Papers

Continuous measurements play a fundamental role in quantum experiments, yet understanding and extracting the maximal possible information in a continuous probe signal remains a significant challenge. In this work, we show that for a wide class of sensors, the quantum Fisher information bound can be saturated through a combined measurement of signals from the original sensor and a suitable system copy. We elucidate the physical mechanism of such a twin-field sensor (TFS) and study its performance across diverse implementations, ranging from two-level atoms to a hybrid quantum Rabi model. In all of these cases, we find that simple photon counting or homodyne detection saturates the theoretical quantum limit. We further prove that the TFS achieves the quantum limits for the joint sensing of pairs of parameters as quantified by the quantum Fisher information matrix.

We compute the large overtone quasinormal frequencies $\omega_n$ of asymptotically AdS black holes with interior near-singularity Kasner epochs. We show that the Kasner exponents can be extracted cleanly from the large $n$ behaviour of the dispersion $\partial \omega_n/\partial k^2$ at $k=0$, where $k$ is a boundary momentum. We show that Kasner transitions, as occur in BKL near-singularity chaos, are audible in the quasinormal frequencies and reveal a map between overtone number $n$ and proper time to the singularity. Our results are obtained using a WKB analysis that isolates non-analytic exponents, determined by the near-singularity spacetime, from non-universal data such as the optical distance from the boundary to the singularity. We check our formulae in several numerical models.

The discovery of superconductivity in bulk bilayer nickelates has established a new platform for exploring high-$T_c$ superconductivity beyond the cuprates. The role of the Ni $3d_{z^2}$-derived $\gamma$ band in the superconductivity of bilayer nickelates remains unresolved. By performing simultaneous resistance and diamagnetism measurements on (La,Pr)$_3$Ni$_2$O$_7$ thin films, we map the vortex melting phase diagram for both in-plane and out-of-plane magnetic fields. For $H\parallel c$, the geometric confinement effect gives rise to pancake vortices. Remarkably, the anisotropy parameter of the vortex melting field $\gamma_{H_m} \equiv H_m^{ab}/H_m^c$ decreases monotonically with decreasing temperature and approaches unity at low temperatures. Within the anisotropic Ginzburg–Landau scaling, $H_m^{ab}/H_m^c = \sqrt{\rho_s^{ab}/\rho_s^c}$ tracks the superfluid-density anisotropy. Such a vortex solid implies a nearly isotropic superfluid density, which is irreconcilable with the strictly two-dimensional $3d_{x^2-y^2}$-derived bands, but naturally explained by a substantial interlayer superfluid contribution from the $3d_{z^2}$-derived $\gamma$ band. Our results provide thermodynamic evidence for a substantial contribution of the $\gamma$ band to superconductivity in bilayer nickelate thin films.

A general scheme of evolution from autocatalytic processes to socio-technological system is discussed from the perspective of maximum energy dissipation principle. The scheme treats the emergence of biological systems as an initial stage in the acceleration of global free energy dissipation. The sequential emergence of qualitatively new levels of organisation (biological cell, multicellular organism, social system) has been proposed, the levels are suggested as the results of cooperation (symbiosis) of the dissipative systems at the previous levels. The cooperation/symbiosis provides sufficient complexity for development of the next, essentially a new level of energy dissipation, leading to a new form of free energy utilization and a new form of information mapping. From a thermodynamic perspective, every qualitatively new level of biological organisation provides an additional step to increase the rate of energy dissipation from qualitatively new sources, essentially widening the number of these sources involved in the utilization.

A common formalization of homeostasis is the free energy principle, a framework that defines a set of desired observation values, or critical states, that the agent should reach or remain close to. Under the free energy principle, an agent should act to maximize the probability of receiving the desired observations. Here we revisit the common approach of solving the problem of maximizing the log probability of the desired observations by maximizing a variational lower bound, the so-called negative free energy. We show that, instead, an approach directly maximizing that probability under the agent's policy is better suited to, and provides a better solution for, the original homeostatic control problem. This is done using hidden Markov model (HMM) control by allowing the policy to act over hidden states or noisy versions thereof while trying to maximize the probability of repeatedly having the desired observations. HMM control largely improves performance over the variational, or free energy, approach. We also show that the optimal policy is strictly deterministic, while the variational approach leads to a stochastic policy approximation. We finally provide a homeostatic reinterpretation of the maximum occupancy principle -a principle proposing that agents ought to maximize the occupancy of action-state path space -by defining homeostatic states as any states that do not immediately entail the termination or death of the agent.

The quantum mechanical problem of a particle in a infinite potential well with slanted walls is studied. The energy eigenvalues are determined by a transcendental equation involving the Airy function of the first kind. Two limiting cases are discussed. Next, the allowed energies are found by graphical and numerical methods. The graphical analysis hints that for large quantum numbers the consecutive energy levels get arbitrarily close together. This asymptotic behavior of the energy spectrum actually holds, as shown by means of an intuitive argument and confirmed by resorting to basic properties of Airy functions. In a sense, Bohr's correspondence principle is more accurately fulfilled than in the cases of the standard particle in a box or the harmonic oscillator. A state is regarded the more confined the less the probability of finding the particle in the classically forbidden region. For some stationary states the confinement degree is calculated and a comparison is made with the harmonic oscillator, for which the ground state is the least confined of all stationary states. In the symmetric case — right and left walls of equal slope — something unexpected happens: beyond a certain critical slope the ground state is no longer the least confined eigenstate. Over and above its interesting physical features, this problem provides students with the opportunity to get acquainted with Airy functions, which do not belong to the standard mathematical repertoire of physics undergraduates.

In this work, we introduced a positive viscosity coefficient into Newtonian dynamics to explore the rotational properties of disk galaxies. Our results show that the rotational behaviors of disk galaxies predicted by this modified Newtonian dynamics share notable similarities with those from the well-known MOND model. Specifically, the modified framework naturally recovers the deep-MOND limit postulated in MOND. Furthermore, we derived an explicit interpolation function relating centripetal acceleration to Newtonian acceleration-a relation that is purely empirical within the MOND model. We also identify key differences from MOND: the critical acceleration a0, regarded as a universal constant in MOND, actually varies with galactic mass and increases for more massive galaxies. Additionally, driven by the anti-dissipation effect of the viscosity coefficient, disk galaxies undergo extremely slow radial expansion over cosmic time, analogous to the expansion of the Universe. But regrettably, the fundamental physical origin of the viscosity coefficient introduced here remains unclear for us. But relevant hints can be found in existing literature, pointing to a promising direction for our future research.

The evolution of DNA sequences can be viewed as stochastic dynamics on a high-dimensional discrete space, but it is unclear when empirical transition biases reduce to an effective energy landscape versus retain irreducible non-equilibrium circulation. Human context-dependent mutation probabilities offer a direct test: every single-nucleotide substitution in a local context has a reverse substitution, so the logarithm of the forward-to-reverse probability ratio defines an antisymmetric field-the human mutation field. We show this field has a dominant gradient component and a smaller but reproducible curl component. Using seven-base human germline substitution probabilities, we infer an effective mutational landscape with a Siamese neural network constrained to predict only energy differences. This model predicts forward-to-reverse log-ratios for held-out mutations with a correlation of about 0.93, close to both an unconstrained predictive reference (0.948) and the empirical reversible ceiling from Hodge projection (about 0.96). Although trained only on mutation probabilities, the inferred landscape largely recovers short-word genomic composition and Chargaff reverse-complement symmetry for sequences up to length four. Deviations from equilibrium structure reveal a small but detectable nonequilibrium component: a residual irreversible circulation violating the Kolmogorov cycle condition for detailed balance, reproducible across African, Asian, and European populations, and strongest in CpG-linked cycles and CpG-transition edges, consistent with methylcytosine deamination. These results give a thermodynamic decomposition of the human mutation field: most mutation bias is organized by a local equilibrium-like energy landscape aligned with genome composition, while the residual circulation points to specific directional mutational mechanisms.

Active systems navigate complex environments through non-equilibrium fluctuations, rendering standard equilibrium transition-rate theories inadequate. Moreover, transition rates provide only partial information on how stochastic dynamics explore metastable states, whereas knowledge of the optimal paths offers deeper physical insight. Using an active Ornstein-Uhlenbeck particle, i.e., a particle driven by exponentially correlated noise, as a paradigmatic model, we establish an exact mapping of the non-Markovian optimal path onto a higher-dimensional Hamiltonian dynamical system so that, for arbitrary force fields, optimal paths can be computed systematically by solving the corresponding Hamilton equations. Tuning the conserved energy allows us to explore diverse dynamical regimes, ranging from classical instanton trajectories strictly confined to the zero-energy surface to finite-time optimal paths at non-zero energies, which can spiral around shoulders of the energy landscape, a distinct signature of the non-Markovian active dynamics.

We obtain the singular ”mother” black hole solution by solving the coupling between Einstein gravity with a cosmological constant and a nonlinear electromagnetic field. The thermodynamic quantities of the ”mother” black hole are first derived in the unconstrained phase space $(S, q, \alpha, P)$, after which the regularity condition $M = q^3/\alpha$ is imposed to obtain the thermodynamic quantities of a class of spherically symmetric AdS regular black holes self-consistently. We distinguish two categories of thermodynamic quantities: fundamental conjugate variables defined by the first law, and thermodynamic response functions constructed from them. For response functions involving second-order derivatives – in particular the heat capacity – we show that the order of constraint imposition and derivative calculation cannot be interchanged, and the correct procedure is to first impose the constraint and then construct the response function. Within this framework, we find that when $P<P_c$, the $G$–$T$ diagram exhibits a behavior qualitatively different from the swallowtail behavior of the standard RN-AdS black hole. Instead, it exhibits an 8-shaped structure for $P<P_z$ and a C-shaped structure for $P_z<P<P_c$, corresponding to first-order and zeroth-order phase transitions between small and large black hole phases, respectively. Imposing the regularity condition thus leads to a richer phase structure for this class of black holes than the standard RN-AdS case.

We numerically investigate the long-time intra-cavity-field dynamics of a periodically pump- modulated pair of coherently coupled Kerr micro-ring resonators. Along a detuning scanning, fixed-phase stroboscopic trajectories change from recurrent regular state to states with positive maximum-Lyapunov growth. Long observation windows near the transition, where finite-time estimates converge slowly. The low- and high-detuning states both retain multi-mode Kerr-comb spectra, while their cycle-to-cycle field organization changes much more strongly. Spatiotemporal intensities, adjacent-cycle profiles, and full-field recurrence measures show a loss of one-period recurrence together with changes in the inter-resonator phase relation, coherent exchange, and dispersive intensity flow. We linearize the coupled equations around the long-time field and examine the growth of an infinitesimal perturbation. The resulting tangent-energy balance shows that the loss contribution changes little along the scanning, whereas the Kerr contribution increases and exceeds the loss magnitude in the high-detuning states with positive Lyapunov growth. A separate dimensional correspondence relates the normalized working range to Si3N4 micro-ring. These results provide a field-resolved description of the long-time dynamical change and its associated perturbation growth.

As is already known, there is a correspondence between circle patterns and the dimer model, which is invariant under Euclidean transformations. We establish a new correspondence that is invariant under the group of Möbius transformations PO(3,1), which is the natural symmetry group of circle patterns. We show that Miquel dynamics preserve the partition function, and that convexity of the t-embedding guarantees positivity of the face weights. We also show that the correspondence has a somewhat hidden symmetry group PO(3,3), which relates to the Lorentz lift of the t-embedding. Finally, we consider isoradial graphs, Doyle spirals, the once-punctured torus and isothermic circle patterns.

Recent developments of universal machine learning interatomic potentials (UMLIPs) offer a fast route for screening molecular crystals based on geometry relaxation and energy ranking, but their reliability across chemically diverse energetic materials remains elusive. In particular, it is unclear whether or not these UMLIPs are over-sensitive to break the desired molecular connectivity for relaxing the periodic crystals. Herein we tested the hypothesis that classical force-field pre-relaxation can provide a more suitable starting geometry for subsequent UMLIP relaxation on a large database of high energy molecular crystals. Three models (MACE, MACE-OFF and UMA) in conjunction with the General Amber Force Field (GAFF) were applied to test this hypothesis. Among them, direct MACE-OFF and UMA showed very high relaxation success and preserved the reference geometries most closely, but they still exhibit failures for some rare cases. Using GAFF pre-relaxation can systematically reduce the number of failed relaxations with lower computational costs. Our comparative failure and robustness analyses revealed distinct trade-offs among the evaluated models. Among them, MACE-OFF achieves a better compromise between potential energy surface smoothness, structural fidelity, and stress convergence, serving as a good choice to provide a reliable foundation for automated structural optimization.

This research proposes a model-free inverse approach for identifying the nonlinear anisotropic single-valued magnetic constitutive characteristics of soft magnetic materials from boundary measurements. Using the harmonic approximation, the internal magnetic flux density B and magnetic field strength H are independently reconstructed from the measured boundary data, thus avoiding the limitation of using a predefined parametric B–H mapping function. Subsequently, the reconstructed fields are spatially averaged along selected collection lines to recover the B–H characteristics of the principal directions. Numerical results demonstrate high reconstruction accuracy for unperturbed data and good robustness against Gaussian perturbations of the boundary measurements, with the overall mean error remaining below 5% for a 10% noise level. These results indicate that under the harmonic-field assumptions, the field-based reconstruction provides a simple and computationally efficient framework for non-invasive identification of nonlinear anisotropic magnetic constitutive characteristics.

This work presents a comparative analysis of Reduced-Order Models (ROMs) applied to incompressible fluid dynamics within geometrically parametrized domains. Two distinct reduced-order solution strategies are investigated and compared: a monolithic coupled solver and a segregated SIMPLE-based algorithm. Their performance is assessed on two steady, two-dimensional benchmark cases: a lid-driven cavity flow and a flow past a cylindrical obstacle. The two algorithms are compared in terms of fields evaluation and aerodynamic coefficients prediction. The computational results highlight a fundamental trade-off between accuracy and numerical efficiency. On the one hand, after an opportune supremizers enrichment, the coupled approach guarantees a faster convergence, despite the need of a larger number of degrees of freedom. On the other hand, the segregated SIMPLE algorithm yields superior reconstruction accuracy, particularly for lower-dimensional reduced spaces, at the cost of a slower convergence rate.

We present a multiwavelength study of the massive star formation region IRAS 16119-5048 (I16119) using ALMA ATOMS Band 3 and QUARKS Band 6 observations, complemented by archival ATCA radio continuum and Spitzer mid-infrared data. The CO (2-1) emission reveals a system of high-velocity streamer-like structures around the central region. Using dendrogram analysis of velocity-channel maps followed by linking in position-position-velocity space, we identify 16 approximately radially distributed streamers whose projected trajectories converge toward a common central region. The kinetic energy of the outflows is at least an order of magnitude lower than those of most known explosive outflows, while their mass entrainment and momentum rates are high compared with typical protostellar outflows, suggesting that I16119 may represent a low-energy explosive outflow candidate. Dense-gas and photodissociation-region tracers reveal shell-like structures associated with the 8 $\mu$m emission, indicating that feedback from the H II region may influence the streamer morphology. The 1.3 mm continuum resolves 27 dense cores along a fragmented filamentary structure. Their separations are consistent with thermal Jeans or cylindrical fragmentation, while the collect-and-collapse scenario is unsupported. The dense cores also show evidence of mass segregation, with the most massive cores concentrated near the inferred explosive centre. We suggest that I16119 is a plausible low-energy explosive outflow candidate, possibly triggered by dynamical interactions among centrally concentrated massive cores. However, the complex velocity structure and possible contamination from individual core-driven outflows prevent a definitive classification. More sensitive, higher angular-resolution observations are required to confirm the nature of the outflow.

Weak sphaleron transitions turn a lepton asymmetry of the Standard Model plasma in the early Universe into a baryon asymmetry, conserving baryon-minus-lepton number $B-L$ and its individual flavored charges. A baryon asymmetry can thus also arise from flavored lepton asymmetries with vanishing $B-L$. Standard equilibrium calculations in the symmetric and broken phases are performed at constant temperature and hence neglect the fact that both the Higgs expectation value and the sphaleron rate vary as functions of temperature across the electroweak crossover. We derive a Boltzmann equation for the baryon number evolution across the crossover and calculate the freeze-out abundance including higher-order corrections to both the grand canonical partition function and the perturbative Higgs expectation value. This yields two sphaleron conversion factors: $C_\text{sph} = 0.3328(5)$ for $B-L$ and $\mathcal{F}_\text{sph} = 0.0279(19)$ for the flavored charges weighted by the charged-lepton Yukawa couplings.

Optical nanofibers fabricated using a standard oxyhydrogen flame exhibit optical losses at wavelengths around 1385~nm due to absorption by embedded hydroxyl groups, posing a challenge for the realization of quantum electrodynamics systems using ytterbium atoms. Here, we establish a method for the reduction of hydroxyl groups by heating them with a laser guided within the optical nanofiber under vacuum conditions. The temperature of the optical nanofiber during heating is estimated by monitoring the phase shift of the transmitted light using an interferometer. As a result, evidence suggesting that hydroxyl groups were desorbed by laser heating was obtained.

We study the use of graph neural networks (GNNs) for finding approximate ground states of Ising models. Efficiently finding these ground states is of broad significance because many combinatorial optimization problems can be formulated as an Ising model with the appropriate choice of couplings and fields. Exactly solving these problems is hard but there are many good heuristic methods. A lineage of these heuristics build from mean-field approximations: one approach uses the leading eigenvector of an appropriately defined matrix, another is the min-sum algorithm, also known as the energetic cavity method. Without modification, GNNs perform worse than both of these methods. We consider small modifications to the GNN to incorporate these heuristics and find that this considerably improves performance. While the modified approach is competitive against other deep-learning approaches, we still find that simulated annealing is reliably at least as good as deep learning methods for the same computational cost.

We propose a scheme for generating high-purity fluorescence two-photon bundles from two spatially separate two-level emitters, whose correlated excitation is mediated by a strongly driven auxiliary emitter. Unlike bosonic-mode-based approaches, the finite excitation space of the two target emitters intrinsically excludes higher-excitation manifolds, and thus eliminates impurity photons associated with undesired higher-excitation states. We further analytically characterize the residual population of off-resonant single-excitation states and show that suppressing the corresponding leakage improves photon bundle purity. Our scheme offers a feasible pathway for constructing high-purity quantum light sources with promising applications in quantum information processing.

Linear response theory provides essential information regarding the excitations of many-body systems, such as atomic nuclei. It yields ground state transition probabilities, or strength functions, from which reaction rates and cross-sections can be derived. These quantities are for example a critical input for astrophysical simulations and modelling of beta-decay. Currently, the most general theoretical framework for modelling global nuclear properties is Energy Density Functional (EDF) theory. Modern approaches for linear response employ the quasiparticle random-phase approximation (QRPA) on top of a mean-field vacuum. This can be done by using conventional matrix QRPA formulations, but can be sped up substantially by using the finite amplitude method (FAM). Nevertheless, obtaining highly-resolved response functions over the complete nuclear chart remains computationally demanding, which limits large-scale applications. This work introduces a Reduced Order Modeling (ROM) approach to emulate Finite Amplitude Method (FAM-QRPA) calculations, significantly reducing the computational cost of obtaining nuclear response functions. By employing a 2D-greedy strategy to interpolate from a small set of snapshots, the emulator achieves a x20 speed-up while maintaining high accuracy across various nuclei, operators, and energy density functionals (EDFs). A second objective of this work is to investigate the correlation between the infinite nuclear matter incompressibility and the ISGMR centroid position of Pb-208, specifically for EDF forms and parametrisations developed in Brussels: the BSk(G)-family. Our results indicate that the correlation does not persist.

The quasiparticle random phase approximation or QRPA has been a foundational many-body technique for decades across quantum chemistry, condensed matter and nuclear physics. Although computing power has increased and the matrix-free Finite Amplitude Method (FAM) exists, the computational complexity of FAM-QRPA calculations remains a limiting factor for the generation of linear response data on atomic nuclei that are crucial for several research fields. In this work, we establish that the FAM-QRPA equations are inherently suited to a reduced order modelling framework and can be emulated efficiently. Moreover, we present a greedy snapshot selection strategy that leverages the reduced cost of FAM-QRPA calculations when the imaginary part of the excitation frequency is large. Even when accounting for its construction, the resulting emulator accelerates strength function calculations by significantly more than an order of magnitude. We demonstrate that this framework and its speed-up generalize to light and heavy nuclei, different numerical representations, and diverse nuclear models including chiral EFT and configuration-interaction shell model approaches, as well as Skyrme, Gogny, and relativistic energy density functionals.

We study the possibility of explaining the recently reported high-energy nuclear recoil event by the LUX-ZEPLIN (LZ) collaboration within the framework of singlet-doublet scalar dark matter (DM). Considering DM to be the CP even mass eigenstate formed out of a scalar doublet and a real scalar singlet, both being odd under an unbroken $Z_2$ symmetry, we find the parameter space of the model consistent with correct relic abundance and direct-detection limits on elastic scattering rates. A large part of the parameter space can also lead to inelastic up-scattering of DM with a rate and recoil energy consistent with the recent LZ event. Depending upon the singlet-doublet mixing, the model allows a much wider range of currently allowed parameter space compared to the pure scalar doublet DM limit, which is disfavored due to non-observations of high-energy neutrinos from solar-captured DM annihilation by the IceCube experiment. Presence of $Z_2$-odd right-handed neutrinos also leads to other interesting phenomenology related to the origin of light neutrino masses and leptogenesis.

We begin with a general question: how does the irreducible mass of a magnetized black hole change when the horizon is not stationary? The null Raychaudhuri equation gives an exact area balance for any smooth null horizon, without assuming stationarity or axisymmetry. When the horizon is axisymmetric and admits an integrable quasilocal Hamiltonian, this geometrical identity becomes an energy balance. The equation keeps area growth, rotational and electromagnetic work, nonstationary focusing, canonical-flux corrections, and internal-boundary terms separate. We then turn to Wang's self-gravitating split-monopole Blandford-Znajek engine. In the weak-field and slow-rotation regime, P/M_H\ll1 and a/M_H\ll1, our general balance reproduces Wang's mass- and angular-momentum loss rates. The irreducible mass, M_{irr}=\sqrt{A_H/(16\pi)}, reveals what those rates do not show by themselves. It measures the part of the rotational work absorbed irreversibly by the horizon. At fixed magnetic flux and under impedance matching, half of the instantaneous rotational work leaves as electromagnetic power. The other half increases the horizon area and M_{irr}. The assumptions behind this reduction are derived explicitly. A minimal nondissipative world-volume action makes the current-sheet contribution vanish through O(p^2\epsilon^2). Direct power counting of Wang's perturbative fields, together with a compatible canonical-flux prescription, gives a relative focusing and canonical correction of O(p^2)+O(\epsilon^2). These estimates mark the range in which the reduced Blandford-Znajek trajectory remains controlled. Extending that trajectory to high spin requires an additional extrapolation. Relating the quasilocal horizon loss to energy measured at infinity requires a separate asymptotic flux calculation.

Carbyne, the sp-hybridized one-dimensional allotrope of carbon, is predicted to be the stiffest known material, with electronic and optical properties set by a single structural parameter, the bond length alternation. However, its intrinsic properties have never been measured: chains synthesized through molecular chemistry carry endgroup and finite-length perturbations that persist even in the longest molecules available, while chains grown inside carbon nanotubes strongly couple to the host, which renormalizes their vibrational frequency by up to 110 cm$^{-1}$ in a diameter-dependent manner. Here, we show that encapsulating and thermally converting hydrogen-capped polyynes inside ultrathin boron nitride nanotubes, structural analogues of carbon nanotubes but electrically insulating, yields carbyne chains in a near-ideal regime, where endgroup, finite length, and host-guest perturbations are reduced to secondary effects. Statistical Raman spectroscopy across 245 locations returns a vibrational frequency distribution an order of magnitude narrower than in carbon nanotubes, an anharmonicity consistent with the universal law for carbyne-like materials, and a bond length alternation matching correlated calculations for the free chain. No photoluminescence is detected, despite the transparent host, as expected for the dipole-forbidden emission of an unperturbed carbyne chain. Boron nitride nanotubes give experimental access to carbyne in its near-ideal form.

Short-lived hadron resonances serve as sensitive probes of the late-stage hadronic medium in heavy-ion collisions. Using the AMPT-HC model, we study ${\rm{K}}^{*}(892)$ production and its hadronic medium effects in Au+Au collisions at $\sqrt{s_{\rm{NN}}} = 3$ GeV, a region of high baryon density. We introduce a phenomenological direct-production mechanism for ${\rm K}^{*}$ by replacing a fraction of the final-state kaons produced in the ${\rm NN} \to {\rm NYK}$ and ${\rm MN} \to {\rm YK}$ channels with ${\rm K}^{*}$ resonances, with the substitution fraction controlled by a parameter $\alpha$ while conserving four-momentum. The direct ${\rm K}^{*}$ is produced early, at about 6 fm/$c$, with little centrality dependence, whereas resonance fusion via ${\rm K}+\pi\to{\rm K}^{*}$ occurs later, with the mean production time increasing from about 8 to 10 fm/$c$ toward central collisions. Consequently, direct ${\rm K}^{*}$ mesons suffer stronger daughter rescattering, leading to a pronounced decrease in reconstruction efficiency toward central collisions, while the ${\rm K}^{*}$ survival rate remains close to unity. Elastic scattering of the daughters also shifts the invariant mass away from the resonance peak, contributing to the background-like component. The ${\rm K}^{*}/{\rm K}$ centrality dependence reflects the competition between direct production and resonance fusion and is sensitive to $\alpha$. At 3 GeV, a moderate direct-production contribution may result in an increasing ${\rm K}^{*}/{\rm K}$ ratio toward central collisions, providing a testable prediction for future measurements.

Physics-informed neural networks (PINNs) represent a growing frontier in using artificial intelligence to solve partial differential equations (PDEs). Automatic differentiation (AD) plays a central role in this paradigm, which is mesh-free and replaces traditional iterative solvers with gradient-based optimization in continuous space. However, the inherent limitations of AD, particularly in handling higher-order derivatives and discontinuous solutions, pose significant challenges for complex problems. This has motivated a growing number of researchers to explore discretization-based constraints as an alternative path. Yet, the respective applicability of these two paradigms remains largely unexplored. In this work, we conduct systematic experiments across a wide spectrum of problems, from simple linear Poisson to high-Mach hypersonic flows with strong discontinuities. Through a rigorous decomposition of approximation, optimization, and truncation errors, we systematically elucidate the fundamental trade-offs and error-governing mechanisms of both paradigms, as well as two representative network architectures: multi-layer perceptron (MLP) and graph neural network (GNN). Our results reveal a consistent trend: as nonlinearity strengthens, the accuracy advantage of discretization-based constraints becomes increasingly pronounced, with smaller optimization errors compensating for the truncation errors. Moreover, the more complex the nonlinearity and boundary conditions, the greater the advantage of GNN over MLP. These insights offer a robust practical guideline for configuring neural PDE solvers in demanding engineering applications. Our source data and code are available at https://github.com/guoxing0809/neuropde_analysis.

Altermagnets acquire a momentum-dependent spin splitting without net magnetization or spin-orbit coupling. This raises the question of whether the transport anisotropy originates in the electrons or the magnons, and whether the magnon-mediated channel distinguishes an altermagnet from a conventional antiferromagnet. We compute the spin-resolved conductivity of a metallic ferromagnet, antiferromagnet, and altermagnet within a common model, treating the spin-diagonal channel with the magnon self-energy and the spin-flip channel to leading order in the electron-magnon coupling. The anisotropy of the charge-spin conversion is dominated by the electronic spin splitting, the magnon branches contributing only marginally. The magnon-mediated spin-flip channel is even under $C_{4}$, so it carries no signature at first order in the anisotropy and cannot on its own distinguish an altermagnet from a conventional antiferromagnet. It does, however, respond linearly to a sublattice-selective perturbation that lowers the bulk $B_{1g}$ symmetry. The resulting susceptibility vanishes identically in the antiferromagnet, is small in the ferromagnet, and is finite in the altermagnet, where the electronic anisotropy ties spin and sublattice together, so that among magnets with no net magnetization it is unique to altermagnetic order. Being even in the magnetic domain index, this response can be measured without preparing a single magnetic-domain sample.

Two-dimensional layered magnetic materials offer a versatile platform for exploring low-dimensional magnetism and coupled many-body interactions in these materials. Chromium sulfur bromide (CrSBr) is a promising candidate for advanced spintronic and optoelectronic applications because of its intrinsic air stability, semiconducting nature, strong in-plane anisotropy, and A-type antiferromagnetic ordering. This review summarizes recent advances in the understanding of the layer-dependent vibrational and excitonic properties of CrSBr, as well as its magneto-optical response, from bulk crystals to the monolayer limit. We examined its crystal structure, magnetic anisotropy, and interlayer spin reorientation, followed by insights into vibrational dynamics and spin-phonon coupling. Particular emphasis is placed on the excitonic landscape, including magnetic-field-sensitive photoluminescence, localized excitonic states, and the coexistence of Frenkel- and Wannier-Mott excitons in the bandgap. Finally, we discuss the challenges and prospects of harnessing the unique layer-dependent properties of CrSBr in spintronic, magneto-optical, and quantum photonic technologies.

The relationship between Regge factorization of amplitudes and the Collins-Soper-Sterman factorization of hadronic cross sections is explored. Seeking a unified description of rapidity divergences in high-energy scattering and transverse-momentum-dependent factorization, a connection emerges between the Collins-Soper kernel and the Regge trajectory. This provides a framework for bridging high-energy and low-transverse-momentum resummation and for future extensions of $k_T$-factorization beyond leading-logarithmic accuracy.