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Optical frequency combs and their spectra of evenly spaced discrete laser lines are essential to modern time and frequency metrology. Recent advances in integrated photonic waveguides enable efficient nonlinear broadening of an initially narrowband frequency comb to multi-octave bandwidth. Here, we study the nonlinear dynamics in the generation of such ultra-broadband spectra where different harmonics of the comb can overlap. We show that a set of interleaved combs with different offset frequencies extending across the entire spectrum can emerge, which transform into a single evenly spaced ultra-broadband frequency comb when the initial comb is offset-free.

Topological singularities of optical response functions -- such as reflection amplitudes -- enable elegant practical applications ranging from analog signal processing to novel molecular sensing approaches. A phase singularity-based refractometric sensor monitors the rapidly evolving argument of the optical field near the point of phase singularity, in contrast to the reflection zero in traditional surface plasmon polariton sensors. This raises a natural question: What happens with the sensitivity and resolution of such a sensor when it operates close to a zero of the response function, where the detected signal may be greatly influenced by various noise sources? In this paper, we systematically study the effect of the shot noise on the performance of a generic phase singularity-based refractometric sensor. We develop a theoretical model of a spectroscopic ellipsometry-based system operating near a phase singularity and couple the macroscopic optical picture of the detection with a quantum shot noise model. Within the developed model, we illustrate how the shot noise of the detector comes into play and study its effect on the sensitivity and resolution of the refractometric sensor. Our results suggest that such an ellipsometry-based phase singularity sensor remains stable even in the presence of shot noise near the point of zero reflection.

We demonstrate LLM agent specification gaming by instructing models to win against a chess engine. We find reasoning models like o1 preview and DeepSeek-R1 will often hack the benchmark by default, while language models like GPT-4o and Claude 3.5 Sonnet need to be told that normal play won't work to hack. We improve upon prior work like (Hubinger et al., 2024; Meinke et al., 2024; Weij et al., 2024) by using realistic task prompts and avoiding excess nudging. Our results suggest reasoning models may resort to hacking to solve difficult problems, as observed in OpenAI (2024)'s o1 Docker escape during cyber capabilities testing.

Nonlinear optical response is a sensitive probe of the geometry and symmetry of electronic Bloch states in solids. Here, we extend this notion to the Bogoliubiov-de-Gennes (BdG) quasiparticles in superconductors. We present a theory of photocurrents in superconductors and show that they sensitively depend on the quantum geometry of the BdG excitation spectrum. For all light polarizations, the photocurrent is proportional to the quantum geometric tensor: for linear polarized light it is related to the quantum metric and for circular polarization -- the Berry curvature dipole of the associated BdG bands. We further relate the photocurrent to the ground state symmetries, providing a symmetry dictionary for the allowed photocurrent responses. For light not at normal incidence to the sample, photocurrent probes time-reversal symmetry breaking in systems with chiral point groups (such as twisted bilayers). We demonstrate that photocurrents allow to probe topology and TRS breaking in twisted $d$-wave superconductors and test the nature of superconductivity in twisted WSe$_2$ and multilayer stacks of rhombohedral graphene. Our results pave the way to contactless measurement of the quantum geometric properties and symmetry of superconductivity in materials and heterostructures., Comment: 6 pages + supplement

New high-refractive-index dielectric materials may enhance many optical technologies by enabling efficient manipulation of light in waveguides, metasurfaces, and nanoscale resonators. Van der Waals materials are particularly promising due to their excitonic response and strong in-plane polarizability. Here we combine ab initio calculations and experiments to discover new high-refractive-index materials. Our screening highlights both known and new promising optical materials, including hafnium disulfide (HfS$_2$), which shows an in-plane refractive index above 3 and large anisotropy in the visible range. We confirm these theoretical predictions through ellipsometry measurements and investigate the photonic potential of HfS$_2$ by fabricating nanodisk resonators, observing optical Mie resonances in the visible spectrum. Over the course of seven days, we observe a structural change in HfS$_2$, which we show can be mitigated by storage in either argon-rich or humidity-reduced environments. This work provides a comparative overview of high-index van der Waals materials and showcases the potential of HfS$_2$ for photonic applications in the visible spectrum., Comment: 5 figures

We derive Lipschitz regularity estimates for an approximate inverse of a general compact operator that depends non-linearly on a vector parameter. The regularity estimates are motivated by the desire to develop neural networks (NN) that compute that approximate inverse and the convergence of the NNs follows from the Lipschitz regularity estimates. Such compact operators arise in inverse wave scattering applications with unbounded domains, and we illustrate our theory by showing that the particular assumptions of our regularity analysis hold for the problem of identifying cracks from far field data. Numerical results using a NN for parameter recovery demonstrate the accuracy, efficiency and robustness of our approach., Comment: 3 figures

Recent work showed that small changes in benchmark questions can reduce LLMs' reasoning and recall. We explore two such changes: pairing questions and adding more answer options, on three benchmarks: WMDP-bio, GPQA, and MMLU variants. We find that for more capable models, these predictably reduce performance, essentially heightening the performance ceiling of a benchmark and unsaturating it again. We suggest this approach can resurrect old benchmarks.

Thermal light dark matter (LDM) with particle masses in the 1 MeV - 1 GeV range could successfully explain the observed dark matter abundance as a relic from the primordial Universe. In this picture, a new feeble interaction acts as a "portal" between the Standard Model and LDM particles, allowing for the exploration of this paradigm at accelerator experiments. In the last years, the "missing energy" experiment NA64e at CERN SPS (Super Proton Synchrotron) has set world-leading constraints in the vector-mediated LDM parameter space, by exploiting a 100 GeV electron beam impinging on an electromagnetic calorimeter, acting as an active target. In this paper, we report a detailed description of the analysis of a preliminary measurement with a 70 GeV positron beam at NA64e, performed during summer 2023 with an accumulated statistic of 1.6 x 10^10 positrons on target. This data set was analyzed with the primary aim of evaluating the performance of the NA64e detector with a lower energy positron beam, towards the realization of the post-LS3 program. The analysis results, other than additionally probing unexplored regions in the LDM parameter space, provide valuable information towards the future NA64e positron campaign.

Writing is a cognitively demanding task involving continuous decision-making, heavy use of working memory, and frequent switching between multiple activities. Scholarly writing is particularly complex as it requires authors to coordinate many pieces of multiform knowledge. To fully understand writers' cognitive thought process, one should fully decode the end-to-end writing data (from individual ideas to final manuscript) and understand their complex cognitive mechanisms in scholarly writing. We introduce ScholaWrite dataset, a first-of-its-kind keystroke corpus of an end-to-end scholarly writing process for complete manuscripts, with thorough annotations of cognitive writing intentions behind each keystroke. Our dataset includes LaTeX-based keystroke data from five preprints with nearly 62K total text changes and annotations across 4 months of paper writing. ScholaWrite shows promising usability and applications (e.g., iterative self-writing), demonstrating the importance of collection of end-to-end writing data, rather than the final manuscript, for the development of future writing assistants to support the cognitive thinking process of scientists. Our de-identified data examples and code are available on our project page., Comment: Equal contribution: Linghe Wang, Minhwa Lee | project page: https://minnesotanlp.github.io/scholawrite/

We give a combinatorial characterization of the identities holding in the semiring of all upper triangular Boolean $n\times n$-matrices and apply the characterization to computational complexity of identity checking, finite axiomatizability of equational theories, and algebraic descriptions of certain classes of recognizable languages., Comment: 17 pages

This memorial article for Mark Sapir provides a brief overview of his life and career. Among his many contributions we highlight two of his most celebrated achievements: his groundbreaking solutions to Burnside-type problems for semigroups and his innovative construction of S-machines. Additionally, reflections from his colleagues and friends offer a heartfelt tribute, blending professional insights with personal memories., Comment: With contributions by Victor Guba, Olga Kharlampovich, Simon M. Goberstein, Stuart W. Margolis, Lev Shneerson, John Meakin, Ilya Kapovich, Eugene Plotkin, Michael Mihalik, Samuel Corson, and Arman Darbinyan

In the $U(3) \times U(3)$ quark NJL model, $\tau$ lepton decays with the production of scalar mesons $f_0(\pi,K])$ and neutrinos are studied, where $f_0=f_0(500), f_0(980)$. It is shown that these decays mainly occur via contact channels and channels with axial-vector mesons $a_1$, $K_1(1270)$ and $K_1(1400)$. All mesons are considered as quark-antiquark states in this case. The obtained results can be considered as predictions for future experiments. The obtained estimates for the branching fractions of the $\tau \to \pi^-2\pi^0 \nu_\tau$ decay taking into account the contributions of the $\rho\pi$ and $f_0(500)\pi$ states are in satisfactory agreement with experimental data., Comment: 7 pages

Trapped ions are among the leading platforms for quantum technologies, particularly in the field of quantum computing. Detecting states of trapped ions is essential for ensuring high-fidelity readouts of quantum states. In this work, we develop and benchmark a set of methods for ion quantum state detection using images obtained by a highly sensitive camera. By transforming the images from the camera and applying conventional and quantum machine learning methods, including convolution, support vector machine (classical and quantum), and quantum annealing, we demonstrate a possibility to detect the positions and quantum states of ytterbium ions in a Paul trap. Quantum state detection is performed with an electron shelving technique: depending on the quantum state of the ion its fluorescence under the influence of a 369.5 nm laser beam is either suppressed or not. We estimate fidelities for conventional and quantum detection techniques. In particular, conventional algorithms for detecting $^{171}$Yb$^{+}$, such as the support vector machine and photon statistics-based method,as well as our quantum annealing-based approach, have achieved perfect fidelity, which is beneficial compared to standard techniques. This result may pave the way for ultrahigh-fidelity detection of trapped ions via conventional and quantum machine learning techniques.

A comprehensive diagnostics of new-generation dispersive elements based on Bragg structures was completed. The influence of inscription parameters on the properties of samples was studied and a threshold inscription intensity of ~ 6.38 TW/cm2 at which the linear absorption coefficient as well as the phase and polarization stresses sharply increase was found. When inscription is made with an average intensity below the threshold, the linear absorption in dry silica samples remains at a level of 10-5 cm-1, which is approximately two orders of magnitude lower than that of currently available commercial samples. The measured values of the dispersion characteristics using a white light interferometer coincided are in a good agreement with the calculated values provided by the manufacturer. The results of the diagnostics show that the new-generation dispersive elements are promising for compressing kilowatt-level radiation of average power., Comment: 9 pages, 8 figures

The powerful EHF radiation generated in a relativistic high-voltage pulsed magnetron of the 8 mm range is experimentally investigated. The factors that negatively affect the generation of EHF radiation are experimentally investigated and analyzed. It is determined that the processes that reduce the efficiency and duration of the generation pulse also include low pressure in the vacuum diode of the magnetron. It is known that the main residual gases in the vacuum diode of a magnetron are air components. During magnetron operation, there is a significant increase in the pressure of the residual atmosphere: hydrocarbons, water vapor, and hydrogen. A vacuum system was designed to evacuate these gases to ensure optimal operation of the magnetron. For the new vacuum system, a cryogenic condensation-adsorption pump was developed and applied, which allowed to increase the rate of pumping out the main residual gases. The peculiarity of the developed pump is that the pumping element with the adsorbent has a working surface that is twice as large as the one in the corrugated form of the sorption cartridge. Another feature of the pump is its efficiency, which is achieved through the use of nitrogen vapor for cooling the inter-wall gap. The use of cryogenic pumping means made it possible to obtain a pressure of 1E-6 Torr, which led to a 25 percent increase in the EHF radiation of the relativistic magnetron., Comment: 5 pages, 5 figures

We show a version of Qi et al. 2023's simple fine-tuning poisoning technique strips GPT-4o's safety guardrails without degrading the model. The BadGPT attack matches best white-box jailbreaks on HarmBench and StrongREJECT. It suffers no token overhead or performance hits common to jailbreaks, as evaluated on tinyMMLU and open-ended generations. Despite having been known for a year, this attack remains easy to execute.

The results of simultaneous measurements of noctilucent clouds (NLC) position in a number of ground-based locations are presented. Observational data of 14 bright NLC events over 5 years is used for building the altitude maps of cloud fields using triangulation technique updated for multi-location case. Statistical distribution of NLC altitude and its change during the summer season is considered. Mean NLC altitudes are compared with colorimetric technique based on the same data and simple radiation transfer model. This can be used to check the model and estimate the accuracy of single-camera technique of NLC altitude measurements. Results and methods are suggested for net ground-based survey of noctilucent clouds., Comment: 13 pages, 8 figures, submitted to Journal of Atmospheric and Solar-Terrestrial Physics

From 2012 to 2023, the PRISMA-32 array was in operation at the Experimental Complex NEVOD (MEPhI, Moscow). The purpose of the array was to study extensive air showers by detecting the air-shower neutron and electron-photon components using unshielded neutron detectors. To expand the capabilities of this facility, including for the study of cosmic and geophysical phenomena with a neutron flux, its upgrade was carried out. During the upgrade, a dedicated measuring channel for studying variations of the neutron background and the processes affecting these variations was created. To achieve this, the photomultipliers, the integrating amplifiers, the digitalizing electronics and the high-voltage power supply system were replaced. The paper describes the structure of the upgraded array, which was named PRISMA-36, and presents the results of studying the characteristics of the main elements of its "variation" channel. A method for identifying signals caused by neutron capture and the determined criteria for their selection are discussed. An example of a Forbush decrease, caused by a X1.1-class flare and recorded with the variation channel of the PRISMA-36 array, is given., Comment: 19 pages, 21 figures

We saturate a high-school-level hacking benchmark with plain LLM agent design. Concretely, we obtain 95% performance on InterCode-CTF, a popular offensive security benchmark, using prompting, tool use, and multiple attempts. This beats prior work by Phuong et al. 2024 (29%) and Abramovich et al. 2024 (72%). Our results suggest that current LLMs have surpassed the high school level in offensive cybersecurity. Their hacking capabilities remain underelicited: our ReAct&Plan prompting strategy solves many challenges in 1-2 turns without complex engineering or advanced harnessing.

The paper describes the application of deep neural networks for the searchdeviations from the Standard Model predictions at the Wtb vertex in the processes of single and double resonant top quark production with identical final state tWb. Monte-Carlo events preliminary classified by first level neural network as corresponding to single or double resonant top quark production are analyzed by two second level neural networks if there is a possible contribution of the anomalous right-handed vector operator into Wtb vertex or events are corresponded to the Standard Model. The second level neural networks are different for single and double resonant classes. The classes depend differently on anomalous contribution and such splitting leads to better sensitivity. The developed statistical model is used to set constraints on the anomalous right-handed vector operator at the Wtb vertex in different regions of phase space. It is demonstrated that the proposed method allows to increase the efficiency of a search for the anomalous contributions to the Wtb vertex., Comment: 10 pages, 3 figures

A new Highly-Granular time-of-flight Neutron Detector (HGND) is being developed and constructed to measure azimuthal neutron flow and neutron yields in nucleus-nucleus interactions in heavy-ion collisions with energies up to 4A GeV in the fixed target experiment BM@N at JINR. Details of the detector design and results of performance studies for neutron identification and reconstruction are shown. Comparison of simulations for different options of the HGND layout at the BM@N is presented. Several proposed methods of neutron reconstruction including machine learning and cluster methods are discussed.

It has been previously demonstrated [Panov et al. Physics of Atomic Nuclei 84(2021)1037] that the TAIGA-HiSCORE Cherenkov array, originally built for cosmic ray physics and ultrahigh-energy gamma-ray astronomy studies using the extensive air shower method, can be used in conventional optical astronomy for wide-field searches for rare nanosecond optical transients of astrophysical origin. The FOV of the facility is on the scale of 1~ster, and it is capable of detecting very rare transients in the visible light range with fluxes greater than approximately 3000~quanta/m$^2$/10~ns (10~ns is the apparatus integration time) and pulse durations of 10\,ns. Among the potential sources of distant nanosecond optical transients are the evaporation of primary black holes, magnetic reconnection in the accretion disks of black holes, and signals from distant lasers of extraterrestrial civilizations. The paper describes the methods and results of the search for optical transients using the TAIGA-HiSCORE Cherenkov array from 2018 to 2022 (four winter seasons of data collection). No reliable astrophysical candidates for optical transients were found. We set an upper bound on the flux of the searched events as $\sim 1\times10^{-3}$\,events/ster/h., Comment: 20 figures, 46 pages, submitted to Astronomy Reports

The paper proposes a new approach for approximating the lateral distribution functions (LDF) of Cherenkov light emitted by the electromagnetic component of extensive air showers (EAS) in the Earth's atmosphere. The information basis of the study is a series of simulations with the CORSIKA code. To approximate the LDF atmospheric Cherenkov light the probability density functions of one-dimensional fractional stable distributions were used. The results obtained in the work allow us to propose a fast modeling method for the CORSIKA code using a procedure similar to the Nishimura-Kamata-Greisen (NKG) for calculating the LDF of the EAS electromagnetic component., Comment: 11 pages, 2 figures, 38th All-Russian Conference on Cosmic Rays

Since its release, ImageNet-1k dataset has become a gold standard for evaluating model performance. It has served as the foundation for numerous other datasets and training tasks in computer vision. As models have improved in accuracy, issues related to label correctness have become increasingly apparent. In this blog post, we analyze the issues in the ImageNet-1k dataset, including incorrect labels, overlapping or ambiguous class definitions, training-evaluation domain shifts, and image duplicates. The solutions for some problems are straightforward. For others, we hope to start a broader conversation about refining this influential dataset to better serve future research.

Magnetic Josephson Junctions (MJJs) are a special class of hybrid systems where antagonistic correlations coexist, thus providing a key for advances in weak superconductivity, superconducting spintronics and quantum computation. So far, the memory properties of MJJs have been mostly investigated in view of digital electronics and for spintronic devices at liquid-helium temperature. At the operating temperature of quantum circuits, a magnetic order can rise in a Superconductor (S) at the S/Ferromagnet (F) interface, i.e., the inverse proximity effect (IPE), thus leading to a significant modification of the magnetic field patterns in MJJs. In this work, we have carried out a comparative investigation of the magnetic behavior of tunnel MJJs with a strong ferromagnetic layer inserted in the layout of both Nb and Al JJs, respectively. The comparative analysis validates the crucial role of the temperature, the fundamental scaling energies of S/F coupling systems, and the transparency of the S/F interface. This investigation points out that the IPE is a key aspect to consider when designing tunnel MJJs operating well below 4 K and thus in the perspective of hybrid superconducting quantum architectures., Comment: 14 pages, 4 figures, published in Low Temperature Physics

The performance of the scintillation wall (ScWall) has been studied in the first physics run at the Baryonic Matter at Nuclotron (BM@N) in Xe+CsI reaction at a xenon beam energy of 3.8 and 3.0 AGeV. The design and functionality of the ScWall emphasizing its ability to detect charged spectator fragments produced in nucleus-nucleus interactions are shown. The simulation results regarding ScWall's capability to determine collision geometry and the comparison between measured and simulated charged spectators fragments spectra are discussed.

Van der Waals (vdW) materials are becoming increasingly popular in scientific and industrial applications because of their unique mixture of record electronic, optical, and mechanical properties. However, nanostructuring of vdW materials is still in its infancy and strongly depends on the specific vdW crystal. As a result, the universal self-assembled technology of vdW materials nanostructuring opens vast technological prospects. This work demonstrates an express and universal synthesis method of vdW nanoparticles with well-defined geometry using femtosecond laser ablation and fragmentation. The disarming simplicity of the technique allows us to create nanoparticles from over 50 vdW precursor materials covering transition metal chalcogenides, MXenes, and other vdW materials. Obtained nanoparticles manifest perfectly defined crystalline structures and diverse shapes, from nanospheres to nanocubes and nanotetrahedrons. Thus, our work provides a new paradigm for vdW nanostructuring with a vast potential of tunability for size, shape, and materials specific to the particular application., Comment: 24 pages, 6 figures

We consider a generalization of the forest fire model on $\mathbb{Z}_+$ with ignition at zero only, studied in [arXiv:0907.1821]. Unlike that model, we allow delays in the spread of the fires as well as the non-zero burning time of individual ``trees''. We obtain some general properties for this model, which cover, among others, the phenomena of an ``infinite fire'', not present in the original model.

This paper presents the multiplicity of neutral and charged hadrons produced in 90 GeV$/c$ proton-carbon interactions from a dataset taken by the NA61/SHINE experiment in 2017. Particle identification via dE/dx was performed for the charged hadrons $\pi^\pm$, $K^\pm$, and $p / \bar{p}$; the neutral hadrons $K^0_S$, $\Lambda$, and $\bar{\Lambda}$ were identified via an invariant mass analysis of their decays to charged hadrons. Double-differential multiplicity results as a function of laboratory momentum and polar angle are presented for each particle species; these results provide vital constraints on the predicted neutrino beam flux for current and future long-baseline neutrino oscillation experiments.

The decay widths of $V \to K(\pi) l \bar{\nu}_l $ are calculated within the Nambu--Jona-Lasinio model, where $V=K^*, \rho, \omega, \phi$ and $l=\mu, e$. The results are obtained using the previously fixed model parameters without introducing any arbitrary parameters. The obtained results are considered as predictions due to the absence of experimental data., Comment: 7 pages, 2 figures

We present the first complete two-loop calculation of the electric dipole moment of the electron, as well as the rates of the lepton-flavor violating decays $\mu \to e + \gamma$ and $\tau \to e/\mu + \gamma$, in the unconstrained two-Higgs doublet model. We include the most general Yukawa interactions of the Higgs doublets with the Standard Model fermions up to quadratic order, and allow for generic phases in the Higgs potential. A python implementation of our results is provided via a public git repository., Comment: 22 pages, 5 figures; corrected typos, extended discussion, added link to python implementation of results

Attacks powered by Large Language Model (LLM) agents represent a growing threat to modern cybersecurity. To address this concern, we present LLM Honeypot, a system designed to monitor autonomous AI hacking agents. By augmenting a standard SSH honeypot with prompt injection and time-based analysis techniques, our framework aims to distinguish LLM agents among all attackers. Over a trial deployment of about three months in a public environment, we collected 8,130,731 hacking attempts and 8 potential AI agents. Our work demonstrates the emergence of AI-driven threats and their current level of usage, serving as an early warning of malicious LLM agents in the wild.

The paper is concerned with the development of Lyapunov methods for the analysis of equilibrium stability in a dynamical system on the space of probability measures driven by a non-local continuity equation. We derive sufficient conditions of stability of an equilibrium distribution relying on an analysis of a non-smooth Lyapunov function. For the linear dynamics we reduce the stability analysis to a study of a quadratic form on a tangent space to the space of probability measures. These results are illustrated by the studies of the stability of the equilibrium measure for gradient flow in the space of probability measures and Gibbs measure for a system of coupled mathematical pendulums.

Thanks to their record high refractive index and giant optical anisotropy, van der Waals (vdW) materials have accelerated the development of nanophotonics. However, traditional high refractive index materials, such as titanium dioxide (TiO2), still dominate in the most important visible range. This is due to the current lack of transparent vdW materials across the entire visible spectrum. In this context, we propose that germanium disulfide (GeS2) could offer a significant breakthrough. With its high refractive index, negligible losses, and biaxial optical anisotropy across the whole visible range, GeS2 has the potential to complement TiO2 and close the application gap of vdW materials in the visible spectrum. The addition of GeS2 could have a profound impact on the design of van der Waals nanophotonic circuits for any operation wavelength from ultraviolet to infrared, emphasizing the significance of the potential impact of GeS2 on the field of nanophotonics., Comment: 15 pages, 4 figures

A search for Dark Sectors is performed using the unique M2 beam line at the CERN Super Proton Synchrotron. New particles ($X$) could be produced in the bremsstrahlung-like reaction of high energy 160 GeV muons impinging on an active target, $\mu N\rightarrow\mu NX$, followed by their decays, $X\rightarrow\text{invisible}$. The experimental signature would be a scattered single muon from the target, with about less than half of its initial energy and no activity in the sub-detectors located downstream the interaction point. The full sample of the 2022 run is analyzed through the missing energy/momentum channel, with a total statistics of $(1.98\pm0.02)\times10^{10}$ muons on target. We demonstrate that various muon-philic scenarios involving different types of mediators, such as scalar or vector particles, can be probed simultaneously with such a technique. For the vector-case, besides a $L_\mu-L_\tau$ $Z'$ vector boson, we also consider an invisibly decaying dark photon ($A'\rightarrow\text{invisible}$). This search is complementary to NA64 running with electrons and positrons, thus, opening the possibility to expand the exploration of the thermal light dark matter parameter space by combining the results obtained with the three beams., Comment: 24 pages, 22 figures

We present the first results from a proof-of-concept search for dark sectors via invisible decays of pseudoscalar $\eta$ and $\eta'$ mesons in the NA64h experiment at the CERN SPS. Our novel technique uses the charge-exchange reaction of 50 GeV $\pi^-$ on nuclei of an active target as the source of neutral mesons. The $\eta, \eta' \to invisible$ events would exhibit themselves via a striking signature - the complete disappearance of the incoming beam energy in the detector. No evidence for such events has been found with $2.9\times10^{9}$ pions on target accumulated during one day of data taking. This allows us to set a stringent limit on the branching ratio ${\rm Br}(\eta' \to invisible) < 2.1 \times 10^{-4}$ improving the current bound by a factor of $\simeq3$. We also set a limit on ${\rm Br}(\eta \to invisible) < 1.1 \times 10^{-4}$ comparable with the existing one. These results demonstrate the great potential of our approach and provide clear guidance on how to enhance and extend the sensitivity for dark sector physics from future searches for invisible neutral meson decays., Comment: 5 pages, 3 figures

The Spin Physics Detector collaboration proposes to install a universal detector in the second interaction point of the NICA collider under construction (JINR, Dubna) to study the spin structure of the proton and deuteron and other spin-related phenomena using a unique possibility to operate with polarized proton and deuteron beams at a collision energy up to 27 GeV and a luminosity up to $10^{32}$ cm$^{-2}$ s$^{-1}$. As the main goal, the experiment aims to provide access to the gluon TMD PDFs in the proton and deuteron, as well as the gluon transversity distribution and tensor PDFs in the deuteron, via the measurement of specific single and double spin asymmetries using different complementary probes such as charmonia, open charm, and prompt photon production processes. Other polarized and unpolarized physics is possible, especially at the first stage of NICA operation with reduced luminosity and collision energy of the proton and ion beams. This document is dedicated exclusively to technical issues of the SPD setup construction.

The inclusion of an additional $U(1)$ gauge $L_\mu-L_\tau$ symmetry would release the tension between the measured and the predicted value of the anomalous muon magnetic moment: this paradigm assumes the existence of a new, light $Z^\prime$ vector boson, with dominant coupling to $\mu$ and $\tau$ leptons and interacting with electrons via a loop mechanism. The $L_\mu-L_\tau$ model can also explain the Dark Matter relic abundance, by assuming that the $Z'$ boson acts as a "portal" to a new Dark Sector of particles in Nature, not charged under known interactions. In this work we present the results of the $Z'$ search performed by the NA64-$e$ experiment at CERN SPS, that collected $\sim 9\times10^{11}$ 100 GeV electrons impinging on an active thick target. Despite the suppressed $Z'$ production yield with an electron beam, NA64-$e$ provides the first accelerator-based results excluding the $g-2$ preferred band of the $Z'$ parameter space in the 1 keV $ < m_{Z'} \lesssim 2$ MeV range, in complementarity with the limits recently obtained by the NA64-$\mu$ experiment with a muon beam., Comment: 15 pages, 5 figures. New version with extended exclusion limits down to 1 keV in Z' mass

We present results of atomic-level simulations of damage formation along the paths of swift heavy ions (SHI) decelerated in the electronic stopping regime in amorphous polyethylene. The applied model combines the Monte-Carlo code TREKIS-3, which describes excitation of the electronic and atomic systems around the ion trajectory, with molecular dynamics simulations of the response of the atomic system to the excitation. The simulation results were used to reconstruct the damage configuration, shape and size of the damaged region. We demonstrated that the positions of the maximum energy loss and maximum damage on the ion trajectory do not coincide, being separated by more than 10 micrometers. The difference between the thresholds of damage production by ions with energies realizing the opposite shoulders of the Bragg curve of the electronic stopping was found. We also analyzed the spatial distribution of chemically active fragments of polyethylene chains formed around the ion trajectory as a function of SHI energy.

We exhibit a winning strategy for Synchronizer in the synchronization game on every synchronizing automaton in whose transition monoid the regular D-classes form subsemigroups, Comment: In Proceedings NCMA 2024, arXiv:2409.06120

Kolmogorov-Arnold Networks represent a recent advancement in machine learning, with the potential to outperform traditional perceptron-based neural networks across various domains as well as provide more interpretability with the use of symbolic formulas and pruning. This study explores the application of KANs to specific tasks in high-energy physics. We evaluate the performance of KANs in distinguishing multijet processes in proton-proton collisions and in reconstructing missing transverse momentum in events involving dark matter., Comment: 5 pages, 6 figures

Most general dynamics of an open quantum system is commonly represented by a quantum channel, which is a completely positive trace-preserving map (CPTP or Kraus map). Well-known are the representations of quantum channels by Choi matrices and by Kraus operator-sum representation (OSR). As was shown before, one can use Kraus OSR to parameterize quantum channels by points of a suitable quotient under the action of the unitary group of some complex Stiefel manifold. In this work, we establish a continuity relation (homeomorphism) between the topological space of quantum channels and the quotient of the complex Stiefel manifold. Then the metric on the set of quantum channels induced by the Riemannian metric on the Stiefel manifold is defined. The established relation can be applied to various quantum optimization problems. As an example, we apply it to the analysis of extrema points for a wide variety of quantum control objective functionals defined on the complex Stiefel manifolds, including mean value, generation of quantum gates, thermodynamic quantities involving entropy, etc., Comment: 21 pages

Two-dimensional materials have attracted considerable attention due to their remarkable electronic, mechanical and optical properties, making them prime candidates for next-generation electronic and optoelectronic applications. Despite their widespread use in combination with substrates in practical applications, including the fabrication process and final device assembly, computational studies often neglect the effects of substrate interactions for simplicity. This study presents a novel method for predicting the atomic structure of 2D materials on arbitrary substrates by combining an evolutionary algorithm, a lattice-matching technique, an automated machine learning interatomic potentials training protocol, and the ab initio thermodynamics approach for predicting the possible conditions of experimental synthesis of the predicted 2D structures. Using the Mo-S system on a c-cut sapphire substrate as a case study, we reveal several new stable and metastable structures, including previously known 1H-MoS2 and newly found Pmma Mo3S2, P-1 Mo2S, P21m Mo5S3, and P4mm Mo4S, where the Mo4S structure is specifically stabilized by interaction with the substrate. Electronic band structure calculations of Mo3S2, Mo2S, Mo5S3, and Mo4S showed their metallic behavior, while phonon properties calculations indicated their dynamic stability and substrate-induced modulation of the phonon density of states. Finally, we use the ab initio thermodynamics approach to predict the synthesis conditions of the discovered structures in the parameter space of the commonly used CVD technique. These results provide insights into computational substrate engineering, allowing one to study the substrate effect on the thermodynamic and dynamical stability of 2D materials and to modulate their electronic and phonon properties for their future applications, as well as to provide guide maps for their experimental synthesis.

In the context of simplified models of dark matter, the contributions of a scalar mediator to top quark production processes are considered. Tree-level and one-loop contributions of the mediator's decay into a top-antitop quark pair in two-, three-, and four-top quarks production processes are calculated. A significant contribution from diagrams involving the dark matter mediator is demonstrated in the total cross section for three- and four-top quark production processes, taking into account current experimental limits on model parameters. The perspective of searching for dark matter mediators in the processes under consideration is determined by the ability to reconstruct the final state with modern collider detectors and the experimental sensitivity that has already been achieved for such rare events., Comment: 11 pages, 2 figures, 6 tables

It is shown that the processes $e^+ e^- \to \pi^+ \pi^-$ and $\tau^- \to \pi^- \pi^0 \nu_\tau$ can be described in a unified approach in satisfactory agreement with experiment using the vector coupling constant $g_{\rho} = 6$. In this case, in addition to quark loops, it is also necessary to take into account meson loops corresponding to the next order in $1/N_c$. These loops must be taken into account when describing the $\gamma (W) \to \rho$ transition, as well as in interaction of mesons in the final state., Comment: 10 pages, 9 figures

Superconductor/ferromagnet/superconductor Josephson junctions are paradigmatic systems for studying the delicate interplay of superconductivity and magnetism via proximity effects as well as their composite excitations. Here, we analyse the collective modes (CM) in such a heterostructure by taking into account the interplay between the de-magnetisation field $H_{dem}$ and the field caused by the anisotropy of the ferromagnet $H_{an}$, which was previously neglected. It turns out that the spectrum of composite collective modes, $\omega(k)$, has a qualitatively different form in the case of $H_{dem}H_{an}$. In the first case, the dependence $\omega(k)$ has the same form as in previous studies, whereas in the second case, the spectrum looks completely different. In particular, for moderate or weak anisotropy in ferromagnet the group velocity of collective modes demonstrates inflection point where the group velocity become infinite and is superluminal. Furthermore, this point separates purely real and complex-conjugate solutions for the collective modes and is also {\it exception point}. We show that the difference of the CMs spectra can be revealed by Fiske experiment, i.\,e.\,by measuring the $I-V$ characteristics in the presence of magnetic field and voltage., Comment: 7 pages, 3 figures