures are among the hottest topics in astronomy. This quest is challenged by the brightness contrast between the faint
planet and the overwhelming glare of the host
star, their small angular separation, and observing conditions degraded by optical aberrations. Nulling interferometry is a promising technique to achieve this goal by fulfilling requirements for both high contrast and high angular resolution. Photonic Integrated
Circuits (PICs) provide compactness, design versatility, and scalability needed for nulling. With the PHOTONICS project, we aim to create novel coherent combination architectures, based on a multimode interferometer (MMI) coupler and on-chip active phase control with no moving parts. We present the first lab tests of a four-beam kernel-nuller made out of a single MMI coupler with active phase control: ABCD fringe-tracking and the characterization of the contrast detection limits of a four-beam kernel-nuller.
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All authors Marc-Antoine Martinod, Vincent Foriel, Nick Cvetojevic, Frantz Martinache, Jeronimo Calderon-Gomez, Roxanne Ligi, David Mary
High Energy Physics (Phenomenology)
Spectroscopic parameters of $B_c$ meson
Sinem Küçüky{\i}lmaz and Halil Mutuk
We study the spectroscopy and decays of the $B_c$
meson in a nonrelativistic
quark model in which all observables follow from a single set of wave functions, with
spin-dependent effects included directly in the bound-state equation. With parameters calibrated to the measured $B_c(1S)$ and $B_c(2S)$ masses, we predict the $S$-, $P$-, and $D$-wave spectrum up to $n=5$, the pseudoscalar and vector decay constants with one-loop QCD corrections, the E1 and M1 radiative widths, and the radial Regge trajectories of ten
spin-parity families. The $1P$ multiplet is predicted at 6692–6746~MeV with the normal fine-structure ordering, compatible with
lattice QCD and located in the region of the two structures observed by LHCb in the $B_c^+\gamma$ spectrum. The $1D$ states lie near 7008~MeV, below the $BD$ threshold, and all four $D$-wave families are provided. The decay constant $f_{B_c}=507.1$~MeV is consistent with recent QCD sum-rule results and corresponds to $\mathcal{B}(B_c\to\tau\nu_\tau)\approx3\%$. The E1 widths follow the expected angular weights, while their magnitudes are governed mainly by the radial overlap. The $1P\to1S$ (81–112~keV) and $1D\to1P$ (71–93~keV) widths suggest the $1D\to1P\to1S$ cascade as a promising route toward the first $D$-wave $B_c$ state. The Regge trajectories are nearly linear, with slopes decreasing from about 5.8~GeV$^2$ for the $S$-wave to 4.7–4.8~GeV$^2$ for the $D$-wave states. These results may guide forthcoming measurements at the LHC and future $e^+e^-$ facilities.
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Instrumentation and Methods for Astrophysics
Premature re-entry of the FACSAT-2 nanosatellite: orbital decay and attribution to the maximum of solar cycle 25
Santiago Vargas Dominguez, Mara Valentina Angel and Brayan Nicolas Buitrago
FACSAT-2 Chiribiquete, the second satellite of the Colombian Aerospace Force and the first South American nanosatellite mission dedicated to greenhouse gases, re-entered on 27 October 2025, 926 days after its deployment into a Sun-synchronous orbit, against a declared service life of at least five years and an estimated orbital lifetime of fifteen. The orbital
evolution was built from the epochs of the TLEs (two-line elements) of NORAD ID 56205. We reconstruct its decay using its 3696 orbital elements, the
solar and geomagnetic indices from the OMNI2 database, and NRLMSISE-00 densities sampled along the orbit. Inverting the drag yields a ballistic coefficient of 72.3 kg/m2 (6% statistical, 20% systematic), equivalent to an effective area of 0.047 m2, consistent with the declared geometry. With it, the model reproduces the trajectory with a root-mean-square error of 7.4 km and, calibrated on 2023-2024 alone, the re-entry with a 28-day out-of-sample error. F10.7 averaged 170.8 sfu over the mission, against the 139 sfu of the environmental scenario derived from the official 2019 forecast, which lengthens the orbital lifetime by x1.52; two co-launched CubeSats give x1.50 and x1.57, a consistency check across objects rather than independent evidence. Imposing quiet geomagnetic conditions returns 102 days, 22% of the shortening, with strong sensitivity to the adopted threshold; a superposed-epoch analysis over 149 storms gives a median drag enhancement of x1.92 for the intense events. We discuss the consequences for the design of FACSAT-3 and for the public communication of a mission's expected lifetime.
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Superconductivity
Detection of signals in presence of noise through Josephson junction switching currents
O. V. Pountougnigni, R. Yamapi, C. Tchawoua et al. (+2 more)
Josephson junctions can be employed to reveal a sinusoidal signal in presence of Gaussian noise. To mimic realistic setups, the detection is performed linearly ramping the bias current until a switch to the finite voltage occurs; the analysis of the resulting switching currents can be exploited to decide about the presence of the harmonic drive. The signal is applied in two conditions: with an unknown initial phase (incoherent strategy) and with a known initial phase (coherent strategy). In both conditions, the analysis of the efficiency of the detection, performed through the signal-to-noise ratio, as estimated by the Kumar-Carrol index, shows that the dependence upon the Josephson junction ramp rate is beneficial, especially for relatively fast speed. One can conclude that the collection of the switching currents is a robust technique, and thus it is possible to exploit the advantages of a predetermined finite time to collect the data.
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All authors O. V. Pountougnigni, R. Yamapi, C. Tchawoua, V. Pierro, G. Filatrella
Soft Condensed Matter
Phase diagram morphology shapes droplet propulsion in chemical gradients
Stefan Köstler, Malcolm Steen and David Zwicker
Droplets in complex environments often encounter compositional gradients that drive their propulsion. For example, surfactant gradients induce surface-tension-driven propulsion via the Marangoni effect. Here, we show that such propulsion emerges generically, even in the absence of surfactants. Employing a thin-interface approximation, we derive a compact expression for the droplet velocity in terms of droplet size, viscosity, the sensitivity of surface tension to a regulating component, and the chemical potential gradient of that component. Our theory reveals that droplets move toward regions of lower stability, as encoded in the morphology of the phase diagram, particularly near critical points. Numerical simulations confirm these results, which establish a general route to predicting and designing droplet motility from the phase behavior of complex fluids.
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High Energy Physics (Phenomenology)
Probing Massive Invisible Dark Photons in Higgs Decays via Gluon–Gluon Fusion at ATLAS Run 3
Waqas Ahmed, Ammara Ahmad and Shabbar Raza
The ATLAS Collaboration has searched for
Higgs-
boson decays into a
photon and missing transverse momentum using $135~\mathrm{fb}^{-1}$ of Run~3
proton–
proton collision data at $\sqrt{s}=13.6~\mathrm{TeV}$. For the
benchmark decay $H\to\gamma\gD$ with a massless invisible dark
photon, ATLAS reports observed (expected) 95% confidence-level limits of $1.4\%$ ($1.2\%$) on the branching fraction. We reinterpret this search for a massive detector-invisible dark
photon with $0\leq m_{\gD}\leq70~\gev$, focusing on
Higgs production through
gluon–
gluon fusion. \audit{The relative signal acceptance, normalized to the massless
benchmark, remains nearly unchanged up to $m_{\gD}\simeq40~\gev$, but decreases to $0.888$, $0.736$, and $0.524$ at $50$, $60$, and $70~\gev$, respectively, as the
photon-$p_T$ and transverse-mass spectra move toward the analysis thresholds.} Using the published massless
gluon–
gluon-fusion yield for normalization, we obtain simplified expected (observed) 95% confidence-level limits on $\BR(H\to\gamma\gD)$ from $1.64\%$ ($1.76\%$) at $m_{\gD}=30~\gev$ to $3.50\%$ ($3.75\%$) at $70~\gev$. These results extend the ATLAS interpretation to massive invisible dark
photons and quantify the resulting loss of sensitivity at large dark-
photon mass.
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High Energy Physics (Theory)
Braneworld tidal charge through the classical double copy
Juan C. La Cruz and Jesús A. Rodríguez
We investigate the classical double copy of the rotating black-hole geometry induced on the brane in the Randall-Sundrum II scenario. The influence of the five-dimensional bulk is encoded in the effective four-dimensional geometry through a
tidal charge, while the metric admits a Kerr-Schild representation over a flat background. We construct the corresponding single and zeroth copies and find that their regular sources are entirely proportional to the
tidal charge, whereas the mass-dependent contribution is source-free in the regular region. Comparison with Kerr-Newman reveals a formal correspondence between the
tidal charge and the squared electromagnetic charge at the level of the induced geometry and its double copies, despite their different physical origins and the fact that the
tidal charge may take either sign. When an electromagnetic field is included on the brane, both contributions enter the low-energy Kerr-Schild geometry and its double copies only through the combination $Q^2+\beta$. These results illustrate how physically distinct brane and bulk contributions can become indistinguishable in the classical double copy of an effective geometry.
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Quantum Physics
Statistical mechanics of multipartite entanglement in hypergraph states
Paolo Scarafile, Giorgia Trotta, Paolo Facchi et al. (+4 more)
We investigate multipartite
entanglement in a particular family of pure $n$-
qubit hypergraph states through a statistical-mechanics framework, where the average bipartite purity maps onto an effective
Hamiltonian of $2^n$ classical binary
spins. In this correspondence, each hypergraph state uniquely corresponds to a classical
spin configuration, while temperature serves as a control parameter that continuously interpolates between a uniform ensemble of random hypergraph states at high temperature and maximally multipartite entangled states (MMES) at zero temperature. Remarkably, the exponential of the zero-temperature
entropy directly gives the number of MMES within the set of hypergraph states. For small system sizes ($n \leq 5$), we perform an exact enumeration, fully characterizing the energy landscape and associated thermodynamic observables, and validating known MMES counts. For larger systems ($n = 6$ and $7$), where exact methods become computationally infeasible, we employ simulated annealing and parallel tempering
algorithms to efficiently sample the exponentially large state space. Our analysis yields quantitative predictions of the number of MMES and reveals how
entanglement is statistically distributed across the sets of hypergraph states. These results establish hypergraph states as an ideal platform for investigating multipartite
entanglement through thermodynamic methods, offering both computational advances and physical insights into the structure of
quantum entanglement in restricted families of
quantum states.
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All authors Paolo Scarafile, Giorgia Trotta, Paolo Facchi, Giuseppe Magnifico, Giorgio Parisi, Saverio Pascazio, Karol Życzkowski
Mathematical Physics
Proactive Incentive Regulation in Multi-Agent Systems with Environmental Feedback
Xinyang Cao, Shijia Hua and Linjie Liu
In environmental feedback systems, self-interested behaviors of rational
agents often undermine cooperation and environmental sustainability. Although punitive incentive mechanisms are widely recognized as effective in addressing such social dilemmas, the timing of their implementation under different environmental conditions remains insufficiently understood. In this paper, we develop a multi-
agent environmental feedback game framework with coupled incentive intensities across resource states. We investigate how system dynamics vary with incentive intensity under both resource-abundant and resource-scarce conditions. Theoretical analysis shows that imposing penalties in resource-abundant states can transform the system from a tragedy of the commons into a bistable regime that supports full cooperation. In contrast, imposing penalties in resource-scarce states leads to complex dynamical behaviors, including interior stability, heteroclinic cycles, and
Hopf bifurcations, which hinder the emergence of stable cooperation. These results highlight the importance of timing in incentive regulation. Proactive intervention under favorable environmental conditions is more effective in sustaining cooperation than delayed enforcement after environmental degradation.
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Strongly Correlated Electrons
Carrier-mediated spin helices in low-dimensional systems: Josephson-interference features and correlation renormalization
Yung-Yeh Chang and Chen-Hsuan Hsu
Carrier-induced helical magnetism can arise in interacting one-dimensional systems coupled to localized moments. Here, we investigate the coupled-wire sliding-Luttinger-
liquid counterparts with and without valley degrees of freedom, using isolated Tomonaga-Luttinger
liquids as reference limits. The carrier
spin susceptibility mediates a Ruderman-Kittel-Kasuya-Yosida interaction that selects the helical ordering wave vector, while interchannel correlations lock the relative helix phases and stabilize a collective quasi-two-dimensional texture. Using a variational treatment, we estimate the helix-induced partial gap and analyze the reconstruction of the remaining gapless carrier modes. To probe the spatial texture through transport, we incorporate the helix into an anisotropic
superconductor-normal-metal-
superconductor Josephson junction motivated by the coupled-channel structure of twisted
bilayer WTe$_2$. We exploit flux focusing near the junction interfaces to make an applied in-plane field a controlled probe of the
spin helix. Relative to junctions without the helix, the helical exchange field modifies the central-lobe width and relative lobe weights. In the transverse-channel geometry, it also produces field-dependent side-lobe asymmetry and central-peak displacement, which remain negligible in the matched references for the parameters considered. The reconstructed carrier sector also exhibits modified local-density-of-states exponents,
spin-relaxation behavior, and competing correlations, with distinct signatures in isolated and coupled-wire systems. Our results connect collective helical order in coupled-wire systems to carrier-sector reconstruction and identify field-tunable Josephson interferometry as a complementary transport probe of the spatial
spin texture.
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Instrumentation and Methods for Astrophysics
Natural coordinates for constrained correlation functions: Partial autocorrelations and the geometry of positive power spectra
Thomas Erben
Two-point correlation functions are a standard summary statistic in
cosmic shear and large-scale-structure analyses. Their values are, however, constrained: non-negativity of the underlying power spectrum restricts any admissible sequence of correlation coefficients $(r_1,\ldots,r_N)$ to a bounded convex region, described in the one-dimensional case by the recursive interval geometry of Schneider & Hartlap (2009). Their formalism introduces an affine variable $x_n$ that maps the admissible interval for $r_n$, given $r_1,\ldots,r_{n-1}$, to $[-1,+1]$. We identify $x_n$ with the partial autocorrelation coefficient $\alpha_n$ of the associated positive Toeplitz correlation
matrix, a classical quantity in time-series analysis. The partial autocorrelations thus provide natural coordinates on the admissible region, each $\alpha_n$ varying independently in $[-1,+1]$. This identification makes the standard partial-autocorrelation toolbox directly applicable. The admissible intervals for $r_n$, cumbersome to obtain at higher order in the original determinant-based formalism, now follow from an $\mathcal{O}(N^2)$ recursion at arbitrary order. The inverse
hyperbolic tangent used in the quasi-Gaussian likelihood construction of Wilking & Schneider (2013) becomes Fisher's $z$-transformation of partial autocorrelations, providing a classical statistical interpretation of its empirical Gaussianising effect. Numerical experiments illustrate the practical use of these natural coordinates in the tested one-dimensional settings. Higher-dimensional isotropic constraints require additional
geometric input and lie outside the direct scope of this identification.
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Instrumentation and Methods for Astrophysics
Development of a Photonically Generated Frequency Reference for Space VLBI
Hannah Tomio, Kohei Yamamoto, Charlotte Zehnder et al. (+5 more)
Space-based Very Long Baseline Interferometry (VLBI) can improve both the angular and temporal resolution of images over terrestrial VLBI techniques. Future space VLBI (sVLBI) missions are targeting higher observation frequencies than modern, terrestrial VLBI, and therefore these missions will require higher stability frequency references than standard hydrogen masers. While existing frequency references for space-based applications have concentrated on long-term stability, in this effort, we present a frequency reference with high short-term stability intended for sVLBI missions. This reference leverages developments in cavity-stabilized
lasers from the
Laser Interferometer Space
Antenna (LISA) mission and commercial efforts towards a robust, space-qualifiable optical frequency comb. We describe the implementation and experimental results of this system with a path to spaceflight, which demonstrates an Allan deviation of $3.26 \times 10^{-14}$ at 1 second, $6.00 \times 10^{-15}$ at 10 seconds, and $6.73 \times 10^{-15}$ at 30 seconds for the 100 MHz frequency reference signal, and show that this performance meets the needs of future sVLBI missions.
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All authors Hannah Tomio, Kohei Yamamoto, Charlotte Zehnder, Guangning Yang, Kenji Numata, Andrew Attar, Henry Timmers, Holly Leopardi
Solar and Stellar Astrophysics
Oblique kink waves in solar coronal streamers
Aleksandr V. Rubtsov, Valery M. Nakariakov, Dmitri Yu. Klimushkin et al. (+1 more)
Coronal streamer kink waves excited by an impact of coronal mass ejections (CMEs) are routinely used to estimate the coronal Alfvén speed. These estimates generally assume wave propagation parallel to the
equilibrium magnetic field directed radially outward to the Sun, in the plane of the sky. However, the geometry of CME impacts naturally allows for oblique propagation. We investigate the properties of obliquely propagating kink waves guided by a
plasma slab with a central current sheet representing a coronal streamer stalk. We consider both cold and warm streamer
plasmas and analyse influence of propagation obliquity on wave dispersion, eigenfunctions, and seismological diagnostics. We find that increasing the propagation obliquity reduces the phase speed owing to both projection effects and the intrinsic dependence of the phase speed on the propagation angle. The wave structure also undergoes a gradual transition from a body mode to a surface mode, leading to stronger perturbations at the slab boundaries and enhanced wave localization. Consequently, for a given energy deposited by a CME impact, oblique kink waves are expected to produce larger observable amplitudes than field-aligned waves. Applying the developed theory to streamer waves reported previously, we infer Alfvén speeds in the range of 50-500 km/s. We show that neglecting wave propagation obliquity may underestimate the Alfvén speed by up to a factor of 1.5. These results demonstrate that wave propagation obliquity should be taken into account in coronal seismology of streamer waves and that stereoscopic observations will be required to constrain the true propagation direction.
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All authors Aleksandr V. Rubtsov, Valery M. Nakariakov, Dmitri Yu. Klimushkin, Ding Yuan
Mathematical Physics
Payoffs and perception mediate environmental feedback in an N-player trust game with Q-learning
Ruqiang Guo, Zhaoyi Hu, Fangfang Wang et al. (+1 more)
Trust develops through learning, while collective behavior can alter the environment in which later decisions are made. Reinforcement-learning models describe adaptation, and eco-evolutionary models describe behavior-environment feedback, but how an endogenous environment changes trust through material incentives and perceived states remains unclear. We couple a fixed-role, two-population hierarchical trust game populated by heterogeneous tabular $Q$-learning
agents to a centered endogenous environment. For the main feedback comparisons, we initialize the fixed-payoff baseline and feedback branches from the same learned state to control for prior learning. We then compare responses when payoff parameters or the observed environmental tier vary. As the payoff multiplication factor increased, successful trust in the fixed-payoff game crossed from a low to a higher finite-horizon level, led by risk-seeking investors. Environmental feedback promoted trust near perception-tier boundaries and reinforced its decline at the high-return operating point. At the high-return operating point, payoff feedback reinforced the learning-driven decline in trust. Stronger drive and longer horizons deepened this negative effect. Compared with a fixed-payoff trust game, environmental feedback carries past collective outcomes into future payoffs and observed states.
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All authors Ruqiang Guo, Zhaoyi Hu, Fangfang Wang, Linjie Liu
Quantum Gases
Fold Catastrophes in a Hopf Texture Driven by a Navier–Stokes Blow-Up Analog
Antti J. Niemi
A two-component Bose–Einstein condensate can host a pseudospin
Hopf texture coupled to the viscous normal flow of its thermal cloud. Motivated by OpenAI's reported finite-time Navier–Stokes singular solution, we evolve such a texture in a smooth flow reproducing the geometry and similarity scaling of the collapsing axisymmetric core. The
evolution creates and annihilates preimage pairs while preserving the
Hopf charge. The first one-to-three transition exhibits the square-root opening characteristic of a Thom $A_2$ fold. A subsequent three-to-five transition precedes a burst-like regime of recurrent fold catastrophes and near-caustic activity.
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