Papers

We study edge observables in three-dimensional Maxwell theory on null boundaries using a Hamiltonian formulation adapted to null foliations. We consider three backgrounds: Minkowski spacetime, the BTZ black hole, and de Sitter space, where the relevant boundaries are, respectively, null infinity, the black hole horizon, and the cosmological horizon. In all three cases we find, besides the usual $U(1)$ charge, a second edge observable associated with an intrinsic symmetry on the null boundary. The two charges are well defined quasilocally. They form a centrally extended algebra which, in Fourier modes, becomes two independent Abelian Kac-Moody algebras with opposite levels. Thus, the same centrally extended edge structure appears at both asymptotic and finite-distance null boundaries.

Beam monitoring detectors play an important role in experimental control and radiological protection by enabling the real-time characterization of particle and photon beams. They provide information on beam intensity, position, and scattering, helping to ensure measurement accuracy, protect sensitive detectors, and quantify stray radiation in the surrounding environment. In this work, a Geant4 simulation was developed to investigate the performance of an X-ray beam monitoring detector (BMD) composed of six hexagonal BC404 plastic scintillators arranged to provide high granularity, using a reflector with a realistic reflectivity of 93%. Under the simulation conditions considered in this study, the detector exhibited an intrinsic time resolution of 100.8 $\pm$ 2.0~ps. The results indicated that only about 10% of the incident photons interacted with the detector, suggesting that the proposed design could be used for beam characterization while minimally perturbing the primary beam. In addition, the X-ray multiplicity decreased with distance according to an inverse-square dependence. A backscatter study performed using a water phantom showed that approximately 6% of the incident beam was detected as scattered radiation. These results suggest that the proposed detector may be a useful tool for X-ray beam characterization and for studies related to scatter radiation and radiological protection. Further experimental validation is required to confirm these findings.

SN 2018ibb is one of the best pair-instability supernova (PISN) candidates identified to date. It, however, showed unexpected blue flux excess in late-phase spectra, likely originating from the interaction between supernova (SN) ejecta and dense circumstellar matter (CSM). We develop synthetic light-curve models of PISNe interacting with dense CSM and estimate the CSM properties of SN 2018ibb by comparing the synthetic and observed light curves. We found that the bolometric luminosity evolution of SN 2018ibb from 150 d after the peak can be well reproduced by the interaction with the CSM formed by a mass-loss rate of 0.01(v_CSM/1,000 km/s) Msun/yr, where v_CSM is the CSM velocity. The observed luminosity break at around 300 d from the peak indicates that the CSM interaction ended at this time and the dense CSM radius was 8.5e16 cm. The CSM radius then implies that the mass loss of the progenitor was enhanced for 28/(v_CSM/1,000 km/s) yr before explosion. We conclude that PISN progenitors may experience short-term mass-loss enhancement within decades before explosion, similar to what is often observed in progenitors of core-collapse SNe.

X-ray spectroscopy techniques probe chemical states in systems with atom-site specificity; however, the site-selective characterization of local bond environments in novel research materials often relies on a combination of reference spectra, multiple complementary spectroscopic techniques and electronic structure calculations. Auger-electron spectroscopy has long accompanied x-ray photoelectron spectroscopy as a second modality to resolve chemical states with overlapping core-electron binding energies. Here I show that the wealth of information encoded in the Auger spectrum offers the opportunity to train convolutional neural networks for site-selective functional group classification in organic molecules directly from the Auger spectrum lineshape. Furthermore, the inclusion of the core-electron binding energy as an additional modality improves the classification, either by augmenting the input fitted intensities with the binding energy or by conditioning the classification on the binding energy via feature-wise linear modulation layers. The latter approach was previously developed for visual reasoning in image classification, and the present results show that this is the more robust approach for including the binding energy. This work demonstrates the potential for new data-driven characterization capabilities in spectroscopic techniques that are information-rich but difficult to interpret.

We report the discovery of extreme 37 GHz radio variability in early-stage active galactic nuclei (AGN). Most of these sources belong to the class of narrow-line Seyfert 1 (NLS1) galaxies, which harbour fast-growing, low-mass supermassive black holes that accrete at high Eddington ratios. At 37 GHz, these extraordinary AGN exhibit amplitude variability of three to four orders of magnitude over timescales of a few days. Notably, despite several attempts, we have not detected relativistic jets in these sources, suggesting that this phenomenon may occur very close to the black hole and may represent a new form of AGN variability. One of these sources, which flared at 37 GHz, was followed up with the Karl G. Jansky Very Large Array and Swift XRT/UVOT. Based on these observations, we estimated an e-folding timescale of mere hours, leading to variability brightness temperatures and variability Doppler factors that are extremely difficult to explain by an incoherent emitter. This suggests a possible detection of coherent emission from an AGN, although more observations will be needed to distinguish between alternative scenarios.

We propose a dark matter model in which the symmetry-breaking pattern SU(3)_dark -> SO(3)_dark x Z_2 produces absolutely stable point-like topological defects classified by pi_2(SU(3)/[SO(3) x Z_2]) = Z. The lightest neutral member chi^0 of the resulting dark octet, with mass M(chi^0) = 165.67 GeV, couples to Standard Model fields only through a kinetic-mixing portal (g_f = 10^-3) and gravity. A dark Higgs triplet Delta_dark with vacuum expectation value v_Delta = 17 GeV and Yukawa coupling y_chi = 0.10 generates a tree-level splitting Delta M(chi^+ - chi^0) = 1.70 GeV, opening the decay chi^+ -> chi^0 + phi^+ and ensuring that chi^0 is the unique stable relic. An extended Gell-Mann-Okubo mass operator incorporating the quantum number darkicity T_dark predicts three scale-independent mass ratios, r_21 = M(chi^++)/M(chi^0) = 1.089 +/- 0.005, r_31 = M(Sigma^0_dark)/M(chi^0) = 1.163 +/- 0.006, and r_41 = M(Lambda_dark)/M(chi^0) = 1.260 +/- 0.008, falsifiable at FCC-ee. Eight coupled Boltzmann equations with co-annihilation yield Omega_DM h^2 = 0.120 at M_0 = 208.67 GeV. Self-interaction cross-sections satisfy all astrophysical bounds from dwarf galaxies to the Bullet Cluster. The model predicts a stochastic gravitational-wave background at f_* = 1.65 mHz (LISA, SNR = 8.5) and dark acoustic oscillations at r_DAO = 2.3 +/- 0.4 Mpc (SKA).

In thin-film lithium niobate Mach-Zehnder modulators, half-wave voltage and bandwidth are tied to the same design parameters; hence, improving one usually costs the other. Several methods have been pursued in the past to alleviate this tradeoff. Specifically, the bias voltage can be reduced through non-centered placement of optical waveguides with respect to electrodes, slow-wave optical gratings, and high-permittivity cladding layers. Bandwidth can be enhanced through implementing periodic segmented electrodes and exploiting low-permittivity bottom cladding and substrate materials. The objective of this work is to study the augmentative impact of these methods. We pursue a rigorous modeling and optimization approach to achieve this objective, estimate the impact of each augmentation, and evaluate the ultimate performance of TFLN MZMs based on these methods. It is shown that a co-designed structure that incorporates all these enhancing methods can attain a drive voltage of 0.84 V and a modulation bandwidth of almost 220 GHz.

We explore the heat-rectification properties of a two-phase fluid confined in a nano-chamber with one wall coated with end-grafted polymers using molecular-dynamics simulations. We find a significant thermal diode effect for a wide range of chamber fillings for both very stiff and fully flexible polymers. A stationary heat flux is imposed on the system by fixing the walls at two different temperatures, computing the heat flow as a function of the filling density. The fluid presents a liquid phase, located close to the cold wall, and, for many fillings, a vapor phase in contact with the hot wall. A vapor-liquid interface is also present and located at different distances from the walls, depending on the fluid filling. We study the system by comparing two operational modes: a direct mode, in which the polymers are grafted on the hot wall and exposed to the vapor phase. In the inverse mode, the wall temperatures are swapped and the fluid rearranges to adapt to the interchanged temperature gradient. We calculate the mean heat flow, number density and temperature profiles for the stationary state in both modes. From them, we computed the density and temperature profiles, heat rectification coefficient, and resistivity profiles, for the two studied extreme cases of polymer bending rigidity. We found that, the nano-chamber presents a significant degree of heat rectification with different characteristics and filling density ranges. We describe the conditions to be met to obtain high thermal rectification as regards fluid filling, polymer properties and fluid-polymer affinity. They can be fine-tuned according to the application or material availability. In the direction parallel to the walls the system is easily scalable towards macroscopic sizes, without affecting the thermal rectification. This makes the soft-diode mechanism very versatile in geometry, size and materials choice.

Precise manipulation of liquid droplets underpins lab-on-a-chip platforms for diagnostics, chemical synthesis, and biological assays. Yet autonomous droplet transport through confined geometries of varying complexity remains an open challenge. Droplets exhibit contact-angle hysteresis, deformability, and capillary pinning, which make their response to actuation nonlinear and history dependent, that classical controllers and pre-programmed trajectories cannot cope in multi-turn environments. Here we demonstrate autonomous navigation of a liquid droplet through geometries of increasing complexity on a gravity driven (Labyrinth) platform using model-based reinforcement learning. A thin silicone oil film reduces contact-line pinning while two-axis tilt supplies the gravitational driving force, and an overhead camera tracks the droplet in real time. An offline-trained policy discovers effective tilt strategies from limited physical interaction data, without simulation or analytical droplet models. The system operates under partial observability, as oil-film thickness, instantaneous contact angle, and droplet deformation state remain hidden from the controller. Despite these challenges, the learned policy achieves reliable navigation across straight, right-angle, and curved-arc paths, including outside-corner geometries. We further demonstrate that a policy trained on a simpler geometry transfers to complex ones, succeeding zero-shot on right-angle and staircase paths and reaching full success on a curved arc with a fifth of the training data. The findings suggest promising avenues for enabling droplet based microfluidic systems to serve as intelligent chemical laboratories.

The coherent conversion between microwave and optical photons, known as quantum transduction, is critical for connecting superconducting processors to optical networks. Existing methods are limited by complications associated with optical pumping. We propose a pump-free microwave-optical Bell-pair source for teleportation-based transduction. Using a spin or atomic system resonantly coupled to optical and microwave cavities, the scheme generates loss-robust heralded Bell pairs. Across color centers, atomic ensembles, and phonon-mediated systems, this assembly achieves kilohertz-range heralding rates with high fidelity.

Reaching compressible flow has usually forced lattice Boltzmann methods to abandon the compact stencil or the strict locality that make them efficient. We give up neither, solving the compressible Navier–Stokes–Fourier equations with a scheme that transports only the conserved mass, momentum and energy. The viscous stress and heat flux depend on gradients of the velocity and temperature. To capture them, existing compressible schemes go beyond a single lattice of the conserved fields. They enlarge the velocity set, carry the stress and heat flux as extra transported fields, place the energy on a separate grid, or give up exact streaming for an off-lattice advection. We instead recover the gradients from the non-equilibrium part of the distributions already present, inside the collision. No field beyond the conserved state is transported, no neighbour is read, streaming stays exact, and every computation runs in single precision. The method carries five fields where a transported-flux scheme carries fourteen, at a fraction of the memory and $4.9$ times the throughput. Verified against the exact Sod and Becker shock solutions and a supersonic Taylor–Green vortex, it tracks the direct-numerical-simulation reference on the kinetic energy and stays within the reference-solver spread on both dissipation rates.

Visible dynamics and mean dissipation need not determine the collective phases of rare histories. We construct local Markov models with identical ordinary visible path distributions, stationary states, mean entropy production, mean jump activity and driving affinities, yet different phases when histories are weighted by their full entropy production. Visible configurations modulate hidden driven cycles, whose exact elimination turns kinetic correlations into interactions. A positive spectral reduction separates hidden relaxation from collective modes. Periodic binary models retain opposite phases with entropy variances matched at every observation time. For conserved particles, a pair matches the first two joint cumulants of entropy and hidden activity at every observation time, yet selects segregation or a fluctuating state with suppressed long-wavelength density noise. Bound-state transport and fermionic evolution determine their contrasting dynamics. At a clean Ising critical midpoint, the entropy source couples quadratically to the thermal perturbation, making the fourth cumulant the first to detect the critical susceptibility. Its rate per site grows logarithmically, with an exact cutoff set by system size and observation time. For two quenched disorder ensembles, exact sample-response formulas and numerical evidence support a finite fourth-cumulant density despite very slow relaxation; a weak-disorder continuum response admits a controlled Borel sum. A common positive hidden eigenvector characterizes autonomous selected dynamics. When this condition fails, a finite network develops visible memory while preserving its ordinary visible process and mean diagnostics. These results identify kinetic information missed by aggregate thermodynamic observations.

We present qdmag, a computational utility for calculating the magnetization of magnetic molecules in a time-varying external magnetic field by solving a generalized Lindblad quantum master equation with spin-phonon coupling treated as a dissipation term. The package relies on the spin Hamiltonian formalism, which includes both the magnetic exchange interactions and the zero-field splitting (ZFS) interaction. Different types of magnetic exchange interaction and ZFS terms up to 12th order, which are written in terms of the extended Stevens operators, are supported. qdmag enables long-time evolution of magnetization for up to a few milliseconds, which is achieved through a staircase approximation of the magnetic field as a function of time. For high-dimensional spin Hamiltonians, a lower-dimensional effective Hamiltonian is constructed to make the calculations computationally feasible. Three case studies of one-spin, two-spin, and three-spin systems are presented to demonstrate the usage of qdmag. Our work offers a computational tool to bridge the gap between theoretical development and numerical calculations of spin dynamics in the presence of spin-phonon coupling.

In nonlinear prediction, two state representations with the same local uncertainty volume can have radically different predictive value. We consider differentiable finite-time dynamics together with a quadratic terminal requirement that specifies which terminal state differences matter. Pulling this requirement back through the tangent map defines a requirement-induced predictive geometry on the present tangent space. This geometry is fixed by the dynamics and the requirement; under the fixed local uncertainty-volume constraint used here, the capacity parameter fixes only the scale of the representation that realizes it. We show that the unique optimal covariance has the inverse predictive shape and, equivalently, that optimality is characterized by isotropization of propagated uncertainty in the terminal requirement geometry. The gain over a baseline-isotropic representation is the arithmetic-to-geometric mean ratio of the predictive spectrum, making it a coordinate-invariant measure of predictive anisotropy. In Euclidean coordinates this yields a general finite-time spectral law, and for two-dimensional area-preserving dynamics an exact identity between predictive gain and the condition number of the optimal geometry. Stronger directional stretching therefore increases potential predictive gain only together with the anisotropy required to realize it; bounding that anisotropy imposes a finite gain ceiling. Standard-map and double-pendulum calculations demonstrate these relations in nonlinear Hamiltonian systems. The framework provides a basis for adaptive sensing, state estimation, and model-predictive computation in which representation geometry is matched to predicted task consequences.

The age of a young star is difficult to measure and yet is a fundamental property that is essential for understanding stellar evolution. Accurate age indicators across the early phases of low-mass stars are scarce and often rely on properties of the circumstellar environment. We investigate stellar surface gravity as a practical age estimator from the class I to the class III phases of low-mass stars. Gravity increases monotonically as young stars descend their Hayashi tracks. Gravity is a physical property of the central star and is independent of the circumstellar environment or evolutionary models. Also, gravity can be measured for individual objects. We performed two tests for the reliability of gravity as an age indicator: (1) the relative ages of the components of young binary stars and (2) the relative ages of a young moving group. We show that young binary stars have consistent gravities, as expected, if they are coeval. Similarly, we find similar gravities among the TW Hya group and derive a median age of 12.8 +/- 1.2 Myr. In both cases, differences in gravities may reflect real differences in the ages. We show that there is no correlation between veiling emission and gravity, showing that circumstellar disk emission does not affect our ability to infer ages from measurements of photospheric stellar gravity.

Additively manufactured soft-magnetic Fe–Co is consistently harder than wrought material of the same composition, and controlling that excess is the central obstacle to printing electrical machines from these alloys. The literature attributes it to B2 chemical ordering, untested because the anisotropy of the ordered state had not been measured for this alloy and because printed material had never been compared with wrought material at matched grain size. In this study we supply both. Calibrating on wrought Fe–49Co–2V at a known order parameter fixes the ordered-state domain-wall energy and caps every pinning channel independent of grain size. Ordering then falls orders of magnitude short of the measured excess, and a tenfold change in antiphase-domain size leaves coercivity unchanged. What ordering controls is the wall energy, and that effect is small and bounded. The excess is retained defect content, which moves process optimization from post-build annealing to in-build defect control.

We study the sensitivity of top-quark pair production at the FCC-ee to heavy new physics, parametrised in the Standard Model effective field theory, using discriminants based on matrix elements. The analysis includes detector reconstruction effects, obtained with a fast simulation of the IDEA detector concept, and jet flavour tagging. We consider dimension-six operators that modify the electroweak couplings of the top quark or generate four-fermion interactions, at leading order and in diagrams with two resonant top quarks. The full six-body kinematic information is employed to maximise the discrimination power against the Standard Model. Two bins per dimension in the space of 12 discriminants, one per operator considered, provide a simple and robust methodology to set nearly optimal multidimensional constraints. Bounds on the new physics scale can reach values up to 30 TeV in a single-operator fit and up to 5 TeV in a global multi-operator fit. A combination with High-Luminosity LHC prospects on top-quark operators shows complementary sensitivities which help lift approximate degeneracies.

Auger-electron spectroscopy has long accompanied x-ray photoelectron spectroscopy as a second modality to resolve chemical states with overlapping core-electron binding energies. However, analyzing the Auger spectrum is challenged by its complexity and the computational expense of its simulation. Here we demonstrate that the physical connection, and thus inter-task relationship, between the generation of a core-hole and its corresponding Auger-Meitner decay enables inductive knowledge transfer through the training of a multi-task graph neural network to predict both observables from a common graph embedding. Both task losses are combined with learned weights via the uncertainty weighting procedure. Overall, the single-task and multi-task models predict calculated and experimental Auger lineshapes with good accuracy in most cases. The performance between the two task regimes is similar, with the single-task models generally having better predictions of the finer peak structures in the spectrum. The present results demonstrate that multi-task training is a promising avenue for future developments of universal x-ray spectroscopy models with learned representations that map the molecular structure to a multitude of techniques.

A previously-developed analytical treatment of the "Larger-Angle Emission" model for GRBs and afterglows is further developed to include the effect of a fixed magnetic field orientation. This model, has the uncanny ability to unify the prompt and delayed emissions and to account easily for the entire diversity of Swift X-ray light-curves. The LAE model is applied to seven GRBs (060526, 060614, 060714, 060729, 061007, 061121, 100902, 130427A) with well-sampled 0.3 keV/10 keV Swift/XRT and optical light-curves, displaying well-monitored four phases (GRB, Tail, Plateau, post-Plateau), to illustrate its power and limitations and to determine its five fundamental parameters. The one-and-only Core parameter Gamma_c*theta_c is determined by the GRB and afterglow temporal milestones (i.e. by the dynamical range of the Tail and Plateau), and may have an universal value around 3.0, with narrower Cores (smaller theta_c) being more relativistic (higher Gamma_c). Flat Plateaus require an Envelope angular structure close to Gamma(theta) ~ 1/theta^2. A magnetic field parallel to the direction of the relativistic flow yields more curved prompt/GRB and delayed/afterglow light-curves than a perpendicular or isotropic field, with curvature $\Delta \alpha$ defined as the difference between the flux asymptotic power-law decay indices at the beginning and end of each phase. The curvature Delta alpha_grb of the GRB light-curves arising from the uniform Core is set only by the B-field orientation, and a perpendicular or isotropic B-field is equally often found, but a parallel field is never identified for the Core. The curvature Delta alpha_ag of the afterglow light-curves from the power-law Envelope depends on B-orientation and three other parameters. The Envelope B-field orientation can be identified for only three afterglows, where a parallel B is found.

We use a stellar-mass complete sample of $\sim 36{,}000$ galaxies from GAMA/eFEDS to test whether AGN activity depends on environment independent of stellar mass. To isolate this effect, we introduce $\delta_{\rm rank}$, a novel local overdensity metric defined within narrow stellar mass bins. Our main result is that X-ray-selected AGNs show a clear environmental trend, the AGN fraction rises from $\sim 4\%$ in low-density regions to $\sim 6\%$ in high-density regions, with a sharp transition at $\delta_{\rm rank} \sim 0.4$. This environmental dependence is absent for WISE-selected and broad-line AGN, and Eddington ratios show no variation across environments. We also found that for galaxies with $\mathrm{SFR} > 15\,M_\odot\,\mathrm{yr}^{-1}$, X-ray AGN fraction is approximately 5%, 60% and 20% in low, mid and high $\delta_{\rm rank}$ galaxies. We show that relationship between AGN fraction and SFR varies dramatically with both environment and selection method. We conclude that environment on scales of $\sim 5h^{-1}\,\mathrm{Mpc}$ regulates X-ray AGN triggering efficiency.

A crossover transition from hadronic to quark matter during the merger of neutron stars can lead to interesting observational consequences in the emergent gravitational radiation. In particular, the increased pressure in the crossover density region ($2-5$ times the nuclear saturation density) can lead to an extended duration of high-frequency ($\sim 2-3.5$ kHz) gravitational wave emission during the post-merger epoch. We study the universality relations for a variety of equations of state with and without a crossover transition to a quark mater based upon the QHC19 and QHC21 EoSs. We find that the long-duration post-merger gravitational-wave emission is more pronounced in the QHC21 EoS. We then consider universality relations among various observable quantities that have been identified in simulations with hadronic equations of state. We show that there are deviations from the universality relations for some quantities that may ultimately provide an observational signal that such a transition has occurred.

This work presents the first steps for simulating kinetic plasmas with collisions using the characteristic mapping method (CMM). The CMM is a semi-Lagrangian method that explores a semi-group structure to store diffeomorphic flow maps efficiently. Using the semi-group structure, individual submaps can be composed to relate the flow backward in time to its initial food point. The novelty of the presented work is handling the source term by storing sub-integrals that correspond to the individual sub-maps and allow efficient integration. Furthermore, we use the Lagrangian structure to avoid implicit time integration in the hydrodynamic regime, which is known to be stiff. We benchmark our method on the Boltzmann-BGK and Vlasov-Poisson-BGK equations and consider different test cases, the Sod shock tube problem and nonlinear Landau damping for different Knudsen numbers. We show third-order spatial and temporal convergence and illustrate the fine-scale zoom property of CMM for the bump-on-tail instability.

In this work we establish general constitutive equations for a relativistic plasma composed of an arbitrary number of classical, charged, and chemically non-reacting species in the presence of a background electromagnetic field. The intensity of the electromagnetic force acting on either species is assumed to be comparable with the gradients of the state variables and is thus considered as a first-order driving force for dissipation within the gradient expansion. Assuming that the species share the same temperature and velocity flow when in equilibrium, we determine the entropy production and establish constitutive equations in terms of first-order frame invariant quantities. Conditions on the corresponding transport coefficients are given in order to comply with Onsager's reciprocal relations and the second law of thermodynamics. In particular, we discuss cross effects for the binary mixture which may be relevant for astrophysical and cosmological applications. Finally, we derive a complete set of evolution equations governing the dynamics of a binary mixture propagating on an arbitrary spacetime background.

We present near-infrared spectroscopic observations of L1415-IRS, a Class I type young stellar object that underwent a factor of $>$30 photometric outburst in the early 2000s. Ours is the first reported spectroscopy of this deeply embedded source. Both components of L1415-IRS present continuum plus $H_2$ emission. The southern component has additional weak HI Br$\gamma$ and $CO$ emission. Based upon our spectrum and evidence of a declining lightcurve, we hypothesize that either: the outburst was not large enough and therefore hot enough to produce the FU Ori type absorption spectrum commonly interpreted as an accretion disk atmosphere, or the source has already recovered from FU Ori-type equatorial accretion to re-establish T Tauri-type magnetospheric accretion.

Van der Waals heterostructures offer a direct way of combining two-dimensional (2D) materials with different electronic properties, such as 2D semiconductors, metals, and superconductors, in a single device. Bilayer graphene (BLG) is particularly attractive in this context, as its electrically tunable band gap enables local control of tunnel barriers and quantum dots. Here, we realize an all-2D hybrid platform based on BLG proximitized by superconducting NbSe$_2$. Using local electrostatic gates, we define tunnel barriers and quantum dots at different distances from the lateral superconductor-semiconductor interface. The quantum dots serve as local spectroscopic probes of the proximitized BLG channel segment, forming tunable superconductor-quantum dot-normal conductor junction devices. Coulomb blockade and finite-bias spectroscopy reveal a proximity-induced superconducting gap of up to $80\,\mathrm{\mu eV}$ and allow to track its evolution with increasing distance from the NbSe$_2$ contact. We find that the local density of states remains suppressed over distances exceeding 1 $\mu$m, consistent with superconducting proximity through a highly ballistic BLG channel. Our results show that BLG-superconductor hybrids offer a controllable platform where quantum dots and quantum point contacts can be well combined with superconductivity.

In this work, we present an improved version of the formulation of the four auxiliary bosons originally proposed by Kotliar and Ruckenstein, adapted to describe a quantum dot in the Kondo regime with finite electron-electron interaction U. The proposed refinement provides a more accurate treatment of strong electronic correlations while preserving the analytical tractability of the original approach, thereby enabling a reliable description of transport properties in nanoscale systems. Benchmark calculations show good agreement with the results of the numerical renormalization group, supporting the validity of the improved formulation. Our approach therefore provides an efficient and robust framework for investigating transport through strongly correlated quantum dots.

The sign-structure of a quantum many-body ground state is a central quantity in fixed-node approaches to mitigating the Fermion sign problem. For continuum electronic-structure Hamiltonians, the correct sign-structure is sufficient to compute exact ground state properties; on the other hand, lattice fixed-node approaches retain an additional dependence on trial wave-function amplitudes which are improved upon non-optimally while preserving their sign structure. Here we consider an iterative map obtained by repeatedly replacing the fixed-node trial state with the ground state of its associated lattice fixed-node Hamiltonian (independent of whether and how a practical algorithm could implement this iteration). We show the fixed points of this map are eigenstates of the Hamiltonian and reduced Hamiltonian resulting in at most one fixed point in the interior of each sign chamber. We prove that the ground state fixed point is stable and that the boundary of the ground state sign chamber is repulsive. This shows the amplitude dependence beyond having the correct ground state sign-structure disappears under self-consistent iteration. In other sign chambers, energy descent can be obstructed by the imposed sign structure; this tension leads to the iteration driving select amplitudes to zero producing `support collapse' onto chamber boundaries and corresponding to reduced Hamiltonians. Excited-state fixed points are therefore provably unstable and flow toward lower-energy boundary fixed points. We show sign chamber boundaries have a directional stability; boundary points attractive in one direction are repulsive under a sign flip. By revealing the geometry and stability structure of iterative fixed-node dynamics, our results clarify the foundations of a central approach to the Fermion sign problem and motivate potential new algorithmic strategies.

This paper is concerned with multivariable stochastic Hamiltonian systems governed by an ordinary differential equation for the position and an Ito stochastic differential equation for the momentum. The momentum dynamics involve both conservative and nonconservative forcing including Langevin viscous damping and the Wiener process as a random force. The setting allows for rotational degrees of freedom, a non-quadratic potential energy function and position-dependent mass, diffusion and damping matrices. In addition to modelling nonlinear physical dynamics subject to random forcing, the system is motivated by a stochastic optimisation viewpoint, where the search for global minima of the potential energy (for example, using the gradient descent) is carried out through convergence to a Boltzmann equilibrium measure which favours smaller values of this function. Under certain regularity conditions, we show that the $\chi^2$-divergence or, equivalently, Renyi's second-order relative entropy with respect to the invariant measure has a nonpositive time derivative and thus provides a Lyapunov functional candidate for this convergence. However, this derivative vanishes at some moments of time, which is related to the behaviour of the probability distribution of the momentum conditioned on the position and has a link to a family of auxiliary quantum harmonic oscillator Hamiltonians parameterised by the position space of the underlying classical system. This position-momentum conditioning is used in order to prove that such pre-equilibrium break times in the entropy dissipation are isolated, thus making the $\chi^2$-divergence a strictly decreasing Lyapunov functional for the Fokker-Planck-Kolmogorov equation which governs the joint position-momentum distribution in such systems.

We study bottomonium $\Upsilon$($n$S) production in ${\rm O}+{\rm O}$ collisions at $\sqrt{s_{NN}}=5.36$~TeV, including both cold nuclear-matter (CNM) effects and final-state interactions in a short-lived quark-gluon plasma. The CNM baseline is calculated using the EPPS21 nuclear parton distribution functions together with coherent energy loss and transverse momentum broadening. Hot-medium effects are evaluated with two transport approaches coupled to the same centrality-resolved 3+1D aHydroQP background: the QTRAJ-NLO open-quantum-system calculation, implemented with the QTraj code, and the TAMU-NP semiclassical rates, including primordial suppression and regeneration. The CNM effects give a moderate, state-independent suppression, dominated by the nPDF modification. The energy loss and transverse momentum broadening contribution remains at the few-percent level. Both transport approaches predict a sequential suppression pattern, $R_{AA}^{\Upsilon(1\rm{S})}>R_{AA}^{\Upsilon(2\rm{S})}>R_{AA}^{\Upsilon(3\rm{S})}$, with the strongest suppression around midrapidity in central collisions. The suppression of the ground state is similar in the two approaches but differs for the excited states. Since the CNM factor is common to all states, double ratios provide a direct measure of the relative hot-medium suppression. Our results support the conclusion that ${\rm O}+{\rm O}$ collisions at the LHC can produce a short-lived QGP capable of modifying bottomonium yields.

The EXFOR library is a nearly complete database for experimental radionuclide production cross sections for light charged-particle induced reactions, and retrieval of the experimental cross sections in EXFOR is the first step in determination of the best estimate of the radionuclide production cross section. The EXFOR format was designed with 80-column punched cards as the recording media, but the format is still preferred for compilation and exchange of the nuclear reaction data. The format is suitable for reading and processing by EXFOR compilers, but it is not a good choice for reading by EXFOR users with modern computer languages such as Python. We have recently attempted to lower the barrier for modern software engineers to access the information stored in the EXFOR by developing tools converting an EXFOR file to (1) the HTML format for human reading (X4IVEW), and (2) the CX4 (Compact EXFOR) format for tabulation and plotting (X4TOCX). This article introduces X4VIEW and a preliminary version of X4TOCX with the radionuclide production cross section as an example.