In this paper, we present a complete proof of the so-called First On-ShellTheorem that determines dynamical content of the unfolded equations for freesymmetric massless fields of arbitrary integer spin in any dimension andarbitrary integer or half-integer spin in four dimensions. This is achieved bycalculation of the respective $\sigma_-$ cohomology both in the tensor languagein Minkowski space of any dimension and in terms of spinors in $AdS_4$. In the$d$-dimensional case $H^p(\sigma_-)$ is computed for any $p$ and interpretationof $H^p(\sigma_-)$ is given both for the original Fronsdal system and for theassociated systems of higher form fields.
The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ioncollisions enables the exploration of the fundamental properties of matterunder extreme conditions. Non-central collisions can produce strong magneticfields on the order of $10^{18}$ Gauss, which offers a probe into theelectrical conductivity of the QGP. In particular, quarks and anti-quarks carryopposite charges and receive contrary electromagnetic forces that alter theirmomenta. This phenomenon can be manifested in the collective motion offinal-state particles, specifically in the rapidity-odd directed flow, denotedas $v_1(\mathsf{y})$. Here we present the charge-dependent measurements of$dv_1/d\mathsf{y}$ near midrapidities for $\pi^{\pm}$, $K^{\pm}$, and$p(\bar{p})$ in Au+Au and isobar ($_{44}^{96}$Ru+$_{44}^{96}$Ru and$_{40}^{96}$Zr+$_{40}^{96}$Zr) collisions at $\sqrt{s_{\rm NN}}=$ 200 GeV, andin Au+Au collisions at 27 GeV, recorded by the STAR detector at theRelativistic Heavy Ion Collider. The combined dependence of the $v_1$ signal oncollision system, particle species, and collision centrality can bequalitatively and semi-quantitatively understood as several effects onconstituent quarks. While the results in central events can be explained by the$u$ and $d$ quarks transported from initial-state nuclei, those in peripheralevents reveal the impacts of the electromagnetic field on the QGP. Our data putvaluable constraints on the electrical conductivity of the QGP in theoreticalcalculations.
We study intermittent coherent structures in solar wind magnetic turbulencefrom MHD to kinetic plasma scales using Parker Solar Probe data during itsfirst perihelion (at 0.17 au), when the satellite was in the Alfv\'enic slowwind of 340 km/s. The coherent structures are energetic events localized intime and covering wide range of scales. We detect them using Morlet wavelets.For the first time, we apply a multi-scale analyses in physical space to studythese structures. At MHD scales within the inertial range, times scales $\tau\in (1, 10^{2} )$ s, we find (i) current sheets including switchback boundariesand (ii) Alfv\'en vortices. Within these events, there are embedded structuresat smaller scales: typically Alfv\'en vortices at ion scales, $\tau \in (0.08,1)$ s, and a compressible vortices at sub-ion scales, $\tau \in (8,80)$ ms. Thenumber of coherent structures grows toward smaller scales: we observe about$\sim 200$ events during 5 h time interval at MHD scales, $\sim 10^{3}$ eventsai ion scales and $\sim 10^{4}$ events at sub-ion scales. In general, there aremultiple structures of ion and sub-ion scales embedded within one MHDstructure. There are also examples of ion and sub-ion scales structures outsideof MHD structures. To quantify the relative importance of different type ofstructures, we do a statistical comparison of the observed structures with theexpectations of models of the current sheets and vortices. This comparison isbased on amplitude anisotropy of magnetic fluctuations within the structures.The results show the dominance of Alfv\'en vortices at all scales in contrastto the widespread view of dominance of current sheets. This means that Alfv\'envortices are important building blocs of solar wind turbulence.
We study interactions of higher-spin massless fields $\varphi$ with conservedcurrents multilinear in the off-shell matter fields $\phi$. Specifically, wefocus on the 3d case where a slight modification of the $\sigma_-$-cohomologytechnique developed earlier is directly applicable to control nontriviality ofthe interaction vertices at the convention that the vertices removable by alocal field redefinition of a higher-spin field or having schematic form$F(\varphi) G(\phi)$, where $F(\varphi)$ is a gauge invariant field strength ofa free higher-spin field, are called deformationally trivial. It isdemonstrated how the $\sigma_-$-cohomology approach can be applied to theanalysis of nonlinear vertices. Generally, deformationally trivial vertices arenot $\sigma_-$-closed while the deformationally non-trivial ones must be in$H(\sigma_-)$. It is shown that, at least in the $3d$ case, the relevantcohomology group $H^1(\sigma_-)=0$ and, hence, no deformationally non-trivialoff-shell vertices exist. On the other hand, there exists an infinite class ofdeformationally trivial vertices, that includes the vertex recently proposedfor spin three. Our analysis goes beyond the higher-spin vertices allowing toshow that, at least in three dimensions, nonlinear combinations of theoff-shell scalar fields and their derivatives cannot obey non-trivialequations.
We study the holographic duality between higher-spin (HS) gravity in 4d andfree vector models in 3d, with special attention to the role of N=2supersymmetry (SUSY). For the type-A bosonic bulk theory, dual to spin-0 fieldson the boundary, there exists a twistor-space description; this maps bothsingle-trace boundary operators and linearized bulk fields tospacetime-independent twistor functions, whose HS-algebra products compute allboundary correlators. Here, we extend this description to the type-B bosonictheory (dual to spin-1/2 fields on the boundary), and to the supersymmetrictheory containing both. A key role is played by boundary bilocals, which intype-A are dual to the Didenko-Vasiliev 1/2-BPS "black hole". We extend this toan infinite family of linearized 1/2-BPS "black hole" solutions. Remarkably,the full supersymmetric theory (along with the SUSY generators) fits in thesame space of twistor functions as the type-A theory. Instead of two sets ofbosonic bulk fields, the formalism sees one set of linearized fields, but withboth types of boundary data allowed.
This paper completes the analysis initiated in the companion workarXiv:2403.02283 -- referred to as Paper I -- by showing how Vasiliev's 4Dhigher-spin gravity (HSG) and 3D coloured conformal matter fields coupled toconformal higher-spin gauge fields and colour gauge fields (coloured conformalHSG, or CCHSG) emerge as consistent reductions of a common parent model. Thelatter is a Frobenius-Chern-Simons model with superconnection valued in afractional-spin extension of Vasiliev's higher-spin algebra, and was definedand studied in Paper I. Here, we i) realize HSG as a subcase of a more general4D reduction, describing HSG coupled to coloured, fractional-spin matter, whichwe refer to as 4D fractional-spin gravity; ii) study the CCHSG model, inparticular exhibiting the crucial role played by novel colour gauge fields incoupling conformal matter to conformal HSG, thereby completing the models dueto Vasiliev and Nilsson; iii) extract conformal currents and composite colouredsources in an expansion of the CCHSG model around 3D Minkowskian leaves; andiv) compare our results with Vasiliev's holography proposal of arXiv:1203.5554.The common origin of HSG and CCHSG, besides relating the two models directly,is the starting point for establishing the holographic correspondence betweenthe two models via overlap conditions, to be presented separately.
Brillouin light scattering (BLS) spectroscopy is a powerful tool fordetecting spin waves in magnetic thin films and nanostructures. Despitecomprehensive access to spin-wave properties, BLS spectroscopy suffers from thelimited wavenumber of detectable spin waves and the typically relatively lowsensitivity. In this work, we present the results of numerical simulationsbased on the recently developed analytical model describing plasmon-enhancedBLS. The effective susceptibility is defined for a single plasmonicnanoparticle in the shape of an ellipsoid of rotation, for the sandwichedplasmonic nanoparticles separated by a dielectric spacer, as well as for thearray of plasmonic resonators on the surface of a magnetic film. It is shownthat the eccentricity of the metal nanoparticles, which describes their shape,plays a key role in the enhancement of the BLS signal. The optimal conditionsfor BLS enhancement are numerically defined for gold and silver plasmon systemsfor photons of different energies. The presented results define the roadmap forthe experimental realization of plasmon-enhanced BLS spectroscopy.
Motivated by the need for realistic, dynamically self-consistent, evolvinggalaxy models that avoid the complexity of full, and zoom-in, cosmologicalsimulations, we have developed NEXUS, an integral framework to create andevolve synthetic galaxies made of collisionless and gaseous components. NEXUSleverages the power of publicly available, tried-and-tested packages: thestellar-dynamics, action-based library AGAMA; and the adaptive mesh refinement,N-body/hydrodynamical code RAMSES, modified to meet our needs. In addition, wemake use of a proprietary module to account for galaxy formation physics,including gas cooling and heating, star formation, stellar feedback, andchemical enrichment. NEXUS' basic functionality consists in the generation ofbespoke initial conditions (ICs) for a diversity of galaxy models, which areadvanced in time to simulate the galaxy's evolution. The fully self-consistentICs are generated with a distribution-function based approach, as implementedin the galaxy modelling module of AGAMA -- up to now restricted tocollisionless components, extended in this work to treat two types of gaseousconfigurations: hot halos and gas discs. NEXUS allows constructing equilibriummodels with disc gas fractions $0~\leq~f_{\rm gas}~\leq~1$, appropriate tomodel both low- and high-redshift galaxies. Similarly, the framework is ideallysuited to the study of galactic ecology, i.e. the dynamical interplay betweenstars and gas over billions of years. As a validation and illustration of ourframework, we reproduce several isolated galaxy model setups reported inearlier studies, and present a new, `nested bar' galaxy simulation. Futureupgrades of NEXUS will include magneto-hydrodynamics and highly energeticparticle (`cosmic ray') heating.