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Physics

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Friday 3 July

High Energy Physics (Phenomenology)

George, I and the curvaton

Konstantinos Dimopoulos

George Lazarides was a pivotal collaborator and friend to me. We worked together on several projects, developing and exploiting the curvaton hypothesis, which was new at the time. This is a brief overview of our joint research.

Optics

Free-space multipass optical parametric amplifier

Milan Fayat, Giovanni Cichelli, Michele Natile et al. (+5 more)

Scaling the efficiency of optical parametric amplifiers (OPAs) without degrading spatio-temporal pulse quality is fundamentally limited by spatio-temporal walk-off, intensity dependent gain, and back-conversion. Here, we numerically and experimentally demonstrate an OPA architecture based on a free-propagating quasi-periodic geometry that overcomes these bottlenecks. Operating within a single nonlinear crystal, the system utilizes pass-by-pass dichroic idler rejection to suppress back-conversion, a birefringent crystal for temporal resynchronization, and free-space diffraction to improve the spatial overlap along propagation. Starting from 1.9 {\mu}J 330 fs pulses at 515 nm and a continuous-wave seed at 783 nm, the generation of 0.8 {\mu}J 160 fs signal pulses at the same wave-length is obtained at a repetition rate of 500 kHz. This simple architecture achieves a 64% quantum efficiency, a 42% pump-to-signal conversion efficiency, and 80 dB of gain while maintaining excellent spatial and temporal quality, providing a scalable platform for ultrafast sources with arbitrary emission wavelengths
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All authors Milan Fayat, Giovanni Cichelli, Michele Natile, Yoann Zaouter, Marie Ouillé, Patrick Georges, Marc Hanna, Xavier Délen

High Energy Astrophysical Phenomena

A Square Kilometre Array Pulsar Census

E. F. Keane, V. Graber, L. Levin et al. (+7 more)

Most of the pulsar science case with the Square Kilometre Array (SKA) depends on long-term precision timing of a large number of pulsars, as well as their astrometric measurements using very long baseline interferometry (VLBI). However, before we can time them, or VLBI them, we must first find them. Here, we describe the considerations and strategies needed when planning an all-sky blind pulsar survey using the SKA. Based on our understanding of the pulsar population, the performance of the now-under-construction SKA elements, and practical constraints such as evading radio frequency interference, we project pulsar survey yields; this is done using two complementary methods for a number of illustrative survey designs, combining SKA-Low and SKA-Mid Bands 1 and 2 in a variety of ways. A composite survey using both SKA-Mid and SKA-Low is optimal, with Mid Band 2 focused in the plane. We find that, given its much higher effective area and survey speed, the best strategy is to use SKA-Low to cover as much sky as possible, ideally also overlapping with the areas covered by Mid. We find that an all-sky blind survey with Phase 1 of the SKA with the AA* array assembly will detect $\sim10,000$ slow pulsars and $\sim 800$ millisecond pulsars (MSPs) if SKA-Mid covers the region within $5\deg$ of the plane, while higher latitudes will be covered with SKA-Low. For the same survey region the yield with AA4 is $\sim 20\%$ higher, but this increases considerably by broadening the range covered by SKA-Mid Bands 1 and 2. In particular one could expect a yield of $\sim 1300$ MSPs with AA4. The pulsar census will enable us to set new constraints on the uncertain physical properties of the entire neutron star population. This will be crucial for addressing major SKA science questions including the dense-matter equation of state, strong-field gravity tests, and gravitational wave astronomy.
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All authors E. F. Keane, V. Graber, L. Levin, C. M. Tan, O. A. Johnson, C. Ng, C. Pardo-Araujo, M. Ronchi, D. Vohl, M. Xue

2607.03090 · 3 Jul · Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no: AASKAII/Keane01. Advancing Astrophysics with the SKA II (AASKA II) outlines the transformative scientific advances that will be enabled by the SKA telescopes. An earlier version of this chapter was published in The Open Journal of Astrophysics with arXiv ID: arXiv:2512.16153

Abstract PDF $PLSR ×9$GRAV ×1$NEUT ×1$RDIO ×1 +1

High Energy Astrophysical Phenomena

Understanding the Neutron Star Population with the SKAO Telescopes

L. Levin, M. Bagchi, M. Burgay et al. (+12 more)

The known population of non-accreting neutron stars is ever growing and currently consists of more than 3500 sources. Pulsar surveys with the SKAO telescopes will greatly increase the known population, adding radio pulsars to every subgroup in the radio-loud neutron star family. These discoveries will not only add to the current understanding of neutron star physics by increasing the known sample, but will undoubtedly also uncover new types of sources that will challenge our theories of a wide range of physical phenomena. A broad variety of scientific studies will be made possible by a significantly increased population of neutron stars, unravelling questions such as: How do isolated pulsars evolve with time; What is the connection between magnetars, high B-field pulsars, and the newly discovered long-period pulsars; How is a pulsar's spin-down related to its radio emission; What is the nuclear equation of state? Increasing the numbers of pulsars in binary systems enables both larger numbers and higher precision tests of gravitational theories and general relativity, as well as probing the neutron star mass distribution. The excellent sensitivity of the SKAO telescopes combined with the wide field of view, large numbers of simultaneous tied-array beams that will be searched in real time, wide range of observing frequencies, and the ability to form multiple sub-arrays will make the SKAO an excellent facility for neutron star research. This chapter presents an overview of different types of neutron stars and discusses how the SKAO will aid in our understanding of the neutron star population.
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All authors L. Levin, M. Bagchi, M. Burgay, A. T. Deller, V. Graber, A. Igoshev, M. Kramer, D. Lorimer, B. Posselt, T. Prabu, K. Rajwade, N. Rea, B. Stappers, T. M. Tauris, P. Weltevrede

2607.03087 · 3 Jul · Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report number AASKAII/Levin01. Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes. An earlier version of this chapter was published in The Open Journal of Astrophysics with arXiv ID: arXiv:2512.16156

Abstract PDF $NEUT ×9$STAR ×9$PLSR ×7$RDIO ×3 +3

Strongly Correlated Electrons

Quantum magnetism of the spin-1 kagome-lattice antiferromagnet

Katsuhiro Morita

We investigate the spin-1 kagome-lattice Heisenberg antiferromagnet using large-scale Lanczos diagonalization and the finite-temperature Lanczos method. The zero-temperature magnetization process exhibits plateaus at $m=0$, $1/3$, $7/9$, and $8/9$, where $m$ is the normalized magnetization. The $m=0$ plateau is identified as a trimer valence-bond-crystal state, while the high-field plateaus at $m=7/9$ and $8/9$ are identified as magnon crystals. In particular, the $m=8/9$ plateau corresponds to the exact localized-magnon crystal state. A smoothed zero-temperature magnetization curve constructed using the Gaussian-kernel smoothing method indicates magnetization jumps at the lower-field edge of the $m=1/3$ plateau and at the upper-field edges of the $m=7/9$ and $8/9$ plateaus. At finite temperatures, the specific heat exhibits a double-peak structure with peaks around $T/J\simeq0.1$ and $T/J\simeq1.1$, and the low-temperature peak may be related to trimer valence-bond-crystal ordering. The finite-temperature magnetization curves show that the $m=1/3$ plateau remains visible at low temperatures, whereas the high-field plateaus are rapidly smeared out by thermal effects. These results provide benchmark data for thermodynamic and high-field magnetization measurements in candidate spin-1 kagome-lattice materials.
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High Energy Physics (Phenomenology)

Flipped rotating axion: Baryogenesis and Dark Matter

Konstantinos Dimopoulos

It is shown that the co-genesis of baryon asymmetry and dark matter can be achieved through the rotation of a spectator axion-like particle, because of a flip in the vacuum manifold's orientation at the end of inflation. This can occur if the axion has a periodic non-minimal coupling to gravity (while preserving the discrete shift symmetry) in non-oscillating inflation models, where the inflaton field is characterised by a runaway potential. Our rotating axion can generate the baryon asymmetry of the Universe through spontaneous baryogenesis, while at a later epoch it can oscillate as dark matter. We show that in order to avoid fragmentation of the axion condensate during the rotation, we require the non-minimal coupling $\xi\sim(f/m_P)^2$, where $f$ is the axion decay constant.
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Astrophysics of Galaxies

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde VI. The photodissociation region M17SW

X. Zhao, X. D. Tang, C. Henkel et al. (+20 more)

The kinetic temperature structure of the photodissociation region M17SW was mapped using the IRAM 30 m telescope. This mapping employed the para-H2CO triplet (J(KaKc) = 303-202, 322-221, and 321-220) near 218 GHz on a scale of ~0.2 pc. The kinetic temperatures were derived by modeling the average H2CO line ratios (322-221/303-202 + 321-220/303-202) with the RADEX non-local thermodynamic equilibrium approach. These temperatures range from 28 to 181 K with an average of 54.2 +/- 0.3 K at a spatial density of 5.5x10^5 cm^-3. Comparing with the temperature measurements obtained from multiple transitions of NH3 (1,1)-(6,6) and the far infrared (FIR) dust continuum, the H2CO lines show temperatures similar to those measured by NH3 but slightly higher than values derived from FIR observations. The high kinetic temperatures observed from H2CO are associated with the ultracompact H II region UC1, dense clumps, as well as H2O and CH3OH masers, showing a similar distribution as NH3. This indicates that dense gas in the M17SW region is heated by star formation activity. The presence of a significant gas temperature gradient across the M17SW region, as measured by H2CO and NH3, provides direct evidence for gas heated predominantly by radiation emitted from the OB star cluster NGC 6618. On a smaller scale, the dense gas surrounding the dense clumps experiences significant heating from internal protostars and/or young stellar objects. Higher temperatures traced by H2CO are linked to turbulence on a scale of ~0.2 pc. The complex temperature structure of the M17SW region is revealed by H2CO and NH3, which may be attributed to both large-scale external radiative heating and small-scale internal radiative and turbulent heating.
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All authors X. Zhao, X. D. Tang, C. Henkel, K. M. Menten, Y. Gong, Y. Sun, Y. P. Ao, T. Liu, X. Lu, D. Li, Y. X. He, K. Wang, X. P. Chen, J. W. Wu, J. Esimbek, J. J. Zhou, X. W. Zheng, J. J. Qiu, J. S. Li, C. S. Luo, Q. Zhao, L. D. Liu, C. Y. Wang

High Energy Astrophysical Phenomena

Galactic Centre Pulsars with the SKAO

F. Abbate, A. Carleo, S. Chatterjee et al. (+18 more)

The detection of a pulsar closely orbiting our Galaxy's supermassive black hole - Sagittarius~A* - is one of the ultimate prizes in pulsar astrophysics. The relativistic effects expected in such a system could far exceed those currently observable in compact binaries such as double neutron stars and pulsar white dwarfs. In addition, pulsars offer the opportunity to study the magneto-ionic properties of Earth's nearest galactic nucleus in unprecedented detail. For these reasons, and more, a multitude of pulsar searches of the Galactic Centre have been undertaken, with the outcome of just seven pulsar detections within a projected distance of 100\,pc from Sagittarius~A*. It is currently understood that a larger underlying population likely exists, but it is not until observations with the SKA have started that this population can be revealed. In this chapter, we look at important updates since the publication of the last SKAO science book and offer a focused view of observing strategies and likely outcomes with the updated SKAO design.
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All authors F. Abbate, A. Carleo, S. Chatterjee, J. Cordes, P. B. Demorest, G. Desvignes, R.P. Eatough, E. Hackmann, Z. Hu, M. Kramer, J. Lazio, K.J. Lee, K. Liu, I. Rammala-Zitha, S.M. Ransom, G.Saowanit, L. Shao, P. Torne, R. Wharton, J. Wongphechauxsorn, W. Zhu

Applied Physics

Complex Refractive Index Determination via Microspectroscopy Through Magnifying Optics: Challenges and Opportunities

Julian Schwarz, Johannes Bauer, Mathias Rommel et al. (+1 more)

For the design and optimization of optoelectronic devices, accurate knowledge of the complex refractive indices of the constituent materials is essential. Herein, we present a fast and non-destructive approach for the extraction of the refractive indices from reflectance and transmittance spectra of samples with lateral dimensions down to the micrometer scale. Microspectroscopy, based on the combination of a standard optical microscope and a spectrometer, enables the assessment of the optical response of multilayer stacks using high-magnification optics with correspondingly large numerical apertures. Employing a numerical formalism explicitly accounting for the influence of the numerical aperture, allows for precise retrieval of the refractive index without resorting to dispersion models. We demonstrate the applicability of the proposed method for large-area, homogeneous, optically incoherent samples such as transparent glasses and absorbing 4H-SiC, for a SixNy thin film on glass substrate, and for mechanically exfoliated flakes of highly oriented pyrolytic graphite and MoO3, as representatives of uniaxial and biaxial optical anisotropy. While the results prove excellent agreement with values reported in literature, the case of graphite highlights the limitation for probing the out-of-plane refractive indices due to reduced sensitivity. Finally, we discuss possible extensions towards retrieving the full anisotropic tensor of the refractive index, establishing the proposed approach as a methodologically sound alternative to spectroscopic ellipsometry.
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All authors Julian Schwarz, Johannes Bauer, Mathias Rommel, Andreas Hutzler

Mesoscale and Nanoscale Physics

Effects of Impurity Scattering on Orbital Hall Conductivity and Orbital Transport in Ru-based Alloys

Yumin Yang, Yanxu Chen, Wenqi Xu et al. (+1 more)

The role of impurity scattering in the generation and transport of orbital current remains less established than in conventional spin Hall systems. Here we investigate Ru-based nonmagnet/ferromagnet bilayers in which the impurity scattering is tuned by Cu or Ti alloying. According to SOT measurement and thickness-dependent drift-diffusion analysis, we extract the effective orbital Hall conductivity and the orbital diffusion length. We find that the orbital Hall effect in polycrystalline Ru is dominated by intrinsic mechanism that is moderately robust against weak disorder but suppressed by stronger alloy disorder. However, the orbital diffusion length remains nearly unchanged at approximately 14 nm over the investigated impurity range. This behavior indicates that orbital transport is not governed simply by an impurity scattering. Together with previous temperature-dependent measurements, our results show that static impurities and dynamic lattice disorder affect orbital transport through distinct microscopic channels. These results provide new insight into how disorder governs orbital generation and transport, and offer experimental guidance for developing high-efficient orbitronic materials.
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All authors Yumin Yang, Yanxu Chen, Wenqi Xu, Dahai Wei

Astrophysics of Galaxies

Jet–ISM Interactions in Gaseous Disks: Simulating Kinetic Feedback in the Radio Galaxy 3C 326 N

Mayur B. Shende, Dipanjan Mukherjee, N. P. H. Nesvadba et al. (+4 more)

Several radio galaxies, such as 3C\,326\,N, show signatures of jet–ISM coupling, but a complete theoretical framework for explaining them is still lacking. Interpreting these observations requires a detailed understanding of the gas distribution, geometry, and outflow energetics. In this paper, we use three-dimensional relativistic hydrodynamic simulations to investigate jet–ISM coupling in inhomogeneous gaseous disks, exploring a parameter space spanning different cloud configurations, jet powers, and central disk densities. Our simulations incorporate a numerical turbulence injection scheme that maintains vertical support in the disk, preventing the unphysical collapse encountered in previous studies. We find that jet–ISM coupling is strongly governed by the underlying cloud configuration, leading to distinct outflow morphologies, velocity dispersions, and kinetic energies. Simulations with small-scale ($l_{\rm c,max}=50$~pc) clouds produce the highest velocity dispersions and kinetic energies, whereas large-scale cloud configurations ($l_{\rm c,max}=250$~pc) yield the lowest values, with mixed cloud distributions exhibiting intermediate behavior. In addition, mixed cloud configurations give rise to asymmetric jet propagation, naturally producing unequal lobe lengths similar to those observed in radio galaxies. We compare our fiducial simulation (a $10^{45}\,\rm erg\,s^{-1}$ jet interacting with a mixed cloud configuration) with observations of 3C\,326\,N, focusing on the morphology of the jet-driven bubble, synthetic emission and the gas kinematics. Our results successfully reproduce the observed properties, providing strong evidence that jet–ISM interactions can account for the wide bubble and the complex gas kinematics observed in this system.
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All authors Mayur B. Shende, Dipanjan Mukherjee, N. P. H. Nesvadba, Geoffrey Bicknell, James Leftley, Moun Meenakshi, Raghav Gogia

High Energy Physics (Phenomenology)

Majoron Dark Energy via Freezing Induced by Quantum Coherence

Keunsu Cheon, Sin Kyu Kang and Jungjai Lee

We propose a nonequilibrium mechanism for Majoron dark energy in which the late-time freezing of a physical Majoron is induced by quantum coherence in a hidden pseudo-Dirac sterile fermion reservoir. The evolving Majoron background derivatively couples to the hidden pseudo-Dirac number current and drives a lagged reservoir response with a finite memory time. In the short-memory regime, the causal response kernel reduces to \(\dot X+\Gamma_{\rm PD}X=\beta\ddot\phi\). The leading linear-response matching \(Q=\alpha X\) then yields an effective scalar equation containing the exchange structure \(q_{\rm exch}\ddot\phi/\dot\phi\). We show that this term can dynamically suppress the Majoron velocity and sustain a response-dominated freezing branch even when the intrinsic Majoron mass is larger than the present Hubble scale. The microscopic origin of the lag variable is identified with the phase-lagged off-diagonal coherence of the hidden pseudo-Dirac ensemble, while the response strength is controlled by a response-weighted hidden density rather than by an independent gravitating component. The resulting state is a metastable nonequilibrium frozen phase with \(w_\phi\simeq -1\), rather than an exactly static cosmological constant.
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Optics

Robust optical design and closed-form tolerancing through autodiff-based Hessian spectral analysis

Bastien Laville and Benjamin Aymard

Robust optical design demands quantitative knowledge of how manufacturing and alignment tolerances degrade system performance. We show that analysing the perturbation eigenmodes of the Hessian matrix gives qualitative insight about the mechanisms of performance degradation (such as couplings) that is invisible to classical sensitivity-matrix analysis based on the Jacobian alone. Via the envelope theorem, we prove that the first-order sensitivity of the fully compensated system is identical to that of the uncompensated one; refocusing only acts at second order through the Schur complement of the Hessian. We propose the trace of the tolerance-scaled Hessian %,$\Tr(\mathbf{S}\mathbf{H}\mathbf{S})$, as a single scalar robustness metric. Demonstrated on an off-axis three-mirror anastigmat and scaled to a twenty-three-parameter surface-figure model, eigenmode decomposition reveals the dominant sensitivity directions and yields deterministic tolerance budgets that replace costly Monte Carlo sampling.
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Materials Science

Chiropiezoelectric Energy Harvesting from Lattice-Handedness-Controlled Selenium Nanowires

Oleksii Ohiienko, Wookjin Jung and Jihyeon Yeom

The growth of wearable electronics, soft robotics, and Internet-of-Things systems has intensified the demand for inorganic piezoelectric materials that harvest weak biomechanical energy. Advances through composition optimization, defect engineering, strain engineering, and orientation control have improved existing electromechanical responses, but have not introduced a new mechanism for enhancing piezoelectricity. Here we propose atomic chirality engineering as a design principle for inorganic piezoelectric nanomaterials. Unlike conventional strategies that modify composition or morphology, atomic chirality alters the handedness of the crystal lattice itself, adding a degree of freedom for controlling dipole alignment, electromechanical coupling, and potentially spin-dependent transport. Using atomically chiral trigonal selenium nanowires as a model system, we show that crystal handedness alone changes piezoelectric performance at identical chemical composition. Piezoresponse force microscopy resolved a consistent enantiomeric difference, with right-handed D-Se nanowires reaching a higher effective piezoelectric coefficient than their left-handed counterparts, and flexible nanogenerators and self-powered acoustic sensors built from the two enantiomers produced distinct outputs under identical deformation. This work establishes atomic chirality as a distinct route for designing piezoelectric materials, one that may extend across non-centrosymmetric inorganic semiconductors for sustainable energy harvesting and wearable sensing.
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High Energy Astrophysical Phenomena

Numerical Simulations of Restarted Jets – I. Dynamics

Prathamesh Ratnaparkhi, Dipanjan Mukherjee, Gianluigi Bodo et al. (+3 more)

We performed high-resolution three-dimensional relativistic magnetohydrodynamic (RMHD) simulations of restarted jets evolving within the cavity of a previous jet episode, using the PLUTO code. The simulations cover a spatial domain of $50\;\mbox{kpc}$ with a resolution of $40\;\mbox{pc}$. Three suites of simulations were performed to understand the impact of jet power, magnetic fields and quiescence time on the evolution of restarted jets. The restarted jets undergo a complex, multi-stage evolution, with the remnant cocoon relaxing from an initially conical structure to a mushroom-shaped morphology via an intermediate cylindrical phase. As the cocoon of the initial jet expands, dense material entrained by fluid instabilities such as Kelvin-Helmholtz and Rayleigh-Taylor significantly alter the conditions within it. As a result, the interaction of the restarted jet with the cocoon is markedly different from that of the initial jet with the ambient medium. In particular, we find that the restarted jet propagates ballistically through the rarefied remnant cocoon, without creating prominent backflows. Deceleration of the jet and associated backflows are observed only when it encounters dense structures. The structure and strength of the shocks in restarted jets are affected by jet power, magnetic field strength, and quiescence time. Finally, we discuss the implications of the dynamics for observed properties of radio galaxies.
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All authors Prathamesh Ratnaparkhi, Dipanjan Mukherjee, Gianluigi Bodo, Paola Rossi, Marisa Brienza, Raffaella Morganti

Instrumentation and Methods for Astrophysics

The SKAO Pulsar Timing Array

Ryan M. Shannon, N. D. Ramesh Bhat, Aurélien Chalumeau et al. (+22 more)

Pulsar timing arrays (PTAs) are ensembles of millisecond pulsars observed for years to decades. The primary goal of PTAs is to study gravitational-wave astronomy at nanohertz frequencies, with secondary goals of undertaking other fundamental tests of physics and astronomy. Recently, compelling evidence has emerged in established PTA experiments for the presence of a gravitational-wave background. To accelerate a confident detection of such a signal and then study gravitational-wave emitting sources, it is necessary to observe a larger number of millisecond pulsars to greater timing precision. The SKAO telescopes, which will be a factor of three to four greater in sensitivity compared to any other southern hemisphere facility, are poised to make such an impact. In this chapter, we motivate an SKAO pulsar timing array (SKAO PTA) experiment. We discuss the classes of gravitational waves present in PTA observations and how an SKAO PTA can detect and study them. We then describe the sources that can produce these signals. We discuss the astrophysical noise sources that must be mitigated to undertake the most sensitive searches. We then describe a realistic PTA experiment implemented with the SKA and place it in context alongside other PTA experiments likely ongoing in the 2030s. We describe the techniques necessary to search for gravitational waves in the SKAO PTA and motivate how very long baseline interferometry can improve the sensitivity of an SKAO PTA. The SKAO PTA will provide a view of the Universe complementary to those of the other large facilities of the 2030s.
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All authors Ryan M. Shannon, N. D. Ramesh Bhat, Aurélien Chalumeau, Siyuan Chen, H. Thankful Cromartie, A. Gopakumar, Kathrin Grunthal, Jeffrey S. Hazboun, Francesco Iraci, Bhal Chandra Joshi, Ryo Kato, Michael J. Keith, Kejia Lee, Kuo Liu, Hannah Middleton, Matthew T. Miles, Chiara M. F. Mingarelli, Aditya Parthasarathy, Daniel J. Reardon, Golam M. Shaifullah, Keitaro Takahashi, Caterina Tiburzi, Riccardo J. Truant, Xiao Xue, Andrew Zic

2607.03059 · 3 Jul · Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Shannon01. A previous version of the SKAO PTA science case was published in The Open Journal of Astrophysics (arXiv:2512.16163). Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes

Abstract PDF $PLSR ×5$TSCP ×1

Instrumentation and Detectors

Miniaturized Photoacoustic Spectroscopy Gas Probe for In-Situ Detection in Oil

Yi Zhong, Yuxiang Zhao and Ping Lu

This paper designs and develops a miniaturized photoacoustic spectroscopy gas probe with acoustic pressure enhancement for in-situ detection in oil-immersed power equipment. The probe adopts a single-cavity single-fiber structure, integrating the photoacoustic cell and the Fabry-Pérot optical sensing cavity within a ceramic ferrule with an outer diameter of only 800 um. Through the electro-mechanical-acoustic equivalent model analysis of the semi-open photoacoustic cell, the enhancement mechanism is revealed that reducing the radius of the photoacoustic cell can form a flat region in the acoustic pressure response. The CrAgAu composite metal diaphragm is fabricated by electron-beam evaporation, and the gas vents are precisely machined by focused-ion-beam etching, successfully realizing the preparation of the sensor prototype. Experimental results demonstrate that the sensor exhibits a flat acoustic response in the frequency range of 2800-10000 Hz with a sensitivity of -15 dB re 1 mV/Pa. Using acetylene as the target gas, the detection limit reaches 71.4 ppb (with an integration time of 130 s) at the optimal operating frequency of 3275 Hz, and the linearity exceeds 0.998. In-oil tests verify its stable detection capability in oil-phase environments, providing a miniaturized, high-sensitivity all-optical technical solution for in-situ monitoring of dissolved gases in transformer oil.
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Quantum Physics

Single-acquisition tomography of photonic qubits with structured media

Francesco Di Colandrea, Yingwen Zhang, John Grace et al. (+3 more)

Quantum state tomography is an essential tool for characterizing quantum systems and underpins nearly every experimental realization of quantum technologies. Conventional tomography relies on performing a sequence of projective measurements on many identical copies of a quantum state, requiring the measurement apparatus to be reconfigured between successive acquisitions. As the Hilbert-space dimension increases, the number of required measurements grows rapidly; in practice, additional overcomplete measurements are often performed to improve robustness to experimental imperfections. Here, we introduce a tomography platform based on structured anisotropic media that performs informationally complete measurements of photonic polarization qubits within a single acquisition. The approach employs three liquid-crystal metasurfaces with spatially varying optic-axis orientations that transform the input polarization into a far-field distribution of discrete transverse-momentum modes. Each diffraction pattern uniquely determines the polarization state, enabling its reconstruction without sequential changes to the measurement apparatus. Unlike previous implementations, our scheme is intrinsically photon-number independent: the same optical device operates identically for arbitrary photon numbers, while the desired photon-number sector can be selected afterwards through post-selection of the corresponding $n$-fold coincidence events. We experimentally demonstrate single-frame quantum state tomography of both single- and two-photon polarization states, providing a simple and scalable route toward efficient quantum-state characterization.
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All authors Francesco Di Colandrea, Yingwen Zhang, John Grace, Dilip Paneru, Alessio D'Errico, Ebrahim Karimi

High Energy Astrophysical Phenomena

FAST Pulsar Database III. Snapshots of nulling, mode-changing and subpulse modulation of 374 pulsars

Yi Yan, J. L. Han, J. Xu et al. (+8 more)

Based on sensitive L-band (1.0 to 1.5 GHz) observations of pulsars using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we analyzed single-pulse sequences from FAST-detected pulsars and identified nulling, mode changing, or subpulse modulation phenomena in 374 sources. Among these, nulling has been detected in 160 pulsars, with 127 cases reported for the first time. Emission mode changes have been observed in 52 pulsars, including 51 first-time detections. Subpulse modulation has been identified in 272 pulsars, 180 of which are newly revealed, with the majority displaying subpulse drifting behavior. Subpulse drifting in some pulsars exhibits distinct modes with varying drift properties, leading to mode changes and divergent mean profiles. Statistics on pulsar parameters show that pulsars exhibiting nulling and/or subpulse modulation tend to be older, with longer periods and lower spin-down energy-loss rates. The modulation period P3 is predominantly correlated with pulsar rotation periods, magnetic field strengths, and spin-down energy loss.
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All authors Yi Yan, J. L. Han, J. Xu, N. N. Cai, W. Q. Su, P. F. Wang, C. Wang, T. Wang, D. J. Zhou, W. C. Jing, Z. L. Yang

Instrumentation and Methods for Astrophysics

nmma: An extended Bayesian framework for Nuclear Multimessenger Astronomy in the Era of Next-Generation Detectors

Henrik Rose, Hauke Koehn, Thibeau Wouters et al. (+4 more)

Context. The joint analysis of different (astro-)physical messengers, in particular gravitational-wave data and electromagnetic follow-up observations, allows us to establish, explore and deepen links between different physical fields. As new survey capacities and improved detection methods will lead to a significant increase in the number of multimessenger detections in the upcoming decades, efficient and versatile software frameworks are essential to maximise the scientific outcome of such multimessenger studies. Aims. We present a major upgrade to the Nuclear Multimessenger Astronomy (nmma) framework, incorporating various recent developments in theoretical modelling and machine learning in a modularised and easily extendable Bayesian framework. For the first time, this allows direct sampling on nuclear parameters alongside gravitational-wave, kilonova and afterglow parameters. Methods. We combine fast surrogate models for electromagnetic transients with speed-ups from emulators that map nuclear parameters to macroscopic neutron-star properties. Additional acceleration methods for the evaluation of state-of-the-art waveform approximants enable full Bayesian analyses of multimessenger events at the speed required in the era of next-generation detectors. Results. We demonstrate the capabilities of the upgraded nmma framework through a series of representative applications. Reanalysing the 2017 multi-messenger detection of a neutron-star merger, we achieve 20- to 60-fold speed-ups while using more detailed physical models compared to previous studies. Moreover, we demonstrate for a hypothetical future detection how we can simultaneously constrain nuclear parameters and the Hubble parameter with robustly quantified uncertainties.
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All authors Henrik Rose, Hauke Koehn, Thibeau Wouters, Peter T. H. Pang, Mattia Bulla, Michael W. Coughlin, Tim Dietrich

Optics

Programmable Hybrid Exceptional Points in Passive Scattering Networks

Kaiyuan Wang, Niall Byrnes and Matthew R. Foreman

Exceptional points (EPs) have long promised enhanced sensing of physical signals, but have practically been limited by simultaneous enhancement of noise. Aligning an EP's non-analytic response with target perturbations while suppressing noise has, however, remained challenging. Here we show that fully passive, phase-tuned multi-port scattering networks enable scattering EPs with tailored anisotropic response to perturbations. We leverage projection-induced non-unitarity to realize effective non-Hermitian behavior when measuring only a subset of system ports. By formulating EP design in terms of the discriminant of the projected scattering sub-block and its directional derivatives, we give control-counting rules relating the number of programmable link phases to achievable Riemann surface topologies. We demonstrate our framework in a four-port photonic network by designing both an anisotropic EP and a Dirac-type EP with linear splitting along two parametric directions. We further suppress the global thermal drift response of a network-based sensor to a 3/2 power-law scaling while retaining square-root sensitivity to localized signals. Since the effective non-Hermiticity arises purely from port projection, our approach transfers to integrated photonic and microwave meshes, acoustic circuits, and projected metasurfaces, offering a phase-only route to reconfigurable non-Hermitian response and noise-robust EP sensing.
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Statistical Mechanics · Cross-listed from cs.LG

Out-of-distribution Neural Inference in Dynamical Ising Models

Yuan-Bin Zhu, Shuang Qiao and Shi-Ju Ran

Neural networks are increasingly used to infer hidden physical structure from dynamical observations, yet it remains unclear whether their out-of-distribution performance reflects transferable physical rule learning. We address this question in a controlled inverse problem: reconstructing interaction graphs of a kinetic Ising model from Glauber magnetization trajectories. Across convolutional, graph, Transformer, and hybrid architectures, we find that data-driven training produces distinct and reproducible statistical strategies under topology and temperature shifts. Edge-population diagnostics reveal that Transformer-based models tend to preserve the link density of the training ensemble, whereas convolutional models can collapse toward sparse- or no-link predictions that appear out-of-distribution stable by exploiting the majority no-link class. Thus, high in-distribution accuracy and apparent out-of-distribution robustness do not necessarily imply a learned dynamics-to-structure rule. Instead, neural reconstruction can be governed by architecture-dependent statistical priors. Our results identify a concrete failure mode of standard data-driven learning in physical inverse problems and motivate rule-guided principles for machine-learning-assisted scientific discovery.
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Fluid Dynamics

Contrary to Newtonian trends: Early flow transition and drag enhancement at low to intermediate Reynolds number flows of structured fluids

Kartik, Anant Chauhan and Chandi Sasmal

The flow of structured fluids, such as polymeric and micellar solutions, involves a strong two-way coupling between flow kinematics and internal microstructural dynamics, including polymer stretching, micellar scission, and reformation. These interactions yield complex nonlinear rheological responses, including viscoelasticity, shear-thinning, and thixotropy. In this study, we perform high-fidelity numerical simulations of micellar solution flow past a circular cylinder using the Modified Bautista-Manero (MBM) model, which couples a viscoelastic constitutive equation with a kinetic equation for fluidity to capture reversible micellar breakage and reformation. Model parameters are derived from quantitative fitting of experimental data for the EHAC-NaSal system. Our results reveal substantially richer flow dynamics than in Newtonian fluids under the same conditions. Transitions to unsteady flow occur at significantly lower Reynolds numbers, indicating greater instability driven by microstructural effects. At intermediate Reynolds numbers, micellar flows exhibit quasi-periodic behaviour, contrasting with classical periodic vortex shedding in Newtonian cases. Unlike the monotonic drag reduction in Newtonian fluids, micellar solutions show an anomalous drag increase. Wake characteristics reverse with regime: larger recirculation zones at low Reynolds numbers but more compact wakes in unsteady flows. Lift coefficients and Strouhal numbers are consistently increased. Vorticity fields display pronounced spatial localisation within thin near-wake shear layers. A dynamic mode decomposition analysis reveals coexisting unstable time-decaying and self-sustained modes in micellar flows, whereas only self-sustained modes appear in Newtonian cases.
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General Relativity and Quantum Cosmology

Black holes in f(R) theory of gravity with compact extra dimensions

Arkady Popov and Sergey Rubin

We study static, spherically symmetric solutions in $f(R)$ gravity within a $D = 4+n$-dimensional spacetime, where the extra dimensions form a compact $n$-sphere of constant radius. We derive an exact solution in which the four-dimensional part of the metric corresponds to the Schwarzschild - de Sitter metric, while the extra dimensions are stabilized at a constant radius $L_0$. A consistency condition relates the size of the internal space to the effective four-dimensional cosmological constant $\Lambda_4 = (n-1)/L_0^2$, which is generally too large to be compatible with observations. To overcome this issue, we include the vacuum polarization effects of quantized matter fields nonminimally coupled to curvature. Using the semiclassical approach, we obtain an asymptotically flat four-dimensional Schwarzschild solution as a limiting case, where the size of the extra sphere is determined by the vacuum expectation values of the quantum fields. Finally, we discuss the dependence of the effective four-dimensional Planck mass and the extra-dimensional radius on the radial coordinate.
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Instrumentation and Detectors

A New High-Intensity Source for Ultracold Neutrons

K. Abe, S. Ahmed, B. Algohi et al. (+78 more)

The TRIUMF UltraCold Advanced Neutron (TUCAN) collaboration has completed a new superthermal source for ultracold neutrons (UCNs) at TRIUMF. Neutrons produced in a spallation target are moderated in heavy water and liquid deuterium, and are converted to ultracold neutrons by inelastic scattering inside superfluid $^4$He at around 1.1 K. During commissioning of the completed moderation and conversion system, including the liquid-deuterium moderator, up to $1.47(2)\times 10^7$ UCNs were detected outside the source in the experimental area following a 60 s accumulation period. At the same location, continuous operation produced detector rates of up to $6.75(3)\times 10^7$ UCN/s, and a density of 165.6(1) UCN/cm$^3$ was achieved in a 25.4 L external vessel. These measurements demonstrate high-intensity operation of a spallation-driven He-II UCN source, including extraction and transport to an external experimental area.
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All authors K. Abe, S. Ahmed, B. Algohi, D. Anthony, L. Barron-Palos, Y. Bylinsky, M. Bosse, M.P. Bradley, A. Brossard, J. Chak, R. Chiba, C. Davis, R. de Vries, K. Dong, K. Drury, B. Franke, D. Fujimoto, R. Fujitani, M. Gericke, P. Giampa, C. Gibson, R. Golub, K. Hatanaka, T. Hepworth, T. Higuchi, A. Jaison, B. Jamieson, K. Jorgensen-Fullam, M. Katotoka, S. Kawasaki, M. Kitaguchi, W. Klassen, E. Klemets, E. Korkmaz, E. Korobkina, F. Kuchler, C. Lamb, M. Lavvaf, A. Lejuez, T. Lightbody, T. Lindner, S. Longo, K.W. Madison, J. Malcolm, J. Mammei, R. Mammei, C. Marshall, J.W. Martin, R. Matsumiya, M. McCrea, E. Miller, M. Miller, K. Mishima, T. Mohammadi, T. Momose, M. Nalbandian, T. Okamura, S. Pankratz, R. Patni, R. Picker, V. Purcell, K. Qiao, Y.-N. Rao, W. Rathnakela, T. Reimer, D. Salazar, W. Schreyer, T. Shima, H.M. Shimizu, S. Sidhu, S. Stargardter, R. Stutters, P. Switzer, Tushar, M. Uzair, S. Vanbergen, W.T.H. van Oers, N. Yazdandoost, Q. Ye, A. Zahra, L. Zhang

Soft Condensed Matter

Entropy functional universality: Correlation, response, many-body interaction, multi-component, quantum, hyperfunctional, and Ornstein-Zernike structure

Matthias Schmidt

We give a comprehensive account of the recent entropy functional theory for the equilibrium statistical mechanics of classical many-body systems (arXiv:2606.28240). The approach is formally exact and based on a joint grand potential minimization principle for the one-body density and the global pair distance distribution. These variational fields depend respectively on position and on scalar distance, which retains the low computational complexity of standard density functional theory. Correlation effects are contained in a unique excess entropy functional, which is universal across all systems with pairwise interparticle potentials. Functional differentiation yields entropic direct correlation functionals that generate entropic response and fluctuation correlation functions via coupled Ornstein-Zernike equations. Two alternative proofs are given for the existence and uniqueness of the underlying metadensity functional map, based on generalizations of either Levy's constrained search method or Mermin-Evans proof by contradiction. Simple excess entropy approximations yield the standard mean-field and second-virial excess free energy density functionals. We describe exact entropic functional line integrals, make connections to the recent one-body fluctuation profiles, and generalize the entropy approach beyond pairwise interparticle potentials via parametric dependence or reduction operators. We also lay out the formulation for multi-component systems, the hyperfunctional for general observables, and the quantum entropy functional.
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Instrumentation and Methods for Astrophysics

Rapid Response Triggering for Radio Transients with the SKA Observatory

G. E. Anderson, S. I. Chastain, A. P. Curtin et al. (+10 more)

Rapid-response triggering is when a telescope is able to automatically respond to an external or internal astronomical transient alert, causing it to rapidly repoint at that position in the sky to catch its earliest radio emission. Both SKA-Low and SKA-Mid will have the ability to perform rapid-response triggering observations on externally detected transients as well as those detected within the data streams. We first give a brief overview of those radio instruments with active rapid-response observing modes. We then describe the different science cases motivating the need for this observing capability on SKAO and how the additional sensitivity afforded by the SKAO will enable us to answer fundamental questions relating to particle acceleration, transient central engines, coherent emission models and outflow physics in astrophysical systems spanning the range from the Sun to the high redshift Universe. Several suggestions relating to existing technologies and necessary SKAO system requirements are described. Through this chapter, we aim to ensure this is an existing, common and useful capability for the SKA Observatory.
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All authors G. E. Anderson, S. I. Chastain, A. P. Curtin, K. Gourdji, N. Hurley-Walker, C. W. James, R. F. Mandow, B. Marcote, D. Oberoi, K. M. Rajwade, K. Rose, A. Rowlinson, F. Schüssler

Superconductivity

When Repulsion Creates Pairing: A New Perspective on Unconventional Superconductivity

Patrick Navez

Despite the repulsive Coulomb law and the Pauli statistics that do not favor bound states, attraction between electrons or holes is nevertheless possible in the context of many body interaction and of valley potential landscapes, reminiscent of exotic superconducting materials. In particular, in 1965, Kohn and Luttinger published a note revealing that the dynamical screening of the repulsive Coulomb interaction leads, under certain conditions, to an effective attraction necessary for the formation of Cooper pairs. We propose such a formalism adapted to the cuprates, where the screening arises from the superexchange dynamics of virtual holes in the oxygen orbitals of the $Cu O_2$ plane. Inspired from the Bardeen-Copper-Schrieffer (BCS) theory, we can derive some predictions for the temperature-doping phase diagram (pseudo-gap, strange metal, antiferromagnetism, superconducting, and normal states) in semi-quantitative agreement with observations.
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Optics

MEMS Fiber-Tip Photoacoustic Spectrometer for In Situ Microscale Trace Gas Sensing

Xingjie Liu, Mengqi Wu and Ping Lu

To meet the stringent requirements for miniaturized and highly sensitive trace gas sensing in space-constrained scenarios, including power equipment monitoring, minimally invasive biomedical diagnostics, and in situ lithium-battery analysis, we report a MEMS-integrated fiber-tip photoacoustic spectrometer (MFPAS). The device incorporates a Fabry-Perot (F-P) photoacoustic sensor formed by directly butt-coupling a single-mode fiber (SMF) to a 3 mm x 3 mm MEMS chip with a 100-nm-thick low-pressure chemical vapor deposition (LPCVD) Si$_3$N$_4$ diaphragm. The resulting approximately 200-$\mu$m deep silicon microcavity functions simultaneously as a photoacoustic gas cell and an acoustic confinement cavity. A micro-aperture fabricated at the diaphragm periphery by focused ion beam (FIB) milling serves as both a gas diffusion channel and an acoustic high-pass filter, suppressing ambient low-frequency pressure fluctuations and stabilizing the F-P quadrature point without active servo control. In gas-phase measurements, the sensor achieves a noise-equivalent concentration (NEC) of 58.5 ppb@1s, with a rapid response time of 6 s. Benefiting from its ultra-small cavity volume of approximately 1.5 nL, the device is further adapted through structural packaging for in situ dissolved gas analysis in transformer oil, where it achieves an NEC of 230 ppb@1s and a T90 response time of 320 s in the oil phase. By combining nanoliter-scale detection volume, ppb-level sensitivity, rapid response, and wafer-scale batch fabrication compatibility, the proposed MFPAS bridges MEMS diaphragm micromachining and FIB-enabled gas exchange engineering. This design overcomes the intrinsic gas-exchange limitation of conventional sealed-diaphragm optical microphones and offers significant potential for power equipment monitoring and in situ health diagnostics.
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Fluid Dynamics

Stability of gas flow past viscoelastic compliant solid

Mandeep Deka

Stability of a high-speed gas flow past a compliant solid is impacted by two distinct features: high solid-to-fluid density ratio ($\rho_r$), and flow compressibility when flow speeds are comparable to acoustic speed. This study investigates the linear stability of a shear-driven compressible gas flow past a compliant substrate modelled as a continuum Neo-Hookean solid. Numerical solutions of the eigenvalue problem reveal that at high density ratios, the dominant instabilities are the elastic shear-waves of the solid. Our study shows that flow compressibility exerts a non-monotonic effect on the growth rate of the elastic modes; the growth rate increases with increase in Mach number up to $\mbox{Ma} \approx 2$ before subsequently decreasing. Furthermore, for compressible flows, strong thermal-coupling renders the base state highly sensitive to both the solid-to-fluid thermal conductivity ratio and the substrate's bottom-surface temperature. Numerical results demonstrate that increasing the conductivity ratio destabilizes the system, whereas increasing the bottom wall temperature is stabilizing. The stability equations, analyzed in the asymptotic limit of $\rho_r \mbox{Re} \gg 1$, reveals that the fluid-solid system de-couples at the leading order with the elastic modes emerging as a solution of the linear elasticity equations under free-shear condition at the interface. We derive a closed-form expression for the leading-order growth rate of the instability, which shows an excellent agreement with the numerical solution. This expression explicitly quantifies the influence of fluid stresses at the interface, which can in-turn be expressed as integrals of the flow solution isolating the distinct physical mechanisms driving the instability.
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