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Physics

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Wednesday 24 June

Disordered Systems and Neural Networks

Weight geometry governs functional memory in complex systems

Elkaïoum M. Moutuou and Habib Benali

Complex systems, from gene regulatory networks to neural circuits and ecological food webs, exhibit rich functional behaviour that topology alone does not capture. Yet functional complexity remains difficult to quantify independently of structural organisation. Here we introduce a thermodynamic framework in which functional complexity is characterised through the hierarchical organisation of functional memory, quantifying how the influence of past interactions is distributed and progressively compressed across scales. Across thirty-four empirical networks spanning biological, ecological, social, technological, and biophysical systems and several orders of magnitude in size and density, real interaction strengths organise functional memory at greater hierarchical depth than random weight assignment on the same topology in every domain studied. The framework further reveals that functional memory occupies a remarkably low-dimensional space, collapsing onto four recurrent dynamical organisations. Comparisons with null models that selectively perturb weighted transport geometry, mesoscale wiring, and directionality show that these structural ingredients play distinct roles: weighted transport geometry systematically governs memory depth, whereas mesoscale wiring organises memory across scales and directionality modulates the response of the cascade to structural perturbation. The same comparisons provide an operational criterion for determining whether network weights encode functionally meaningful structure beyond topology. These results establish weighted transport geometry as a primary organiser of functional memory and provide a quantitative framework for studying functional complexity in directed weighted networks.
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Disordered Systems and Neural Networks

Kinetic metric for basins of attraction of RNA secondary structures and analysis of the ultrametricity of the energy landscape

A.P. Zubarev

A method for testing the hypothesis of an ultrametric organization of the energy landscape of RNA secondary structures is proposed, based on the analysis of the kinetics of transitions between basins of attraction. The method is based on a kinetic metric constructed from the spectral decomposition of the symmetrized Kramers transition rate matrix and the Mahalanobis distance, and it is not an ultrametric by construction. A computational scheme has been developed that includes automatic filtering of noise eigenmodes and a procedure for analyzing disconnected structure graphs. The performance of the method is demonstrated on a sample of reference and random RNAs.
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Instrumentation and Methods for Astrophysics

On-Sky Single-photon Time resolution of 35 ps with White Rabbit synchronization: towards the measurement of the size of a White Dwarf star

F. Izraelevitch-Patitucci, S. Tolila, I. Ellafi et al. (+7 more)

The IC4Stars (Intensity Correlation for Stars) project aims to measure the diameter of the white dwarf star Sirius B, using Intensity Interferometry. In this work we present our latest efforts and the milestones achieved in the last year. We report laboratory characterization of the single-photon detectors, TDC and synchronization electronics. We describe an observation campaign where we demonstrated on-sky time resolution below 35 ps RMS, synchronizing two TDCs using the White Rabbit protocol and a 30 m telecom fiber. We developed the data acquisition of the raw time tags, and an algorithm to compute the second-order correlation function.
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All authors F. Izraelevitch-Patitucci, S. Tolila, I. Ellafi, J.-P. Rivet, M. Hugbart, G. Labeyrie, O. Lai, A. Zmija, W. Guerin, R. Kaiser

Quantum Physics

Collective rotational cat states of molecules in microwave cavities

Volker Karle, Florian Kluibenschedl, Mikhail Lemeshko et al. (+1 more)

We show theoretically that an ensemble of polar molecules coupled to a microwave cavity supports hybrid rotational-photonic cat states. The cavity couples to a symmetric rotor in the bright manifold of $N$ molecules with $\sqrt{N}$-enhancement. In the dispersive limit of the collective strong coupling regime, virtual multilevel transitions induce an effective Kerr nonlinearity, as confirmed by Wigner tomography and a Schrieffer-Wolff analysis, leading to parity-locked cat structure in the cavity sectors. Collective molecular rotations thus provide a new route to hybrid light-matter cat states.
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All authors Volker Karle, Florian Kluibenschedl, Mikhail Lemeshko, Vasil Rokaj

Astrophysics of Galaxies

Compact radio galaxies: the case of FR0s

R. D. Baldi, A. Capetti, G. Giovannini et al. (+20 more)

Fanaroff-Riley type 0 (FR0) radio galaxies, a newly-identified and abundant population of low-power radio-loud active galactic nuclei, present a significant challenge to our understanding of radio galaxy evolution. Unlike their more extended FRI and FRII counterparts, FR0s are characterized by compact (from pc to a few kpc) radio morphologies with weak or absent large-scale jets, despite having optical host galaxy properties and central black hole masses similar to classical, more powerful radio galaxies. Their compactness and prevalence suggest they may represent an early stage of radio galaxy evolution or indicate a fundamentally different accretion and ejection mechanism. The Square Kilometre Array (SKA), with its continuum survey and VLBI capabilities, offers a transformative opportunity to study FR0 radio galaxies at unprecedented angular resolution and sensitivity. Milliarcsecond (mas) angular resolution VLBI observations will probe their parsec-scale structure, providing critical insights into the nature of their jets, accretion-ejection physics, and the interplay between nuclear activity and the surrounding environment. Continuum and polarization surveys will enable a systematic study of their population properties, distribution, and radio spectra across a wide range of redshifts in relation to other populations of radio galaxies.
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All authors R. D. Baldi, A. Capetti, G. Giovannini, S. Amarantidis, M. Brienza, G. Bruni, J. Chilufya, A. Costa, M. Gitti, D. V. Lal, G. Migliori, J. Moldon, M. Orienti, F. Panessa, I. Prandoni, M. Puig-Subirà, R. M. Samir, S. Shabala, F. Shankar, C. Spingola, F. Tavecchio, F. Ubertosi, B. Vaidya

Fluid Dynamics

Implementation and Extension of the Variance-Reduced BGK Method in PICLas

Leon Teichröb, Félix Garmirian and Marcel Pfeiffer

Traditional particle-based kinetic methods, such as DSMC, suffer from prohibitive computational cost in low-signal flows, where the deviation from thermodynamic equilibrium is small and statistical noise overwhelms the signal of interest. The Variance-Reduced BGK-DSMC scheme is further advanced and implemented to support this class of flows in the open-source gas-kinetics framework PICLas. Modified versions of flow estimators and collision operators enhancing stability are developed. The Shakhov and Ellipsoidal Statistical models for BGK are demonstrated, along with entirely new features such as adaptive equilibria, variable particle weights and domain axisymmetry. The implementation is validated using synthetic benchmarks, 1D, 2D and axisymmetric simulations. Comparison of VRBGK to BGK simulations shows exact agreement of the models. A further comparison with an analytical solution of thermal transpiration in a microchannel showcases the low-signal efficiency of the method as well as newly proposed features.
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Cosmology and Nongalactic Astrophysics

The PAU Survey and Euclid: Analysing photometric redshifts from realistically simulated narrow-band photometry with Flagship 2

A. Wittje, H. Hildebrandt, D. Navarro-Gironés et al. (+154 more)

The study of the large-scale structure of the Universe and the distribution of galaxies has been greatly advanced by the application of various types of photometric redshift estimation techniques. The Physics of the Accelerating Universe Survey (PAUS) is a state-of-the-art imaging survey, designed to provide high-quality photometric data in 40 optical narrow-band filters. In this paper, we present an in-depth analysis of the photometric redshifts obtained from PAUS using realistic simulations. Based on the Euclid Flagship 2 catalogue, we generate PAUS-like simulations with realistic photometric noise and target selection. The mock catalogue is used to explore the accuracy and precision of photometric redshifts of PAUS, investigating the impact of noise and depth, and combinations of broad- and narrow-band data. The simulations reproduce the observed PAUS performance well, with a robust photometric redshift scatter of $\sigma_{NMAD}/(1+z)\!=\!0.011$ for a mock subsample resembling the spectroscopic validation sample of the data. For the complete PAUS-like sample, which can only be evaluated in the simulation, we find $\sigma_{NMAD}/(1+z)\!=\!0.028$ for $i_{\rm AB}\!\lesssim\!23$ and outlier fractions below 10%. Forecasts indicate that including Euclid photometry in a joint analysis could further reduce scatter and outlier fractions, especially for faint galaxy populations. The hypothetical case of deeper PAUS observations over a limited sky area, forecasting the potential for future narrow- or medium-band surveys, in combination with Euclid's deep photometry, achieves scatter as low as $\sigma_{NMAD}/(1+z)\!=\!0.011$ and outlier fractions below 4% for $i_{\rm AB}\!<\!23.5$.
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All authors A. Wittje, H. Hildebrandt, D. Navarro-Gironés, E. J. Gonzalez, J. L. van den Busch, E. Gaztanaga, M. Eriksen, A. H. Wright, R. Casas, J. Carretero, F. J. Castander, E. Fernandez, P. Fosalba, J. García-Bellido, H. Hoekstra, R. Miquel, C. Padilla, P. Renard, E. Sanchez, I. Sevilla-Noarbe, P. Tallada-Crespí, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, M. Bolzonella, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, V. F. Cardone, M. Castellano, G. Castignani, S. Cavuoti, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Crocce, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, C. A. J. Duncan, X. Dupac, S. Escoffier, M. Farina, R. Farinelli, S. Farrens, F. Faustini, S. Ferriol, F. Finelli, S. Fotopoulou, N. Fourmanoit, M. Frailis, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, M. Kilbinger, B. Kubik, M. Kümmel, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, R. Nakajima, C. Neissner, S.-M. Niemi, S. Paltani, F. Pasian, K. Pedersen, V. Pettorino, A. Pezzotta, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, A. Secroun, E. Sefusatti, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, A. N. Taylor, H. I. Teplitz, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, A. Veropalumbo, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, A. Montoro, M. Sereno

Quantum Physics

A Candidate Framework for Free-Space Quantum Key Distribution based on Geometrical-Configuration Modulation

Yu-Ming Bai, Yu-Xuan Liu, Ming-Han Ding et al. (+1 more)

This paper proposes a candidate framework for free-space quantum key distribution (QKD) based on geometrical-configuration modulation (GM). In the minimal implementation considered here, Alice coherently splits a single photon emitted from one source into two spatial output modes with a tunable separation, and uses the source separation $R$ as the GM variable that defines the prepared single-photon spatial superposition state. Bob records the single-photon detection coordinate in the far field or Fourier plane, providing the correlated data used for soft-input information reconciliation. Based on this physical mechanism, we first establish an $R-x$ protocol model in which the source separation $R$ and the single-photon detection coordinate $x$ are random variables, and further propose an $R-\Delta x$ extension based on the difference variable $\Delta x$ between adjacent accepted detection events to mitigate slowly varying center drift in free-space links. The framework specifies state preparation, far-field conditional probabilities, soft-input information generation, parameter estimation, reconciliation, and asymptotic candidate key-rate formulas. A complete composable security analysis further requires derive an explicit computable upper bound on Eve's information from experimentally observed parameters, together with finite-key analysis and experimental validation under free-space conditions. The proposed candidate framework (GM-QKD) provides a modulation approach based on spatial degrees of freedom in which the source geometry serves as the modulation variable.
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All authors Yu-Ming Bai, Yu-Xuan Liu, Ming-Han Ding, Jun-Lin Li

High Energy Astrophysical Phenomena

Study for curvature radiation and magnetic pair creation process on polar-cap region of magnetic white dwarf

Bingyan Wang and Jumpei Takata

Rapidly rotating, strongly magnetized white dwarfs (WDs) have been proposed as potential sites of rotation-powered activity analogous to that of a neutron star pulsar. In this study, we investigate particle acceleration, radiation processes, pair creation and resulting synchrotron radiation in the polar cap acceleration region. Within the framework of the space-charge-limited flow model, we examine how these processes depend on the spin period and surface magnetic field using both one-dimensional numerical calculations and analytical estimates. To explore the impact of the magnetic field geometry on the accelerating process, we consider both a pure dipole field and a combination of dipole and quadrupole fields. The inclusion of a quadrupole component reduces the curvature radius of the magnetic field lines, and significantly enhances the accelerating field, leading to more efficient radiation and pair creation processes. Using this framework, we evaluate the WD death line with a more consistent treatment of the relevant physical processes than the previous studies. We find that the pair creation process can occur for spin periods $P\lesssim100$~s, when the dipole field strength $B_{*,d}\lesssim10^{10}$~G, indicating that pair creation is difficult to sustain in currently known magnetic WDs. We discuss the implications of our model for rotation-powered activity in rapidly spinning isolated magnetic WDs and for the possible WD interpretation of long-period radio transients.
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Instrumentation and Detectors

Positron Emission Tomography with quantum-entangled Compton events: first imaging results at clinically relevant activities

Mihael Makek, Ana Marija Kožuljević, Tomislav Bokulić et al. (+4 more)

In Positron Emission Tomography, a potential, yet unutilized enhancement, may come from exploiting the quantum entanglement of the annihilation quanta, inscribed in the correlation of their polarizations. To investigate this, we built a PET demonstrator capable of measuring polarization correlations of annihilation quanta by their Compton scattering, based on single-layer scintillator polarimeters. We present a detailed study of the imaging of two $^{68}$Ge line sources, 45 MBq each, to extract the spatial resolution and assess image quality. The results show that a spatial resolution of 2.5$\pm$0.1 mm is obtained using single-pixel events, while resolutions obtained with polarization-correlated Compton events range from 3.6$\pm$0.3 mm to 4.9$\pm$0.3 mm, depending on data selection criteria. We also found that the polarization-correlated Compton events exhibit up to 20% higher average signal to random background ratio compared to the single-pixel events. We also present the first imaging of the NEMA NU-4 phantom filled with a $^{68}$Ga solution of 378 MBq initial activity, successfully combining polarization-correlated events with conventional single-pixel event selection. Based on the extracted spatial resolution, signal-to-background, signal-to-noise, contrast, and contrast-to-noise ratio, we estimate that up to 10% sensitivity increase may be attained by exploiting the polarization-correlated events, while preserving a high image quality.
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All authors Mihael Makek, Ana Marija Kožuljević, Tomislav Bokulić, Darko Grošev, Zdenka Kuncic, Siddharth Parashari, Luka Pavelić

High Energy Physics (Theory)

Massive fields in 3D Minkowski space and boundary correlators

Sudipta Dutta

A codimension-one Carrollian CFT on null infinity has been proposed as the putative dual description of asymptotically flat spacetimes and has so far been successful in describing the massless S-matrices in one higher dimension. In this work, we investigate the current proposal of Carrollian holography to include the massive fields in the bulk. We discover a broader class of correlation functions in two-dimensional Carrollian CFTs and show that they encode massive scattering amplitudes in three-dimensional Minkowski spacetime. We also construct a bulk-to-boundary propagator that generalizes the one already existing for massless fields.
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Exactly Solvable and Integrable Systems

Global Results on the Classification of Two-Component Integrable Evolutionary Systems

Alexander V. Mikhailov, Vladimir Novikov and Jing Ping Wang

We derive necessary and sufficient integrability conditions for two-component polynomial evolutionary systems of odd order in $(1+1)$ dimensions. Integrable systems are members of infinite hierarchies of commuting symmetries, which are characterised by their spectral invariants. We prove that there are precisely $24$ possible spectral classes of integrable hierarchies. As an application, we obtain a complete classification of integrable homogeneous hierarchies whose lowest-order equations are of order 3 and 5. The resulting classification naturally splits into two classes. The C–integrable systems are reduced, by means of differential substitutions, to linear–triangular form, while the S–integrable systems are related, through linear changes of variables and differential substitutions, to canonical Drinfeld–Sokolov KdV-type systems associated with affine Lie algebras of rank two.
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Astrophysics of Galaxies

AGN Jets from Formation to Dissipation

Anne-Kathrin Baczko, Eleni Vardoulaki, Etienne Bonnassieux et al. (+26 more)

Active Galactic Nuclei (AGN) are among the most energetic phenomena in the Universe, capable of launching powerful relativistic jets that extend from sub-parsec to megaparsec scales. These jets play a crucial role in regulating star formation, redistributing energy and matter, and shaping the evolution of galaxies and their environments. Despite decades of study, a comprehensive understanding of how AGN jets form, propagate, and dissipate remains elusive. The aim of this chapter is to highlight how the future capabilities of the the Square Kilometre Array (SKA), as a standalone array as well as in combination with Very Long Baseline Interferometry (VLBI) arrays and multi-wavelength facilities, will transform our capabilities to study the co-evolution of AGN jets and their host galaxies from jet formation to dissipation scales.
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All authors Anne-Kathrin Baczko, Eleni Vardoulaki, Etienne Bonnassieux, Manel Perucho, Marisa Brienza, Marcus Brüggen, Emmanuel K. Bempong-Manful, Robert Beswick, Florian Eppel, Damien Gratadour, Jonas Heßdörfer, Kiara Hervella-Seoane, Matthias Kadler, Jae-Young Kim, Aretaios Lalakos, Leah K. Morabito, Dhanya G. Nair, Felix Pötzl, Jack Radcliffe, Luca Ricci, Eduardo Ros, Jan Röder, Florian Rösch, Ainara Saiz-Pérez, Hrishikesh Shetgaonkar, Cyril Tasse, Francesco Ubertosi, Jun Yang, J. Anton Zensus

Quantum Physics

Benchmarking Dark Matter Search using a Parity-Check Protocol with Machine-Learning Optimized Pulses

Yu-Han Chang, Ilya Moskalenko, Marko Kuzmanović et al. (+7 more)

We report on an improved microwave detection protocol for dark matter candidates such as the axion and the dark photon. We employ a superconducting transmon qubit dispersively coupled to a double-cavity system, enabling quantum non-demolition measurements of the photon occupation in a relatively short-lived storage cavity. To reduce the experimental cycle time and enhance sensitivity for axion and dark-photon searches, we operate this detector in a regime of increased qubit-cavity coupling, resulting in Stark shifts of 4.6 MHz. In this regime, conventional control pulses suffer from strong frequency-detuning sensitivity and photon-number-dependent errors. We address this limitation by implementing frequency-detuning-robust $\pi/2$ pulses (obtained by machine-learning optimization) that preserve high-fidelity qubit control over a bandwidth of approximately 20 MHz. We experimentally validate this protocol and demonstrate single-photon detection performance comparable to previous implementations, despite significantly reduced qubit coherence times and storage-cavity lifetimes. Using parity-based measurement sequences combined with a Hidden Markov Model (HMM) analysis, we achieve background rates on the order of $\mathcal{O}(20)$ Hz. In the absence of a magnetic field, we derive exclusion limits on the dark photon model for dark matter, reaching a sensitivity to the kinetic mixing angle of $\epsilon_{95\%} \sim 1\times10^{-14}$ at 5.051 GHz. These results establish machine-learning robust control as a key enabler for faster, more scalable microwave quantum sensors for dark-matter searches.
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All authors Yu-Han Chang, Ilya Moskalenko, Marko Kuzmanović, Ognjen Stanisavljević, Isak Björkman, David Díez-Ibáñez, Yikun Gu, Akash V. Dixit, Igor G. Irastorza, Gheorghe Sorin Paraoanu

Earth and Planetary Astrophysics

Substructures in Planet-Forming Disks with the SKAO

Yinhao Wu, Jessica Speedie, Sebastián Pérez et al. (+33 more)

Disks of gas and dust orbiting young stars are the arenas and material reservoirs for planet formation. Over the past decade, multiwavelength observations, from infrared to radio, have resolved the spatial distribution of hundreds of protoplanetary disks in nearby star-forming regions, revealing a diverse zoo of substructures. These substructures are morphological features such as rings, gaps, spirals, vortices, asymmetries, warps, or clumps that trace variations in density, temperature, or composition relative to an otherwise smooth distribution of gas and dust. Many unknowns persist as to the origin of these substructures, their role in planet assembly, and their true properties. SKA-Mid Band 5b continuum observations, offering angular resolutions of $\sim 0.05''$ ($\sim 0.15''$) with AA4 (AA*) at $12.5$ GHz / $2.4$ cm, will enable new progress at this frontier. In this chapter, we outline the open questions in the field of disk substructure that SKA-Mid is uniquely poised to address, with a lens on dust thermal emission.
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All authors Yinhao Wu, Jessica Speedie, Sebastián Pérez, John D. Ilee, Takahiro Ueda, Claudia Toci, Daniel J. Price, Asmita Bhandare, Eleonora Bianchi, Tilman Birnstiel, Richard A. Booth, Tyler L. Bourke, Gemma Busquet, Simon Casassus, Yi-Xian Chen, Claudio Codella, Nicolás Cuello, Ruobing Dong, Antonio Garufi, Greta Guidi, Cassandra Hall, Haochang Jiang, Izaskun Jiménez-Serra, Hauyu Baobab Liu, Mayank Narang, Elenia Pacetti, Jaime Pineda, Paola Pinilla, Linda Podio, Danai Polychroni, Giovanni Sabatini, Eugenio Schisano, Leonardo Testi, Diego Turrini, Marion Villenave, David Wilner

Computational Physics

Monte Carlo Physics-informed Neural Networks for Inverse Multiscale Heat Conduction Problems via the Phonon Boltzmann Transport Equation

Qingyi Lin, Chuang Zhang, Xuhui Meng et al. (+1 more)

Inferring thermal fields and thermophysical properties from limited measurements is a fundamental challenge in micro- and nanoscale heat conduction, where the classical Fourier law breaks down and the phonon Boltzmann transport equation (BTE) is needed to capture non-diffusive transport effects. In this work, we extend Monte Carlo physics-informed neural networks (MC-PINNs), originally developed for forward phonon BTE problems [J. Comput. Phys. 542, 114364, 2025], to inverse multiscale heat conduction problems. Two representative classes of inverse problems are considered: (i) reconstructing the full thermal field from sparse interior temperature measurements when boundary conditions are unknown, and (ii) simultaneously inferring the unknown relaxation time together with the thermal field. Problem-specific MC-PINN architectures and training strategies are designed for each class. The mesh-free Monte Carlo sampling strategy enables a unified treatment across diffusive, transitional, and ballistic transport regimes without requiring a priori knowledge of the relaxation time. The proposed method is evaluated on quasi-one-dimensional, quasi-two-dimensional, and three-dimensional benchmark problems covering a wide range of Knudsen numbers, as well as on a realistic 3D fin field-effect transistor (FinFET) structure. Results demonstrate that MC-PINNs consistently outperform purely data-driven deep neural networks, particularly in the sparse-data regime, and can accurately infer spatially uniform relaxation times. For spatially varying relaxation times, the inferred distributions capture the dominant thermal response, and numerical simulations using the recovered parameters reproduce the macroscopic fields with good accuracy. These findings establish MC-PINNs as an effective and physically consistent framework for inverse thermal analysis at micro- and nanoscales.
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All authors Qingyi Lin, Chuang Zhang, Xuhui Meng, Zhaoli Guo

General Relativity and Quantum Cosmology

Separability of the motion of spinning test particles in curved space-time

Vojtěch Witzany and Viktor Skoupý

Solving for the motion of spinning test particles in curved spacetimes is important for modeling gravitational-wave inspirals of spinning compact binaries. We build a Hamiltonian formalism in worldline-adapted tetrads for the spinning test particle and formulate a corresponding Hamilton-Jacobi equation valid to linear order in spin. We prove that when the geodesic motion in a spacetime and the parallel transport along said geodesics are both separable, then so is the corresponding Hamilton-Jacobi equation. We illustrate this in black hole, plane wave, and cosmological spacetimes.
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Quantum Physics

A Short Note on the Generators of Controlled Quantum Gates

Richard M. Milbradt and Christian B. Mendl

We present the analytical generators for arbitrary multi-qubit controlled gates. Closed forms for the generating Hamiltonians are given for gates with both multiple control and target qubits, as well as for arbitrary control conditions. This allows us to go beyond gate-based simulations of quantum circuits and incorporate decoherence and other noise in simulations of quantum computers. We exemplify this by simulating the impact of a harmonic oscillator interacting with two qubits during the application of a controlled NOT gate.
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Fluid Dynamics

Stages of turbulence generation and decay in a T-shaped mixer

Mohammad Mehdi Zamani Asl and Marc Avila

The T-shaped mixer is widely used in fundamental studies of chemical engineering. Its transitional regime is well understood, whereas the turbulent dynamics has received scarce attention so far. Here we perform direct numerical simulations of the turbulent regime for Reynolds numbers up to $Re=2000$ at Schmidt number $Sc=1$. Our analysis reveals two distinct stages along the mixing channel prior to relaxation toward duct flow. Near the junction, a jet-like flow forms and exhibits the approximately self-similar behaviour of transitional planar jets. Subsequently, a decay region characterised by power-law decay of turbulent kinetic energy, dissipation and scalar variance emerges. For the velocity field, the observed exponents are consistent with those of decaying turbulence in bounded domains, whereas the scalar-variance exponent is consistent with that of unbounded turbulence. We argue that this apparent discrepancy is a consequence of the mixing process progressing from the center of the channel toward the side walls in the decay region, while turbulence already fills the channel cross-section entirely at the end of the jet region.The time-averaged mixing state presents error-function profiles of the scalar in the transverse direction, similar to the laminar cases, and is quantified here through a stream-wise evolving effective diffusion coefficient.
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High Energy Physics (Phenomenology)

Dark Photons from Red Dwarfs

Stefan Vogl and Xun-Jie Xu

Light dark photons can be produced in stellar systems and thus contribute to the stellar cooling rate. The additional cooling changes the evolution of the star and has an impact on various observable properties such as radius, photon luminosity or the emitted neutrino fluxes. This has been exploited before to derive limits based on observations of the Sun, horizontal branch stars and red giants. Given the wealth of astrophysical data collected in the last decade and the improvements in modeling stellar evolution it is interesting to investigate whether other stellar systems offer a complementary avenue towards testing dark photons. In this work, we study the effect on an alternative class of stars. We focus on the impact of dark photon induced cooling on red dwarfs, i.e. the lowest mass stars on the Hydrogen main sequence. Running simulations of the evolution of red dwarfs with dark photon cooling we determine the impact on the mass-radius relation. Combining our simulations with precise determination of mass and radius derived from observations of eclipsing binaries that have recently become available, we derive competitive limits which outperform the solar ones in a significant part of the parameter space.
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Optics

Approaching the Quantum Limit of Optical Rotatory Dispersion: From First-Principles to Single-Photon Monochromators

Xianglun Ma, Junyan Zhu and Fang Lu

Optical rotatory dispersion (ORD) in chiral media, classically demonstrated as the "sweet monochromator," provides a robust mechanism for liquid-tunable spectral filtering. However, the ultimate physical boundaries governing its spectral bandwidth remain fundamentally unexplored beyond classical electromagnetic theory. Here, we present a comprehensive framework bridging macroscopic optical filtering with the quantum electrodynamic (QED) limits of chiral light-matter interaction. Using time-dependent density functional theory (TD-DFT) combined with Boltzmann conformational averaging, we accurately compute the ORD curves of representative saccharide systems, revealing that the theoretical minimum bandwidth is intrinsically tied to the anomalous dispersion (Cotton effect) near the molecular absorption band. While our macroscopic experiments demonstrate a classical bandwidth limit of ~ 20 nm due to heterogeneous broadening and instrumental constraints, our first-principles calculations predict achievable sub-nanometer bandwidths utilizing visible-absorbing chiral molecules. Furthermore, we extrapolate this framework to the strict quantum limit, proposing a single-photon QED architecture operating at ultra-low temperatures (~ 10 mK). In this regime, the spectral purity is constrained solely by the natural lifetime of the molecular excited state, governed by the Heisenberg uncertainty principle. This work establishes the ultimate theoretical criteria for chiral optical filters and pioneers the concept of the "quantum monochromator" for ultrasensitive chiral spectroscopy and quantum information processing.
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Mathematical Physics

Equilibrium states for non relativistic Bose gases and the Gross-Pitaevskii limit

Stefano Galanda and Nicola Pinamonti

In this paper, we present the construction of equilibrium states for a gas of weakly interacting non-relativistic bosons, focusing on the case of a non-trivial background field in infinitely extended space. Building upon a method introduced by Araki and further developed by Fredenhagen and Lindner, we derive the generating function of the correlation functions of the theory as a suitable series. By applying a Hubbard-Stratonovich transformation, we rewrite this quantity into a more mathematically tractable form, allowing us to establish the convergence of the corresponding loop vertex expansion in certain intermediate regimes. Furthermore, we isolate the tree diagrams that produce the scattering length in the dispersion relations of the two-point function of the state within the Gross-Pitaevskii regime. Finally, we use this scattering length to renormalise the background and the two-point function of the fluctuations and we discuss convergence of the generating function of the connected correlation functions of the renormalised theory in the limit of vanishing temperature.
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Chemical Physics

Category Theoretic Framework for Chemistry I: a Tower of Chemistry

Kyunghoon Han

Many laws of chemistry are exact within a limited scope and acquire a separate caveat outside it, and the caveats are usually treated as unrelated. This work argues that they share one cause. Each caveat marks a point where a question is asked of a description too coarse to answer it: the question belongs to a richer level of structure than the description carries. To make these levels explicit, the paper builds a tower of categories over the free symmetric monoidal category of a Petri net, the simplest categorical presentation of a reaction network. The levels, from the bottom up, are stoichiometry, thermochemistry, equilibrium, reaction kinetics, reaction mechanism, molecular geometry, and electronic structure. Each adds one kind of chemical content over the level below, and a forgetful functor runs back down. One question runs through the tower: what can a level express that the level below cannot? Answering it places each measurable quantity at the level where it lives, and identifies the content the levels below could record but not account for. The method is then turned on with two pieces of known chemistry. It recasts a classical criterion for when a reaction network has a unique stable equilibrium, the deficiency-zero theorem, as the rigidity of a single forgetful fibre. It also follows one familiar reaction up the tower: the ring opening that the Woodward-Hoffmann rules govern. At each level, from stoichiometry to electronic structure, the reaction becomes a distinct categorical object.
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General Relativity and Quantum Cosmology

Temporal Correlation Statistic for Intrinsic Phase Fluctuation in Double White Dwarf Gravitational-Wave Signals

Naoki Seto

We present a framework to probe intrinsic stochastic fluctuation in the orbital phase evolution of long-lived double white dwarf binaries through gravitational-wave observations with LISA. To capture the essential structure of the fluctuation, we introduce a minimal quadratic statistic that isolates its temporal correlation. We derive a simple analytic scaling relation for the signal-to-noise ratio of this correlation statistic, explicitly showing its dependence on the total observation time and the intrinsic phase correlation time.
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Earth and Planetary Astrophysics

Young asteroid pair candidates in the Jovian Trojan population

Jindřich Žižka

The number of asteroid pairs, unbound asteroids with a common origin and similar heliocentric orbits, has increased rapidly since their discovery. However, to date, only a small number of asteroid pairs have been identified in the outer main belt and especially within the Hilda and Jupiter Trojan populations. Except for a few binaries and collisional families, only one 360 Myr-old pair (258656) 2002 ES76 - (635224) 2013 CC41 is known among the Jupiter Trojans. During our survey, using GPU-accelerated integrations of the Jovian swarms, we identified two new promising pair candidates younger than 2.5 Myr. Pair (264119) Georgeorton - 2024 CN most likely formed either 427-500 kyr or 527-536 kyr ago, whereas pair (8060) Anius - (542262) 2013 BL has an estimated age of 2367-2421 kyr. Our results show that young asteroid pairs can arise even within the sparse population of Jupiter Trojans, opening new questions about their formation.
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Quantum Physics

Sp(2N, R) interferometry in multi-mode Gaussian bosonic systems for optimal metrology and quantum control

Chenwei Lv and Renbao Liu

Multi-mode interferometers for bosons in Gaussian states are important systems for quantum metrology with precision beyond the standard quantum limit and for bosonic quantum computing. However, there is a lack of theoretical foundation for generic $N$-mode Gaussian interferometry. In this work, we study quantum metrology and quantum control in multi-mode bosonic systems with quadratic Hamiltonians, exploiting the fundamental Sp$(2N,R)$ symmetry of such interferometers. We show that the optimal quantum control to maximize sensitivity requires aligning squeezing and displacement in the same direction. We propose Sp$(2N,R)$ echo, a multi-mode generalization of the SU$(1,1)$ interferometry, to achieve the sensitivity of phase estimation set by the quantum Fisher information. In addition, we introduce a geometrical means for reversing many-body dynamics with Sp$(2N,R)$ dynamical symmetry, such as dynamics of the bosonic Kitaev chain. Our schemes are readily realizable in optical, atomic, and mechanical platforms.
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Materials Science

Thermoelectric response of a ferroelectric insulator

Ryo Iguchi, Takashi Teranishi, Sakyo Hirose et al. (+4 more)

Thermoelectric effects enable the conversion between heat and electricity without moving parts. While conventionally associated with mobile charges, we report thermoelectricity caused by bound charges in the form of temperature changes measured by multi-harmonic lock-in thermography of a ferroelectric under an ac electric field. The observed temperature gradient depends on the field-induced displacement current, a Peltier effect in a dielectric material. Its coefficient exceeds 100 V around the ferroelectric-paraelectric phase transition, which is several orders of magnitude greater than reported values in conductors. Our findings uncover previously hidden functionalities of ferroelectric materials for thermal management by directional heat transport in ferroelectrics.
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All authors Ryo Iguchi, Takashi Teranishi, Sakyo Hirose, Ping Tang, Jun Kano, Gerrit E.W. Bauer, Ken-ichi Uchida

Chaotic Dynamics

Symbol sequences from three-rotor coincidences and their word-complexity

Govind S. Krishnaswami and Anirudh Rameshan

In the three-rotor problem, three equally massive point particles move on a circle interacting via attractive pairwise cosine potentials. Rotors can represent superconducting phases of metallic segments in a chain of coupled Josephson junctions. We propose a digitization of the classical dynamics that records successive pair and triple coincidences of rotors using four symbols. Rotor coincidences correspond to boundaries in a disjoint partition of the configuration torus into cells where the rotors are ordered clockwise and anticlockwise. It is shown that isolated rotor coincidences must be crossings. Despite being a rather coarse digitization, we find that replacing trajectories by coincidence symbol sequences captures significant qualitative features of the dynamics through word statistics. Word-complexity $C_n$ measures the diversity of $n$-letter words in the symbol sequence while topological entropy governs asymptotic exponential growth of $C_n$. Sequences from periodic orbits have a word-complexity that saturates at the period. Ultra-high-energy trajectories with irrational `slope' are quasiperiodic. We show that they have zero entropy and $C_n = n+3$ by examining limiting slopes and by a mapping to Sturmian sequences. We examine their grammar rules and propose how their right-special words may be identified. On the other hand, numerical investigation of sequences from globally chaotic orbits leads us to conjecture an exponentially growing word-complexity $C_n = 3 \times 2^{n-1}$ with a topological entropy $\log 2$. We identify grammar rules that imply this conjectured word-complexity and model the resulting sequences as a subshift of finite type, unlike those at ultra-high energies which are not topological Markov chains.
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Physics and Society

Space-based Missile Defense

David Wright

This paper reviews the technical issues underlying space-based boost-phase missile defense and examines the current technology available for space-based interceptors and the characteristics of the missiles such a system would face. It then analyzes a particular space-based missile defense system that has been proposed to intercept in boost, ascent, and midcourse phases to illustrate the details of such an analysis and the constraints imposed on such systems by the physics of operating in space.
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General Relativity and Quantum Cosmology · Cross-listed from math.DG

$C^0$-inextendibility of a class of warped-product black hole spacetimes

Karim Mosani

We adapt Sbierski's proof of $C^0$-inextendibility of the maximal analytic Schwarzschild spacetime to a broad class of warped-product black hole spacetimes with a static exterior region. These spacetimes are globally hyperbolic, have a codimension-two Riemannian fibre and a radial coordinate $(r)$, which serves as the warping function of the fibre. They admit a spacetime singularity as $r \to 0$, characterised by the divergence of the Kretschmann scalar. This class encompasses nonvacuum black hole models and geometries beyond spherical symmetry. Under suitable assumptions, including that the fibre is closed (compact without boundary), connected, homogeneous, and orientable, we establish future $C^0$-inextendibility for spacetimes in this class. The result further extends to spacetimes possessing more than one regular black hole horizon.
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