This paper presents a measurement of the charge-parity ($C\!P$) structure of the Yukawa coupling between the Higgs boson (H) and tau leptons, using proton-proton collision data at $\sqrt{s}$ = 13.6 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 62.4 fb$^{1}$. Angular correlations between the decay products of tau leptons produced in H $\to$ $ττ$ decays are exploited to constrain the effective $C\!P$ mixing angle $α^{\mathrm{H}ττ}$, which parameterizes the admixture of scalar and pseudoscalar couplings. The mixing angle is measured to be $α^{\mathrm{H}ττ}$ = (36$^{+33}_{-30}$)$^\circ$, compared with an expected value of (0 $\pm$ 19)$^\circ$ under the standard model hypothesis. When combined with the previous CMS measurement using data collected at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 138 fb$^{-1}$, the mixing angle is determined to be (7 $\pm$ 16)$^\circ$, with an expected value of (0 $\pm$ 14)$^\circ$. This result represents the most precise measurement by CMS of the $C\!P$ nature of the Higgs boson coupling to tau leptons, with an expected precision that is the best achieved by any experiment to date.

During the Summer of 2025 the LHC collided protons with oxygen, oxygen with oxygen and neon with neon. The ATLAS experiment recorded these data with its Forward Proton detectors (AFP) inserted on both: the proton and ion sides. This allows access to many interesting studies with scattered fragments being tagged. A few analysis ideas are presented followed by preliminary studies of what could be visible in the AFP.

A search for dijet resonances in the mass range of 100-250 GeV is presented using proton-proton collision data recorded by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Conventional searches for hadronic resonances in the sub-TeV regime are heavily constrained by high jet trigger thresholds required to manage the overwhelming rate of Standard Model multijet background processes described by quantum chromodynamics. To overcome this limitation, this analysis uses a novel strategy that separately reconstructs multiple proton-proton interactions per bunch crossing, known as pile-up collisions. The dataset was collected by the ATLAS experiment using single-electron and single-muon triggers in 2016-2018 corresponding to an integrated luminosity of 1.30 pb$^{-1}$, which represents the effective luminosity of pile-up collisions recorded alongside triggered events. This constitutes the first application of pile-up collisions to probe low dijet mass scales. No significant excess is observed above the background expectation and exclusion limits are set for a generic Gaussian model and a simplified dark matter model featuring an axial-vector mediator with coupling to quarks.

The Migdal effect predicts that a nuclear recoil can be accompanied by detectable atomic ionization or excitation signals, even at the low energies expected from interactions of sub-GeV dark matter particles with atomic nuclei. Liquid xenon-based dark matter experiments have projected substantial sensitivity gains to light dark matter based on this effect, underscoring the importance of its direct characterization in xenon. In this Letter, we draw on our theoretical and experimental studies of nuclear recoil Migdal interactions to discuss their predicted characteristics and corresponding observable signatures in liquid xenon detectors. We examine the challenges of directly observing Migdal signals using neutron-induced xenon recoils and outline possible measurement strategies and necessary background mitigation measures to allow a definitive confirmation of the Migdal effect in liquid xenon.

Generalizing the gravitational potential first proposed in [1] we derive a large class of relativistic singularity free theories of gravity, which reduce to flat spacetime at large distances. We verify that for the chosen gravitational potential the force and the space-time curvature resolve the singularity and vanish at large distances. We show that those singularity free black hole solutions generically have a two horizon structure. Furthermore, we show that there is a subclass of potentials which produce a geometries geodesically complete through the origin. We discuss the implications of the effects resulting from such theories and show that black holes solutions are predicted to have minimum allowed mass.

We compute neutral scalar and neutral massless Dirac greybody factors and Hawking spectra for the positive-cosmological-constant branch of the Einstein--Euler--Heisenberg black hole. The finite region between the black-hole and cosmological horizons is treated as a two-sided scattering problem, with direct numerical integrations providing the transmission coefficients and a sixth-order WKB calculation used as a local check near the barrier top. Along the reference family studied here, increasing the Euler--Heisenberg coupling raises the dominant scalar and Dirac barriers and shifts the half-transmission frequencies upward. At fixed charge and nonlinear coupling, increasing the cosmological constant contracts the static patch and lowers the dominant greybody thresholds. The luminosity is controlled as much by the de Sitter temperature prescription as by the greybody factors: event-horizon prescriptions brighten the emission as the nonlinear correction grows, whereas effective static-patch temperatures give much smaller rates and can reverse the trend. Thus the evaporation interpretation is not unique unless the temperature convention is specified explicitly.

We show that the remaining diagonal Einstein equations in the Carter-projective sector of stationary axisymmetric spacetimes are equivalent to a single sourced master equation. The projective structure is taken as the input fixed by the off-diagonal Einstein equations. In the anti-aligned exponential branch, which contains the Kerr--Carter and Plebański--Demiański real section, the remaining diagonal Einstein system reduces to \[ \mathcal L_{\rm CP}[Δ,Y] =16πΣ\left( T_{\hat0\hat0}+T_{\hat3\hat3} \right), \] where \(Δ(r)\) and \(Y(x)\) are the radial and angular structure functions. The reduction is accompanied by two geometric diagonal identities of the Einstein tensor, which become algebraic compatibility conditions on admissible matter sources. In the homogeneous limit, the vacuum--\(Λ\) Kerr--Carter and Plebański--Demiański families are recovered as solutions of the same master operator. We also show the projective covariance of the construction and discuss compatible sources, including the aligned Maxwell field and separable anisotropic examples.

We study the critical gravitational collapse of a spherically symmetric massless scalar field in asymptotically anti-de Sitter (AdS) spacetime. The scalar field potential adopted here is inversely proportional to the square of the AdS curvature radius $\ell$, and the system admits a well-known exact static solution. Working in polar coordinates, we first confirm that type II critical collapse occurs for a range of distinct initial configurations when $\ell=8$, where the measured echoing period and critical exponent are in excellent agreement with Choptuik's classic results. We then fine-tune the initial amplitude of the scalar field for a series of AdS radii $\ell$, performing calculations in both polar coordinates and double null coordinates to cross-validate our results. We find that the form of the potential does not alter the critical behavior of gravitational collapse in any meaningful way: in particular, both the echoing period ($Δ\approx 3.4$) and critical exponent ($γ\approx 0.37$) remain essentially unchanged across all tested values of $\ell$.

In gravitational physics, matter does not merely move within spacetime; it also determines the light cones that define causal relations. What happens when the matter that determines these light cones is itself in a quantum state? We address this question in a controlled low-energy setting: a massless scalar field propagating in the spacetime with the Newtonian gravitational potential sourced by a non-relativistic quantum particle. We show that the light cones are affected by an operator-valued Shapiro delay, with the three consequences: (i) causal-boundary shifts are promoted to noncommuting observables, giving the causal structure an irreducible quantum uncertainty; (ii) the causal relation between two fixed spacetime points can become a superposition of timelike and spacelike configurations; and (iii) tracing out the source smears the Wightman light-cone singularity, producing an effective UV cutoff. Thus, quantum matter does not merely fluctuate within spacetime; it makes the causal structure itself quantum, even without quantized gravitons.

We investigate the fate of an observer falling towards a Kerr black hole. The tidal forces are computed for arbitrary trajectories of an observer, and we specify them along the polar axis in order to remain as far as possible from the ring-shaped singularity. Our analysis shows that an observer is not tidally disrupted during the fall provided that the black hole mass exceeds a critical value, which depends on its spin. In practice, any supermassive black hole represents a suitable candidate to allow an observer to traverse the black hole without severe deformation. In contrast, stellar-mass rotating black holes do not satisfy the mass condition and are expected to subject the observer to extreme tidal forces leading to its destruction during the plunge.

We present a designer method for flat Friedman-Robertson-Walker space-times within the framework of Horndeski's scalar-tensor theory. As a result, one can find subclasses of Horndeski's scalar-tensor theory within which cosmological solutions exist without ghosts and Laplace instabilities. As an example, we found subclasses of Horndeski's theory for exponential and power-law inflation models of the Universe without pathologies.

Gravitational lensing of gravitational waves (GWs) can produce multiple images in the geometric optics limit. These lensed GW images arrive at different times, are amplified by different magnification factors, and are shifted by constant phases. With current understanding, the occurrence of lensed events stands at a few per thousand events, and the number of GW detections is a few hundred with the ground-based detector network. However, with the inclusion of the sub-threshold events, the total number of detections crosses a few thousand. Therefore, a search that includes both types of events yields a higher chance of lensing detection. In this work, we carry out the first model-independent lensing search using a cross-correlation-based technique GLANCE over the entire volume of the GWTC-4 strain data, containing $\sim 90$ super-events $\sim 800$ sub-events forming a total of $\sim 11,000$ event pairs with a higher False Alarm Rate (FAR) event rate allowing to search deep in the noise dominated regime. We further conduct their spectrogram checks to inspect data quality, sky-map overlap of the interesting pairs, and a Bayesian parameter exploration of the sub-event to make a robust lensing detection. Although the search indicated four pairs of potential events with cross-correlation significance $\geq 2σ$, none were above $3σ$ at both the LIGO-Hanford and LIGO-Livingston detectors. This makes it possible to strongly rule out the presence of any statistically significant sub-threshold lensed GW event in GWTC-4. The null detection translates to an upper bound on the lensing detection rate to be $\leq$ 1.5/yr with inclusion of the sub-threshold event candidates. In the future, with more observation time, the detection of lensed GW can be possible from the current generation of GW detectors.

In this paper, the shadow of the four-dimensional charged AdS black hole surrounded by string cloud and quintessence is derived. The shadow radius shows a strictly monotonic and invertible correlation with the event horizon radius. The phase structures of the black hole for different parameters are reproduced through traditional thermodynamic geometry, which are similar to a van der Waals system. By analyzing the phase structure of the black hole in the context of shadows, thermodynamical phase structures with the shadow radius as the variable replicate the phase transition with the event horizon radius as the variable. We present the energy emission rates for massless and massive particles and discover that the maximum emission frequency can also serve as a useful tool for thermodynamic analysis. We firstly study and systematically establish shadow thermodynamics under the background of string cloud and quintessence, and our results reveal the independent regulatory mechanism of dark components on phase transitions as well as the universal topological invariance of the phase transition structure.

Echo models phenomenologically encode possible near-horizon structure by replacing the purely ingoing horizon-side condition with an effective reflecting inner boundary near the would-be horizon. We study this idea in a controlled transfer-function model consisting of a compactly supported one-dimensional barrier and a Robin wall at a large negative tortoise coordinate. The aim is not to propose a new echo mechanism or to make an observational claim, but to analyze the standard cavity denominator in a benchmark model with explicit normalizations. All rigorous $O(L^{-2})$ localization estimates are proved for this compactly supported model.

We investigate the dynamics of charged particles around a Schwarzschild-like black hole sourced by a Kalb-Ramond field and immersed in a uniform external magnetic field. The Kalb-Ramond field introduces a Lorentz violation parameter $l$ that modifies the spacetime geometry, while the magnetic field profoundly influences the trajectories through the Lorentz force, leading to a rich variety of orbital behaviours including curled (epicyclic) motion and dramatic transitions between distinct energy boundary configurations. We derive the full equations of motion, the effective potential, and the fundamental frequencies of quasi-periodic oscillations, and perform a comprehensive Monte Carlo Markov Chain (MCMC) analysis using observational data from the microquasars GRO 1655-40, XTE 1550-564, and GRS 1915+105. The pure Schwarzschild model is statistically ruled out for all three sources. For GRO 1655-40 and XTE 1550-564, only the combined effect of the magnetic field and Lorentz violation yields statistically robust models, with best-fit values $\mathcal{B}\sim 0.03$-$0.04$ and $l\sim 0.08$--$0.10$. Remarkably, for GRS 1915+105, the most massive object in our sample, the Lorentz violation parameter alone is sufficient to model the QPO frequencies, yielding an optimal fit with $ΔAIC = ΔBIC = 0$. Across all three objects, a clear trend emerges: the required value of $l$ decreases as the mass of the astrophysical object increases, suggesting a mass-dependent scaling of the Kalb-Ramond parameter. These findings establish the combined KR and magnetic field framework as a viable and statistically robust scenario for modeling QPOs in microquasars, and indicate that Lorentz-violating modifications to gravity may leave observable imprints in the strong-field regime, offering new avenues for testing quantum-gravity phenomenology with current and next-generation X-ray missions.

We develop a branch-sensitive thermodynamic framework for higher-curvature black holes using the off-shell Gibbs free energy $G_{\rm off}$ and the Wald entropy$S_W$ as the basic data. On fixed-parameter slices, equilibrium black holes are stationary points of $G_{\rm off}$, and their local stability is governed by the Hessian $H=S'_W(r_h)T'(r_h)$, rather than by the temperature slope alone. For the five-dimensional charged regular AdS black hole in quasi-topological gravity, $S_W$ remains monotonic on the physical branch, so the usual temperature-slope rule is recovered only as a special consequence. The same off-shell structure also gives the local $A_3$ cusp normal form near criticality, yielding the mean-field $1/2$ branch separation exponent and explaining why smooth nondegenerate observables, such as the Lyapunov exponent, inherit the same scaling. In Lovelock black holes, $S'_W$ can change sign on non-planar branches, reversing the temperature slope stability assignment. However, on ghost-free and branch-regular Lovelock exteriors $S'_W$ remains positive. Thus the off-shell Hessian criterion also diagnoses why the ordinary slope rule is protected on physically admissible black holes branches.

We regularize the Aichelburg-Sexl shock-wave metric for massless particles by smearing the point-like source over a string-inspired length scale $l_0$, obtaining a singularity-free gravitational potential. A coordinate transformation reveals that the transverse geometry is a zero-throat Einstein-Rosen wormhole, providing an explicit geometric realization of the ER=EPR conjecture for entangled photons. Crucially, we show that the gravitational self-energy depends on the photon's longitudinal extent $L$ (its wavelength) and, for a transversely separated photon pair, is suppressed by a factor $1/L$, giving $E^{\rm GSE}\sim 4G(\hbarω)^2/(c^4 L)\ln(d^2/l_0^2)$. For the coincident back-to-back pair created in $e^{+} e^{-}\to2γ$, the wormhole carries no additional binding energy; the logarithmic interaction energy emerges only after the entangled photons separate to a distance $d$, stretching the ER bridge. We further provide an entanglement-entropy interpretation: by computing the entanglement entropy of null intervals in the shock-wave geometry and introducing an effective entanglement temperature $k_B T_{\rm ent}\sim\hbar c/(2πL)$, we recover the same scaling and normalization of the gravitational self-energy. For optical photons the corresponding collapse time exceeds $10^{30}$ years, making isolated photons immune to gravity-induced wave-function collapse. These findings establish a rigorous playground for testing ER=EPR and reveal a deep suppression of quantum-gravity effects for ultra-relativistic quanta.

We investigate the relation between gravitational dynamics and the second law of thermodynamics in a non-equilibrium framework. Extending Jacobson's thermodynamic derivation of the Einstein equations, we introduce a stochastic geometric flow for the spacetime metric and define entropy production as the ratio between forward and time-reversed trajectories. We show that entropy production is governed by curvature and matter contributions, and that its vanishing selects configurations satisfying the Einstein field equations. Classical general relativity thus emerges as the reversible limit of an underlying stochastic geometro-dynamics, while the second law arises from its non-equilibrium evolution.

Gravitational-wave inference for long signals, like those from binary neutron-star (BNS) systems, requires waveform models that are both physically faithful and computationally efficient, otherwise, one risks drawing incorrect conclusions about nuclear matter from observations. To address this challenge, we present a frequency-domain implementation of the accurate SEOBNRv5THM waveform model for quasi-circular, spin-aligned BNS systems within the effective-one-body framework. Our approach combines the stationary-phase approximation (SPA) for the early inspiral with a fast Fourier transform treatment of the late- and post-inspiral regime, applied mode-by-mode. Our hybrid approach retains the efficiency of the SPA without affecting the waveform accuracy close to merger, where matter effects are most significant. The resulting waveform's generation speed can be further decreased using modern parameter-estimation techniques, such as multibanding and relative binning. We demonstrate excellent agreement with the baseline SEOBNRv5THM model in both mismatches and when analyzing real and synthetic data, and show how waveform systematics could affect BNS detections in upcoming observational runs and new facilities on the ground. We find that our method significantly reduces computational costs, enabling faithful parameter estimation for BNS signals within practical runtimes of order days. Our procedure can be readily extended to coalescing binary black hole systems.

In the present study, we explore the fundamental properties of static, spherically symmetric quark stars composed of quark matter with an interacting quark equation of state (EoS) within the framework of Ricci-Determinant gravity. To this end, we adopt the relativistic stellar structure equations for compact objects derived in the literature. Our primary objective is to investigate deviations from General Relativity (GR) in key physical characteristics, particularly the mass--radius relation and stability criteria, arising from the free parameters of this extended gravitational theory. We see that, unlike the hadronic case, the model predicts a reduction in the compactness of quark stars. This parameter is also sensitive to gravitational binding-energy analysis, revealing a breakdown of the assumed universality. Furthermore, the formation of objects with high central densities is restricted by the instability conditions that arise when the contribution of perturbative terms exceeds by approximately half the contribution of ordinary GR, indicating a clear limitation in the theory.

One of the most popular competitors to the CDM paradigm as an explanation for the late-time acceleration of the universe is the modification of general relativity (GR), with models such as $f(R)$ gravity among the main motivations. In this study, we consider an exponential $f(R)$ gravity model as a possible extensions of the GR. The extra scalar degrees of freedom and their effects on the cosmic expansion and structure formation are continuously considered in this scenario. By combining the PPS, BBN, CC, DESI-DR2, and CMB datasets, we imposed limitations on this model. We performed a detailed statistical analysis of the free model parameter $b$ together with the standard cosmological parameters. Our analysis yields values of $H_0$ that are slightly lower than those obtained in $Λ$CDM, indicating no significant relaxation of the $H_0$ tension. In contrast, the model predicts systematically higher values of $S_8$, leading to a moderate alleviation of the $S_8$ tension by up to $\sim 1.2σ$ when late-time datasets are included. Overall, these results demonstrate that although the considered $f(R)$ gravity model does not resolve all cosmological tensions simultaneously, it provides a consistent improvement in the description of large-scale structure formation.

We study a dyonic black hole in a Lorentz-violating gravity that carries a background Kalb--Ramond field and is pierced by a cloud of strings. The resulting metric reduces to the recent Lin--Liu--Liu solution when the string density~$ξ$ is switched off, and to the Duan and Yang solutions in further degenerate limits. We work out the timelike circular geodesics and read off the quasi-periodic oscillation (QPO) frequencies $ν_ϕ$, $ν_r$ and $ν_θ$ within both the relativistic-precession and epicyclic-resonance models. We then map these frequencies onto the observed twin-peak signals of XTE~J1550$-$564, GRO~J1655$-$40 and GRS~1915$+$105, and place constraints on $(\ell, ξ)$ from a Markov chain Monte Carlo (MCMC) fit. We extract the full thermodynamic dictionary, first law and Smarr relation included, and follow the heat capacity, free energy and sparsity of Hawking radiation through their dependence on the four parameters $(M, Q, p, \ell, ξ)$. Finally, we compute the spectral energy emission rate and look at the photon-sphere and shadow radii in the presence of the cosmic string. The Lorentz-violating coupling $\ell$, the magnetic charge $p$, and the string density $ξ$ all leave distinct fingerprints on the dynamical, thermodynamic and radiative observables, with $ξ$ exerting the strongest pull on the ISCO, the shadow size and the sparsity of Hawking emission

We describe a multi-neck spacetime wormhole with a simple metric tensor and a simple injective map without coordinate patching. An intra-universe, non-thin-shell, non-spherically-symmetric 3-neck spacetime wormhole is geometrically constructed by spherically inverting a 3-torus. We place the resulting Dupin hypercyclide in a synchronous reference frame. The three necks are arranged around a central point and satisfy topological and geometric spacetime wormhole definitions. Asserting this metric tensor as an exact solution of Einstein's field equations in global coordinates generates diagonal Ricci and stress-energy tensors, and a Riemann curvature tensor with only six nonzero entries. The local inertial frame at every point of the coordinate system is comoving with the triple wormhole. This non-vacuum solution answers affirmatively the question posed by Einstein and Rosen (1935) of whether or not multi-neck solutions exist. The wormhole solution contains negative energy density as is expected to hold the necks open; however, geodesic paths through each neck exist which encounter only positive energy density. The spatial manifold is a trivariate Dupin hypercyclide. The spherically inverted equal-radii 3-torus is unbounded, asymptotically flat and admits a global isothermal coordinate system that further simplifies the curvature tensors.

Distilling the intrinsic physics of the superconducting CuO2 plane from the complexities of charge-reservoir layers is a defining challenge in high-temperature superconductivity. While superconducting electron-doped infinite-layer cuprates have been synthesized, controllable and uniform hole doping has long remained elusive despite exploratory attempts, limiting spectroscopic insights. Here, we realize bipolar doping across infinite-layer (Sr,Eu)CuO2 and (Ca,Li)CuO2+δ single-crystalline thin films, mapping the electronic phase diagram. Both electron- and hole-doped films show pronounced electrical resistance anisotropy, indicating the quasi-two-dimensional nature of the CuO2 planes. Angle-resolved photoemission spectroscopy across electron- and hole-doped regimes reveals persistent antiferromagnetic band folding coexisting with superconductivity. Remarkably, at a hole doping ~0.07 determined by Luttinger volume, the antiferromagnetic folding emerges from Fermi arcs within the film's single Fermi surface, with the onset superconducting transition temperature exceeding 60 K. These findings redefine the interplay between magnetic order and superconductivity and establish a definitive platform to investigate the intrinsic mechanism of high-temperature superconducting cuprates.

The coexistence of topological and spin-polarized electronic states within a single material platform provides an attractive route toward emergent quantum phenomena and spintronic functionalities. However, materials simultaneously exhibiting spin-gapless semiconducting (SGS) behavior and Weyl semimetallicity remain exceedingly rare. Here, using first-principles calculations, we identify the half-Heusler compound KCrSe as an ideal spin-gapless Weyl semimetal. Transport calculations reveal a weak temperature dependence of the longitudinal conductivity and relatively small Seebeck coefficients, providing further evidence of its SGS nature. KCrSe hosts a single pair of Weyl nodes-the minimum number permitted in a Weyl semimetal-located in close proximity to the Fermi level (E$_\text{F}$), resulting in exceptionally clean bulk and surface electronic spectra. The nontrivial Berry curvature associated with these Weyl nodes gives rise to sizable anomalous transport responses, including an anomalous Hall conductivity of $σ_{xy}^{A}\sim 90.76~\mathrm{S\,cm^{-1}}$ and an anomalous Nernst conductivity of $α_{xy}^{A}\sim 0.15~\mathrm{A\,m^{-1}K^{-1}}$ at E$_\text{F}$, with substantially enhanced values at lower energies. The combination of an ideal Weyl topology, fully spin-polarized low-energy states, and finite anomalous transport establishes KCrSe as a promising platform for designing high-efficiency topological spintronic devices.

Random packings of disordered rigid rods exhibit emergent cohesion, as exemplified in a nest of twigs that is self-equilibrated, free-standing structures. We analyze the geometric motif underlying this cohesion using a rod packing that maximizes the average crossing number subject to non-penetration constraints. We show that this protocol leads to self-caging: collective geometric constraints that prevent rod escape even in finite systems with free boundaries, leading to packings that remain mechanically cohesive due to a combination of purely repulsive and frictional interactions. We show that self-caging is controlled by the available free-volume in translational and rotational configuration spaces, which is minimal when $N/(Zα)=1/3$ where $N$ is the number of rods, $α$ is the aspect ratio, and $Z$ is the average coordination number. Our results establish a minimal geometric motif for entanglement-induced cohesion in athermal rod packings, with implications for cohesive granular matter without attractive forces.

We explicitly distinguish Hall viscosity as defined relative to the strain field vs. relative to an emergent vielbein or metric field and discuss it for graphene-like systems. Aside from the gravitational or vielbein/metric related ``geometric'' Hall viscosity prevailing throughout the literature, a contribution proportional to the Hall conductivity, the ``electronic'' Hall viscosity, due to the emergent strain induced gauge field exists. We unify both contributions within the ``emergent'' Hall viscosity, determine it explicitly for graphene in the semimetal and Semenoff semiconducting phases for integer quantum Hall states and in the latter case compare it to its non-relativistic limit. Under these circumstances two topological invariants enter the emergent Hall viscosity in the presence of translational and rotational symmetry which we derive in the Green function representation of Wigner-Weyl calculus. We discuss experimental perspectives for extracting the emergent Hall viscosity.

Electron-phonon coupling (EPC) - the interaction between conduction electrons and quantized atomic vibrations - plays a central role in condensed matter physics and determines some of the most important properties of materials, such as electrical resistivity and superconductivity. Conventionally, EPC is assumed to be induced by the ionic electrostatic background, and electronic spin plays no role in the process. In stark contrast with this view, here we uncover a direct spin-mediated coupling mechanism between electrons and transverse polar phonons in a metal. Using far-infrared light absorption measurements of the model system SrTiO$_3$ in a magnetic field, we observe a strong spin-mediated EPC that is quantitatively consistent with recent theoretical predictions, and that generates chiral phonon modes with large effective magnetic moments. The extracted coupling strength is in good agreement with ab initio estimates and sufficiently high to explain superconductivity in SrTiO$_3$, thereby resolving a long-standing conundrum. Spin-chiral EPC should generically appear in all metals with polar phonons, and the present work could be of relevance to spintronics applications and to uncovering the origins of superconductivity in layered materials, metals with Dirac points in their electronic dispersions, and nearly ferroelectric superconductors.

Ferroelectric materials, characterized by spontaneous electric polarization, exhibit remarkable parallels with fluid dynamics, where polarization flux behaves similarly to fluid flow. Understanding polarization distribution in confined geometries at the nanoscale is crucial for both fundamental physics and technological applications. Here, we show that the classical Bernoulli principle, which describes the conservation of the energy flux along velocity streamlines in a moving fluid, can be extended to the conservation of polarization flux in ferroelectric nanorods with varying cross-sectional areas. Geometric constrictions lead to an increase in polarization, resembling fluid acceleration in a narrowing pipe, while expansions cause a decrease. Beyond a critical expansion, phase separation occurs, giving rise to topological polarization structures such as polarization bubbles, curls and Hopfions. This effect extends to soft ferroelectrics, including ferroelectric nematic liquid crystals, where polarization flux conservation governs the formation of complex mesoscale states.

The axial dispersion of polymers in microchannels depends on an interplay between microchannel geometry, polymer architecture, and hydrodynamics. Here, we investigate the axial dispersion of linear, comb, and star polymers in parallel-plate and sinusoidal expansion-contraction microchannels at dilute concentrations using multiparticle collision dynamics simulations. The polymers all contain the same number of monomers but differ in their architecture, and their concentration is fixed at either one value that is dilute for all polymers or the same value relative to the overlap concentration for each polymer. The dispersion coefficients measured at a nominal solvent volumetric flow rate are found to depend on both architecture and concentration. We show that the dispersion coefficients collapse as a function of the Péclet number after accounting for confinement effects on the polymer diffusion coefficient and polymer contributions to the flow field, and the dispersion coefficients in the parallel-plate microchannel can be reasonably predicted using a theory that accounts for inhomogeneous distribution of the polymers in the microchannel.