Abstract We study the relativistic quantum dynamics of spin-0 particles in the spacetime of a spinning cosmic string that carries both spacelike disclination (conical deficit $$\alpha $$ α ) and screw dislocation (torsion $$J_{z}$$ J z ) together with frame dragging ( $$J_{t}$$ J t ). Using the Feshbach–Villars (FV) reformulation of the Klein–Gordon equation, we obtain a first-order Hamiltonian with a positive-definite density, enabling a clean probabilistic interpretation for bosons in curved/topologically nontrivial backgrounds. In the weak-field regime (retaining terms $$\mathcal {O}(G)$$ O ( G ) and discarding the $$\mathcal {O}(G^{2})$$ O ( G 2 ) contribution that would otherwise lead to (double)-confluent Heun behavior), separation of variables in a finite cylinder of radius $$R_{0}$$ R 0 yields a Bessel radial equation with an effective index $$\nu (\alpha ,J_{t},J_{z};E,k)$$ ν ( α , J t , J z ; E , k ) that mixes rotation and torsion. The hard-wall condition $$J_{\nu }(\kappa R_{0})=0$$ J ν ( κ R 0 ) = 0 quantizes the spectrum, $$\begin{aligned} E_{n}^{2}=m^{2}+k^{2}+\big (j_{\nu ,n}/R_{0}\big )^{2}. \end{aligned}$$ E n 2 = m 2 + k 2 + ( j ν , n / R 0 ) 2 . Working in the stationary positive-energy sector, we derive closed-form normalized eigenfunctions and FV densities, and we evaluate information-theoretic indicators (Fisher information and Shannon entropy) directly from the FV probability density. We find that increased effective confinement (via geometry/torsion) enhances Fisher information and reduces position-space Shannon entropy, quantitatively linking defect parameters to localization/complexity. The FV framework thus provides a robust, computationally transparent route to spectroscopy and information measures for scalar particles in rotating/torsional string backgrounds, and it smoothly reproduces the pure-rotation, pure-torsion, and flat-spacetime limits.

Abstract Using the data from the Van Allen Probes, we statistically studied 2.1 MeV electron flux oscillation events in the Earth's outer radiation belt during non‐storm activities. Based on the different magnetic local times (MLT), the oscillation events are divided into “dayside events” (DE, 6 ≤ MLT ≤ 18) and “nightside events” (NE, 18 < MLT < 6). These NEs are divided into “weak substorm events” (WSE, AE < 200 nT) and “strong substorm events” (SSE, AE > 200 nT). The SSE is further divided into “strong substorm with low solar wind dynamic pressure change (ΔPsw) events” (SSLP, AE > 200 nT, ΔPsw < 5 nPa) and “strong substorm with high ΔPsw events” (SSHP, AE > 200 nT, ΔPsw > 5 nPa). Our statistical results show that: (a) For DE, WSE, and SSHP, ΔPsw and solar wind speed (Vsw) are the main factors affecting the oscillation location, while ΔPsw is the dominant factor affecting the oscillation amplitude. The interplanetary magnetic field Bz component has no significant effects on the oscillations of DE. These results support the idea that these oscillations are mainly caused by ultralow frequency (ULF) waves excited by ΔPsw; (b) For SSLP, substorm activity and Vsw do not affect the oscillation location. However, the intense substorm activity and ΔPsw can cause a large oscillation amplitude. This shows the idea that these oscillations are mainly caused by a combination of ULF waves excited by ΔPsw and substorm activity. These can help us further understand the ULF waves and relativistic electron dynamics of the Earth's outer radiation belt.

Unveiling Relativistic Jet Dynamics with Dynamic Mode Decomposition

We study the conservative dynamics of spinless compact objects in a general effective theory of gravity, which includes a metric and an arbitrary number of scalar fields, through O(G3). Departures from Einstein gravity, which preserve general coordinate and local Lorentz invariance, are characterized by higher-derivative terms in a Lagrangian whose coupling constants scale as powers of a “new-physics” length scale, ℓ. For a purely metric theory we compute the contributions from the leading and subleading higher-curvature curvature corrections. In four dimensions these are cubic and quartic curvature terms, i.e. orders ℓ4 and ℓ6. We also study a general multi-scalar-tensor theory of gravity to order ℓ4, which includes both Einstein-dilaton-Gauss-Bonnet and dynamical Chern-Simons higher-order couplings. Specifically, we compute the radial action in a post-Minkowskian approximation for scattering orbits to the two-loop order. The result encodes the fully relativistic dynamics of the compact objects and serves as a generating function for gauge-invariant orbital observables for both bound and unbound binary systems. Where overlapping post-Newtonian results are available, we have verified agreement.

Abstract Relativistic quantum invariance plays prominent roles in the study of quantum field theories, typically QED and QCD. We utilize the idea of interpolating the instant form dynamics (IFD) and the light-front dynamics (LFD) to realize the relativistic quantum invariance of QED and QCD. Reviewing the connection between LFD and IFD using the idea of interpolating the two different forms of the relativistic dynamics, one can learn the distinguished features of each form and how one may utilize those distinguished features in solving the complicated relativistic quantum field theoretic problems more effectively. This review aims at presenting the basic first-hand knowledge of connecting the IFD and the LFD using the idea of interpolation, and demonstrating explicit examples of its utility in QED and QCD.

We investigate the properties of charmonium systems in strong external magnetic fields using a relativistic light-front Hamiltonian approach within the basis light-front quantization framework. By solving the eigenvalue problem for the invariant mass squared operator with confinement potentials and one-gluon-exchange interactions, we obtain the mass spectrum and wave functions under varying magnetic fields. Our results reveal significant spectral modifications through the Zeeman effect, including ηc−J/ψ mixing and magnetic sublevel splitting. Momentum density analysis demonstrates wave function deformation, with transverse momentum broadening and longitudinal narrowing under strong fields, alongside structural shifts in parton distributions such as double-hump profiles in excited states. Relativistic corrections and center-of-mass coupling critically drive these dynamics, highlighting the necessity of a relativistic framework for QCD bound states in extreme magnetic environments.

Relativistic electrons (>1 MeV) in the Earth's radiation belt, known as “killer electrons,” are primarily influenced by solar wind disturbances and geomagnetic activities. This study proposes a popular explainable machine learning tool, the Deep SHapley Additive exPlanations (Deep SHAP), for studying the spatiotemporal variations of radiation belt relativistic electron fluxes during realistic geomagnetic storm events. The fundamental machine learning framework is derived from the artificial neural networks proposed by Yuan et al. [“Predicting radiation belt relativistic electron flux from sub-relativistic electron fluxes using machine learning,” Phys. Fluids 37(2), 026618 (2025)], utilizing sub-relativistic electron fluxes (a few hundred kiloelectronvolts) as inputs. Analysis of the estimated SHAP values for all input parameters revealed that the lower envelopes of the auroral electrojet index positively contribute to the relativistic electron enhancement during the main and recovery phases of a geomagnetic storm on 17 March 2013, while the Symmetric Horizontal Component of the Geomagnetic Field and Nsw (solar wind density) index negatively influence them at higher L shells (the distance from Earth's center to the equatorial crossing point of a magnetic field line). In addition, spatial location and sub-relativistic electrons also significantly influence the relativistic electron dynamics. From the perspective of the explainable machine learning method, it is confirmed that the relativistic electrons are significantly influenced by the sub-relativistic electrons, the impinging of solar winds, and the occurrence of geomagnetic storms and substorms. The current work helps reveal the underlying physical mechanisms of radiation belt electron dynamics and facilitates the optimization of space weather prediction models.

In order to explore better electron radiation properties, we introduce laser pulses with different chirps and different pulse widths to drive electrons to produce relativistic nonlinear Thomson scattering. We numerically simulate electron radiation.The relativistic electron dynamics and resulting Thomson scattering spectra are calculated using a nonlinear model, incorporating the electronic response function under chirped conditions. We found that under the influence of chirp, the laser pulse width produces a regular change in the radiation properties of excited electrons. The peak radiation pulse increases and then decreases with increasing pulse width, while the FWHM decreases with increasing pulse width, Almost 103 orders of magnitude larger in chirped condition than in no-chirp condition, and the radiation characteristics of negative chirp are Almost an order of magnitude less than positive chirp for the same pulse width and the same absolute value of chirp parameter. In addition, we verify that the electronic response function still holds under chirp conditions, and we are surprised to find that the electronic response function can also be used to measure the gain of chirp on the radiated power, which provides a brand new perspective for the deep understanding of the role of chirp. This work suggests potential applications in high-field physics and compact radiation source design, where chirp engineering could enhance performance.

Revealing noncanonical Hamiltonian structures in relativistic fluid dynamics

A theoretical framework has been established to investigate the modulational instability of electromagnetic waves in magnetized electron–positron plasmas. The framework is capable of analyzing electromagnetic waves of any intensity and plasmas at any temperature. A fully relativistic hydrodynamic model, incorporating relativistic velocities and thermal effects, is used to describe the relativistic dynamics of particles in plasmas. Under the weakly magnetized approximation, a modified nonlinear Schrödinger equation, governing the dynamics of the envelope of electromagnetic waves in plasmas, is obtained. The growth rate of the modulational instability is then given both theoretically and numerically. By analyzing the dependence of the growth rate on some key physical parameters, the coupled interplay of relativistic effects, ponderomotive forces, thermal effects and magnetic fields on electromagnetic waves can be clarified. The findings demonstrate that specific combinations of physical parameters can significantly enhance modulational instability, providing a theoretical basis for controlling the propagation of electromagnetic waves in plasmas. This framework has broad applicability to most current laser–plasma experiments and high-energy radiation phenomena from stellar surfaces.

Low-density meter-scale plasma waveguides produced in meter-scale supersonic gas jets have paved the way for recent demonstrations of all-optical multi-gigaelectronvolt laser wakefield acceleration (LWFA). This paper reviews recent advances by the University of Maryland, which have enabled these results, focusing on the development of elongated supersonic gas jets up to ∼1 m in length, experimental and simulation studies of plasma waveguide formation, and a new three-stage model for relativistic pulse propagation dynamics in these waveguides. We also present results from recent LWFA experiments conducted at the Laboratory for Advanced Lasers and Extreme Photonics at Colorado State University demonstrating high charge, low divergence electron bunches to ∼10 GeV, with laser-to-electron beam efficiency of at least ∼30%.

In this article, we consider the Israel–Stewart equations of relativistic viscous fluid dynamics with bulk viscosity. We investigate the evolution of the equations linearized about solutions that satisfy the physical vacuum boundary condition and establish local well-posedness of the corresponding Cauchy problem.

IARD 2024 The 14th Biennial Conference on Classical and Quantum Relativistic Dynamics of Particles and Fields The International Association for Relativistic Dynamics was organized in February 1998 in Houston, Texas, with John R. Fanchi as president. Although the subject of relativistic dynamics has been explored, from both classical and quantum mechanical points of view, since the work of Einstein and Dirac, its most striking development has been in the framework of quantum field theory. The very accurate calculations of spectral and scattering properties, for example, of the anomalous magnetic moment of the electron and the Lamb shift in quantum electrodynamics, and many qualitative features of the strong and electroweak interactions, demonstrate the very great power of description achieved in this framework. Yet, many fundamental questions remain to be clarified, such as the structure of classical relativistic dynamical theories on the level of Hamilton and Lagrange in Minkowski space as well as on the curved manifolds of general relativity. There, moreover, remain the important questions of the covariant classical description of systems at high energy for which particle production effects are not large, such as discussed in Synge’s book, The Relativistic Gas, and in Balescu’s book on relativistic statistical mechanics, and the development of a consistent single and many body relativistic quantum theory. In recent years, highly accurate telescopes and advanced facilities for computation have brought a high level of interest in cosmological problems, such as the structure of galaxies (dark matter) and the apparently anomalous expansion of the universe (dark energy). Some of the papers reported here deal with these problems, as well as other fundamental related issues. It was for this purpose, to bring together researchers from a wide variety of fields, such as particle physics, astrophysics, cosmology, foundations of relativity theory, and mathematical physics, with a common interest in relativistic dynamics, to investigate fundamental questions of this type, that this Association was founded. The second meeting took place in 2000 at Bar Ilan University in Israel, the third, in 2002, at Howard University in Washington, D.C., and the fourth, in 2004, in Saas Fee, Switzerland. Subsequent meeting took place in 2006 at the University of Connecticut Storrs, in 2008 at Aristotle University of Thessalonica, in 2010 at National Dong Hwa University, Hualien, Taiwan, in 2012 at the Galileo Galilei Institute for Theoretical Physics (GGI) in Florence, in 2014 as the University of Connecticut Storrs, Connecticut, in 2016 at Jožef Stefan Institute in Ljubljana, Slovenia, and in 2018 in Mérida, Yucatán, Mexico, under the sponsorship of the Instituto Politécnic Nacional. The 2020 meeting, planned for Czech Technical University in Prague, was successfully held online at the height of the Covid-19 pandemic, and the physical meeting in Prague was delayed to 2022. IARD 2024 was held at Aalto University near Helsinki, Finland. List of Scientific Advisory Committee and International Organizing Committee and Editorial Board of the proceedings are available in this Pdf.

We explore the relationship between linear and non-linear causality in theories of dissipative relativistic fluid dynamics. While for some fluid-dynamical theories, a linearized causality analysis can be used to determine whether the full non-linear theory is causal, for others it can not. As an illustration, we study relativistic viscous magnetohydrodynamics supplemented by a neutral-particle current, with resistive corrections to the conservation of magnetic flux. The dissipative theory has 10 transport coefficients, including anisotropic viscosities, electric resistivities, and neutral-particle conductivities. We show how causality properties of this magnetohydrodynamic theory, in the most general fluid frame, may be understood from the linearized analysis.

In this paper, we present a novel scheme for the controlled generation of tunable narrowband γ-ray radiation by ultrarelativistic positron beams inside acoustically driven periodically bent crystals. A novel acoustic crystalline undulator is presented, in which the excitation of a silicon single crystal along the (100) planar direction by a piezoelectric transducer periodically modulates the crystal lattice in the [100] axial direction. An ultrarelativistic positron beam is directed diagonally into the crystal and propagates along the (110) planes. The lattice modulation forces the positrons to follow periodic trajectories, resulting in the emission of undulator radiation in the MeV range. A computational methodology for the design and development of such acoustically based light sources is presented together with the results of simulations demonstrating the favorable properties of the proposed technology. The longitudinal acoustic strains induced in the crystal by high-frequency piezoelectric elements are calculated by finite element simulations. The resulting bending profiles of the deformed crystal planes are used as geometrical conditions for the relativistic molecular dynamics simulations that calculate the positron trajectories and the spectral distribution of the emitted radiation. The results show a strong enhancement of the emitted radiation within a narrow spectral band defined by the bending period, demonstrating the feasibility and potential of the proposed technology. Published by the American Physical Society 2025

The recent development of the field correlator method (FCM) is discussed, with applications to the most interesting areas of QCD physics obtained in the lattice data and experiment. These areas include: the connection of colorelectric (CE) confinement with the basic quark and gluon condensates; the explicit form of the colorelectric deconfinement at a growing temperature T; the theory of the colormagnetic (CM) confinement at all temperatures; the theory of strong decays, the theory of parton distribution function (PDF), and jets in the instantaneous formalism with confinement. We demonstrate that the field correlator method with instantaneous formalism and confinement (instead of the light cone formalism and pure perturbation theory) can provide the way to the theory of QCD, which helps to describe world data without phenomenological parameters. Published by the American Physical Society 2025

Lie–Poisson electrodynamics describes the semi-classical limit of non-commutative U(1) gauge theory, characterized by Lie-algebra-type non-commutativity. We focus on the mechanics of a charged point-like particle moving in a given gauge background. First, we derive explicit expressions for gauge-invariant variables representing the particle’s position. Second, we provide a detailed formulation of the classical action and the corresponding equations of motion, which recover standard relativistic dynamics in the commutative limit. We illustrate our findings by exploring the exactly solvable Kepler problem in the context of the λ-Minkowski (or the angular) non-commutativity, along with other examples.

Extreme mass ratio inspirals (EMRIs) are anticipated to be primary gravitational wave sources for the Laser Interferometer Space Antenna (LISA). They form in dense nuclear clusters when a compact object is captured by the central massive black holes (MBHs) as a consequence of the frequent two-body interactions occurring between orbiting objects. The physics of this process is complex and requires detailed statistical modelling of a multi-body relativistic system. We present a novel Monte Carlo approach to evolving the post-Newtonian (PN) equations of motion of a compact object orbiting an MBH. The approach accounts for the effects of two-body relaxation locally on the fly, without leveraging on the common approximation of orbit-averaging. We applied our method to study the function S(a_0), describing the fraction of EMRI to total captures (including EMRIs and direct plunges, DPs) as a function of the initial semi-major axis a_0 for compact objects orbiting central MBHs with M_ M M sun . The past two decades have consolidated a picture in which S(a_0)→ 0 at large initial semi-major axes, with a sharp transition from EMRIs to DPs occurring around a critical scale a_ c. A recent study challenges this notion for low-mass MBHs, finding EMRIs forming at a≫ c which were called `cliffhangers'. Our simulations confirm the existence of cliffhanger EMRIs, which we find to be more common then previously inferred. Cliffhangers start to appear for M_∙ M and can account for up to 55% of the overall EMRIs forming at those masses. We find S(a_0) ≫ 0 for a ≫ c M much higher than previously found. We test how these results are influenced by different assumptions on the dynamics used to evolve the system and treatment of two-body relaxation. We find that the PN description of the system greatly enhances the number of EMRIs by shifting a_ c to larger values at all MBH masses. Conversely, the local treatment of relaxation has a mass-dependent impact, significantly boosting the number of cliffhangers at low MBH masses compared to an orbit-averaged treatment. These findings highlight the shortcomings of standard approximations used in the EMRI literature and the importance of carefully modelling the (relativistic) dynamics of these systems. The emerging picture is more complex than previously thought, and should be considered in future estimates of rates and properties of EMRIs detectable by LISA.

We investigate the effects of two types of spiral dislocation (the distortion of the radial line, labeled as spiral dislocation I, and the distortion of a circle, labeled as spiral dislocation II) on the relativistic dynamics of the Klein–Gordon (KG) oscillator fields, both in the presence and absence of external magnetic fields. In this context, our investigations show that while spiral dislocation I affects the energies of the KG oscillators (with or without the magnetic field), spiral dislocation II has, interestingly, no effect on the KG oscillator’s energies unless a magnetic field is applied. However, for both types of spiral dislocations, we observe that the corresponding wave functions incorporate the effects of the dislocation parameter. Our findings are based on the exact solvability and conditional exact solvability (associated with the biconfluent Heun polynomials) of the KG oscillators (with or without the magnetic field, respectively) for spiral dislocation I, and the exact solvability of the KG oscillators (with or without the magnetic field) for spiral dislocation II. The exact solvability of the latter suggests that the oscillator’s frequency is solely determined by the magnetic field strength.

We study the time evolution of a state of a relativistic quantum field theory restricted to a spatial subregion Ω. More precisely, we use the Feynman-Vernon influence functional formalism to describe the dynamics of the field theory in the interior of Ω arising after integrating out the degrees of freedom in the exterior. We show how the influence of the environment gets encoded in a boundary term. Furthermore, we derive a stochastic equation of motion for the field expectation value in the interior. We find that the boundary conditions obtained in this way are energy nonconserving and nonlocal in space and time. Our results find applications in understanding the emergence of local thermalization in relativistic quantum field theories and the relationship between quantum field theory and relativistic fluid dynamics. Published by the American Physical Society 2025