arXiv subjects

Andrei Afanasev

Publications and source records attributed to Andrei Afanasev.

At least 19 recordsLinked to original sources

arXiv2026

Diffractive Two-Photon Exchange and Beam Normal-Spin Asymmetries for Elastic Electron Scattering on Nuclei

We developed a theoretical approach to elastic electron scattering on nuclei that includes a two-photon-exchange mechanism responsible for parity-conserving single-spin beam asymmetries. The two-photon-exchange amplitude at small scattering angles is treated in a diffractive framework similar to that of pion-nucleus elastic scattering applied to the nuclei $^{12}_{6}$C, $^{40}_{20}$Ca and $^{208}_{82}$Pb. The predicted kinematic features of the beam polarization asymmetries for different nuclei may reconcile Jefferson Lab's experimental results at finite scattering angles with a forward limit given by an optical theorem, potentially resolving the so-called ``PREX Puzzle" for $^{208}_{82}$Pb.

nucl-th↗

arXiv2026

Non-Diffractive Topological Spin Textures of Relativistic Twisted Fermion Beams

In optics and acoustics, in structured beams, non-diffracting polarization measures in clearly diffracting beams, and spin direction distributions in the core of these waves that have Skyrmionic behavior have been found. We here study the equivalents of these for fermions and show that in corresponding circumstances the non-diffractive spin textures persist independently of spin, statistics, or kinematics (or propagation speed of the structured wave). As a part of the study, we present LG solutions for Dirac particles valid for both relativistic and non-relativistic kinematics.

physics.optics↗

arXiv2026

Amplitude-Based Analysis of QED Radiative Corrections to Electroproduction of $η$-Mesons on Protons

A formalism for radiative correction calculations in exclusive $η$ electroproduction on the proton is presented, extending the treatment developed for the pion channel. The EXCLURAD code is used in the radiative correction procedure with EtaMAID-2023 multipole amplitudes. The cross-section correction factor $δ$ varies by up to ${\sim}\,30\%$ across the resonance region $W = 1.49$-$2.0$ GeV at $E_{\rm beam} = 6.535$ GeV, with a local maximum near $W \simeq 1.66$ GeV driven by the $S_{11}(1535)$ and $S_{11}(1650)$ resonances. The beam-spin asymmetry is suppressed by 15-25% at the same kinematics. Numerical results covering $Q^2 = 0.3$-$4.0$ GeV$^2$ and the full angular range are provided for kinematics relevant to CLAS12 experiments at Jefferson Lab.

hep-ph↗

arXiv2026

Dynamics of Transverse Spin and Longitudinal Fields of Cylindrical Vector Beams in Optically Active Media

Due to the inhomogeneous polarisation across the beam profile, cylindrical vector beams interact with optically active media in a complex manner. Here, we analyse evolution of polarisation of cylindrical vector beams propagating in an isotropic optically-active medium. After identifying polarisation normal modes of three-dimensional electromagnetic fields, we predict periodic inter-conversion between azimuthally- and radially-polarised modes of the beams accompanied by rotation of the transverse optical spin and pulsing field during the propagation. Theory and simulations are validated by experimental observations. The observed effects maybe important for imaging in biological chiral media, enhanced chiral sensing and enantioselective spectroscopy, nonlinear optics in chiral media, and generally enhanced spin-orbit coupling and nanoscale vector field engineering.

physics.optics↗

arXiv2025

Universal nondiffractive topological spin textures in vortex cores of light and sound

We report universal skyrmionic spin textures in the cores of optical and acoustic vortex beams, described within the framework of Laguerre-Gaussian modes. We analytically demonstrate nondiffractive propagating spin merons, independent of whether the field is transverse or longitudinal, with their sign controlled by the wavefront helicity. Experimental confirmation is provided in acoustics through full three-dimensional measurements of the velocity vector field. Although these phenomena are intrinsic to vortex cores, we also show that the claimed universality breaks down for higher-order topological charges, depending on the carrier mode, here exemplified using the Bessel framework.

physics.optics↗

arXiv2025

A Beamdump Facility at Jefferson Lab

This White Paper is exploring the potential of intense secondary muon, neutrino, and (hypothetical) light dark matter beams produced in interactions of high-intensity electron beams with beam dumps. Light dark matter searches with the approved Beam Dump eXperiment (BDX) are driving the realization of a new underground vault at Jefferson Lab that could be extended to a Beamdump Facility with minimal additional installations. The paper summarizes contributions and discussions from the International Workshop on Secondary Beams at Jefferson Lab (BDX & Beyond). Several possible muon physics applications and neutrino detector technologies for Jefferson Lab are highlighted. The potential of a secondary neutron beam will be addressed in a future edition.

physics.acc-ph↗

arXiv2025

Semi-inclusive pion electroproduction at the highest transverse momenta

At the energies of present and future electron accelerators designed to study the structure of hadrons, there is a regime where hard pion electroproduction proceeds by a perturbatively calculable process in QCD. The process is not the leading twist fragmentation one but rather a higher twist process that produces kinematically isolated pions. Semi-inclusive data may teach us more about parton distribution functions of the target and the pion distribution amplitude. In addition, there is a connection to generalized parton distribution calculations of exclusive electroproduction of mesons in that the perturbative kernel is the same.

hep-ph↗

arXiv2025

Soft-Photon Contribution into Two-Photon Exchange Corrections for Azimuthal Asymmetries of SIDIS

It is demonstrated that two-photon exchange (TPE) corrections to the cross-section of unpolarized semi-inclusive deep-inelastic scattering (SIDIS) generate azimuthal-dependent terms and the corresponding $\braket{\cos{(nϕ)}}$ moments. A quark-diquark model of a nucleon was used in the calculations along with a soft-photon approximation. The infrared divergences in the intermediate steps of calculation are regularized with the fictitious photon mass that cancels out in the final result when the soft-photon bremsstrahlung process and interference terms are added. The calculations employ Mathematica ``LoopTools" package to evaluate the loop integrals. TPE corrections are analyzed in the kinematics of planned experiments at Jefferson Lab.

hep-ph↗

arXiv2024

Contribution of $π^0$ Exchange in Elastic Muon-Proton Scattering

The effect of the lepton's mass is significantly enhanced when the beam's energy is on the order of the lepton's mass. In the case of electrons, this corresponds to beam momenta on the order of a few MeV and is negligible in higher energy experiments. In this study, we calculate the differential cross section $dσ/ dΩ$ for the helicity-flip meson exchange interference in elastic muon-proton $(μp)$ scattering $μ^- p \rightarrow μ^- p$. In particular, we examine the $π^0$ meson exchange in the $t$-channel for a longitudinally polarized beam and a transversely polarized target. We demonstrate the contribution to be larger for muons due to the lepton mass difference. Then we construct the corresponding beam-target double-spin asymmetries for the target polarized normal and parallel to the momentum transfer in the Breit frame, and then consider the model dependence of the calculation from the estimation of the $π^0 μμ$ vertex. The contribution was found to be on the order of $\sim .15\%$ for muons in the kinematic region of the MUSE experiment.

nucl-th↗

arXiv2024

Non-Divergent Spinning Substructures Near Acoustic Field Nodes

In this work, we examine the extraordinary behavior of polarization and spin angular momentum (AM) density in the vicinity of longitudinal field zeros in three-dimensional monochromatic acoustic fields. We demonstrate that, as governed by the continuity equation, the velocity fields of arbitrary acoustic sources maintain non-diffractive elliptical polarization structures that enclose longitudinal field zeros, despite having divergent transverse spatial profiles of intensity. Furthermore, embedded in these nonparaxial field contours, for infinite distance, are threads of circular polarization singularities. We illuminate these inherent properties in acoustic vortex fields, dipole arrays, and the famous Young's double slit experiment. Our results reveal novel characteristics of vector sound waves that provide a platform for future studies and applications of structured acoustic waves and chiral acoustic phenomena.

physics.class-ph↗

arXiv2024

Non-Diffracting Polarisation Features around Far-Field Zeros of Electromagnetic Radiation

Light from any physical source diffracts over space, as spherical wavefronts grow and energy density is spread out. Diffractive effects pose fundamental limits to light-based technologies, including communications, spectroscopy, and metrology. Polarisation becomes paraxial in the far field limit and, by ignoring longitudinal field components, the rich physics of non-paraxial fields which exist in near-fields or a beam's tight focus are lost. The longitudinal field cannot, however, be ignored when transverse field components vanish (in a transverse field zero) and carry a small non-paraxial region to infinity. We show that a transverse field zero is always accompanied by non-diffracting polarisation structures, whose geometries are independent of the distance to the source, including an enclosing intensity ratio tube, and parallel, non-diverging polarisation singularities. We illustrate these features in multipole radiation and in double slit interference, two examples which have time-fixed transverse field zeros. Non-diffracting structures with changing position are coupled to time-varying zeros, which are present in all far field radiation.

physics.optics↗

arXiv2023

Radiative Corrections: From Medium to High Energy Experiments

Radiative corrections are crucial for modern high-precision physics experiments, and are an area of active research in the experimental and theoretical community. Here we provide an overview of the state of the field of radiative corrections with a focus on several topics: lepton-proton scattering, QED corrections in deep-inelastic scattering, and in radiative light-hadron decays. Particular emphasis is placed on the two-photon exchange, believed to be responsible for the proton form-factor discrepancy, and associated Monte-Carlo codes. We encourage the community to continue developing theoretical techniques to treat radiative corrections, and perform experimental tests of these corrections.

hep-ph↗

arXiv2023

Quantum Information Science and Technology for Nuclear Physics. Input into U.S. Long-Range Planning, 2023

In preparation for the 2023 NSAC Long Range Plan (LRP), members of the Nuclear Science community gathered to discuss the current state of, and plans for further leveraging opportunities in, QIST in NP research at the Quantum Information Science for U.S. Nuclear Physics Long Range Planning workshop, held in Santa Fe, New Mexico on January 31 - February 1, 2023. The workshop included 45 in-person participants and 53 remote attendees. The outcome of the workshop identified strategic plans and requirements for the next 5-10 years to advance quantum sensing and quantum simulations within NP, and to develop a diverse quantum-ready workforce. The plans include resolutions endorsed by the participants to address the compelling scientific opportunities at the intersections of NP and QIST. These endorsements are aligned with similar affirmations by the LRP Computational Nuclear Physics and AI/ML Workshop, the Nuclear Structure, Reactions, and Astrophysics LRP Town Hall, and the Fundamental Symmetries, Neutrons, and Neutrinos LRP Town Hall communities.

nucl-ex↗

arXiv2022

Topology and Polarization of Optical Vortex Fields from Atomic Phased Arrays

We developed theoretical formalism for generation of optical vortices by phased arrays of atoms. Using Jacobi-Anger expansion, we demonstrate the resulting field topology and determine the least number of array elements necessary for generation of vortices with a given topological charge. Vector vortices were considered, taking into account both spin and orbital angular momenta of electromagnetic fields. It was found that for the vortex field near the phase singularity, the transverse-position dependence of 3D polarization parameters is independent of the distance to the radiation source.

quant-ph↗

arXiv2022

Non-Diffractive 3D Polarisation Features of Optical Vortex Beams

Vector optical vortices exhibit complex polarisation patterns due to the interplay between spin and orbital angular momenta. Here we demonstrate, both analytically and with simulations, that certain polarisation features of optical vortex beams maintain constant transverse spatial dimensions independently of beam divergence due to diffraction. These polarisation features appear in the vicinity of the phase singularity and are associated with the presence of longitudinal electric fields. The predicted effect may prove important in metrology and high resolution imaging applications.

physics.optics↗

arXiv2022

Superkicks and momentum density tests via micromanipulation

There is an unsettled problem in choosing the correct expressions for the local momentum density and angular momentum density of electromagnetic fields (or indeed, of any non-scalar field). If one only examines plane waves, the problem is moot, as the known possible expressions all give the same result. The momentum and angular momentum density expressions are generally obtained from the energy-momentum tensor, in turn obtained from a Lagrangian. The electrodynamic expressions obtained by the canonical procedure are not the same as the symmetric Belinfante reworking. For the interaction of matter with structured light, for example, twisted photons, this is important; there are drastically different predictions for forces and angular momenta induced on small test objects. We show situations where the two predictions can be checked, with numerical estimates of the size of the effects.

physics.optics↗

arXiv2022

Vorticity of Twisted Spinor Fields

Spinor fields with a vortex structure in free space that allow them to have arbitrary integer orbital angular momentum along the direction of motion have been studied for some time. Relatively new is the observation in a certain context that the vortex center of this field structure is, unlike a classical whirlpool, not singular. We point out that there are several ways to calculate the local velocity of the spinor field and that all but one show a singular vorticity at the vortex line. That one, using the Dirac bilinear current with no derivatives, is the only one so far (to our knowledge) studied in the literature in this context and we further show how to understand an apparent conflict in the existing results.

quant-ph↗

arXiv2022

Superkicks and the photon angular and linear momentum density

We address a problem of proper definition of momentum density for spatially structured electromagnetic fields. We show that the expressions for the momentum and angular momentum obtained locally are not the same when one uses the canonical energy-momentum tensor instead of the symmetric Belinfante energy-momentum tensor in electrodynamics. This has important consequences for interaction of matter with structured light, for example, twisted photons; and would give drastically different results for forces and angular momenta induced on small test objects. We show, with numerical estimates of the size of the effects, situations where the canonical and symmetrized forms induce very different torques or (superkick) recoil momenta on small objects or atomic rotors, over a broad range of circumstances.

quant-ph↗