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Physics

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Friday 3 July

Physics Education

Physical Systems as Objects: A Structural Correspondence for Computational Physics Education

Luis E. Sánchez-González

Physical systems and objects in the object-oriented programming (OOP) paradigm share a common organizational structure: identity, state, and governing laws. We argue that making this structural correspondence explicit, rather than leaving it as tacit knowledge embedded in scientific software, provides a natural and general basis for teaching computational physics. The correspondence is independent of both programming language and mathematical formalism, applying equally to differential equations, eigenvalue problems, and variational principles. To illustrate this idea, we present Ollin, an open-source Python framework for computational physics education organized around the correspondence principle. Four examples spanning mechanics, celestial mechanics, quantum mechanics, and variational optics demonstrate that the same representational structure can be preserved across diverse physical domains. In each case, the class definition serves as the physical model, its attributes encode the state and physical parameters of the system, and its methods encode the governing laws, regardless of whether those laws are integrated, diagonalized, or optimized. More broadly, the correspondence principle provides a conceptual framework for relating the organization of physical models to the organization of code.
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Fluid Dynamics

Development and application of a multiphase Lagrangian structure function model in anisotropic turbulence

Andrew P. Grace and David Richter

The energetic response of inertial particles to turbulent flow motions is important for both a fundamental understanding of the multi-phase dynamics at play, and for applications such as reduced-order models of particle dispersion processes, and their two-way coupled effects onto the flow phase. Numerous studies focus on the energetics of ensembles of particles in homogeneous isotropic turbulence, where the influence of flow anisotropy (such as that provided by boundary conditions, or other external forcing) is not considered a priori. In this work, we investigate the role of flow anisotropy on the Eulerian scale-wise particle phase energetics in a turbulent wall bounded flow for settling inertial Lagrangian particles. By using coupled Eulerian-Lagrangian direct numerical simulations at moderate Reynolds number, we aim to unravel the complex dependency of the scale-wise particle energetics on the turbulence intensity, particle inertia, and particle settling. In particular, we focus on how the developing anisotropy of the underlying turbulent flow (derived from the presence of the wall) is donated to the particle phase, and how particle inertia and settling preserve this large scale anisotropy into the formally isotropic scale range of the flow. We derive an exact (but unclosed) conservation law for the particle phase energetics at arbitrary scale, and use an asymptotic argument to help elucidate our DNS data. We discuss the relative changes to the quasi-streamwise and vertical components of the fluctuating particle field, and finish by discussing the implications of anisotropic non-local effects for more general flows, and the implications for continuum models of inertial settling Lagrangian particles.
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High Energy Physics (Theory)

Quantum nucleation of black hole mimickers via chaos dominated tunneling

Ulf Danielsson, Suvendu Giri, Vyshnav Mohan et al. (+1 more)

Black hole mimickers, ultracompact horizonless objects, have been proposed as alternatives to black holes in a variety of settings, including extensions of general relativity and scenarios involving matter sectors beyond the Standard Model. Their formation in gravitational collapse of matter requires quantum mechanical tunneling to occur on a length scale of the order of the Schwarzschild radius of the corresponding black hole. We propose a mechanism, based on multichannel enhancement catalyzed by quantum chaotic dynamics, that can dramatically amplify the quantum mechanical transmission across a tunneling barrier. We explore, in particular, how the nucleation of a string theoretic black shell is enhanced via this mechanism. We anticipate similar results to hold for other proposed black hole mimickers.
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All authors Ulf Danielsson, Suvendu Giri, Vyshnav Mohan, Larus Thorlacius

Physics and Society

The limits of visitation entropy as a summary of mobility patterns

Sílvia de Sojo, Sune Lehmann and Laura Alessandretti

Visitation entropy, the Shannon entropy of an individual's distribution of visits across locations, is a widely used metric in the human mobility literature. Yet, its widespread use rests on assumptions that are rarely made explicit: entropy is defined over a fixed set of states, and estimating it empirically requires abundant, well-sampled observations. The limitations that arise when entropy is used outside this setting have been documented and explored in fields such as statistical physics, ecology, and cryptography. The implications for mobility studies, however, remain unclear. Here, we leverage synthetic and empirical trajectories to systematically examine the strengths and weaknesses of visitation entropy as a measure for characterizing human mobility. We show that, for a sequence of locations visited by an individual, the visitation entropy primarily reflects the number of unique locations visited and sequence length, which together explain 90.7% of its variance in empirical data. We also show that shorter sequences systematically lead to an underestimation of entropy, showing finite-sample bias to be a key limitation. As a result, comparisons of groups based on visitation entropy should be treated with caution. We find that apparent entropy gaps between genders, commuters and non-commuters, and urban and rural residents are reduced, or reversed, once sequence length and the number of unique locations are taken into account. Finally, we show that these issues can be addressed by controlling for sequence length and the number of unique locations, and by complementing entropy with structural network measures, which provide more nuanced insight into how mobility is organized beyond the aspects that entropy alone captures.
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Optics

Hz-resolution wide-span photonic integrated terahertz signal analyzer

Aleksei Gaier, Jiawen Liu, Ekaterina Mironova et al. (+2 more)

Wide-span spectral and noise characterization at millimeter-wave and terahertz frequencies is increasingly important for emerging wireless, sensing, and spectroscopy systems, yet remains challenging for conventional electronic instrumentation because of the complexity and calibration burden of extender-, multiplier-, and mixer-chain architectures. Here we show that photonics can provide attractive alternatives to this highly challenging electronic instrumentation through an antenna-coupled thin-film lithium niobate electro-optic receiver. Our implementation performs fast spectral reconstruction across the widely separated WR 9.0 (80-125 GHz) and WR 2.8 (240-380 GHz) bands with a single component, with carrier-frequency errors below 3 MHz, scan speeds up to 25 THz/s, and a displayed average noise level below -104 dBm/Hz. We then extend to Hz-level resolution and demonstrate phase-noise characterisation capabilities across these ultra-wide bands by using a mode-locked femtosecond-laser frequency comb as a sampling clock, mapping high-frequency carriers to aliased intermediate-frequency tones. We validate the method by measuring the phase noise of 90.225 GHz and 270.675 GHz carriers using the same chip and system configuration. We further improve the sensitivity of the phase-noise measurement through cross-correlation between two optical probe-pulse channels. Finally, we show that the same technique can be applied synchronously to ten widely spaced frequencies distributed across more than 100 GHz, with the option to quantify their mutual coherence. These results establish TFLN integrated photonics as a scalable route toward compact millimeter-wave/terahertz instrumentation.
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All authors Aleksei Gaier, Jiawen Liu, Ekaterina Mironova, Gabriel Julg, Ileana-Cristina Benea-Chelmus

High Energy Physics (Theory)

Finite path integral limits work in cases where the perturbative series is not Borel summable

Ariel Edery

The perturbative expansion in powers of the coupling of observables in quantum field theory and quantum mechanics is known to yield an asymptotic series. If the original physical system is well-behaved and a finite observable is expected, this can often be calculated via a Borel resummation of the asymptotic series. However, there are cases where a system is well-behaved and the series is not Borel summable. This typically occurs when the physical system has a non-trivial vacuum structure. It has recently been shown that if the perturbative series is carried out under finite path integral limits, one can obtain a convergent series that yields observables even at strong coupling. This was recently used to obtain the energy at strong coupling for the anharmonic oscillator. This is a Borel summable case so the question is whether finite path integral limits work when the series is not Borel summable. To begin answering this question we consider a simple non-Borel summable case: the series stemming from a basic integral where the function has a double-well shape and hence two minima. The integral has an exact analytical expression that the series can be compared to. Under finite integral limits that run from $-L$ to $L$, where $L$ is finite, positive and real, we develop two perturbative series in powers of the coupling: one by expanding the integral about the local maximum at the origin and the other by expanding it about one of the minima. In both cases, we obtain an absolutely convergent series and the series sums to the exact analytical expression of the original integral in the infinite $L$ limit. It is significant that a perturbative expansion about one of the minima reproduces the exact analytical expression because this implies that it captures the full effect of both minima.
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Quantum Physics

Dynamical zero modes and boundary dependence in dynamical quantum phase transitions

Siyan Lin, Xu Feng, Xiuhua Tian et al. (+1 more)

Boundary conditions are usually expected to cause only finite-size corrections to bulk quantities, but this expectation can fail for dynamical quantum phase transitions. In this work, we show that such boundary dependence is encoded in dynamical zero modes (DZMs) of the Loschmidt matrix, which are defined as singular vectors whose singular values vanish in the thermodynamic limit. Using the Su-Schrieffer-Heeger (SSH), extended SSH, and Kitaev models as examples, we find that the time interval where the Loschmidt rate functions (LRFs) under periodic and open boundary conditions differ coincides with the emergence of DZMs in the open-boundary Loschmidt matrix. These modes carry the boundary-dependent contribution: removing them from the open-boundary LRF recovers the periodic-boundary result. We further show that these DZMs lead to finite-precision numerical instability, since their finite-size singular values decay exponentially with system size and eventually become unresolved in fixed-precision arithmetic. A reliable small-size branch before this loss of precision can be used to estimate the LRF in the thermodynamic limit by linear extrapolation. Our results identify DZMs as both a diagnostic of boundary-dependent LRFs and the origin of the associated numerical instability.
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All authors Siyan Lin, Xu Feng, Xiuhua Tian, Shu Chen

Quantum Physics

Design of an Electrically Tunable Microtoroid for Frequency Selection of Polarization-Entangled Photons

Yichi Zhang, Enqi Ke and Judith Su

Encoding quantum information into discrete optical frequencies, or "frequency bins," uses different colors of light as additional information channels, allowing each photon to carry more information than polarization alone. We present a computational design for an electrically tunable silica microtoroid that selects desired frequency channels after a polarization-entangled photon pair has been generated without disturbing the photons' polarization entanglement. In the proposed architecture, the 750 nm signal photon passes through the microtoroid, while its entangled 880 nm partner bypasses the resonator and serves as a reference for the selected frequency channel. The principal challenge is resonator birefringence: because horizontally and vertically polarized light resonate at slightly different frequencies, the selected frequency can reveal the photon's polarization state and weaken the quantum correlation between the photon pair. We solve this problem by adding a small lithium-niobate tuning element controlled with a single applied voltage. The voltage shifts the resonator so that it responds almost identically to horizontally and vertically polarized light, reducing the remaining mismatch to only 0.286 optical linewidths across nine frequency channels. The photons remain strongly entangled after passing through the device, with a concurrence of C = 0.969, a Bell-state fidelity of F = 0.981, and a Bell parameter of S_max = 2.785. If the relative timing between the frequency channels is also controlled, the same device can generate a nine-channel polarization-frequency hyperentangled state with an effective dimension of K = 8.97. This computational design provides a compact, electrically tunable bridge between polarization-entangled photon sources and future high-capacity quantum photonic systems.
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Fluid Dynamics

Acoustic Loading Beneath High-Speed Flow Over a Compression Ramp at Different Angles

Ritu Raj Kumar, Nagabhushana Rao Vadlamani and Amareshwara Sainadh Chamarthi

Large-eddy simulations are performed to characterize the pressure fluctuations beneath a hypersonic boundary layer approaching a compression corner. The simulations are carried out at Mach 6.04 and an inlet momentum-thickness Reynolds number of $Re_{\theta}=4340$. The compression-corner angle is varied over $10^\circ$, $20^\circ$, $30^\circ$, and $34^\circ$ spanning attached to strongly separated regimes. The peak root-mean-square wall-pressure fluctuations intensity increases sharply with separation strength, rising by $312\%$ from R20 to R30 and a further $67\%$ from R30 to R34, with the peak located downstream of reattachment. Notably, acoustic loading increases from 140 dB in the approach flow to $\approx177$ dB downstream of reattachment in the $34^\circ$ case. Further analysis reveals that intense intermittent pressure events are concentrated near the shock foot, spatially distinct from the peak acoustic-loading region, where fluctuations are relatively sustained. With increasing interaction strength, spectral energy shifts from turbulence-dominated high frequencies to broadband low-frequency motion. Band-isolated acoustic loading maps reveal high-frequency fluctuations as the dominant contributor across the interaction zone, with low-frequency fluctuations becoming locally comparable in the R34 case near the separation region. Spatio-temporal maps of bandpass-filtered pressure fluctuations reveal downstream convecting Kelvin-Helmholtz structures and upstream propagating pressure waves near the shock foot.
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High Energy Physics (Theory)

Berry Picking: Random Wave Chaos Hierarchy for BPS Microstate Geometries

Vladan Djukić, Milica Stepanović and Mihailo Čubrović

We estimate the strength of chaos of probe waves and probe geodesics in different smooth supergravity backgrounds of decreasing supersymmetry and/or increasing length of the AdS throat in the interior. Since BPS spectra are highly degenerate and thus do not display the level repulsion that ordinarily diagnoses chaos, we propose compliance with the Berry random wave hypothesis for probe wavefunctions as a new notion of BPS chaos suited to the supergravity regime. The wave chaos becomes stronger and stronger with less supersymmetry and longer throats (i.e., as we approach black hole solutions). Geodesic motion shows the opposite trend, becoming more and more regular. We explain this dichotomy by the existence of stable periodic orbits inside long throats while the overall measure of KAM tori decreases. Computing the Rényi entropies for the dual CFT states in the weak coupling regime, we show that they do not have such universal behavior.
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Materials Science

Dyna-Mat: End-to-end benchmarking of foundation machine learning interatomic potentials in finite-temperature ensembles

Mikołaj J. Gawkowski, Nongnuch Artrith, Silvia Bonfanti et al. (+14 more)

Foundation machine learning interatomic potentials (MLIPs) are increasingly being used as drop-in replacements for first-principles calculations, enabling simulations of materials at length and time scales that were previously inaccessible. However, due to lack of ground truth data, their accuracy on structural and dynamical observables in finite thermodynamic ensembles is yet to be established. Here, we introduce Dyna-Mat-v1.0, a benchmark dataset of condensed-phase first-principles molecular dynamics trajectories designed to test foundation MLIPs at realistic finite-temperature conditions. Using this dataset, we evaluate 15 foundation MLIPs across four model tiers by comparing both single-point energy and force errors on first-principles configurations and observables generated from MLIP-driven trajectories. We find that "on average" models with lower single-point force errors also yield lower errors for structural and dynamical observables. However, there are individual systems for which low force errors lead to qualitative failures in the predicted structure. Pressure remains poorly described across most models, pointing to limitations in the density functional theory stress labels available in current large-scale training datasets. Finally, we construct an accuracy-cost Pareto frontier to identify the best trade-offs for molecular dynamics with foundation MLIPs, finding that the latest generation of cross-trained models is close to Pareto-optimal according to the accuracy metrics considered here. Overall, Dyna-Mat-v1.0 shows that end-to-end finite-temperature validation is essential for quantifying the predictive behaviour of foundation MLIPs, and provides a simple, scalable route for assessing them beyond static and harmonic benchmarks relevant to materials design.
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All authors Mikołaj J. Gawkowski, Nongnuch Artrith, Silvia Bonfanti, Abhijeet Sadashiv Gangan, Hendrik H. Heenen, Joseph Kioseoglou, Ivor Lončarić, Hemanadhan Myneni, Janosh Riebesell, Mariana Rossi, Matthias Rupp, Jonathan Schmidt, Shubham Sharma, Benjamin X. Shi, Antoni Wadowski, Lukas Hörmann, Venkat Kapil

Astrophysics of Galaxies

Euclid: Discovery of 31 new quasars at $6.6 < z < 7.8$

D. Yang, J. F. Hennawi, F. Guarneri et al. (+211 more)

We report the discovery of 31 new high-$z$ quasars in the redshift range $6.6 < z < 7.8$. These quasars were selected from approximately 3000 deg$^2$ of sky covered during the first 1.5 years of the Euclid Wide Survey, representing the initial results of the Euclid high-$z$ quasar search. Our candidate selection employed multiple machine-learning and probabilistic techniques applied to the Euclid $I_E$, $Y_E$, $J_E$, and $H_E$ images, supplemented by ancillary $z$-band data when available. Spectroscopic follow-up observations were carried out with Keck, Magellan, and the Large Binocular Telescope (LBT). Among the new discoveries, there are 12 quasars at $z \geq 7$, more than doubling the number of previously known quasars at $z \geq 7$. The newly discovered quasars exhibit $21.2 < J_E < 23.2$ ($-25.5 < M_{1450} < -23.6$), extending quasar studies to the faint end of the quasar luminosity function (QLF) at $z \gtrsim 7$. The quasar with the highest-$z$, EUCL J172902.75+641018.1 at $z \approx 7.77$, sets the new redshift record for the most distant quasar ever reported. These discoveries demonstrate Euclid's transformative role in high-$z$ quasar discovery and set the stage for future follow-up studies of the early galaxies hosting quasars, supermassive black hole growth, and the intergalactic medium in the epoch of reionisation.
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All authors D. Yang, J. F. Hennawi, F. Guarneri, J. Wolf, S. Belladitta, J.-T. Schindler, A. C. N. Hughes, E. Bañados, D. J. Mortlock, J. Yang, F. Wang, X. Fan, K. Jahnke, D. Stern, C. J. Willott, A. J. Barth, H. J. A. Rottgering, R. G. Varadaraj, R. Decarli, A.-C. Eilers, M. Ezziati, Y. Fu, J. Huang, X. Jin, Y. Kang, L. N. Martinez-Ramirez, Y. Matsuoka, M. Onoue, R. Pello, R. P. Remigio, W. L. Tee, B. Venemans, G. Vietri, B. Wang, L. J. Abbo, H. Atek, S. Bisogni, S. E. I. Bosman, R. A. A. Bowler, C. J. Conselice, F. B. Davies, C. M. Gutierrez, Y. Harikane, K. Rubinur, C. C. Lovell, M. Magliocchetti, J. Matthee, F. Ricci, M. Scialpi, D. Scott, L. Spinoglio, F. Tarsitano, Y. Toba, F. Walter, J. R. Weaver, G. Zamorani, B. Altieri, A. Amara, S. Andreon, H. Aussel, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, J.-C. Cuillandre, H. Degaudenzi, G. De Lucia, C. Dolding, H. Dole, M. Douspis, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, S. Ferriol, F. Finelli, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. Gwyn, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, M. Jhabvala, S. Kermiche, B. Kubik, K. Kuijken, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, H. J. McCracken, E. Medinaceli, S. Mei, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, J. J. Mohr, A. Mora, M. Moresco, L. Moscardini, E. Munari, R. Nakajima, C. Neissner, R. C. Nichol, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, G. D. Racca, F. Raison, R. Rebolo, A. Renzi, J. Rhodes, G. Riccio, H.-W. Rix, E. Romelli, M. Roncarelli, C. Rosset, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, M. Sauvage, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, S. Serrano, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, J. Steinwagner, P. Tallada-Crespí, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, F. M. Zerbi, E. Zucca, G. Fabbian, M. Huertas-Company, J. Martín-Fleitas, P. Monaco, V. Scottez, M. Viel

Mathematical Physics · Cross-listed from math.NA

Pointwise Error Estimates for Numerical Physics-Informed Neural Networks

Nivar Anwer, Marien Chenaud, José Alves et al. (+1 more)

Physics-informed neural networks are often evaluated by residual losses sampled at finitely many points, which do not by themselves certify pointwise values of a partial differential equation solution. In this work, deterministic pointwise error intervals are developed for mesh-based, piecewise-linear numerical physics-informed neural networks. The proposed error estimation is given for a compatible field, which is the finite-element reconstruction of an admissible prediction on a mesh. The certifying residual is then obtained by applying the finite-dimensional numerical system to this compatible field. For compatible square linear systems, the pointwise error relative to the discrete target has an exact adjoint Green representation, and the computed signed error recovers the finite element solution exactly. Norm-based, inexact, localized, and randomized variants provide computable intervals when the exact correction computation is impractical. The extension from the discrete target to the continuous solution is supplied by comparison estimates. For a one-dimensional coercive reaction-diffusion class, this transfer layer is made fully computable by an explicit residual-based a posteriori estimator with querywise constants. The error bound derivation is extended to nonlinear residual systems with explicit Taylor remainders. Numerical experiments assess compatibility and calibration on manufactured examples, on a large-scale public three-dimensional elasticity benchmark, and on projected neural load families on the same benchmark.
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All authors Nivar Anwer, Marien Chenaud, José Alves, Frédéric Magoulès

Astrophysics of Galaxies

Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at $z \approx 7.7$

S. Belladitta, R. Decarli, E. Bañados et al. (+180 more)

Constraining the co-evolution of supermassive black holes and their host galaxies in the first billion years after the Big Bang is essential for understanding the formation of the earliest cosmic structures. Here, we present IRAM/NOrthern Extended Millimeter Array (NOEMA) observations of the $z \approx 7.7$ quasar EUCL\,J125308.55+705432.3, recently discovered in the first data release of the Euclid Wide Survey. We report the most distant detections of [CII] 158$\mu\mathrm{m}$ and cold dust emission in a quasar host to date. The [CII] emission line sets the systemic redshift at $z=7.6980\pm0.0004$. The source exhibits luminosities of $L_{\rm FIR}=3.6\times10^{12}\,L_{\odot}$ and $L_{[CII]}=2\times10^9\,L_{\odot}$, respectively, a dust mass of 1.4$\times 10^{8}\,M_{\odot}$, and a dynamical mass in the range 0.33-1.3$\times10^{10}\,M_{\odot}$. Remarkably, despite being nearly two magnitudes fainter in the rest-frame UV ($M_{1450}=-24.06$) than previously known $z\approx7.5$ quasars (<M$_{1450}$> $\sim-$26.5), EUCL\,J125308.55+705432.3 exhibits the brightest [CII] emission among them. This indicates that the host galaxy is actively star-forming, with a star-formation rate $>250\,M_{\odot}\,\mathrm{yr}^{-1}$, consistent with recent findings that UV-faint quasars at $z>6$ preferentially reside in [CII]-luminous galaxies. The UV-faintness likely reflects dust obscuration or sub-Eddington accretion, rather than lower host mass, suggesting these systems are at a different stage in their evolution compared to UV-bright quasars. These IRAM/NOEMA observations highlight the power of combining Euclid's wide-area quasar discovery potential with submillimetre follow-up observations to characterise the host galaxies of early supermassive black holes across a broader redshift and luminosity range than previously accessible.
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All authors S. Belladitta, R. Decarli, E. Bañados, F. Walter, D. Yang, F. Guarneri, K. Jahnke, S. Bisogni, S. E. I. Bosman, X. Fan, Y. Fu, J. F. Hennawi, Y. Matsuoka, D. J. Mortlock, M. Onoue, J.-T. Schindler, L. Spinoglio, D. Stern, F. Wang, G. Vietri, C. J. Willott, J. Wolf, J. Yang, R. A. A. Bowler, K. I. Caputi, D. L. Clements, C. M. Gutierrez, H. J. A. Rottgering, D. Scott, F. Shankar, G. Zamorani, A.-C. Eilers, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, J.-G. Cuby, A. Da Silva, H. Degaudenzi, G. De Lucia, H. Dole, M. Douspis, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, P. Fosalba, S. Fotopoulou, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, R. Laureijs, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, S. Marcin, 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, C. Neissner, R. C. Nichol, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, A. Renzi, J. Rhodes, G. Riccio, H.-W. Rix, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, F. M. Zerbi, E. Zucca, J. García-Bellido, J. Martín-Fleitas, P. Monaco, V. Scottez, M. Viel

Quantum Physics

Matter-Field Exchange Generates Entanglement, Not Classical Gravity

Nicetu Tibau Vidal and Aditya Varna Iyer

Aziz and Howl have argued that a hybrid theory with quantum matter and a classical gravitational field can generate entanglement between two massive systems. In their construction, the branch-dependent contribution appears at fourth order through propagators of the quantum matter field in a fixed classical gravitational potential. We analyse this mechanism within the same perturbative QFT framework and show that the effect should not be interpreted as classical gravity mediating entanglement in the sense relevant to BMV-type witnesses. The non-separable term relies on a quantum-matter exchange channel between the two interferometers and is present only when the two systems are modelled as excitations of the same matter field. If distinct, non-interconverting matter fields describe the systems, the corresponding cross-propagator is absent and the Aziz-Howl entangling diagram vanishes. The effect relies on coherent propagation amplitudes of the quantum matter field between the two interferometers, together with postselection onto the original localised branch subspace. Moreover, the inference of entanglement is made after projecting the full QFT evolution onto a restricted final subspace containing the original localised $N$-particle branch states. This projection removes precisely the sectors that would record matter-field contamination, mode deformation, or exchange between the two interferometers. We therefore argue that the Aziz-Howl mechanism is a matter-sector cross-talk effect in a classical background, not entanglement mediated by classical gravitational degrees of freedom. Having identified the channel responsible for the Aziz-Howl contribution, we predict that it can be eliminated by using distinct, non-interconverting matter species in the two interferometers, or by inserting a barrier that suppresses matter-field propagation between them.
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Mesoscale and Nanoscale Physics

Evidence of length scale effect in contact electrification in conducting thin film heterostructures

Paul C. Lou, Ravindra G. Bhardwaj, Anand Katailiha et al. (+2 more)

Contact electrification between two conducting materials is expected to exhibit length scale effect because the screening effect will diminish in conductors as a function of material dimensions. As a consequence, the interfacial charge accumulation will diffuse away from interface/surface to a critical penetration depth as a function of material dimension. This work experimentally demonstrates the length scale effect in a permalloy and degenerately doped p-Si heterostructure system due to the flexoelectricity mediated contact electrification. The contact electrification induced interlayer charge transfer is observed through the whole thickness in case of 400 nm thick p-Si samples. Whereas, the charge carrier diffuses to a depth of 51 nm from the interface in case of 2 um thick Si. The length scale effect also leads to metal-insulator transition in p-Si layers in both cases. These results present a new opportunity to tailor the physical properties in conducting materials using contact electrification.
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All authors Paul C. Lou, Ravindra G. Bhardwaj, Anand Katailiha, W.P. Beyermann, Sandeep Kumar

Astrophysics of Galaxies

PKS 2155-304: Long-Term Optical Photometric Monitoring and Variability Analysis

J. L. Weiss, I. Andruchow, E. J. Marchesini et al. (+6 more)

Through the detailed study of the optical flux behaviour in blazars over time, it is possible to infer the conditions responsible for their observed emission. PKS 2155-304, a BL Lac object detected from radio to TeV energies, is among the brightest blazars in the southern hemisphere. We present optical monitoring spanning over two decades using telescopes at Complejo Astronómico El Leoncito and Estación Astrofísica de Bosque Alegre, Argentina. Differential light curves in the B, V, R, and I bands reveal significant variability on weekly and longer timescales, with occasional changes on sub-four-hour scales. The optical spectral index remained negative, consistent with non-thermal emission, and hardened over the past nine years. Evidence for quasiperiodic behaviour on 20-30 day timescales was found, while correlations with X-ray fluxes were weak, suggesting distinct emission components in the two bands. These results highlight the pronounced optical variability of PKS 2155-304 and provide insight into its multi-band emission mechanisms
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All authors J. L. Weiss, I. Andruchow, E. J. Marchesini, S. Cellone, L. Zibecchi, J. P. Varela, L. Mammana, E. Jofré, R. Petrucci

Quantum Physics

Specifying the operational meaning of quantum reference frames

Augustin Vanrietvelde

In their strongest usage, quantum reference frames have been described as referring to "the measurements performed by a superposed lab", "the perspective of a quantum particle", "the point of view of a superposed observer", etc. While exciting, these operational proposals have remained brief and ambiguous, leading to misinterpretations and criticism. Here, we provide a detailed specification and defense of the notion of a position-superposed lab or observer. We argue that this requires no exotic claims about quantum physics and raises no greater interpretive difficulty than ordinary quantum measurements. We then derive several consequences of taking this operational meaning seriously. We stress that the position-superposed observers that define quantum references frames are different from, and considerably less problematic than, the outcome-superposed observers considered in Wigners' friend scenarios. In particular, we show that outcomes obtained by a position-superposed observer may (without decohering the superposition) be broadcast to a well-localised one, in contrast with Wigner's friend scenarios, which require the outcomes to remain internal to the system at hand. Finally, we defend the possibility to roleplay a quantum reference frame from a classical reference frame.
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History and Philosophy of Physics

Becoming, Duration, and the Evolving Block Universe

Nicolò Cangiotti

The two-times problem asks how the directed, oriented time of biological and conscious systems relates to the time of fundamental physics. The Evolving Block Universe, in which spacetime grows through an irreversible quantum dynamics along physically preferred worldlines, accounts for the direction of physical time and for its emergence across scales up to the time kept by the brain. It leaves open the relation between this physical time and the experience of passage. We argue that Bergson's durée, the continuous qualitative experience of lived time, names this residue and marks the first-person level at which the physical hierarchy reaches its limit. On this reading the two accounts divide the problem between them: the Evolving Block Universe describes its structural, third-person half, and durée its experiential, first-person half. The remaining gap between the two halves is explanatory. It is an instance of the familiar gap between the physical description of a system and the character of its states as they are lived, and it is compatible with physicalism.
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Fluid Dynamics

Experimental and numerical study of the dynamics of sedimenting pairs of semi-flexible fibers close to attractive `aligned' relative configuration

Harish N. Mirajkar, Chandra Shekhar, Yevgen Melikhov et al. (+2 more)

Dynamics of two short semi-flexible fibers settling under gravity in a viscous fluid are investigated at Reynolds numbers Re << 1. We focus on fibers initially relatively close to each other, and we check if later they approach an aligned horizontal configuration, previously identified numerically (Bukowicki and Ekiel-Jezewska, Soft Matter 46 (2019) 9379) as attractive for symmetric initial conditions of moderately elastic filaments. In our experiments, two semi-flexible ball chains sediment in a highly viscous silicone oil. They are initially straight and close to a parallel horizontal relative configuration. Their motion and shape deformation are recorded using two synchronized cameras. For most of the trials, ball chains stay together, with damped oscillations around the symmetric aligned configuration. For a few initial conditions, the ball chains move away horizontally or vertically. To study the behavior over a longer time, we perform numerical simulations, modeling moderately elastic filaments as chains of identical beads, with the centers of consecutive beads connected by springs and with the fibers' elastic resistance to bending. Different initial positions and orientations are considered. Their dynamics are determined by the multipole expansion of the Stokes equations, implemented in the precise Hydromultipole numerical code. For short times, we observe the similar dynamics of semi-flexible ball chains and moderately elastic filaments. We provide examples of long-time numerical simulations illustrating that elastic filaments close to each other can move away horizontally or vertically, but after a long time, come back and perform damped oscillations while approaching the aligned configuration with almost touching filament ends. We confirm the attractive nature of the aligned configuration of very close semi-flexible sedimenting fibers, even if they are far away from each other.
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All authors Harish N. Mirajkar, Chandra Shekhar, Yevgen Melikhov, Piotr Zdybel, Maria L. Ekiel-Jezewska

Quantum Physics

Emergent Quantum Synchronization Without Symmetry Breaking

Juan David Álvarez-Cuartas, Joakim Bergli and John H. Reina

Parametric amplification of a shared cavity mode turns the light–matter coupling phase of a two-ensemble Dicke model into a control parameter. We prove analytically that a cavity-set gain band opens a window of this phase with no static superradiant instability, leaving only a Hopf bifurcation, for arbitrary couplings, spin frequencies, damping rates and ensemble sizes. A $\mathbb{Z}_2$ parity keeps the quantum steady state unique and time independent: every order parameter vanishes and the oscillation lives in a slow parity-odd Liouvillian mode. Truncated-Wigner simulations, validated against exact ones, show that above threshold its quality factor grows linearly with system size and the ensembles phase lock; below threshold, both saturate. Quantum synchronization emerges without symmetry breaking and without requiring entanglement.
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Instrumentation and Methods for Astrophysics

Simulation-based dynamic pointing analysis of AtLAST under wind loading and fast-scan conditions

Aleksej Kiselev, Martin Timpe, Matthias Reichert et al. (+2 more)

The Atacama Large Aperture Submillimeter Telescope (AtLAST) is a next-generation 50-m class single-dish facility concept designed for high-throughput, wide-field mapping at millimetre and submillimetre wavelengths. Its science goals require fast telescope motion while maintaining stringent dynamic pointing stability under realistic environmental and operational conditions. We present an end-to-end dynamic pointing analysis of the current AtLAST design, coupling a flexible structural model of the telescope mount with the intended cascaded main-axis control architecture, pointing-error evaluation, and measured site wind excitation. A key feature of the study is the use of high-rate wind measurements obtained at the AtLAST candidate sites before telescope construction. The measured wind time series are used as dynamic input to evaluate tracking under wind loading for multiple elevation angles, wind-speed classes, and wind angles of attack. The resulting wind-induced dynamic pointing error remains within the allocated tracking-stability budget for all budgeted wind conditions, confirming the adequacy of the current structural concept and main-axis control approach with respect to wind-driven pointing stability. Fast mapping is investigated separately using a Lissajous-daisy scan close to the kinematic limits of the mount. In contrast to the wind-loaded tracking case, the scan-induced response is more strongly linked to finite control bandwidth and trajectory-following accuracy, particularly in elevation. The analysis therefore identifies two distinct dynamic pointing regimes and provides guidance for future control optimization, feedforward strategies, and active compensation concepts.
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All authors Aleksej Kiselev, Martin Timpe, Matthias Reichert, Tony Mroczkowski, Claudia Cicone

Mesoscale and Nanoscale Physics

Emergent $\mathbb{Z}$-type topology in a quasi-one-dimensional extended QWZ model

Zebedeus F. Osseweijer, Lumen Eek and Cristiane Morais Smith

We investigate the emergence of zero-dimensional topological end states in nanoribbons described by the Qi-Wu-Zhang (QWZ) model and its extensions with longer-range couplings. While dimensional reduction from two to one dimension is often assumed to preserve the symmetry classification of the parent system, here an additional symmetry can emerge originating from the real-space geometry of the ribbon. This symmetry acts as a chiral symmetry, combining orbital and spatial transformations, and promotes the effective one-dimensional system from symmetry class D to class BDI. We demonstrate that the existence of such a symmetry depends both on the long and end termination of the ribbon and exhibits an even-odd effect with respect to ribbon width, revealing that the commonly studied rectangular ribbons constitute a special high-symmetry case. For the conventional QWZ model, we derive analytic expressions for the topological phase boundaries of finite-width nanoribbons and characterize the resulting hybridization-gap phases through ($\mathbb{Z}_2 $) and winding-number invariants. We further show that extended QWZ models with longer-range couplings support phases with multiple topological end states and higher winding numbers. These phases arise through distinct mechanisms, including the hybridization of multiple edge modes inherited from higher-Chern-number bulk phases. Our results demonstrate that both long and end termination can fundamentally alter the topological classification of confined Chern insulators, highlighting the interplay between crystalline geometry, emergent symmetries, and dimensional reduction.
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Cosmology and Nongalactic Astrophysics

The heating rate of the Intergalactic Medium by Lyman-$\alpha$ photon scattering

Avery Meiksin

The strength of the 21-cm Cosmic Dawn radio absorption signature against the Cosmic Microwave Background or against a bright background radio source depends on the temperature of the neutral hydrogen in the intergalactic medium. While x-rays from forming galaxies will likely dominate the heating rate, recent models suggest scenarios in which heating by the scattering of Lyman-$\alpha$ photons sourced by the galaxies contributes non-negligibly as well, and may even dominate. The efficiency of Lyman-$\alpha$ photon heating for a point source at high redshift using a numerical solution to the exact radiative transfer equation is provided here. It is found to be a factor of several smaller than the rate computed in the commonly used diffusion approximation to the radiative transfer equation.
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High Energy Physics (Phenomenology)

Analytic result of a three-loop integral family in the Higgs decay to four massive bottom quarks

Jian Wang, Xing Wang and Yefan Wang

When calculating the decay width of $H\to b\bar{b}b\bar{b}$ induced by the effective Higgs-gluon-gluon interaction using the optical theorem, the three-loop Feynman diagrams are encountered. Among them, there is an interesting integral family, which involves not only the sectors evaluated to multiple polylogarithms but also those related to an elliptic curve and a K3 surface. We demonstrate how to construct and solve the canonical differential equation for the entire family, which includes mixing between different sectors, by using the recently proposed algorithm in~\cite{e-collaboration:2025frv, Bree:2025tug}. Analytical results for all master integrals in this family up to the first two orders of $\varepsilon$ are given.
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Chemical Physics

Spectroscopic photorelaxation signatures in pyrazine from nonadiabatic dynamics simulations with coupled cluster theory

Sara Angelico, Eirik F. Kjønstad, Yi-Ping Chang et al. (+3 more)

Despite extensive theoretical and experimental efforts, the mechanisms underlying the ultrafast relaxation of pyrazine after photoexcitation remain challenging to disentangle. Recently, theoretical investigations have been converging towards a three-state mechanism, with an ultrafast decay of the bright ${}^{1}B_{2u}$ state followed by beats in the populations of the low-lying ${}^{1}B_{3u}$ and ${}^{1}A_u$ states. However, a clear agreement between the experimental results and the corresponding theoretical predictions remains elusive. Here, we present a high-level simulation of the ultrafast excited states dynamics of pyrazine using coupled cluster theory with single and double excitations and ab initio multiple spawning, together with predictions of the time-resolved photoelectron spectrum and X-ray absorption spectra at the nitrogen and carbon edges. This is made possible by using a newly developed multistate implementation of similarity constrained coupled cluster theory. We find quantitative agreement with the experimental signature of the ${}^{1}B_{2u}$ decay in the photoelectron spectrum, and qualitative agreement with the available experimental X-ray absorption spectra. Moreover, we detail spectroscopic signatures that should be verifiable in experiments with sufficient resolution in the time and frequency domains. Compared to previous theoretical studies, we provide further detailed insight into the interplay of the states involved in the photorelaxation.
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All authors Sara Angelico, Eirik F. Kjønstad, Yi-Ping Chang, O. Jonathan Fajen, Todd J. Martínez, Henrik Koch

Strongly Correlated Electrons

Quantum Destabilization of Skyrmions in Centrosymmetric Frustrated Magnets

Amit Kumar and Kalpataru Pradhan

We investigate the role of the spin quantum number $s$ on the stability of skyrmions in a $J_1-J_2-J_3$ centrosymmetric quantum Heisenberg model on a square lattice using the neural network quantum states method. Our results reveal that the skyrmion stability $Q$ is severely degraded when transitioning from the semiclassical regime to the extreme quantum limit ($s=1/2$), where it ultimately vanishes. We demonstrate that this destabilization is driven by quantum longitudinal fluctuations, with $Q$ exhibiting a power-law decay as a function of the reciprocal spin moment $1/s$. Notably, the extreme quantum limit ($s=1/2$) deviates drastically from this scaling behavior, exhibiting distinct physics compared to larger spin moments. Furthermore, we reveal the microscopic origin of this decay by establishing a quantitative correspondence between skyrmion stability, entanglement, and local spin magnitude: as the local second Rényi entropy (an indicator of entanglement) increases and the local spin magnitude is suppressed, the skyrmion stability vanishes linearly. This regime marks a quantum state where the skyrmion number $C$ remains as remanent geometric feature of the spin orientations, yet the skyrmion stability $Q$ vanishes due to the longitudinal suppression of the local spin magnitude. Our findings suggest that classically robust skyrmion phases in frustrated lattices are fundamentally restricted to high-spin materials, indicating that a spin moment must of at least $s = 3/2$ is required for the realization of stable, atomic-scale topological textures.
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Chemical Physics

Improving Jet A-1 Thermal-Oxidative Stability through Selective Removal of Unwanted Trace Species via 3.7 Å Chabazite Filtration

Morteza Roostaeinia, Ehsan Alborzi, Xue Yong et al. (+2 more)

The thermal stability of Jet A-1 fuel is strongly affected by trace heteroatomic species that promote thermal oxidative deposit formation, as well as antioxidant additives such as butylated hydroxytoluene, which preserve fuel stability. 3.7 Å chabazite is a tunable microporous adsorbent, but optimizing its composition requires balancing promoter removal against antioxidant loss. Here, we use density functional theory and ab initio molecular dynamics (AIMD) to evaluate this trade-off using two compositional descriptors: framework acidity (Si/Al $= 35$–$8$) and bimetallic substitution (Co, Mg, Zn) at fixed Al content. Lowering Si/Al strengthens adsorption of all species, including BHT, confirming an intrinsic selectivity penalty for acidity-only tuning. In contrast, bimetallic substitution introduces chemically selective behavior, strengthening uptake of specific promoters while either suppressing or enhancing antioxidant adsorption depending on dopant identity. AIMD simulations at 400 K further show that adsorption energy alone is insufficient to describe calculated trends, because molecular mobility inside chabazite can influence residence time and effective capture during fuel treatment. Analysis of the density of states and the participating wavefunctions reveals signatures that are consistent with dopant-dependent adsorption shifts. These results establish a unified adsorption–transport–electronic screening framework for selecting chabazite compositions that remove deposit promoters while preserving antioxidant functionality in Jet A-1 treatment.
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All authors Morteza Roostaeinia, Ehsan Alborzi, Xue Yong, Kyungwha Park, Vsevolod Ivanov

Materials Science

Computational Determination of Optimal Growth Protocols for Metastable Polymorphs

Simon B. Hollweger, Anna Werkovits, Tadeas Lesovsky et al. (+1 more)

The reliable growth of a desired target structure remains a central challenge for organic-inorganic interfaces. Specific interface structures can exhibit properties that are superior compared to those of other possible interface structures, but identifying growth conditions that selectively produce a given surface structure is difficult, particularly when the target structure is thermodynamically metastable. Here, we demonstrate how time-dependent temperature and pressure protocols can be optimized to promote the high-yield formation of a metastable surface polymorph. To this end, we combine kinetic Monte Carlo simulations with a parameterized nucleation-and-growth model and apply optimal control theory to predict growth recipes that maximize the yield of the desired target structure. Applying this approach to a prototypical model of an organic molecules adsorbed on a metal surface, we identify experimentally plausible protocols that guide the system through phase space while avoiding kinetic growth regimes in which formation of the thermodynamically stable structure is favored. Compared to a manually optimized three-step protocol, the optimized control trajectory increases the yield of the desired metastable phase from 73 % to 97 % for the same total protocol duration.
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All authors Simon B. Hollweger, Anna Werkovits, Tadeas Lesovsky, Oliver T. Hofmann

Lattice Field Theory

Running of the Electroweak Gauge Couplings from First Principles

Alessandro Conigli, Dalibor Djukanovic, Georg von Hippel et al. (+6 more)

We present a high-precision calculation of the hadronic running of electroweak gauge couplings from first principles. Employing lattice QCD in the low-energy regime, we achieve permille precision for virtualities $Q^2 \lesssim 12\;\mathrm{GeV}^2$. At $Q^2 \simeq 1\;\mathrm{GeV}^2$, our determination deviates by up to $7\sigma$ from estimates based on $e^+e^-$ measurements. Combining lattice QCD with perturbative QCD via the Euclidean split technique, we obtain for the electromagnetic coupling $\Delta\alpha^{(5)}_{\mathrm{had}}(M_Z^2) = 0.027821(34)_{\mathrm{lat}}(35)_{\mathrm{pQCD}}$, which is more than twice as precise as recent phenomenological determinations. We assess improvement scenarios by which the precision target for next-generation electroweak measurements could be reached.
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All authors Alessandro Conigli, Dalibor Djukanovic, Georg von Hippel, Simon Kuberski, Harvey B. Meyer, Kohtaroh Miura, Konstantin Ottnad, Andreas Risch, Hartmut Wittig