Papers

The quasar main sequence (MS) provides a consistent unification scheme for type I AGNs. This framework, constructed from the relative flux between the optical emissions $\mathrm{H}\beta$ and $\mathrm{Fe\,II\,(\lambda4570)}$, and the $\mathrm{FWHM(H\beta)}$, organizes quasars into two populations (B, A) and the subpopulation xA, which typically consists of highly accreting sources. We explored the use of the UV 1900 blend emissions ($\mathrm{Al\,III}\,\mathrm{\lambda}1860$, $\mathrm{Si\,III]}\,\mathrm{\lambda}1892$, $\mathrm{C\,III]}\,\mathrm{\lambda}1909$) and the $\mathrm{Fe\,III}$ and $\mathrm{Fe\,II}$ transitions between 1700 and 2200 Angstrom as tracers of this main sequence. We fitted these emissions for a sample of 69 low-$z$ ($z\lesssim0.8$) quasars observed with the Hubble Space Telescope (HST) that had available optical measurements, enabling a direct comparison with the optical quasar main sequence. We found a UV plane defined by $\mathrm{FWHM}(\mathrm{Al\,III})$ and the equivalent width of the combined emissions of $\mathrm{Fe\,III}$ and $\mathrm{Fe\,II}$. The plane defined by these parameters mirrors the quasar main sequence in the optical regime and shows a clear distinction between the different populations. The plane also enables the identification of xA sources with high completeness but a non-negligible rate of false positives. Our results suggest that the UV iron emission around the 1900 blend could be used to trace the quasar main sequence trend, offering an alternative way to study this scheme at high redshift.

Photonic temporal interfaces enable dynamic control of light fields, yet strong time reflection at optical frequencies remains challenging because conventional approaches demand large material refractive-index changes on ultrafast timescales. Here, we introduce a resonance-assisted mechanism that harnesses both polarization energy accumulated in a dispersive medium prior to the temporal interface and strongly increased energy supplied by the modulation system. We show that, under a specific critical condition, rapidly increasing the material resonance frequency yields orders-of-magnitude stronger time-reflected power flux density than what conventional plasma-frequency modulation provides. To implement this mechanism in optical systems, we identify two routes based on dielectric and plasmonic structural resonances. For the plasmonic route, we develop an analytical effective-medium model of conducting-oxide cylinder arrays, in which localized surface-plasmon resonances transform the constituent Drude response into a geometrically tunable effective Lorentz response. Using cadmium oxide as a representative material, we predict an enhancement exceeding three orders of magnitude in the summed reflected-mode power coefficient relative to the same homogeneous material under the same modest plasma-frequency modulation, even in the presence of realistic losses. These findings establish spatial resonance engineering as an effective route to strong temporal scattering with reduced demands on intrinsic material tunability.

Flat polar phonon bands in ferroelectrics have been envisioned to realize irreducibly small domains for achieving the highest memory density. However, such bands are extremely rare, with only a one-dimensional flat polar band discovered in ferroelectric hafnia, which gives rise to irreducibly narrow, line-type domains with a half-unit-cell width of 2.7 Angstrom. Here, we report the discovery of a two-dimensional flat polar band in the ferroelectric (BaTiO$_3$)$_1$/(BaXO$_3$)$_1$ superlattice (X = Zr, Sn), which generates extremely localized, noninteracting dipoles within its quarter-unit-cell area that form quasi-degenerate states of irreducible sub-nm$^2$ ferroelectric domains. The estimated ferroelectric domain density, exceeding 300 Tbit/cm$^2$ (assuming one bit per domain) represents a record high among the known ferroelectrics, with independently switchable dipoles at low voltages. The ferroelectric phase hosting two-dimensional flat bands constitutes a competing ground state across superlattice stacking directions and thus can be experimentally realized in both freestanding structures and epitaxial growth on MgO substrates. This discovery opens unprecedented opportunities to explore multidimensional flat polar bands in ferroelectrics and to engineer ultra-dense and low-power memory devices.

Tellurium (Te) is an intriguing one-dimensional (1D) semiconductor that has recently attracted considerable interest as a p-type channel material. However, scalable synthesis methods have lacked control over the orientation and patterning of the Te atomic chains, thus limiting its practical use. Guided by theory, we overcome this challenge using nanowire-shaped templates to achieve oriented, single-crystal growth of Te on amorphous substrates. Strong alignment of Te atomic chains is achieved as template widths are reduced to sub-20 nm. This high structural order, confirmed by 4D scanning transmission electron microscopy, enables the observation of pristine quantum transport phenomena for deterministically patterned Te. Field-effect transistors exhibit well-defined conductance plateaus at 77 K due to population of individual 1D subbands. Furthermore, Coulomb blockade emerges at 1.7 K, with the Te channel acting as a gate-tunable quantum dot. This synthesis approach provides a scalable pathway for integration of Te-based quantum materials for future electronic and quantum technologies.

We perform a systematic study of an economical class of modular $S_3$ lepton-flavor models without enlarging the continuous gauge symmetry or introducing right-handed neutrinos or additional flavon fields. We provide a complete classification of all inequivalent realizations allowed by the $S_3$ singlet–doublet representation structure and the admissible modular-weight assignments. Their phenomenological viability is investigated for both normal ordering (NO) and inverted ordering (IO) using Bayesian model comparison and parameter-correlation analysis based on current neutrino-oscillation data. We identify 18 viable models for NO and 19 for IO, with 14 satisfying the experimental constraints in both orderings. The viable models successfully accommodate current neutrino-oscillation data while yielding nontrivial predictions for leptonic CP violation, Majorana phases, and observables probing the absolute neutrino-mass scale. Among these predictions, the absolute-mass observables provide the clearest separation between the two orderings. At the best-fit points, the predicted ranges of the effective electron-neutrino mass ($m_\beta$) are completely disjoint between NO and IO, whereas those of the sum of neutrino masses ($\sum_i m_i$) and the effective Majorana mass ($m_{\beta\beta}$) show only partial separation. The IO models generally predict a higher absolute neutrino-mass scale and are consequently more strongly constrained by cosmological observations and more accessible to neutrinoless double-beta-decay searches. Our results show that, despite its economical field content, the modular $S_3$ framework accommodates a diverse set of phenomenologically viable lepton-flavor realizations with experimentally testable predictions.

Explosions from stellar collapse are important in nearly all aspects of astronomy: formation of compact remnants (including the potential seeds of supermassive black holes), the production of compact binaries the produce X-ray binaries and radio pulsars, the origin of many of the heavy elements (a critical aspect of galactic chemical evolution), and as standard candles to probe the early universe (including the nature of star formation). Because these explosions occur in extreme conditions, if we can understand them, they can be used to probe fundamental physics: matter at extreme densities (exceeding nuclear densities, quark formation), neutrino physics (including neutrino oscillations) and, in black-hole forming systems, the nature of relativity. Gravitational waves and neutrinos provide the most direct probe of stellar collapse, but these diagnostics require nearby events. Electromagnetic probes, from shock breakout to observations of supernova remnants, can be much more common and provide complementary diagnostics of the explosive engines behind stellar collapse. In this review, we review these electromagnetic diagnostics, the physics behind them and the theory and modeling work we require to take advantage of these probes.

Improving ion transport in solid electrolytes and cathode coatings remains a key challenge for all-solid-state Li-ion batteries because their room-temperature ionic conductivity is still substantially lower than that of liquid electrolytes. In our previous combined experimental and theoretical study, we showed that thermal neutron irradiation enables defect engineering in LiBO$_2$ through the transmutation of $^6$Li and $^{10}$B, generating lattice vacancies that enhance ionic conductivity. Here, we examine whether this approach can be extended to Li$_3$OCl, a representative antiperovskite solid electrolyte. Using density functional theory, we investigate substitutional defects at Li sites involving B, He, and H, associated with B doping and the neutron-capture reactions $^{6}\mathrm{Li}+n\rightarrow\,^{3}\mathrm{H}+\alpha$ and $^{10}\mathrm{B}+n\rightarrow\,^{7}\mathrm{Li}+\alpha+\gamma$. We evaluate defect formation energetics, the resulting structural distortions, and compare these substitutional defects with other mono-, di-, and trication substitutions at Li sites. Our results show that substitutional defects associated with neutron irradiation provide a feasible route to tune the defect chemistry of antiperovskite solid electrolytes and support neutron-driven defect engineering as a strategy for developing advanced materials for high-performance all-solid-state Li-ion batteries.

We show that the small value of the neutrino cross-section rules out superradiance in the laboratory.

The discrete quasi-static response of rate-independent dissipative granular media is addressed. Granular systems are conventionally simulated with methods that are intrinsically dynamic, such as the discrete element (DEM) and discontinuous deformation (DDA) methods, with the particles' accelerations and damping being essential aspects. In contrast, quasi-static methods derive from the static stiffness relationships among the particles. With frictional contacts, an assembly's stiffness is incrementally non-linear and dependent on the direction of loading. The paper resolves this difficulty by casting the response as a linear complementarity problem (LCP). The approach benefits from a foundation of past research on existence, uniqueness, and stability of LCP solutions, which are expounded in a concise set of rules. The LCP of a granular system is derived, accounting for geometric effects that arise from curvatures of particles at their contacts, frictional contact stiffnesses, and displacement constraints on the particles. The paper describes eight aberrant conditions (pathologies) of granular systems, in the forms of various bifurcations and instabilities. When placed in the context of an LCP, the eight conditions are unambiguously defined. These pathologies include three types of bifurcation: discrete, continuous-bounded (not yet reported in the literature), and continuous-unbounded. Not yet reported in the literature is an abrupt discontinuous change in movements upon a continuous change of the data. Methods and results are illustrated with examples of granular systems. Results show that instability and bifurcation are pervasive conditions near failure; that failure and softening are sensitive to the geometric contours of the particles at contacts; and that quasi-static systems can encounter states that require a dynamic transition to resolve a lack of paths consistent with loading.

A resonator with one localized cubic nonlinearity can acquire additional cusp pairs when it is coupled to an otherwise linear network. At first-harmonic order, the cusp locus is a phase contour of the driving-point receptance $G(\Omega)$ at the nonlinear coordinate. We resolve that contour into the contribution of an active pole and its background. For a lightly damped, isolated modal pole on a slowly varying, nearly real background, cusp-pair birth occurs once the participation of that pole at the nonlinear coordinate exceeds a closed-form threshold set by its damping half-width and that background. On the weak-mixing hardening branch generated by a pole above the primary resonance, the birth coupling then grows as the square root of the damping at fixed mode separation, and of the mode separation at fixed damping. The curvature of the full cusp contour determines whether the local fold set opens a gap (beaks type) or creates an isolated loop (lips type). The isolated-pole approximation reduces this classifier to a background-receptance rule whose range of validity is quantified on 100 random networks. The same ensemble tests the pole ladder numerically, while multi-harmonic continuation follows the whole reconnection sequence—connected band, gap, isolated lens, none—in the original equations at the fold of the birth locus, where the classifier is least protected. The construction also extends to coupled-mode Kerr networks, where the driving-point response sets the intrinsic fold geometry and the drive-port transfer response sets its accessibility.

In this work, a QCD-inspired effective model describes dark-state interference in a confined three-state system with two low-energy $Q\overline{Q}$ states, $|1\rangle$ and $|2\rangle$, and a gluon-excited hybrid state, $|H\rangle$. A stationary chromoelectric flux-tube background enters the unperturbed Hamiltonian, while a time-dependent chromoelectric perturbation couples $|1\rangle$ and $|2\rangle$ to $|H\rangle$ in a $\Lambda$-type configuration. Under two-photon\footnote{We retain standard terms like “two-photon” from the EIT literature only by mathematical analogy, but they do not refer to electromagnetic photons but to the effective frequencies and energy mismatches of chromoelectric perturbations and gluonic excitations that connect confined states.} resonance and within a Markovian Gorini-Kossakowski-Sudarshan-Lindblad master equation, the system forms a coherent superposition that decouples from $|H\rangle$, strongly suppressing the steady-state probe susceptibility $\operatorname{Im}\chi_{\text{CE}}$ as lower-state decoherence vanishes. A phenomenological non-Abelian correction to the hybrid energy mainly shifts and reshapes the transparency window rather than creating the interference itself. The model is not a first-principles QCD calculation of medium opacity but a controlled effective link between dark-state interference in quantum optics and reduced confined color dynamics.

The recent ATLAS observation of the $B_c^*(1S)$ meson fixes the ground-state hyperfine splitting and thereby determines the phase space for $B_c^*(1S)\to B_c(1S)\gamma$. We study four $1S$ and $2S$ M1 radiative transitions using relativistic Salpeter wave functions calibrated to the measured ground-state masses, obtaining $\Gamma[B_c^*(1S)\to B_c(1S)\gamma]=5.24\times10^{-2}$~keV. The allowed transitions show no radial cancellation, whereas the hindered $2S\to1S$ amplitudes are residuals of an approximately twenty-fold cancellation across the radial node. A quark-line-resolved analysis shows a strong asymmetry in the crossed hindered channel: the $b$-emission contribution undergoes an $\mathcal O(10^2)$ internal cancellation while the $\bar c$ contribution remains at $\mathcal O(20)$. The corresponding unsigned line strengths show that the small $b$-current is generated by enhanced cancellation rather than by a smaller unsigned contribution. The unmeasured $B_c^*(2S)$ mass remains the main limitation on the $2S\to2S$ radiative width.

The arXiv preprint server originally democratized astronomical research by digitizing the circulation of early manuscripts and removing the financial barriers of journal subscriptions. However, a system designed for the lower publication volumes of the 1990s has fractured under modern research output. Today, the sheer volume of unreviewed manuscripts—often tagged as “submitted,”, “under review”, or “comments welcome”—imposes a severe cognitive “tax” on the community. Researchers are forced to track multiple, unvetted versions of the same work, creating a massive redundant workload. This practice also bypasses the blinded peer-review process by establishing premature precedence, and it takes a heavy toll on early-career researchers. The pressure to rapidly post unvetted results stifles independent research, pushing young scientists toward massive mainstream collaborations where individual creativity gets lost. In this Short Communication, I analyze a decade of astro-ph metadata to quantify this trend. To safeguard both researchers' time and research freedom, I propose bifurcating submissions into two separate streams. Level-1 (peer-reviewed science) would host peer-reviewed science (accompanied by a journal acceptance or final DOI), while Level-2 (pre-review drafts) would be reserved for discussion drafts. This distinction would remove the unfair advantage of establishing false precedence through drafts and drastically cut the daily reading burden by allowing researchers to opt out of tracking unvetted versions.

In this study, a physics-enhanced neural operator framework is proposed to enhance the generalization prediction ability of the cooling layout of a turbine endwall with variable number of film holes. Specifically, inspired by the film cooling superposition principle, we propose a film cooling prediction model, namely superposition-based deep neural operator (SDNO), that divides the endwall temperature field prediction into two stages. In the first stage, the cooling layout of a turbine endwall is divided into several sub-parts with randomly assigned film holes, and a Transformer-based neural operator network, namely Calculate Net, is designed to predict the temperature field of each sub-part. Then, in the second stage, another neural operator network, i.e., Super Net, is trained to combine the temperature fields predicted by Calculate Net for each sub-part and obtain the superposed temperature field of the full cooling layout. Additionally, instead of directly taking the film cooling contours as pixel plots, a signed distance function (SDF) which is sensitive to the variable locations of cooling holes, is designed to encode the location information of cooling holes. Furthermore, the proposed endwall film cooling prediction model is trained with the samples that changing the number of film holes from 1-5 with variable locations. Then, the trained prediction shows excellent generalization prediction ability, which can accurately predict the film effectiveness of the cooling layout with 10-20 film cooling holes that are unseen in the training samples. The proposed SDNO also improves prediction accuracy relative to the fully supervised baseline. With the above, the effectiveness of our proposed prediction model has been well demonstrated.

The Variational Quantum Eigensolver (VQE) requires a large number of measurements to evaluate molecular Hamiltonians. Expressing a molecular Hamiltonian as a linear combination of Pauli strings creates a measurement bottleneck: non-commuting Pauli strings cannot be measured simultaneously. Consequently, mutually commuting Pauli strings must be grouped and measured together to minimise the number of quantum-state preparations. This task maps to the minimum clique cover problem on a commutativity graph, an NP-hard problem typically addressed using classical heuristics. Although an Ising-model formulation has recently been explored on fully connected CMOS Ising machines and demonstrated on physical quantum annealers only at small scale, the embedding cost that governs its behaviour on hardware with sparse connectivity, where each logical variable must be represented by a chain of physical qubits, has not been characterised. In this work, we formulate the Pauli-grouping problem as a standard QUBO colouring model and study its scalability on a D-Wave quantum annealer. Across a series of molecular systems and for both qubit-wise and full commutativity, we quantify the growth in the number of logical variables and the QUBO interaction density, characterise the physical-qubit and chain-length overhead required for embedding on the Zephyr topology, and compare the annealer's time-to-solution and solution quality with those of heuristic classical baselines. This analysis identifies the threshold of molecular complexity beyond which hardware connectivity prevents viable embedding, and shows that a second, practical limit is reached earlier. The threshold therefore measures how far current annealers are from the regime in which pre-optimising a VQE measurement scheme on hardware would be worth considering.

Semiclassical analyses of regular black holes suggest that inner-horizon instabilities can drive the trapped region to evaporate faster than the Hawking time and seed a transient anti-trapped region. Whether this repeats into a cascade terminating in a horizon-free configuration requires a self-consistent solution of the semiclassical Einstein equations, which we do not attempt. Instead, within the static Bardeen family, we show that the renormalized-stress-tensor (RSET) result of Arrechea, Liberati and Spadafora (arXiv:2608.03538) does not by itself force any damping of a hypothetical cascade near extremality, since its near-extremal limit at fixed cycle duration is finite and nonzero. We then prove, under explicit nondegeneracy hypotheses on any static metric family whose horizons merge at a fold point, that the inner-horizon surface gravity scales as |kappa_-| ~ (M-M_crit)^{1/2}, and verify this in two regular black hole families, Bardeen and Hayward, with a quantified systematic uncertainty. A phenomenological closure built on this scaling gives a mass gap decaying as x_n ~ n^{-2}, generalizing to x_n ~ n^{-1/(pq)} for a fold exponent p and an uncalibrated closure exponent q; the required cycle count is a property of the closure, not a physical prediction. As a separate exercise, we build an effective adiabatic model for the outer-horizon mass from the exact Einstein tensor of a generalized Vaidya-Bardeen ansatz matched to the cited RSET flux; the resulting law includes an O(1) correction absent from the naive Schwarzschild-Vaidya relation, relaxes to M_crit only asymptotically, and gives a timescale shorter than the inner-horizon amplification timescale by up to four orders of magnitude away from extremality but longer very close to extremality. We distinguish what is derived under stated assumptions from what the closure simply postulates.

We investigate a regularized charged black hole (BH) spacetime constructed by applying the Simpson-Visser (SV) prescription to a BH in Einstein-Euler-Heisenberg (EEH) theory. The resulting Simpson-Visser Einstein-Euler-Heisenberg (SV-EEH) geometry incorporates nonlinear electromagnetic corrections through the parameter $(a)$ and the SV regularization through the length scale $(b)$. By varying these parameters, spacetime provides a smooth interpolation between a regular BH, a one-way wormhole, and a traversable wormhole configuration. Introducing the effective areal radius $(R=\sqrt{r^{2}+b^{2}})$, we analyze the horizon structure and derive the conditions for degenerate and extremal configurations. Furthermore, we examine the null and timelike geodesic structures, computing the photon sphere radius, the BH shadow size, and the innermost stable circular orbit (ISCO). Our results demonstrate how nonlinear electrodynamics and SV regularization jointly modify the causal and geodesic structure of charged BHs while preserving the appropriate Reissner-Nordström and SV limits.

Designing polymers with targeted properties requires navigating vast chemical spaces from limited labeled data. Here we introduce PolyLatentFlow, a framework based on continuous-time flow matching in latent space for unconditional and conditional polymer generation, together with LlamaUni, a multimodal representation combining polymer sequence and 3D structural information. In unconditional generation, PolyLatentFlow with LlamaUni produced the largest yield of valid candidates novel relative to PolyInfo among the evaluated unconditional generators while maintaining high diversity. For $T_g$ conditioning, generated property distributions shifted systematically across a 200 {\deg}C target range. In multi-property tasks, molecular representations showed similar surrogate target fidelity but differed markedly in validity, training-set replay, and structural proximity to labeled polymers. PolyLatentFlow with LlamaUni consistently combined high validity with low replay and achieved the largest per-attempt yield of nonreplayed target hits for CO$_2$/N$_2$ conditioning. These results demonstrate latent space flow matching for polymer inverse design and identify molecular representation as a key determinant of target control and exploration beyond labeled chemistry.

We study the rational quadratic differential equation \[ \frac{\mathrm{d}y}{\mathrm{d}x} = \frac{ay^2+by+cx}{y^2}, \qquad a,b,c\in\C, \] under the non-degeneracy assumptions \[ c\neq 0,\qquad 2ay+b\not\equiv 0. \] Equivalently, after clearing the denominator, we consider the polynomial vector field \[ \dot{x}=y^2,\qquad \dot{y}=ay^2+by+cx. \] We give a complete, directly checkable classification of its Darboux curves. If $a=0$, no non-constant Darboux polynomial exists. If $a\neq 0$, a non-constant Darboux polynomial exists if and only if \[ c=-ab\qquad\text{or}\qquad c=-2ab. \] In these two cases the unique irreducible Darboux polynomials, up to non-zero constant multiples, are respectively \[ y-ax,\qquad y^2-2bx. \] Consequently every non-constant Darboux polynomial is a non-zero constant multiple of a positive integral power of the corresponding irreducible factor. We then place this classification in the framework of Riccati (R-)integrability and rational potentials. Excluding the exceptional branch $c=-2ab$, the analytic integrability theorem identifies $c=-ab$ as the branch admitting a global Riccati-type analytic first integral. For $c=-2ab$, we compute the first four transverse variational groups along the transformed Darboux divisor over the rational function field. Their dimensions are $1,2,3,4$; the fourth is the full group of invertible fourth-order transverse jets. We prove that this exceptional branch admits no Riccati first integral and hence is not R-integrable. Finally, we relate the branch $c=-ab$ to the Quartic Inverse Riccati (QIR) class and discuss an invariant-based classification problem for quartic Abel equations.

This guide is intended for astronomers new to X-ray astronomy. It provides a brief overview of the data products typically encountered by the user and highlights analysis considerations usually not discussed in more formal introductions to the discipline. In X-ray and $\gamma$-ray astronomy the primary data set is an event list (a table of individually detected photons with position, arrival time, and an instrumental energy estimate) rather than the image or visibility array familiar from other wavelength bands. We describe the files a user typically encounters, including: event lists, the aspect solution, spectra, instrumental responses, exposure maps, lightcurves, source lists, and calibration databases. These data are generally photon-limited and follow Poisson rather than Gaussian statistics. Combined with the coarse energy resolution of X-ray instruments, this means physical models must be fitted by "forward-folding"; we outline this technique and the systematic uncertainties introduced by calibration. Additional topics include: point spread function morphology, cosmic and instrumental backgrounds, pileup, contamination, binning conventions, the Chandra X-Ray Observatory focal plane, and sub-pixel event repositioning. This primer is intended to be generalized, not specific to any telescope or science subject area, although examples draw on Chandra. It was inspired by interactions with the astronomical community over several conferences and through the Chandra X-ray Center (CXC) HelpDesk.

We survey a geometric approach to the Navier-Stokes equations developed by the author over the past fifteen years. The central object is a Riemannian space of fourteen dimensions whose metric is Ricci-flat precisely on the solutions of the Navier-Stokes system, so that the behaviour of a viscous incompressible fluid becomes a property of curvature. The space decomposes into a flat six-dimensional part and two dual quadruples of coordinates, Eulerian and Lagrangian, which exhibits the two classical descriptions of a fluid as two halves of a single geometry. We also recall the associated six-dimensional metric, whose integrability condition is the incompressibility of the fluid; the link with the projective geometry of second-order ordinary differential equations in the sense of E. Cartan; and the use of Cartan's invariants to construct a three-dimensional analogue of the Taylor-Green vortex. An application of the same construction to the equations of rotation of a rigid body is indicated.

Positive Wigner functions can have less Shannon entropy than the vacuum, even arbitrarily close to the vacuum state. We construct physical counterexamples and identify the competition that controls their entropy: the relative entropy to the vacuum phase-space density can exceed twice the mean photon number. A two-level family exhibits a finite window in which coherence lowers entropy while preserving global Wigner positivity. A complementary construction repairs a remote negative tail with an exponentially small thermal admixture; an explicit mixing weight of $2\times10^{-21}$ preserves a rigorously established entropy decrease. Optimisation over all one-mode Wigner-nonnegative states gives the sharp low-energy scale $E^\gamma/[\ln(1/E)]^\beta$, with $\gamma\simeq0.7412$ and $\beta\simeq0.5861$. Because $\gamma<1$, tensor products can have vanishing total energy and trace distance from vacuum while their entropy deficit diverges. We derive the exact half-transmission threshold for universal Shannon-entropy recovery and connect it to companion results showing residual non-Gaussian structure. The counterexamples reveal distinct controls on entropy: coherence sets the local descent, mode number amplifies it, and loss restores the vacuum bound.

In recent times there is considerable unease about the way Artificial Intelligence (AI) powered by large language models is used to do astrophysics, and, assuming that these AIs will get far better in future, several alarming situations are also discussed. In a “white paper,” Hogg argues that extreme cases like allowing AI to write all astrophysics papers or strictly controlling AI are not good choices and posits that it is difficult to adopt moderate policies. I examine the impact of AI on astrophysics by making two rather extreme assumptions: first, that the modern astrophysicist has become increasingly preoccupied with the administrative task of publication over the act of physical discovery (astrophysicists are busy writing papers and have stopped doing astrophysics); and second, that while AI possesses the capacity to synthesize literature and generate manuscripts, they lack the intrinsic ability to perform original astrophysical inquiry (AI can write papers but cannot do astrophysics). I provide some plausible reasons for adopting these assumptions, but, more importantly, extrapolate the implications of these assumptions to argue that AI can have a very positive impact on astrophysics. By situating AI as agents of publication rather than discovery, the focus of the human researcher can be directed towards fundamental astrophysics, leading to very positive growth in the field.

We study the two-field nonlinear dispersive system \[ u_t=u_{xxx}+6uu_x,\qquad v_t=v_{xxx}+6(uv)_x, \] viewed simultaneously as a coupled wave equation, as the tangent covering of Korteweg–de Vries (KdV), and as a Hamiltonian flow on a tangent Poisson manifold. The main purpose is to make these viewpoints interact at theorem level. First, we prove that the Magri Poisson pencil of KdV admits a complete tangent lift to an explicit compatible pair of matrix Hamiltonian operators. The corresponding recursion operator has triangular tangent form and generates the lifted KdV hierarchy. Second, we identify a five-dimensional point-symmetry algebra together with the infinite hierarchy of tangent generalized symmetries. Third, reduction by the traveling-wave subgroup produces a four-dimensional Hamiltonian system that is the complete tangent lift of the scalar KdV profile dynamics. On the nonsingular elliptic locus, the base profile is written in Weierstrass form and every tangent traveling wave is classified explicitly by derivatives with respect to the energy and integration constants.

Estimating the impact of observations newly added to an existing numerical weather prediction (NWP) system requires reintegrating the ensemble forecast from the analysis that assimilates the additional observations, which is laborious and computationally expensive. We therefore propose preemptive EFSO (PEFSO; preemptive ensemble forecast sensitivity to observations), which estimates observation impact without model reintegration by invoking a stronger tangent-linear approximation than that used in EFSO. The estimated impact, however, is merely a scalar quantity at a specified verification time, so it is also valuable to obtain the ensemble forecast in which the remaining additional observations are assimilated after denying the detrimental ones. We refer to this procedure as ADD-SEL, but carrying it out requires reintegration. We therefore propose two methods for updating the ensemble forecast without reintegration as approximations to ADD-SEL, collectively termed ADD-SEL-PRE: one recomputes the ensemble transform matrix (i.e., the Kalman gain), and the other modifies only the innovations at lower cost. Experiments with the Lorenz-96 model examine whether both can be approximated without reintegration. PEFSO estimates observation impact comparable to that obtained by EFSO within the range where the tangent-linear approximation remains valid, even under more practical conditions: an ensemble size of 10, the analysis as the reference state, and only the additional observations available. When additional observations are assimilated after denying detrimental ones, both ADD-SEL-PRE methods update the ensemble forecast, giving forecast errors comparable to those from ADD-SEL, particularly for lead times up to two days, where the tangent-linear approximation is expected to hold.

Self-organisation of granular systems is a key determinant of their macroscopic behaviour and has been studied extensively in assemblies of hard particles. We use numerical simulations to test this understanding in mixtures of hard and soft particles, focusing on cells, the smallest irreducible loops of the contact network, as structural descriptors. We show that, while the cell statistics display robust qualitative features under isotropic compaction, they depend on inter-particle friction, $\mu$, and soft-particle fraction, $\kappa$. Specifically, (i) the quadron area distributions retain a $\Gamma$ form, albeit with parameters that vary systematically with $\mu$ and $\kappa$. (ii) Predictions of the cell order distribution (COD) by maximising the entropy, without taking mechanical stability into consideration, become increasingly inaccurate at large cell orders. (iii) Irrespective of $\mu$, the normalised cell stress distributions collapse onto one master Weibull form, whose only shape parameter depends weakly on $\kappa$. This suggests a quasi-universal form that may deteriorate slightly at very high fractions of soft particles. (iv) Cells align preferentially along the local major principal stress direction, showing the same coordinated stress–structure self-organisation as in hard particles. The relative robustness of cell statistics to the addition of soft particles suggests that hard and hard–soft granular mixtures can be described by one model.

Cooling a quantum state presents a challenge as the external control in active protocols can induce detrimental heating in the system. Passive cooling processes offer a valuable alternative: Here, we present a simple quench protocol to cool a set of qubits with access to an ancillary spin chain. We show that excitations can be transported out of the qubits as quasi-particles, taking the form of magnons in a ferromagnetic ancilla and triplons in a dimerized antiferromagnetic ancilla. This quasi-particle transport mechanism enables cooling towards both individual and highly entangled two-qubit target states. We demonstrate that this cooling mechanism remains robust starting from thermal states and with finite quench ramp times.

Dissipation has been recently demonstrated as a powerful primitive for designing quantum algorithms. We apply this viewpoint directly to linear-system solving, $Ax=b$. We construct a simple purely dissipative Lindbladian whose unique fixed point encodes the linear-system solution. We prove dimension-independent trace-distance mixing in $\Theta(\kappa^2\log(1/\eps))$ time. We then show how to run this Lindbladian on digital quantum computers via collective block encoding and Lindbladian simulation, resulting in an $O\!\left(\kappa^2\log(1/\eps) \frac{\log(\kappa/\eps)}{\log\log(\kappa/\eps)}\right)$ query complexity for both $U_A$, the block encoding of $A$, and $U_b$, the $|b\rangle$ state preparation unitary.

In this work, I investigate the non-relativistic quantum dynamics of spin-1/2 particles in Einstein-Gauss-Bonnet (EGB) gravity and establish a direct connection between higher-curvature corrections, fermionic dynamics, and the phenomenology of compact objects. Starting from the Dirac Hamiltonian in a static, spherically symmetric EGB spacetime, we perform a Fold-Wouthuysen transformation and derive the effective Hamiltonian, including relativistic kinetic, gravitational, spin-orbit, and higher-curvature contributions. Heisenberg equations are then used to obtain the dynamics of velocity, force, and spin, revealing explicit EGB corrections for both translational motion and spin transport. In particular, the spin-orbit sector induces a modified precession frequency whose fractional deviation from general relativity scales as $\delta_{\Omega}=-4(\xi/M^{2})(M/\rho)^{3}$, providing a clear dimensionless signature of the Gauss-Bonnet coupling. Through Ehrenfest's theorem, we also establish the correspondence between the dynamics of quantum operators and their semiclassical gravitational limit. As an astrophysical application, we consider the stellar-mass black hole A0620-00 and show that prospective relative sensitivities in spin precession on the order of $10^{-3}$ to $10^{-4}$ can probe Gauss-Bonnet couplings in the range of approximately $10^{6}$ to $10^{8}\,{\rm m}^{2}$, depending on the orbital radius. This result identifies fermionic spin precession as a complementary channel for testing gravity with higher-curvature corrections and provides a quantum-mechanical framework connecting modified gravitational dynamics to precision phenomenology in strong-gravity regimes.

Intermittency in the solar wind is commonly studied within the inertial and dissipative ranges, where scale-dependent magnetic field distributions become increasingly non-Gaussian toward smaller scales until dissipation becomes important. Conversely, whether Gaussianity is recovered at large scales remains unclear. To address this, we systematically examine magnetic field increment kurtosis over scales from 1 minute to 1 year using more than two decades of in situ observations from NASA's Wind and ACE spacecraft. We find that although kurtosis tends toward Gaussian value of 3 near the correlation scales, it generally remains elevated (super-Gaussian) at larger scales. Kurtosis also varies substantially over time, with pronounced super-Gaussian intervals during high solar activity phases and sporadic sub-Gaussian intervals primarily in the radial component. These results provide evidence for large-scale intermittency in the solar wind, potentially arising from mixing of different solar wind streams and nonstationary driving of solar sources.