In the setting of stochastic Volterra equations, and in particular rough volatility models, we show that conditional expectations are the unique classical solutions to path-dependent PDEs. The latter arise from the functional Itô formula developed by [Viens, F., & Zhang, J. (2019). A martingale approach for fractional Brownian motions and related path dependent PDEs. Ann. Appl. Probab.]. We then leverage these tools to study weak rates of convergence for discretised stochastic integrals of smooth functions of a Riemann-Liouville fractional Brownian motion with Hurst parameter $H \in (0,\frac{1}{2})$. These integrals approximate log-stock prices in rough volatility models. We obtain the optimal weak error rates of order $1$ if the test function is quadratic and of order $(3H+\frac{1}{2})\wedge1$ if the test function is five times differentiable; in particular these conditions are independent of the value of $H$.

Twistronics is an emerging and captivating field in condensed matter physics and material science. However, accurately and efficiently calculating the electronic structures of twisted systems remains a significant challenge. To address this, we have developed MoireStudio, a universal Python-based computational package for twisted electronic structures. Its functionalities include commensurate structure search, structure generation, parameterization, and construction for tight-binding models and continuum models, and the precise incorporation of full relaxation effects. The package is applicable to arbitrary combinations of two-dimensional materials, including rectangular lattices and heterostructures. User-friendly and easy to use, MoireStudio supports parallel large-scale computations, provides visualization capabilities, and offers interfaces with third-party software. It is poised to become a convenient and powerful tool for researchers in twistronics fields.

The brownmillerite-type barium indate (Ba$_2$In$_2$O$_5$) is a potential electrolyte for mixed ionic-electronic conduction in solid oxide fuel cells. Revealing the defect chemistry of this material is key to understanding its ionic and electronic conductivity. In this contribution, we report the existence of oxygen interstitials in a dumbbell configuration, which are also observed in In$_2$O$_3$. Using Density Functional Theory within the generalized gradient approximation, complemented by selected hybrid-functional calculations, we investigate vacancies, various oxygen interstitials, and Frenkel pairs. In doing so, we evaluate the formation energies, charge transition levels, and concentrations as a function of oxygen partial pressure. Our results show that oxygen vacancies and interstitials dominate the intrinsic defect landscape. Among the interstitials, we identify stable dumbbell configurations that remain neutral across the entire band gap. Other interstitial configurations exhibit charged states and become the prevailing compensating defects at high oxygen partial pressures, alongside oxygen vacancies. Our results provide a consistent picture of the thermodynamics of intrinsic defects in barium indate, setting the stage for future investigations of the diffusion dynamics of oxygen vacancies and interstitials.

For first-order optimization of non-convex functions with Lipschitz continuous gradient and Hessian, the best known complexity for reaching an $\varepsilon$-approximation of a stationary point is $\mathcal{O}(\varepsilon^{-7/4})$. Existing algorithms achieving this bound are based on momentum, but are always complemented with safeguard mechanisms that erase the accumulated momentum if a certain condition is violated. Whether such resetting-momentum mechanisms are fundamentally necessary has remained an open question. We show that randomizing the parameters enable to achieve this complexity with high probability when using momentum, without any of such mechanisms. From an analysis perspective, we do so leveraging the continuized method, that interprets the algorithm as a realization of a continuous-time stochastic differential equation involving a Poisson process.

We study the behaviour of the leftmost particle in a semi-infinite particle system on $\mathbb{Z}$, where each particle performs a continuous-time nearest-neighbour random walk, with particle-specific jump rates, subject to the exclusion interaction (i.e., no more than one particle per site). We give conditions, in terms of the jump rates on the system, under which the leftmost particle is recurrent or transient, and develop tools to study its rate of escape in the transient case, including by comparison with an $M/G/\infty$ queue. In particular we show examples in which the leftmost particle can be null recurrent, positive recurrent, ballistically transient, or subdiffusively transient. Finally we indicate the role of the initial condition in determining the dynamics, and show, for example, that sub-ballistic transience can occur started from close-packed initial configurations but not from stationary initial conditions.

We study the relation between the total variation (TV) and Hellinger distances between two Gaussian location mixtures. Our first result establishes a general upper bound: for any two mixing distributions supported on a compact set, the Hellinger distance between the two mixtures is controlled by the TV distance raised to a power $1-o(1)$, where the $o(1)$ term is of order $1/\log\log(1/\mathrm{TV})$. We also construct two sequences of mixing distributions that demonstrate the sharpness of this bound. Taken together, our results resolve an open problem raised in Jia et al. (2023) and thus lead to an entropic characterization of learning Gaussian mixtures in total variation. Our inequality also yields optimal robust estimation of Gaussian mixtures in Hellinger distance, which has a direct implication for bounding the minimax regret of empirical Bayes under Huber contamination.

Observed cyclotron resonant scattering features (CRSFs) in X-ray pulsars (XRPs) exhibit strong variability. In the subcritical luminosity regime, the centroid energy ($E_{CRSF}$) and line width ($σ_{CRSF}$) often show positive correlations with the X-ray luminosity. We investigate the physical origin of the observed variability quantitatively, focusing on the effects of resonant scattering and Doppler shift induced by the plasma flow in the accretion funnel. We developed a relativistic Monte Carlo code to perform detailed radiative transfer calculations in the accretion funnel above the hotspot and derive angle-dependent spectra. Analytical plasma density and velocity profiles were adopted to account for the effects of radiation pressure on the flow. Approximate resonant scattering cross-sections were employed. We varied the accretion luminosity to explore the resulting variability of the CRSF properties. The emergent spectra exhibit a prominent, asymmetric CRSF accompanied by a broad blue wing. The CRSF is systematically redshifted relative to the classical cyclotron energy, with the magnitude of the redshift decreasing at higher luminosities and for larger viewing angles $θ$. Both $E_{CRSF}$ and $σ_{CRSF}$ correlate positively with luminosity for all viewing angles. Their absolute values, however, depend strongly on the viewing angle, indicating substantial variability over the pulse cycle and sensitivity to the system geometry. At fixed luminosity, $E_{CRSF}$ ($σ_{CRSF}$) decreases (increases) with increasing $\cosθ$. Consequently, phase-resolved observations are expected to reveal an anticorrelation between the CRSF centroid energy and width. When applied to the XRP GX 304$-$1, the model reproduces the observed CRSF variability over nearly an order of magnitude in luminosity for geometries in which the accretion funnel is predominantly viewed edge-on.

Jahn--Teller (JT) distortions are a key driver of physical properties in many correlated oxide materials. Cooperative JT distortions, in which long-range orbital order reduces the symmetry of the average structure macroscopically, are common in JT-distorted materials at low temperatures. This long-range order will often melt on heating, \textit{via} a transition to a high-temperature state without long-range orbital order. The nature of this transition has been observed to vary with different materials depending on crystal structure; in LaMnO$_3$ the transition has generally been interpreted as order-disorder, whereas in layered nickelates $A$NiO$_2$ ($A$=Li,Na) there is a displacive transition. Alternatively, recent theoretical work has suggested that previous attributions of order-disorder may in fact be a consequence of phonon anharmonicity, rather than persistence of JT distortions, which would suggest that the displacive transition may be more common than currently believed. In this work, we run Monte Carlo simulations with a simple Hamiltonian which is modified to include terms dependent on the JT amplitude $ρ$, which is allowed to vary within the simulation \textit{via} the Metropolis algorithm. Our simulations yield distributions of JT amplitudes consistent with displacive rather than order-disorder behaviour for both perovskites and layered nickelates, suggesting that displacive-like JT transitions may be more common than previously assumed in both perovskites and layered nickelates. We also find significant differences between the transition observed for perovskites compared with layered nickelates, which we attribute to differing extensivity of configurational entropy on the two lattices, showing the crucial role of lattice geometry in determining behaviour.

Accurate knowledge of the electrical and thermal conductivities and structural properties of hydrogen-helium mixtures under thermodynamic conditions within and beyond the immiscibility range is very important to predict the thermal evolution and internal structure of gas giant planets like Jupiter and Saturn. Here, we propose a novel method to determine the immiscibility boundary accurately without the need for free energy calculations, while providing consistent insights into structural and transport properties of mixtures. We show with direct large-scale ab initio simulations that the insulator-metal transition (IMT) of the hydrogen subsystem is strongly affected by an admixture with a small fraction of helium and occurs at temperatures significantly higher than those of pure hydrogen. At pressures below 150 GPa, the IMT boundary is not related anymore to the H2 subsystem dissociation, the system remains insulating even after the full dissociation of H2 molecules and its transition to an H-He mixture. The offset of the IMT in the H-He mixture relative to the dissociation region in the hydrogen subsystem and the significant reduction of static electrical and thermal conductivity by a factor between two and a few thousand relative to pure hydrogen found in mixtures have consequences for Jupiter and Saturn's thermal evolution, internal structure, and dynamo action, affecting a large fraction of the interior of both planets.

Many previously studied path algebras or self-similar group algebras may be viewed as Steinberg algebras of self-similar groupoids. By way of inverse semigroup algebras, we characterize when the Steinberg algebra of a self-similar groupoid is simple. We show that the simplicity of the reduced $C^*$-algebra of a contracting self-similar groupoid coincides with the simplicity of the Steinberg algebra. As an aside, we show that simplicity of the two algebras sometimes depends only on the skeleton of the self-similar groupoid acting on a strongly connected graph. Finally, we apply our methods to examples including a self-similar groupoid akin to multispinal self-similar groups and a self-similar groupoid built from the well-known Basilica group.

Entanglement distillation, a fundamental building block of quantum networks, enables the purification of noisy entangled states shared among distant nodes by local operations and classical communication. Its practical realization presents several technical challenges, including the storage of quantum states in quantum memory and the execution of coherent quantum operations on multiple copies of states within the quantum memory. In this work, we present an entanglement purification protocol via quantum communication, namely a carrier-assisted entanglement purification protocol, which utilizes two elements only: i) quantum memory for a single-copy entangled state shared by parties and ii) single qubits travelling between parties. We show that the protocol, when single-qubit transmission is noiseless, can purify a noisy entangled state shared by parties. When single-qubit transmission is noisy, the purification relies on types of noisy qubit channels; we characterize Pauli channels such that the protocol works for the purification. We address this limitation by using multiple carrier qubits, and show that for any depolarizing channel with channel fidelity greater than 1/2, the protocol's fixed-point fidelity approaches unity as the number of carriers increases. Our results significantly reduce the experimental overhead required for distilling entanglement: the practical advantage is demonstrated through parameters directly related to the capability of entanglement purification, such as noise in quantum memory, local measurements, channel use, and entanglement fidelity. We envisage that the protocol would make long-distance pure entanglement closer to a practical realization.

We perform fully nonlinear, spherically symmetric numerical simulations of superhorizon false-vacuum-domain (FVD) collapse in a coupled gravity-scalar-fluid system to study primordial black hole (PBH) formation during delayed first-order phase transitions (FOPTs). Using adaptive mesh refinement to resolve the bubble wall, we identify three dynamical outcomes: type B (supercritical) PBHs with an interior baby universe and a bifurcating trapping horizon, type A (subcritical) PBHs with an apparent horizon formed by direct wall collapse, and dispersal with no PBH formation. To separate these three cases, we evaluate two commonly used PBH-formation criteria: the time scale ratio $t_\mathrm{H}/t_\mathrm{V}$ (horizon crossing time versus vacuum-energy domination time) and the local density contrast $δ(t_\mathrm{H})$ at horizon crossing. For the parameter space explored, we find that $t_\mathrm{H}/t_\mathrm{V}$ is a more robust predictor of outcome: type B PBHs form when $t_\mathrm{H}/t_\mathrm{V} \gtrsim 1$ (critical range $\sim 1.1 - 1.6$ in our survey), type A PBHs arise when $t_\mathrm{H}/t_\mathrm{V}$ is below this threshold but remains above a lower bound (typical range $\sim 0.35 - 0.7$), and no-PBH dispersal occurs when $t_\mathrm{H}/t_\mathrm{V}$ falls below this lower bound. When a clear thin-wall FVD boundary exists, $δ(t_\mathrm{H})$ can correspondingly distinguish different outcomes (roughly $δ_c(t_\mathrm{H}) \sim 1 - 1.7$ for type B and $δ_c(t_\mathrm{H}) \sim 0.35 - 0.5$ for type A), but is highly sensitive to wall structure and model details and thus less universal. These results offer new insights into the dynamics of FVD collapse, quantify practical PBH-formation thresholds, and pave the way for precise predictions of PBH abundance from delayed FOPTs.

Muon-spin spectroscopy at continuous sources has stagnated at a stopped muons rate of ~40 kHz for the last few decades. The major limiting factor is the requirement of a single muon in the sample during the typical 10 μs data gate window. To overcome this limit and to be able to perform muon-spin relaxation (μSR) measurements on millimeter-sized samples, one can use vertex reconstruction methods to construct μSR spectra. This is now possible thanks to the availability of very thin monolithic Si-pixel chips, which offer minimal particle scattering and high count rate. Here we present results from a Si-pixel based spectrometer that utilizes vertex reconstruction schemes for the incoming muons and emitted positrons. With this spectrometer we were able to obtain a first vertex reconstructed μSR (VR-μSR) spectrum. The unique capabilities and benefits of such a spectrometer are discussed.

Species populations often modify their environment as they grow. When environmental feedback operates more slowly than population growth, the system can undergo boom-bust dynamics, where the population overshoots its carrying capacity and subsequently collapses. In extreme cases, this collapse leads to total extinction. While deterministic models typically fail to capture these finite-time extinction events, we propose a stochastic framework, derived from an individual-based model, to describe boom-bust-extirpation dynamics. We identify a noise-driven, threshold-like behavior where, depending on initial conditions, the population either undergoes a ``boom'' or is extirpated before the expansion occurs. Furthermore, we characterize a transition between an excitable regime, where most trajectories are captured by the absorbing state immediately after the first bust, and a persistent regime, where most populations reach a metastable state. We show that this transition is governed by the noise strength and the ratio of environmental-to-population timescales. This framework provides a theoretical basis for understanding irreversible transitions in invasive species, plant succession, microbial dynamics, and the elimination of cancerous tumors.

Motivated by a recent conjecture of Misumi and Yumoto relating the number of zero modes of lattice Dirac operators to the sum of the Betti numbers of the underlying spacetime manifold, we study formal naive Dirac operators on a class of graphs admitting such in terms of their zero modes. Our main result is that for graphs on which translations commute, the conjecture of Misumi and Yumoto can be shown and indeed can be strengthened to obtain bounds on the individual Betti numbers rather than merely on their sum. Interpretations of the zero modes in terms of graph quotients and of the representation theory of abelian groups are given, and connections with a homology theory for such graphs are highlighted.

Separating turbulent fluctuations from coherent large-scale background flows is a longstanding challenge in the analysis of numerical simulations and astronomical observations. Traditional approaches commonly rely on decomposition-based techniques such as Fourier or wavelet filtering, which assume that a meaningful separation can be achieved through scale selection. In realistic flows, however, coherent motions and turbulence often overlap across a broad range of scales and interact nonlinearly, making a unique separation inherently ambiguous. In this work, we investigate the robustness of an AI-based turbulence-background separation approach using two-dimensional incompressible Navier-Stokes simulations of decaying hydrodynamic turbulence. The simulations are initialized with a coherent background flow and divergence-free turbulent perturbations with a Kolmogorov-like spectrum and evolve without external forcing, providing a controlled physical testbed. A neural network trained exclusively on static synthetic images is applied to simulation snapshots at different evolutionary stages. The model recovers turbulent fluctuations during early and intermediate stages when partial scale separation is present. At later stages, where nonlinear interactions increasingly mix coherent and turbulent structures, the separation becomes less distinct; nevertheless, the recovered fields remain visually and spectrally consistent with the expected turbulent behavior. Quantitative comparisons with a Fourier filtering baseline show that the AI-based approach achieves comparable reconstruction accuracy while not requiring an explicit spectral cutoff scale. These results suggest that AI models trained on static data can provide a flexible diagnostic tool for turbulence-background separation in time-evolving flows, with potential applications to astrophysical datasets.

The formation of $^{44}\mathrm{Ti}$ in massive stars is thought to occur during explosive nucleosynthesis, however recent studies have shown it can be produced during O-C shell mergers prior to core collapse. We investigate how mixing according to 3D macro physics derived from hydrodynamic simulations impacts pre-supernova O-C shell merger nucleosynthesis and if it can dominate explosive supernova production of $^{44}\mathrm{Ti}$ and other radioactive isotopes. We compare a range of observations and models of explosive $^{44}\mathrm{Ti}$ yields to pre-explosive multi-zone mixing-burning nucleosynthesis simulations of an O-C shell merger in a $15~\mathrm{M_\odot}$ $Z=0.02$ stellar model with mixing conditions corresponding to different 3D hydro mixing scenarios. Radioactive species produced in the $\mathrm{O}$ shell have a multi-dex spread in pre-explosive yield predictions across different 3D mixing scenarios of $1.54~\mathrm{dex}$ and $2.14~\mathrm{dex}$ on average depending on mass cut. $^{44}\mathrm{Ti}$ has the largest spread of $4.78~\mathrm{dex}$ and $4.81~\mathrm{dex}$ depending on mass cut. Further, we show that the pre-explosive production of $^{44}\mathrm{Ti}$ can be larger than the explosive production of models and can match observations. Our results also show that 3D mixing physics enhances $^{44}\mathrm{Ti}$ in 1D models without modifying $^{56}\mathrm{Ni}$ yields. We conclude that quantitative predictions of $^{44}\mathrm{Ti}$ and other radioactive species more broadly require an understanding of the 3D hydrodynamic mixing conditions present during the O-C shell merger.

In these lecture notes, we review recent progress in the study of the stochastic heat equation and its discrete analogue, the directed polymer model, in spatial dimension 2. It was discovered that a phase transition emerges on an intermediate disorder scale, with Edwards-Wilkinson (Gaussian) fluctuations in the sub-critical regime. In the critical window, a unique scaling limit has been identified and named the critical 2d stochastic heat flow. This gives a meaning to the solution of the stochastic heat equation in the critical dimension 2, which lies beyond existing solution theories for singular SPDEs. We outline the proof ideas, introduce the key ingredients, and discuss related literature on disordered systems and singular SPDEs. A list of open questions is also provided.

Achieving parametric excitation in an oscillating physical system involves periodically adjusting one of its parameters to modulate the oscillator's natural frequency. This phenomenon has been observed in numerous systems within physics and engineering, profoundly transforming modern science and technology. Despite rapid progress, the parametric control of collective excitations, such as phonons, remains a challenge while promising to generate novel and intriguing effects in a largely unexplored field. Here, we investigate the terahertz (THz) field-induced dynamics of Raman-active phonons in the perovskite structure of LaAlO$_3$ (LAO). Utilizing intense THz pulses, we demonstrate a novel mechanism of parametric phonon excitation marked by substantial subharmonic components. Theoretical analysis can successfully capture the hallmarks of the observed phenomena in a physical scenario with the THz field inducing a parametric coupling between the Raman mode and pairs of acoustic phonon excitations.

Accurate determination of fireball direction is essential for retrieving trajectories and velocities. Errors in these measurements have significant implications, affecting the calculated pre-impact orbit, influencing mass estimates, and impacting the accuracy of dark flight simulations, where applicable. Here we implement a new atmospheric refraction correction technique that addresses a significant aspect previously overlooked in the field of meteor science. Traditional refraction correction techniques, originally designed for objects positioned at infinite distances, tend to overcompensate when applied to objects within the Earth's atmosphere. To rectify this issue, our study introduces the concept of the atmospheric refraction delta z correction technique, involving the artificial elevation of the observer site height above sea level. We utilize analytically derived formulas for the delta z correction in conjunction with commonly used refraction models, validating these results against a numerical solution that traces light rays through the atmosphere. This ray-tracing model is applied to finely meshed atmospheric layers, yielding precise correction values. We evaluate multiple sources of error in order to quantify the achievable accuracy of the proposed method. Our approach (1) enables the determination of fireball positions with improved astrometric accuracy, (2) removes the explicit dependence on the fireball distance from the observer or its height above Earth's surface within the limits imposed by realistic atmospheric variability, and (3) simplifies meteor data processing by providing a robust framework for analyzing low-elevation fireball observations, for which atmospheric refraction is significant and is automatically corrected by the method. As a result of this work, we provide open, publicly accessible software for calculating the delta z correction.

Local interscale energy transfer in Large Eddy Simulation (LES) is typically diagnosed using the subgrid-scale (SGS) production, $Π^{SGS}$. In this work, an exact algebraic gauge identity is derived, demonstrating that $Π^{SGS}$ is composed of a kernel-integrated increment-based transfer, $Π^{inc}$, and the divergence of a spatial transport current, $\nabla \cdot J$. This identity was verified to machine precision ($10^{-16}$) using the analytical multi-harmonic Womersley solution. Further evaluation was conducted via Direct Numerical Simulation (DNS) of turbulent channel flow at $Re_τ\approx 1000$. It was observed that $\nabla \cdot J$ dominates $Π^{SGS}$ in the near-wall region. The results suggest that $Π^{SGS}$ is not a unique proxy for the local cascade in inhomogeneous flows. A new framework is thus provided for the interpretation of interscale transfer diagnostics in wall-bounded transport phenomena.

We show that a simple nonlinear differential equation (originally studied in the physics of disordered systems) is able to mathematically describe the global population growth over the past 12000 years. Different regimes of population growth since the early Neolithic until today are shown to be all solutions to the same nonlinear differential equation in its various limits. These also include the well-known Malthus (exponential) and Verhulst (logistic) growth regimes, as well as von Foerster's ``doomsday'' formula. All these limits correspond to neglecting higher-order terms in a more general nonlinear dynamic model described by the proposed nonlinear differential equation. While the older models may provide valid fittings to limited time intervals in the global population growth curve in time, their clearly approximate nature prevents them from being predictive over longer periods of time. The proposed comprehensive solution of the proposed model is instead well suited to provide predictions for future scenarios. These include a scenario where the global population could halve as early as 2064 under a deliberately conservative, worst-case assumption that carrying-capacity constraints become abruptly active today.

The nuclear equation of state, which determines the structure and properties of neutron stars, remains subject to substantial theoretical uncertainties, leading to model dependence in predicted observables. Universal relations have emerged as a powerful tool to mitigate this dependence by linking neutron star observables in a framework-independent manner. In this work, we introduce a new universal relation that \emph{bridges} finite nuclei and neutron stars through the dimensionless quantity $ζ= β_{1.4}\tilde{L}^{-1}$, which couples the compactness of a $1.4~M_{\odot}$ neutron star to the slope of the nuclear symmetry energy at saturation. The relation is examined under a broad set of relativistic energy density functionals with point-coupling and meson-exchange interactions, as well as non-relativistic Skyrme functionals. We demonstrate that $ζ$ exhibits a strong exponential correlation with the electric dipole polarizability $α_D$ in finite nuclei across all considered equations of state. By exploiting experimental $α_D$ data for selected neutron-rich nuclei, we constrain $ζ$ and translate these constraints into equation-of-state independent bounds on the neutron star radius $R_{1.4}$ and the symmetry-energy slope $L$, providing insights into the properties of neutron star matter.

Time-optimal control for triple integrator under full box constraints is a fundamental problem in the field of optimal control, which has been widely applied in the industry. However, scenarios involving asymmetric constraints, non-stationary boundary conditions, and active position constraints pose significant challenges. This paper provides a complete characterization of time-optimal switching surfaces for the problem, leading to novel insights into the geometric structure of the optimal control. The active condition of position constraints is derived, which is absent from the literature. An efficient algorithm is proposed, capable of planning time-optimal trajectories under asymmetric full constraints and arbitrary boundary states, with a 100% success rate. Computational time for each trajectory is within approximately 10$μ$s, achieving a 5-order-of-magnitude reduction compared to optimization-based baselines.

Optical absorption is a primary, label-defining contrast across biology, pathology, and materials science, yet three-dimensional quantitative absorption imaging has remained largely inaccessible to the brightfield microscopes used in everyday practice. We introduce quantitative absorption tomography (QAT), which recovers volumetric distributions of the extinction coefficient by treating brightfield image formation as a linear inverse problem in logarithmic intensity space and inverting a three-dimensional absorption optical transfer function. Under weak-scattering conditions, QAT yields spectrally resolved, three-dimensional absorption maps from through-focus image stacks acquired on standard brightfield platforms, without interferometry, coherent illumination, or sample rotation. We use QAT to track melanin dynamics in living melanoma cells without exogenous labels, image pigment organization in intact Petunia hybrida petals in vivo, and reconstruct chromogenic contrast across large H&E-stained human tissue volumes. By establishing absorption as a directly measurable volumetric quantity within standard brightfield workflows, QAT positions chromogenic contrast as a quantitative axis alongside fluorescence- and refractive-index-based imaging.

LISA, the Laser Interferometer Space Antenna, due to launch mid-2035, is a large class space mission by the European Space Agency (ESA). In partnership with NASA and ESA-member states, ESA is on track to launch what is expected to be the first space-based gravitational wave detector. By hosting detectors in space, one gains access to a lower frequency band of gravitational wave sources and, with them, a plethora of new science. To maximise this scientific gain, ESA and NASA selected 20 scientists for the LISA Science Team to carry out and/or lead the necessary actions leading up to LISA's launch. We give a short overview and update of the LISA mission, its science objectives and related waveforms, as well as the work of the LISA Science Team as of April 2026.

Studies of galactic bars have primarily focused on stellar bars, since they can be directly observed through ultraviolet to infrared wavebands. Cosmological as well as idealised simulations reveal that the dark matter (DM) haloes interact with baryonic matter, primarily the stellar bars, dynamically by means of the exchange of angular momentum. In these simulations, the spherical DM halo dynamically responds to interaction with the stellar bar by reshaping its orbital structure in the proximity of the stellar bar, forming a bar-like configuration, called as the Dark Matter (DM) bar. Using N-body simulations of Milky Way analogs we discuss the role of inner halo angular momentum, measured as halo spin parameter λ of the dark matter halo, on formation and evolutionary characteristics of the DM bars. Our systematic study involves haloes with initial spin configurations ranging from λ = 0 to 0.1. The result conveys that DM bar formation and its characteristics are extensively dependent on the initial spin parameter λ of the DM halo. We demonstrate that the strength of the dark matter bar gradually increases with an increase in halo spin in long-term evolution, with a significant impact of stellar bar buckling on dark matter bar strength. The evolutionary characteristics of the DM bar are strongly influenced by the initial spin of the host halo.

The stellar halo of the Milky Way contains the remnants of past accretion events, which could be detectable as substructures in the classical integrals of motion space, such as energy and angular momentum (E-Lz). However, our galaxy also contains a non-axisymmetric stellar bar, which traps stars in resonant orbits, leading to substructures in phase-space. Using a high-resolution magneto-hydrodynamic cosmological zoom-in simulation of a Milky Way analogue, we explore the connection between the bar and the accreted stellar halo. We find that the bar induces prominent substructures, or "ridges", in E-Lz, caused by the resonances. The most pronounced of these is caused by the corotation and the retrograde 1:1 resonances, with weaker ridges visible due to the prograde 1:1 and outer Lindblad resonance. The ridges are present across much of the stellar halo, with variations in radius due to the morphology of different orbital families. We explore the scattering of orbits at the resonances, finding that stars trapped at the 1:1 retrograde resonance become more circularised and have more negative angular momentum. Additionally, stars can move between the corotation and retrograde 1:1 families, thus alternating between prograde and retrograde motion. Due to these scatterings and the pre-existing metallicity gradients in the accreted population, the bar-induced substructures have distinct metallicities compared to stars in the surrounding phase-space. Our results suggest the need for caution when searching the Milky Way stellar halo for accreted substructures in both integral of motions and chemical spaces, since these can be induced by internal perturbations.

We derive the gravitational radiation-reaction (RR) force in the harmonic coordinate system at the fourth-and-a-half post-Newtonian (4.5PN) order in the case of compact binary systems. Dimensional regularization is used to treat the ultra-violet divergences which appear at that order. We prove that the RR acceleration implies the known radiation fluxes at infinity associated with energy, angular momentum, linear momentum, and center-of-mass position. As a consistency check, we verify the manifest Lorentz invariance of the RR acceleration in harmonic coordinates. Our result should be useful for comparisons with other approaches such as the gravitational self force (GSF) and the post-Minkowskian (PM) effective field theory.

We determine the covert capacity for entanglement generation over a noisy quantum channel. While secrecy guarantees that the transmitted information remains inaccessible to an adversary, covert communication ensures that the transmission itself remains undetectable. The entanglement dimension follows a square root law (SRL) in the covert setting, i.e., $O(\sqrt{n})$ Einstein-Podolsky-Rosen (EPR) pairs can be distributed covertly and reliably over $n$ channel uses. We begin with covert communication of classical information under a secrecy constraint. We then leverage this result to construct a coding scheme for covert entanglement generation. Single-letter expressions are derived for the covert key-assisted and unassisted secrecy capacities, as well as for the covert entanglement-generation capacity.