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Physics

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Sunday 14 June

Mathematical Physics

A generalized Stieltjes system with polynomial source

D.Masoero and B.Shapiro

Let $Q$ be a monic polynomial of degree $M+1$. We study the algebraic system \[ \sum_{j\ne i}\frac{1}{x_i-x_j}=Q(x_i),\qquad i=1,\ldots,N, \] for pairwise distinct complex numbers $x_1,\ldots,x_N$, modulo permutations of these numbers. The case $M=0$ is, after a translation, the classical Stieltjes system for the zeros of a Hermite polynomial. We prove that, for arbitrary $Q$, the number of solutions is at most $\binom{N+M}{N}$, and that the coefficient equations for the associated monic Stieltjes polynomial have total intersection multiplicity exactly $\binom{N+M}{N}$. Consequently the bound is attained for all $Q$ in a non-empty Zariski open subset of the affine space of monic polynomials of degree $M+1$. We also describe the solutions when the coefficient of the linear term of $Q$ is large: the system splits into $M+1$ weakly coupled classical Stieltjes systems, one near each zero of $Q$.
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Solar and Stellar Astrophysics

Revisiting Approaches to Stellar White-Light Flare Energy Based on Spatiotemporally Resolved Solar Observations

Yingjie Cai, Yijun Hou, Ting Li et al. (+5 more)

Accurately estimating the bolometric energy of solar and stellar white-light flares (WLFs) is crucial for understanding their physical nature and impact on surrounding planets. However, the lack of spatial resolution in stellar observations forced pioneering stellar WLF studies to adopt simplified energy estimation methods, typically assuming either a constant flare temperature or a fixed radiating area. To assess the physical plausibility of these assumptions, we utilize high-spatiotemporal-resolution solar observations to analyze the true evolution of source region's radiating area and temperature of 70 solar WLFs. It is revealed that both area and temperature of most solar WLFs undergo significant temporal evolution, and the flare area strongly correlates with the flare's peak optical continuum flux. Therefore, we propose a new energy estimation method that permits both flare area and temperature to evolve. Compared with existing methods, our dynamic approach yields systematically lower flare energies, which then prompts us to revisit classical macroscopic scaling laws related to the flare energy. It is further revealed that different energy estimation approaches can systematically alter these scaling relations, calling for a re-examination of these established statistical results and their targeted testing or revision in future work.
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All authors Yingjie Cai, Yijun Hou, Ting Li, Ying Li, Mingde Ding, Dechao Song, Changwen Zeng, Jifeng Liu

High Energy Physics (Phenomenology)

Towards the Detection of Thermal Solar Neutrinos

Carlos A. Argüelles, Christopher V. Cappiello, P. S. Bhupal Dev et al. (+3 more)

We show that $\sim$keV thermal solar neutrinos, arising from electroweak processes in the solar plasma, are kinematically accessible to large-volume dark matter direct detection experiments via electron ionization signatures. Using S2-only data from the XENONnT experiment, we place an upper limit on the thermal solar neutrino flux of $\eta \lesssim 1.2 \times 10^8$ times the standard model predicted value, while paired searches from XENONnT, LZ and PandaX give slightly weaker limits. The future XLZD experiment could improve these limits by orders of magnitude. While still far from a detection, this result establishes low-threshold direct detection experiments as a viable probe of the lowest-energy neutrino sources in astrophysics, with important implications for stellar physics and beyond.
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All authors Carlos A. Argüelles, Christopher V. Cappiello, P. S. Bhupal Dev, Pablo Figueroa, Gonzalo Herrera, Icarus Scoville

Mathematical Physics

N-transform and factorization of the DN-map

M.I.Belishev and D.V.Korikov

Let $(\Omega,g)$ be a smooth compact 3D Riemannian manifold with the smooth boundary $\Gamma$, $\tau(x):={\rm dist\,}(x,\Gamma)$, $x\in\Omega$; $\Omega^\tau:=\{x\in\Omega\,|\,\,{\rm dist\,}(x,\Gamma)<\tau$\}, $\Gamma^\tau:=\{x\in\Omega\,|\,\,{\rm dist\,}(x,\Gamma)=\tau$\}, $\tau\geqslant 0$. For the sake of technical simplicity, we deal with $\Omega$ diffeomorphic to a ball in $\Bbb R^3$. Let $\mathscr P:=\{\nabla p\,|\,\,p\in H^1(\Omega)\}$ be the space of the potential vector fields, and let $\mathscr L_\lambda:=\{\varkappa\nabla\tau\,|\,\,\varkappa\in L_2(\Omega)\}$ be the space of the vector fields parallel to $\nabla\tau$. The N-transform is a map from $\mathscr P$ to $\mathscr L_\lambda$ defined layer-wise (in accordance with $\Omega=\cup_{\tau\geqslant 0}\Gamma^\tau$) by $$ Nh\,\big|_{\Gamma^\tau}:=(P^\tau h)\big|_{\Gamma^{\tau-0}}, \qquad\tau>0, $$ where $P^\tau$ are the projections in $\mathscr P$ onto the subspaces $\mathscr P^\tau:=\{h\in\mathscr P\,|\,\,{\rm supp\,}h\subset\overline{\Omega^\tau}\}$. We show that $N$ is a unitary operator. Let $p=p^f(x)$ be a solution to the Dirichlet problem: $\Delta_g p=0$ in $\Omega\setminus\Gamma$, $p=f$ on $\Gamma$. The DN-map $\Lambda$ is defined by $\Lambda f:=-\langle\nabla p^f,\nabla\tau\rangle$ on $\Gamma$. We show that the N-transform provides a certain factorization $\Lambda^{-1}=V^*V$ and discuss its possible usefulness for determination of $(\Omega,g)$ from $\Lambda$.
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General Relativity and Quantum Cosmology

Geodesics Structure and Light Deflection of Regular Phantom Black Hole

B. Malekolkalami and M. Haditale

The geodesic structure of Regular Phantom Black Holes (RPBH) space–time is analyzed and discussed in three asymptotically cases: Flat, de Sitter (dS), and Anti–de Sitter (AdS). The impact of the important scale parameter $b$\footnote{This parameter determines the coupling strength between phantom field and gravity.} on the trajectory of particles is studied and investigated which can mimic repulsion or attraction. By virtue of Effective Potential (EP) tool, the circular orbits and their stability are discussed. Also, in the asymptotically flat spacetime, the angle of light deflection versus the scale parameter is presented.
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Fluid Dynamics

Effect of Biofouling on Microplastic Transport in a 3-D Global Eulerian Model

Zih-En Tseng, Yue Wu, Chris Ruf et al. (+2 more)

Biofouling – the occupation of microplastic (MP) surfaces by marine microbes – alters particles' buoyancy and transport, yet its effect on the global distribution of MPs has not been well quantified. We present the first three-dimensional global Eulerian model to fully couple MP transport with biofouling, by augmenting the concentration field with an extra dimension representing the biomass attachment density on MP surfaces. This approach embeds time-dependent particle properties directly into the Eulerian concentration field, overcoming a fundamental challenge of tracking property evolution in grid-based models. Idealized simulations show that biofouling significantly reshapes the vertical distribution of MPs when two conditions are met: the particles must be sufficiently buoyant when they are clean to remain near the sea surface, and the local plankton growth rate must exceed the decay rate. In three-dimensional global simulations, biofouling substantially alters the distribution of large MPs ($\gtrsim 10$ $\mu$m): biofouled particles are transported below the mixed layer to 500 m depth, and the subtropical surface garbage patches become more dispersed with reduced peak concentrations. This dispersion is due to a subsurface transport route, where biofouled particles sink into layers with reversed current and are carried outward from the gyre centers before regaining buoyancy. Small particles ($\lesssim 1$ $\mu$m) remain unaffected as they stay effectively neutrally buoyant even when biofouled. A comparison with a global trawler dataset shows that incorporating biofouling reduces the fraction of outlying model-observation data points from 25% to 13%, demonstrating a meaningful improvement in model skill.
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All authors Zih-En Tseng, Yue Wu, Chris Ruf, Dimitris Menemenlis, Yulin Pan

Quantum Physics · Cross-listed from cs.MS

Finite-Dimensional Type I von Neumann Algebras in PyTorch: A GPU-Accelerated Framework for Random Block-Diagonal Operators

Irina Nikolaeva and Andrej Novikov

torch_vn_algebra is a PyTorch library for numerical work with finite-dimensional von Neumann algebras, i.e. direct sums of matrix algebras. These algebras are central to operator algebra theory and, via commutants of symmetries, describe quantum systems with conserved charges or superselection rules. To our knowledge, no numerical software treats them as a data type with their centre, family of traces, conditional expectations, inclusions and functional calculus. The library fills the gap between computer algebra (exact but small-scale) and quantum simulators (large-scale but limited to Hilbert-space matrices): it handles batches of operators on CPUs and GPUs with automatic differentiation, and converts operators, states and channels. Key features: Compact tensor representation: 4D tensor (B, C, kmax, kmax), where B is batch size (e.g. Monte Carlo samples), C is the number of summands, and kmax is the max block size, enabling batched GPU processing. Lazy evaluation: matrix data materialized only on access, avoiding memory waste. Random operator generation: custom eigenvalue distributions; Haar, SU(n), COE, CSE unitary ensembles. Functional calculus and spectral methods: matrix absolute value, square root, inverse, entropy via SVD; automatic switch between exact diagonalization (block size up to 256) and power iteration for extreme eigenvalues. Three trace functionals: Tr_blunt (sum of block traces), Tr_norm (dimension-normalized), tau_vN (faithful normal tracial state). Performance: on a Tesla P100 GPU, processing 20,000 samples of 100x100 operators yields up to 30x speedup over traditional CPU workflows. Availability: open-source at https://gitlab.com/a.hobukob/von_neumann_type_i/
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Quantum Physics

Complete Relational Description of Spin in a Quantum Background

Hannah Troger, Ofek Bengyat, Thomas D. Galley et al. (+1 more)

The standard description of the state of a spin in quantum mechanics presupposes externally fixed directions – a classical background. Can a spin be fully described instead in relation to other quantum mechanical systems? Poulin suggested twenty years ago group averaging over rotations the joint state of a fundamental spin and a reference spin with large angular momentum which, however, yields a classical bit in a probabilistic mixture. We revisit this idea and show that when the quantum reference system is augmented to two large spins, the standard quantum mechanical description of a spin is recovered in the limit of large quantum numbers for the reference system.
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All authors Hannah Troger, Ofek Bengyat, Thomas D. Galley, Marios Christodoulou

Strongly Correlated Electrons

Probing Interfacial Magnetic Anisotropy in \texorpdfstring{CoV$_{2}$O$_{4}$}{CoV2O4} using Spin Hall Magnetoresistance

Sairam Ithineni, Krishna Jha, Aditya A. Wagh et al. (+5 more)

Spin Hall magnetoresistance (SMR) has emerged as a powerful probe for investigating interfacial spin transport and magnetic anisotropy in complex oxide heterostructures. In this work, we investigate the interfacial magnetic anisotropy in Pt/CVO through angle-dependent magnetotransport measurements. Unlike the bulk-sensitive magnetic measurements on both strained CVO and Pt/CVO films, which exhibit a ferrimagnetic transition at $T_{C} \approx 150$ K accompanied by out-of-plane anisotropy that reorients toward in-plane anisotropy below 90 K, SMR reveals a distinct interfacial magnetic anisotropy. The rotational scans of the in-plane transverse SMR at 20 K exhibit substantial hysteresis about [100], while no hysteresis is observed along [110] and [1$\bar{1}$0], indicating a biaxial anisotropy with easy axes along [110] and [1$\bar{1}$0]. Furthermore, the absence of sharp discontinuities in both the in-plane longitudinal and transverse SMR, together with pronounced discontinuities near the in-plane [010] direction during out-of-plane rotation, strongly indicates the presence of in-plane anisotropy. This behavior persists up to 120 K. The discrepancy between the bulk-sensitive magnetic measurements and the SMR response suggests that the Pt/CVO interface retains a magnetic anisotropy distinct from the bulk, highlighting the interfacial sensitivity of SMR. Additionally, the spin mixing conductance is found to be of the order of $10^{14}$ $\Omega^{-1}\mathrm{m}^{-2}$, comparable to other oxide-based spintronic systems. These findings highlight the crucial role of interfacial effects in spin transport and establish Pt/CVO as a promising platform for spintronic applications.
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All authors Sairam Ithineni, Krishna Jha, Aditya A. Wagh, Shwetha G. Bhat, Debashree Nayak, K. Senapati, P.S. Anil Kumar, D. Samal

Accelerator Physics

Study of Nb Surface Under Ultra High Vacuum After Heat Treatments For SRF Cavities

C. Boutelaa, C. Craig, R. Laxdal et al. (+4 more)

Specific heat treatments applied to superconducting radiofrequency (SRF) cavities, such as nitrogen infusion or Mid T baking, aim to improve the quality factor (Q0) at medium accelerating fields (10 to 20 MV/m). These treatments reduce the BCS surface resistance by tuning the mean free path of niobium over a few hundred nanometers, either by diffusing oxygen from the native oxide layer or by diffusing nitrogen after the dissolution of the oxide layer. However, these treatments preclude the usual chemical polishing, as it would reverse the beneficial effects of the heat treatments, making the cavities highly sensitive to surface contamination. In particular, the formation of niobium carbides, which can mask the expected benefits, strongly depends on the annealing conditions, surface preparation, and the materials history. Several hypotheses are considered regard-ing the origin of carbon: vacuum contamination, surface pollution, or internal migration from the niobium itself, potentially enriched with carbon during previous chemi-cal treatments (BCP, EP). This work aims to identify the primary source of carbon responsible for niobium carbide growth, using techniques such as X Ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and secondary ion mass spectrometry (SIMS). The study will also help pinpoint the key influencing parameters, thereby contributing to a better understanding of and potential mitigation strategies for their impact on SRF cavity performance.
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All authors C. Boutelaa, C. Craig, R. Laxdal, P. Kolb, B. Mercier, G. Sattonnay, D. Longuevergne

Astrophysics of Galaxies

Joint Modeling of GD-1 and C-19 as Old Streams

Raymond G. Carlberg, Ting S. Li, Emma Jarvis et al. (+39 more)

DESI observational data for the GD-1 and C-19 streams are compared to stream simulations in an evolving multi-halo potential of a Milky Way-like galaxy based on a cosmological Milky Way-like simulation. The number of subhalos decreases with time and the subhalo-stream encounter velocities rise as the Galaxy and its disk build up their mass. The streams develop from star clusters inserted at $\simeq$1 Gyr after the Big Bang and evolved for 13 Gyr to their current orbital positions. The measured velocity widths of the streams are compared to the matched simulations. Streams in a CDM subhalo population provide the best match to the velocity width, on the average, with considerable scatter. Streams younger than $\simeq$12 Gyr in CDM subhalos are insufficiently hot. Streams in the same potentials but with populations of WDM 5.5 keV subhalos are not, on the average, heated to the observed velocity widths, although some of the realizations do reach the observed levels. The stream density power spectrum measured along the length of the DESI GD-1 sample agrees with the CDM stream simulations, with 1.3 to 2.3 times more power than WDM 7 keV and 5.5 keV simulations. The simulations show that modeling specific streams from the time of the formation of their progenitor clusters is both feasible and necessary to reproduce their stream averaged kinematic properties.
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All authors Raymond G. Carlberg, Ting S. Li, Emma Jarvis, Nasser Mohammed, Joan Najita, Arjun Dey, Sergey E. Koposov, Jakob Piafsky, Leandro Beraldo e Silva, Constance M. Rockosi, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. de la Macorra, Biprateep Dey, P. Doel, A. Font-Ribera, J. E. Forero-Romero, Satya Gontcho A Gontcho, G. Gutierrez, R. Joyce, S. Junea, A. Kremin, O. Lahav, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, J. Silber, G. Tarlé, B.A. Weaver, R. Zhou, H. Zou

Pattern Formation and Solitons

Nonlinear Localized States on a Pyrochlore Lattice

Faustino Palmero Ramos, Avadh Saxena and Panayotis G. Kevrekidis

In the present work we explore a prototypical three-dimensional (3d) lattice possessing a flat band in the form of a pyrochlore lattice in the context of a dispersive nonlinear dynamical model, namely the discrete nonlinear Schrödinger (DNLS) equation. We set up the corresponding steady state and dynamical problems and discuss the linear spectrum of the relevant model before delving into a more detailed analysis of the nonlinear equilibria of the system. For the latter, we analyze the more well-established – at the DNLS level – fundamental discrete soliton states, as well as vortex structures. For the fundamental solitary waves, we connect their existence and stability with how they approach the linear bands. In the vortex case, we identify their stability features for vortices of topological charge $S=1$ and $S=2$ with those of the honeycomb and triangular lattices. An arguably even more intriguing feature of the pyrochlore lattice concerns the compactly supported nonlinear eigenstates stemming from the flat band of the linear spectrum. These compact localized modes are found to possess oscillatory instabilities for a range of propagation constants in the focusing case, although they can be stable in the latter, while they are found to be subject to symmetry-breaking instabilities in the defocusing nonlinearity case. These results offer a glimpse at the nexus of topology, flat band systems and dispersive nonlinear lattices in three spatial dimensions and as such may be a starting point toward a deeper exploration of such an intriguing interplay.
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Optics

Enantio-selective inverse Faraday effect in isotropic chiral molecular mixtures

Raju Adhikary, Ambaresh Sahoo, Matteo Silvestri et al. (+5 more)

Enantiomeric excess detection in a chiral molecular mixture is paramount because very often opposite enantiomers exhibit profound functional dissimilarities that play decisive roles in biochemical applications. Existing chiral sensing methods mostly rely on large operational sample volumes, hindering compatibility with integrated sensing schemes. Here, we propose a novel chiroptical sensing technique based on the inverse Faraday effect in a photonic micro-capillary filled with nl-volume chiral drug solution. We theoretically demonstrate that, upon excitation by intense laser light, an isotropic assembly of chiral drugs produces a static magnetisation, with amplitude and direction depending on the enantiomeric excess. In turn, by measuring the chirally-sensitive static magnetic field in the vicinity of the micro-tube one can retrieve the enantiomeric excess of the chiral drug solution. Our theoretical predictions unlock new opportunities for the development of innovative nanophotonic devices suitable for efficient chiroptical sensing with nl-volume sensitivity.
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All authors Raju Adhikary, Ambaresh Sahoo, Matteo Silvestri, Massimiliano Aschi, Antonio Mecozzi, Davide Tedeschi, Carino Ferrante, Andrea Marini

Materials Science

Surface-Sensitive Mapping of Anisotropic Phonon Cascades in T$_{d}$-WTe$_{2}$

Alp Akbiyik, Felix Kurtz, Nandana Veena Uday et al. (+3 more)

Understanding how energy flows from photoexcited carriers into the lattice is essential for describing nonequilibrium phenomena in low-symmetry quantum materials. Here, we use ultrafast low-energy electron diffraction and diffuse scattering to probe momentum-resolved phonon dynamics at the surface of T$_d$-WTe$_2$, a strongly anisotropic semimetal. Following optical excitation, the Debye–Waller suppression of Bragg peaks exhibits a biexponential increase of the mean-squared atomic displacement, indicating sequential lattice relaxation. Analysis of the diffuse background reveals a preferential intensity build-up parallel to the tungsten-chain axis in the material, attributed to anisotropic electron–phonon coupling during electronic cooling which precedes anharmonic phonon–phonon scattering and subsequent thermalization across the surface Brillouin zone. The results identify a hierarchical relaxation pathway in which energy is first deposited into selected finite-momentum phonons before spreading through the broader lattice bath. Our work highlights the importance of momentum-resolved diffuse scattering for disentangling electron–phonon and phonon–phonon relaxation in anisotropic topological semimetals.
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All authors Alp Akbiyik, Felix Kurtz, Nandana Veena Uday, Sergey V. Yalunin, Claus Ropers, Hannes Böckmann

Cosmology and Nongalactic Astrophysics

Multi-band cross-correlation dark sirens: enhancing cosmological parameter and gravitational-wave bias constraints

Ji-Yu Song, Ya-Nan Du, Yue-Yan Dong et al. (+2 more)

Multi-band gravitational-wave (GW) observation, combining space-borne and ground-based detectors across different frequency bands, can improve the sky localization of compact binary sources by two to three orders of magnitude compared to single-band detection. This enhancement is crucial for cross-correlation dark siren analyses, since the sky localization uncertainty directly determines the noise level of the GW angular power spectrum. In this work, we present the first Fisher forecast for cross-correlation dark siren cosmology with multi-band GW observations, cross-correlating GW events from the Einstein Telescope (ET), Cosmic Explorer (CE), and B-DECIGO with the Chinese Space-station Survey Telescope photometric galaxy survey. We compare three network configurations: the multi-band B-DECIGO+ET+2CE (BDET2CE), the ground-only ET+2CE (ET2CE), and B-DECIGO alone. In the $\Lambda$CDM model, BDET2CE achieves $\sigma(h)/h = 0.35\%$, improving by $37\%$ over the ground-only ET2CE ($0.55\%$) and by $86\%$ over B-DECIGO alone ($2.45\%$). Extending to the $w_0w_a$CDM framework, the multi-band advantage on cosmological parameters becomes more moderate, with BDET2CE improving $\sigma(h)/h$ by $\sim 4\%$ over ET2CE and $\sim 22\%$ over B-DECIGO. The most striking advantage of multi-band observation lies in the per-bin measurement of the GW clustering bias $b_{\rm GW}(z)$: at $z \sim 1-2$, BDET2CE constrains the bias to $\sim 3\%$ precision, compared to $\sim 8-60\%$ for ET2CE and $\sim 20-33\%$ for B-DECIGO. These precise, redshift-resolved bias measurements open a new avenue for probing the astrophysics of compact binary mergers, enabling constraints on formation channels such as isolated binary evolution and dynamical assembly that predict distinct clustering signatures.
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All authors Ji-Yu Song, Ya-Nan Du, Yue-Yan Dong, Jing-Fei Zhang, Xin Zhang

Instrumentation and Methods for Astrophysics

Shigatse Astronomical Site Testing. I. Cloud-cover Climatology and Selected Local Meteorological Conditions

Baiyu Zhang, Hejun Yang, Xiaojun Dong et al. (+15 more)

As the first paper in a Shigatse astronomical site-testing series, we present a multi-source assessment of cloud cover and selected local meteorological conditions at the Shigatse 40 m site on the southern Tibetan Plateau. The study combines CALIPSO-GOCCP active-lidar climatology, ISCCP HXG passive-satellite cloud fields, conventional total-cloud-amount observations from the Shigatse Meteorological Station, and on-site Weather Station measurements. Together, these records characterize Shigatse as a southern-plateau monsoon-transition cloud regime: the active-lidar climatology gives a moderate-to-low annual cloud fraction, and the cloudier months are concentrated in the June–September monsoon interval. In GOCCP, the annual mean cloud fraction is 42.1%, while the October–May low-cloud season has a mean cloud fraction of 26.3%, compared with 73.7% during the June–September monsoon interval. ISCCP gives higher absolute cloud fractions but supports the same seasonal phase and local spatial placement. The aligned 1988–2013 meteorological-station record gives a total-cloud-amount <=40% fraction of 80.7% during October–May, rising to 90.7% in the November–January core, and decreasing to 39.9% during June–September. The 2024–2025 Weather Station archive further shows high fractions of valid samples satisfying the adopted meteorological criteria during the low-cloud months: 92.6% for the October–May night-time proxy and 94.6% for the corresponding 24 h samples. These results identify Shigatse as a measured lower-latitude southern-plateau cloud-cover reference within China's site-testing network, with a well-defined October–May low-cloud observing period and a Shigatse–Ali low-cloud corridor for subsequent regional site testing.
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All authors Baiyu Zhang, Hejun Yang, Xiaojun Dong, Lingling Wang, Juean Luobu, Minfeng Gu, Xiyan Peng, Hao Luo, Yindun Mao, ZhaoXiang Qi, Basangzeren, Qihang He, Guojie Feng, Chunhai Bai, Ali Esamdin, Wenbo Gu, Siqi Wang, Zihuang Cao

High Energy Physics (Phenomenology)

Rescuing flavor-symmetry-forbidden leptogenesis within the left-right symmetric framework

Yan Shao and Zhen-hua Zhao

While the type-I seesaw model provides a unified framework for explaining the origin of neutrino masses and the baryon asymmetry of the Universe, flavor symmetries offer an attractive approach to understanding the observed neutrino mixing pattern. However, in many flavor-symmetry-based type-I seesaw models, either the Dirac neutrino mass matrix $M^{}_{\rm D}$ or the right-handed-neutrino mass matrix $M^{}_{\rm R}$ is constrained to be proportional to the identity matrix, which prevents the conventional leptogenesis mechanism from working. In this paper, without breaking the original flavor structure dictated by the employed flavor symmetries, we investigate whether such forbidden leptogenesis scenarios can be rescued within the framework of the left-right symmetric model. We show that, in these scenarios, the contribution of the Higgs triplet present in the left-right symmetric model to the CP asymmetries of right-handed neutrino decays can successfully reproduce the observed baryon asymmetry.
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Fluid Dynamics

Coherent structures modeling in stenotic transitional flow via resolvent analysis

Alexandre Villié, Simon Demange and Kilian Oberleithner

This study investigates the capability of linear modeling to characterize the transitional dynamics in an axisymmetric stenosis and attempts a low-order representation of the turbulent stresses. The transition to turbulence in stenotic flows generates wall shear stress fluctuations that strongly influence the progression of cardiovascular diseases and the risk of plaque rupture. A description of the linear mechanisms driving the forced dynamics at Reynolds number beyond transition is currently missing. Linear modeling of coherent structures is leveraged to identify the flow amplification mechanisms using the mean field from a LES at Re=4000. Global linear stability analysis reveals an unstable and sinuous stationary eigenmode that is known to destabilize the flow at lower Reynolds numbers through a weak Coanda-type wall attachment. At intermediate frequencies, resolvent analysis identifies a second amplification region within the shear-layer where the most amplified fluctuations are axisymmetric, in contrast to findings from studies at lower Reynolds numbers. The linear model is validated against SPOD. At intermediate frequencies, the optimal resolvent response mode demonstrates both high gain separation and strong alignment with the leading SPOD mode. The low-rank nature of the resolvent operator is leveraged to reconstruct the turbulent kinetic energy (TKE) and turbulent wall shear stress (tWSS) from the optimal response mode. In the immediate post-stenotic zone, axisymmetric fluctuations dominate the tWSS and exhibit low-rank dynamics. Our findings highlight that linear mechanisms effectively capture the complex post-stenotic dynamics. The successful reconstruction of turbulent quantities from mean flow data alone opens new predictive possibilities of key turbulent quantities.
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Materials Science

Intrinsic linewidths of confined phonons in few-layer hBN

Aleksandar Radic, Jack Kelsall and Akshay Rao

Understanding lattice vibrations in two-dimensional (2D) materials is essential for controlling thermal transport, mechanical response, and energy dissipation in nanoscale devices. However, the intrinsic lifetimes of low-energy phonon modes, particularly those that are optically silent, remain largely unexplored. Here we use helium-3 spin-echo spectroscopy to resolve low-energy phonons at the surface of hexagonal boron nitride (hBN) and measure their intrinsic linewidths. We observe the flexural and Rayleigh wave modes and extract the bending rigidity of a quasi-freestanding hBN monolayer. We further report the simultaneous observation of multiple surface-confined interlayer shear modes whose energies agree closely with linear-chain model predictions. By resolving their intrinsic linewidths, we demonstrate a strong confinement-induced reduction in phonon lifetimes, with a near order of magnitude increase in linewidth between the four- and two-layer modes. The temperature dependence of the linewidths indicates that phonon-phonon scattering dominates between 160-360K, while the systematic broadening with decreasing layer number reveals the impact of confinement on phonon decay. These results reveal how reduced dimensionality affects the decay of interlayer shearing modes in hBN, providing direct insight into the phonon lifetimes, confinement effects, and dissipation pathways that govern the dynamical behaviour of two-dimensional materials.
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Quantum Physics

Trainable Quantum Channels as Computational Primitives for Quantum Learning

Jingwei Wen, Runqing Zhang, Xusheng Xu et al. (+6 more)

Variational quantum learning is traditionally constrained to unitary dynamics, often treating quantum channels as detrimental noise. In this work, we reformulate the quantum channels as trainable computational primitives and establish a non-unitary quantum machine learning framework grounded in open-system dynamics. We demonstrate that the outputs of channel-enhanced quantum models form a structured superposition of multiple functional components. Each component is governed by an effective observable whose spectrum can be adaptively modulated during training, a significant departure from the spectral invariance in unitary transformations. Moreover, the proposed framework generalizes conventional unitary quantum models by retaining them as a special case while introducing additional non-unitary degrees of freedom. Furthermore, we reveal that trainable quantum channels enrich the optimization geometry through ensemble-averaged gradient and additional optimization directions induced by the Kraus operators. Extensive experiments on classification tasks using trainable amplitude-damping and phase-damping channels confirm enhanced optimization dynamics and predictive performance. In addition, we experimentally validate the proposed framework through hardware inference using ten-qubit quantum models implemented on the superconducting quantum processor, confirming its practical feasibility and hardware compatibility. Our work provides a principled approach for leveraging quantum channels as trainable resources and advances the design of high-performance quantum learning architectures.
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All authors Jingwei Wen, Runqing Zhang, Xusheng Xu, Xiaoxiao Hu, Jize Han, Ling Qian, Tiejun Wang, Shijie Wei, Guilu Long

Mesoscale and Nanoscale Physics

Spin-induced and orbital quantum backflow in Pauli theory

Tomasz Radożycki

We show that quantum backflow in spin-$\tfrac{1}{2}$ systems within the Pauli framework can arise from spin-dependent contributions to the probability current. We construct explicit two-mode states in which the orbital current reduces to a uniform drift, so that no interference between longitudinal momentum components is present in this sector. In such configurations, backflow is generated entirely by spinor structure, which induces time-dependent modulations of the local current leading to flux reversal, while the longitudinal momentum distribution remains strictly supported on positive momenta. We derive analytical conditions for backflow in terms of spinor and momentum parameters, allowing direct control of the effect via internal degrees of freedom. We further analyze spatial coarse-graining, showing exponential suppression of interference and a qualitatively different scaling of orbital and spin contributions, with spin-induced backflow remaining robust in regimes where orbital effects are strongly suppressed.
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Optics

Polarization-controlled optical backflow in paraxial electromagnetic beams

Tomasz Radożycki

Optical backflow in paraxial Gaussian beams is investigated within the Maxwell framework. Scalar potential representations are employed to identify conditions under which the longitudinal Poynting component becomes negative, showing that backflow is enabled by local suppression of the leading-order transverse field and the dominance of higher-order vectorial contributions. The spatial topology of backflow regions is shown to be governed by polarization through the number of independent local constraints on the transverse field. When the local polarization phase is free, as in the generic case of circular polarization, the leading-order field vanishes only at isolated points, giving rise to point-like backflow regions (extended curves may arise if an additional global phase constraint is imposed). In contrast, when the polarization phase is locally fixed, as for linear, radial, or azimuthal polarization, the suppression condition reduces to a single real constraint, resulting in extended backflow curves. Analytical Gaussian-polynomial solutions explicitly illustrate these effects. These results clarify the role of vectorial interference, establish a polarization-controlled backflow geometry, and provide a foundation for further studies of optical backflow in structured and nonparaxial beam configurations, as well as potential applications in optical manipulation and structured light design.
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Fluid Dynamics

Quantum vortex in a fluid flow: negative effective mass and a novel mechanism for turbulence formation

S.V. Talalov

We explore the movement of a thin, circular quantum vortex filament within an infinite cylindrical pipe. The fluid surrounding the vortex ring moves through the pipe at a non-zero velocity denoted by $v$. Our study examines the energy spectrum $E = E(p)$, where $p$ represents the total momentum of a vortex ring. We have demonstrated that the function $E(p)$ significantly depends on the velocity $v$. The discovered spectrum $E(p)$ reveals the existence of states with both negative and extremely large effective masses. We also explored the hypothesis regarding the existence of coupled vortex pairs possessing finite summary effective masses. Every pair consists of vortices that possess both positive and negative masses, with the magnitude of these masses being unrestricted. In our model, the criterion for the appearance of these states is based on comparing two numbers. The first is seen as a quantum counterpart to the Reynolds number, while the second represents its critical value for a flow with a single vortex. We also explore how this studied effect might contribute to the emergence of quantum turbulence. This study discusses a method for determining the critical Reynolds number in quantum turbulence, using the proposed model as a framework. Here, we use a new quantization technique for classical closed vortex filaments developed by the author earlier.
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Quantum Physics

MAPS: A Novel Multi-Axial Projective Sphere for Geometrically Visualizing Higher d-Valued Quantum State-Space of Qudits

Ali Al-Bayaty

Visualizing the d-valued quantum state-space of quantum systems serves as a foundational pillar for the scientific research and practical applications in quantum computing and information science, where d >= 2. The 2-valued quantum states of a qubit are elegantly visualized on the three-dimensional Bloch sphere. In contrast, expanding this geometrical paradigm to visualize higher d-valued quantum states of a qudit (d >= 3), e.g., a qutrit (d=3), ququadit (d=4), and quintit (d=5), leads to severe structural and topological complexities. This paper introduces a new generalized three-dimensional framework to effectively visualize higher d-valued quantum states of a qudit, in the aspects of ease of illustration, structural simplicity, and natural representation for researchers and engineers. We called this new framework the "multi-axial projective sphere (MAPS)", which consists of n projectional intersecting spatial axes, where 0 <= n <= d-1. We also propose a group of novel d-valued phase axial-based gates, to swivel and shift d-valued quantum states of a qudit along these n axes. Our generalized framework could be used for visualizing high-dimensional data for practical applications, e.g., machine learning, quantum machine learning, and quantum chemistry, where every axis of the MAPS represents a single feature of such data with its corresponding distinct values.
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Optics

Two mechanisms of backward optical forces on Rayleigh particles in structured paraxial light

Tomasz Radożycki

A theoretical and numerical study of optical forces acting on a Rayleigh particle in a paraxial Gaussian light beam exhibiting regions of optical backflow is presented. Within the dipole approximation, the total optical force is decomposed into gradient, scattering, and spin-curl terms. Vector fields satisfying the exact paraxial Maxwell equations are employed to describe the structured light configuration responsible for two distinct mechanisms leading to backward optical forces. The first originates from the local reversal of the Poynting vector, which induces a negative longitudinal momentum flux, while the second arises from the spin-dependent component of the force associated with the spatial variation of the optical spin density. Analytical expressions and numerical simulations confirm that both mechanisms can produce backward motion of a Rayleigh particle under appropriate beam conditions. These results provide a unified physical picture of backward-directed optical forces in Gaussian beams and open possibilities for particle manipulation in structured light fields.
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Disordered Systems and Neural Networks

Machine Learning Topological Order from Defect Partition Functions

Kazem Bitaghsir Fadafan, Wei Cui, Babak Haghighat et al. (+1 more)

We introduce a machine learning framework for extracting Ising topological order from defect partition functions of the two-dimensional Ising model on a torus. Restricted Boltzmann Machines (RBMs) are trained on Ising model data sampled at criticality across topological sectors. We take a component-wise square-root map of the learned distributions which naturally produces candidate wavefunctions for the (2+1)-dimensional Ising TQFT. As a nontrivial consistency check, we extract the modular S-matrix from overlaps of the resulting states and recover the expected Ising modular data. Our results demonstrate that neural network representations can capture both critical fluctuations and emergent topological structure, providing a data-driven route from lattice statistical mechanics to topological quantum field theory.
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All authors Kazem Bitaghsir Fadafan, Wei Cui, Babak Haghighat, Shailesh Lal

High Energy Physics (Phenomenology)

Why fluctuations of conserved charges in the confining regime above $T_{ch}$ behave as if the quarks were free?

L. Ya. Glozman

Some cumulants of the fluctuations of conserved charges soon above the chiral crossover behave as if the quarks were free. This was taken by many as evidence of deconfinement. At the same temperatures the mesonic correlators reveal the chiral spin and SU(4) symmetries, indicating that the propagating degrees of freedom are massless quarks connected into color singlets by the chromoelectric confining string. These correlators are qualitatively different from the free quark gas. Here we clarify the reason for the difference. The conserved quark number densities do not propagate in time but do propagate in spatial directions. The mesonic propagators calculated in full QCD differ radically from the free quark loop (quark gas) above T_ch. In contrast, the quark number density spatial propagator in full QCD at T > 220 MeV is very close to the free quark loop. In other words, the conserved charges do not see confinement, in contrast to the mesonic correlators. This is consistent with the well understood quark-hadron duality at T=0 in e^+e^- -> hadrons, where at invariant masses above 2 GeV the cross-section in the confining regime is represented by the free quark loop plus small perturbative corrections. All these features above T_ch but below the deconfinement temperature T_d can be combined within the following microscopic picture of the stringy fluid matter. It is a medium of the overlapping strongly interacting color singlet clusters. The quark interchanges between the clusters, required by Paili principle, make the quarks quasifree, which is reflected in fluctuations of conserved charges.
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High Energy Physics (Theory)

An integrable deformation of the sine(sinh)-Gordon model – Non-Lie algebra

Meseret Asrat

In this paper we present an integrable model in two dimensions. It is a deformation of the sine(sinh)-Gordon model. We give its Lax connection. We also obtain its (classical) $r$-matrix. It satisfies the classical Yang-Baxter equation. Thus, the model is a classical integrable field theory in two dimensions. The underlying algebra is a ${\cal Z}$-graded non-Lie alternative Akivis algebra. An alternative Akivis algebra is the tangent space at the identity of an analytic alternative loop as a Lie algebra is the tangent space at the identity of a Lie group. We expect the model to be integrable at the quantum level. We also give a family of classically integrable models which are related to the Poisson-Boltzmann equation in two dimensions.
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High Energy Physics (Theory)

Entanglement islands of 2D charged scalar-hairy black holes on the brane

Qingsong Li, Yuxuan Liu and Wenjie Zhu

We investigate the entanglement dynamics and Page curve of a 2D brane Maxwell-Scalar (MS) black hole coupled to thermal baths in double holography. Computing the entanglement entropy via the island formula, we find that injecting electric charge and scalar source into the system produce opposite effects: the former increases the degrees of freedom (DOF) on the brane by enhancing the effective global tension, thereby raising the saturation entropy of the system; conversely, the latter reduces the DOF on the brane by lowering the effective local tension near the IR geometry, ultimately suppressing the entanglement. Despite the non-trivial backreaction from the matter fields, the pre-saturation entanglement dynamics remain robust. We identify an early-time quadratic growth corresponding to the pre-local-thermalization phase, which smoothly transitions into a late-time linear growth. Furthermore, the scale of the Page time is governed by a competition between thermal excitations and the brane DOF. Higher temperatures accelerate the onset of the Page time by exciting more Hawking modes, while abundant DOF delay it by increasing the saturated entropy.
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Mathematical Physics

Flowing to Normality and the Fate of the Single Ring Theorem

Joshua Feinberg, Roman Riser, Richard Scalettar et al. (+1 more)

Random non-hermitian matrix ensembles with double-sided rotation invariance obey, in the limit of large matrix size, the Single Ring Theorem, which states that the support of the mean eigenvalue distribution in the complex plane is either a disk or an annulus. In contrast, rotational-invariant random normal matrix ensembles can have mean eigenvalue densities supported over any number of concentric annuli in the complex plane. In this paper we introduce and investigate, both analytically and numerically, a non-hermitian matrix model which flows from a generic matrix distribution obeying the Single Ring Theorem to a distribution of normal matrices by tuning a parameter which penalizes non-normality. We observe numerically breakdown of the Single Ring Theorem as the model flows towards normality, and determine the critical value of the parameter at which the transition occurs. We also study in detail the behavior of the singular values of these matrices under the flow. These singular values form a Fermi gas confined to the positive half-line. In particular, we find that at small values of the flow parameter, the interparticle spacings in the gas exhibit Wigner-Dyson repulsion, whereas for asymptotically large values of the flow parameter, at the normal matrix endpoint of the flow, the spacing statistics is Poissonian. The flow interpolates continuously between these two types of statistics. However, this change in statistics is not related directly to breaking of the Single Ring Theorem, which occurs very early-on along the flow, in the regime of Wigner-Dyson statistics. Finally, we introduce a certain ensemble of random permutations associated with the gas, and make a conjecture on how to use it in order to reconstruct approximately the average density of complex eigenvalues from that of the singular values in the large-$N$ limit.
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All authors Joshua Feinberg, Roman Riser, Richard Scalettar, Anthony Zee