Search

Highlights • We study interference behaviors between spin-orbit coupled Bose-Einstein condensates confined in a harmonic trap. • We map out the role of the spin-orbit coupling, the energy detuning and relative phases during the collisions. • It is found that the spin-orbit coupling controls the population transfer among the condensates. Abstract We study interference behaviors between spin-orbit-coupled Bose-Einstein condensates confined in a harmonic trap. By solving the coupled nonlinear Schrödinger equations in the real-time domain, interference properties of the pseudo-spin condensates are carefully investigated in different parameter regimes. We map out the role of the spin-orbit coupling, the energy detuning and relative phases during the collisions. It is also found that the spin-orbit coupling controls the population transfer between the condensates. The presentation of spin-orbit coupling enriches the dynamical process of the bright soliton interference. [ABSTRACT FROM AUTHOR]

We present the KKMCee 5.00.2 Monte Carlo event generator for lepton and quark pair production for the high energy electron-positron annihilation process. It is still the most sophisticated event generator for such processes. Its entire source code is re-written in the modern C++ language. It reproduces all features of the older KKMC code in Fortran 77. However, a number of improvements in the Monte Carlo algorithm are also implemented. Most importantly, it is intended to be a starting point for the future improvements, which will be mandatory for the future high precision lepton collider projects. As in the older version, in addition to higher order QED corrections, it includes so-called O (α 1.5) genuine weak corrections using a version of the classic DIZET library and polarized τ decays using TAUOLA program. Both DIZET and TAUOLA external libraries are still in Fortran 77. In addition, a HEPMC3 interface to other MC programs, like parton showers and detector simulation, replaces the older HepEvt interface. The HEPMC3 interface is also exploited in the implementation of the additional photon final state emissions in τ decays using an external PHOTOS library rewritten in C. Program title: KKMCee 5.00.2 CPC Library link to program files: https://doi.org/10.17632/7drvvhbw92.1 Licensing provisions: GPL-3.0 Programming languages: C++, FORTRAN77 External routines: CERN ROOT library, PHOTOS, HepMC v.3.0, TAUOLA, PHOTOS, FOAM, HEPMC3 Nature of the problem: Fermion pair production is and will be used as an important data source for precise tests of the standard electroweak theory at a high luminosity future circular collider near the Z resonance and above and/or at the future linear lepton colliders of higher energies than those at LEP. The QED corrections to fermion pair production (especially τ leptons) have to be known to at least second order, including spin polarization effects, with 4-5 digit precision. The Standard Model predictions at the sub-permille precision level, taking into account multiple emission of photons for realistic experimental acceptances, can only be obtained using a Monte Carlo event generator. The realistic and precise simulation of τ lepton decays taking into account spin effects is an indispensable ingredient in the Monte Carlo event generator for the fermion pair production process. Solution method: Monte Carlo methods are used to simulate most of the two-fermion final-state processes in e + e − collisions in the presence of multiphoton initial and final state radiation. The multiphoton effects are described in the framework of coherent exclusive exponentiation (CEEX) extending/upgrading the older Yennie–Frautschi–Suura exclusive exponentiation (EEX) scheme. CEEX treats correctly to infinite order not only infrared cancellations but also QED interferences, including suppression of initial-final state interferences for narrow resonances. The matrix element according to the older YFS exponentiation is also implemented for the testing purpose. For τ leptons, the appropriate simulation of a very rich spectrum of the decays is included. Beam polarization and spin effects, both longitudinal and transverse, in tau decays are properly taken into account. Gaussian beam spread and an arbitrary spectrum of the beamstrahlung are also optionally simulated. The present version of the program is rewritten to C++ but in many respects corresponds to its FORTRAN predecessor KKMC v.4.13 [1] with later minor modifications in v. 4.32 [2]. Additional comments including restrictions and unusual features: In the present version, electron (Bhabha) and t -quark final states are not included. (It is planned for a future version.) Third-order QED corrections in the leading-logarithmic approximation are included only in the auxiliary older YFS/EEX matrix element. The electroweak corrections should not be trusted above the t -quark threshold. The total cross section for light quarks for s < 10 GeV (including narrow resonances) requires an improvement using experimental data. The program does not provide any handles for the beyond the Standard Model (BSM) physics, for instance in the Born Z boson couplings or in the electroweak (EW) formfactors. Running time depends on the CMS energy, final fermion type, upper phase space limit of the photon energy, and whether variable weight events or WT=1 events are generated. On a PC/Linux with a 2.2 GHz processor, producing 100k variable weight events at s = M Z takes 25 sec. of CPU time for μ -pairs and 30 sec. for τ -pairs including decays. At s = 189 GeV 100k events with WT=1 costs 1200 sec. for μ -pairs and 830 sec. for τ -pairs (less hard photons). [1] S. Jadach, B.F.L. Ward, Z. Was, Comput. Phys. Commun. 130 (2000) 260. [2] A. Arbuzov, S. Jadach, Z. Was, B.F.L. Ward, S.A. Yost, Comput. Phys. Commun. 260 (2021) 107734. [ABSTRACT FROM AUTHOR]

We apply our recently developed, quantum, nonadiabatic, two-dimensional finite element method [ Warehime etal., J. Chem. Phys. 142,034108 (2015).] to estimate the probability of the nonadiabatic reaction in spin-polarized Li(²S) + CaH(²Σ+). This spin-orbit-induced reaction leads to trap loss due to the opening of a barrierless pathway to the Ca(¹S) + LiH(¹Σ+) products. To investigate this reaction we calculate three two-dimensional radial cuts of the potential energy surfaces for the triplet and singlet electronic states. We also calculate the spin-orbit coupling matrix element between these two electronic states. From our nonadiabatic scattering calculations we estimate the spin-flip probability in the sympathetic cooling of the CaH molecule with ultracold Li atoms to be small: on the order of 10-7 and increasing to 10-4 at higher temperatures. We estimate the order of the rate constant in our reduced dimensionality approach for the reaction proceeding on the singlet potential at a temperature of t K to be 10-10 cm³/s. This is of the same order as the measured value of 3.6 x 10-10 cm³/s [Singh et al., Phys. Rev. Lett. 108, 203201 (2012)]. This reaction rate is at least seven orders of magnitude larger than our estimated rate of the spin-orbit-induced triplet to singlet reaction. Our nonadiabatic result is encouraging for the experimental prospects for this title system. [ABSTRACT FROM AUTHOR]

In this paper we present an analysis of the spin behavior of electrons propagating through a laser field. We present an experimentally realizable scenario in which spin-dependent effects of the interaction between the laser and the electrons are dominant. The laser interaction strength and incident electron velocity are in the nonrelativistic domain. This analysis may thus lead to novel methods of creating and characterizing spin-polarized nonrelativistic femtosecond electron pulses. [ABSTRACT FROM AUTHOR]

We study nonperturbative multiphoton electron-positron pair creation in ultrastrong electromagnetic fields formed by two counterpropagating pulses with elliptic polarization. Our numerical approach allows us to take into account the temporal as well as the spatial variation of the standing electromagnetic field. The spin and momentum resolved pair creation probabilities feature characteristic Rabi oscillations and resonance spectra. Therefore, each laser frequency features a specific momentum distribution of the created particles. We find that, depending on the relative polarization of both pulses, the created electrons may be spin polarized along the direction of field propagation. [ABSTRACT FROM AUTHOR]

A recently demonstrated technique of continuous indirect pumping enables a high level of atomic spin polarization to be generated in thermal alkali-metal vapors, without compromising the coherence lifetime through power broadening from the pump laser. The indirect pumping process combines optical excitation and spinexchange collisions. Here we describe the pumping process and the role of spin-exchange collisions for the case of amplitude-modulated optical excitation. We demonstrate that effective spin-exchange decoherence is modified by the measurement geometry and dynamics. Decoherence changes are studied through magneto-optical-rotation signals. The studies presented here are particularly important for optimizing the performance of an atomic magnetometer operating in the quantum nondemolition configuration in a nonzero-magnetic-field environment. [ABSTRACT FROM AUTHOR]

We investigate quarkonium mass spectra in external constant magnetic fields by using QCD sum rules. We first discuss a general framework of QCD sum rules necessary for properly extracting meson spectra from current correlators computed in the presence of strong magnetic fields, that is, a consistent treatment of mixing effects caused in the mesonic degrees of freedom. We then implement operator product expansions for pseudoscalar and vector heavy-quark current correlators by taking into account external constant magnetic fields as operators and obtain mass shifts of the lowest-lying bound states ηc and J/ψ in the static limit with their vanishing spatial momenta. Comparing results from QCD sum rules with those from hadronic effective theories, we find that the dominant origin of mass shifts comes from a mixing between ηc and J/ψ with a longitudinal spin polarization, accompanied by other subdominant effects such as mixing with higher excited states and continua. [ABSTRACT FROM AUTHOR]

We revisit the large instanton contribution to the gluon Pauli form factor of the constituent quark noted by Kochelev. We check that it contributes sizably to the single spin asymmetry in polarized p↑p → πX. We use it to predict a large double spin asymmetry in doubly polarized p↑p↑ → ππX. [ABSTRACT FROM AUTHOR]

In this paper, we report on a laser spectroscopy measurement of 84-87Rb isotopes in superfluid helium (He II) at 1.8 K using laser-radio-frequency double-resonance spectroscopy. Rb ion beams (> 60 MeV/u) provided by the RIKEN projectile fragment separator (RIPS) were injected and trapped into He II. The stopping position of atoms in He II was precisely confirmed by laser spectroscopy. By optically pumping the trapped Rb isotopes, large atomic spin polarization (up to 40%) of each observed isotope in the ground state was achieved. The laser-radio-frequency double-resonance spectra were observed for stable 85,87Rb isotopes as well as for unstable isotopes 84,84m.86Rb by scanning a weak magnetic field with a fixed-frequency RF field. From the measured Zeeman splitting, nuclear spin values for 84m,84-87Rb isotopes were determined with reasonable accuracy. The number of ions injected into He II for the resonance spectra measurement was on the order of 104 particles per second. This work may open new opportunities for the study of various particles trapped in condensed helium in several fields. [ABSTRACT FROM AUTHOR]

The distributions of Compton and Thomson radiation for a shaped laser pulse colliding with a free electron are calculated in the framework of quantum and classical electrodynamics, respectively. We introduce a scaling law for the Compton and the Thomson frequency distributions which universally applies to long and short incident pulses. Thus, we extend the validity of frequency scaling postulated in previous studies comparing nonlinear Compton and Thomson processes. The scaling law introduced in this paper relates the Compton no-spin flipping process to the Thomson process over nearly the entire spectrum of emitted radiation, including its high-energy portion. By applying the frequency scaling, we identify that both spin and polarization effects are responsible for differences between classical and quantum results. The same frequency scaling applies to angular distributions and to temporal power distributions of emitted radiation, which we illustrate numerically. [ABSTRACT FROM AUTHOR]

Motivated by the remarkable experimental control of synthetic gauge fields in ultracold atomic systems, we investigate the effect of an artificial Rashba spin-orbit coupling on the spin polarization of a two-dimensional repulsive Fermi gas. By using a variational many-body wave function, based on a suitable spinorial structure, we find that the polarization properties of the system are indeed controlled by the interplay between spin-orbit coupling and repulsive interaction. In particular, two main effects are found: (1) The Rashba coupling determines a gradual increase of the degree of polarization beyond the critical repulsive interaction strength, at variance with conventional two-dimensional Stoner instability. (2) The critical interaction strength, above which finite polarization is developed, shows a dependence on the Rashba coupling, i.e., it is enhanced in case the Rashba coupling exceeds a critical value. A simple analytic expression for the critical interaction strength is further derived in the context of our variational formulation, which allows for a straightforward and insightful analysis of the present problem. [ABSTRACT FROM AUTHOR]

We study in three dimensions the problem of a spatially homogeneous zero-temperature ideal Fermi gas of spin-polarized particles of mass m perturbed by the presence of a single distinguishable impurity of mass M. The interaction between the impurity and the fermions involves only the partial s wave through the scattering length a and has negligible range b compared to the inverse Fermi wave number 1/kp of the gas. Through the interactions with the Fermi gas the impurity gives birth to a quasiparticle, which will be here a Fermi polaron (or more precisely a monomeron). We consider the general case of an impurity moving with wave vector K ≠ 0: Then the quasiparticle acquires a finite lifetime in its initial momentum channel because it can radiate particle-hole pairs in the Fermi sea. A description of the system using a variational approach, based on a finite number of particle-hole excitations of the Fermi sea, then becomes inappropriate around K = 0. We rely thus upon perturbation theory, where the small and negative parameter kFa → 0- excludes any branches other than the monomeronic one in the ground state (as, e.g., the dimeronic one), and allows us a systematic study of the system. We calculate the impurity self-energy Σ(2),(K,ω) up to second order included in a. Remarkably, we obtain an analytical explicit expression for Σ(2)(K,ω), allowing us to study its derivatives in the plane (K,ω). These present interesting singularities, which in general appear in the third-order derivatives ⇿Σ(2)(K,ω). In the special case of equal masses, M = m, singularities appear already in the physically more accessible second-order derivatives 32Σ,2,(K,ω); using a self-consistent heuristic approach based on Σ(2) we then regularize the divergence of the second-order derivative ⇿ΔE(K) of the complex energy of the quasiparticle found in Trefzger and Castin [Europhys. Lett. 104, 50005 (2013)] at K = kF, and we predict an interesting scaling law in the neighborhood of K = kF. As a by product of our theory we have access to all moments of the momentum of the particle-hole pair emitted by the impurity while damping its motion in the Fermi sea at the level of Fermi's golden rule. [ABSTRACT FROM AUTHOR]

Electron elastic scattering off a spin-polarized Cr(...3d54s1, 7S) atom is theoretically studied in the region of electron energies up to 15 eV using both a one-electron "spin-polarized" Hartree-Fock approximation and a multielectron spin-polarized random-phase approximation with exchange. It is found that scattering phase shifts of oppositely spin-polarized incoming electrons and corresponding cross sections of the scattering reactions significantly differ from each other, in general, even without accounting for spin-orbit interaction. This is shown to be associated with the presence of two semifilled 3d5 and 4s¹ subshells in the Cr configuration which induce considerably different exchange in the interaction of oppositely spin-polarized incoming electrons with the atom target. The importance of electron correlation in the e- + Cr elastic-scattering process is revealed. Moreover, correlation is shown to induce strong differences between scattering of oppositely spin-polarized electrons off Cr. A physically transparent interpretation for the latter is provided. [ABSTRACT FROM AUTHOR]

The ability to produce liter volumes of highly-spin-polarized 129Xe enables a wide range of investigations, most notably in the fields of materials science and biomedical magnetic resonance imaging. However, for nearly all polarizers built to date, both peak 129Xe polarization and the rate at which it is produced fall far below those predicted by the standard model of Rb metal vapor, spin-exchange optical pumping (SEOP). In this work we comprehensively characterized a high-volume flow-through 129Xe polarizer using three different SEOP cells with internal volumes of 100, 200, and 300 cm3 and two types of optical sources: a broad-spectrum 111-W laser [full width at half maximum (FWHM) equal to 1.92 nm] and a line-narrowed 71 -W laser (FWHM equal to 0.39 nm). By measuring 129Xe polarization as a function of gas flow rate, we extracted the peak polarization and polarization production rate across a wide range of laser absorption levels. Peak polarization for all cells consistently remained a factor of 2-3 times lower than predicted at all absorption levels. Moreover, although production rates increased with laser absorption, they did so much more slowly than predicted by the standard theoretical model and basic spin-exchange efficiency arguments. Underperformance was most notable in the smallest optical cells. We propose that all these systematic deviations from theory can be explained by invoking the presence of paramagnetic Rb clusters within the vapor. Cluster formation within saturated alkali-metal vapors is well established and their interaction with resonant laser light was recently shown to create plasmalike conditions. Such cluster systems cause both Rb and 129Xe depolarization, as well as excess photon scattering. These effects were incorporated into the SEOP model by assuming that clusters are activated in proportion to excitedstate Rb number density and by further estimating physically reasonable values for the nanocluster-induced velocity-averaged spin-destruction cross section for Rb (‹σcluster-Rbν› ≈ 4 x 10-7 cm³ s-1), the 129Xe relaxation cross section (‹σcluster-Xeν› ≈ 4 x 10-13 cm³ s-1), and a non-wavelength-specific photon-scattering cross section (σcluster-Rbν ≈ 4 x 10-12 cm²). The resulting modified SEOP model now closely matches experimental observations. [ABSTRACT FROM AUTHOR]

We study the important, yet widely overlooked, role of gluons for spin transport with a connection to local parity violation in quark gluon plasmas. We employ the formalism of quantum kinetic theory to quarks in weakly coupled quantum chromodynamics to derive the source terms for quark spin polarization. These source terms involve parity-odd correlators of dynamically generated color fields in near-equilibrium quark gluon plasmas and give rise to locally fluctuating axial charge currents. Our results provide a possible explanation for the spin alignment of vector mesons measured in high-energy nuclear collisions. [ABSTRACT FROM AUTHOR]

Using a data sample of ψ(3770) events collected with the BESIII detector at BEPCII corresponding to an integrated luminosity of 2.9  fb-1, we report a measurement of Λ spin polarization in e+e-→Λ̅ Λ at √s=3.773  GeV. The significance of polarization is found to be 2σ including the systematic uncertainty, which implies a zero phase between the transition amplitudes of the Λ̅Λ helicity states. This phase can be interpreted in terms of psionic form factors, and is determined to be ΔΦΨ=ΦΨE-ΦΨM=(71+66-46±5)°. Similarly, the ratio between the form factors is found to be Rψ=|GΨE/GΨM|=0.48+0.21-0.35±0.03. The first uncertainties are statistical and the second systematic. [ABSTRACT FROM AUTHOR]

Spin-polarized scanning tunneling microscopy is identified as a suitable experimental technique to investigate the quantitative quality of Lieb-Robinson bounds on the signal velocity. The latest, most general bound is simplified and it is shown that there is a discrepancy by a factor of approximately 4 between the corresponding limit speed and some estimated exact velocities in atomic spin chains. The observed discrepancy facilitates conclusions for a further mathematical improvement of Lieb-Robinson bounds. The real signal propagation can be modified with several experimental parameters from which the bounds are independent. This enables the application of Lieb-Robinson bounds as upper limits on the enhancement of the real signal speed for information transport in spintronic devices. [ABSTRACT FROM AUTHOR]

We investigate strong-coupling corrections to single-particle excitations in the normal state of a spin-polarized unitary Fermi gas. Within the framework of an extended T-matrix approximation, we calculate the single-particle density of states, as well as the single-particle spectral weight, to show that the so-called pseudogap phenomenon gradually disappears with increasing magnitude of an effective magnetic field. In the highly spin-polarized regime, the calculated spin polarization as a function of the effective magnetic field agrees well with the recent experiment on a 6Li Fermi gas. Although this experiment has been considered to be incompatible with the existence of the pseudogap in an unpolarized Fermi gas, our result clarifies that the observed spin polarization in the highly spin-polarized regime and the pseudogap in the unpolarized limit can be explained in a consistent manner when one correctly includes effects of population imbalance on single-particle excitations. Since it is a crucial issue to clarify whether the pseudogap exists or not in the BCS-BEC crossover regime of an ultracold Fermi gas, our results would be useful for the understanding of this strongly interacting fermion system. [ABSTRACT FROM AUTHOR]

Axial charge in a QCD plasma is P- and CP-odd. We propose and study P- and CP-odd observables in photon and dilepton emissions from an axially charged QCD plasma, which may provide possible experimental evidences of axial charge fluctuation and triangle anomaly in the plasma created in heavy-ion collisions. Our observables measure spin alignments of the emitted photons and dileptons, and are shown to be related to the imaginary part of chiral magnetic conductivity at finite frequency-momentum, which ultimately arises from the underlying triangle anomaly of the QCD plasma with a finite axial charge density. We present an exemplar computation of these observables in a strongly coupled regime using AdS/CFT correspondence. [ABSTRACT FROM AUTHOR]

We report the anomalous D'yakonov-Perel' spin relaxation in ultracold spin-orbit-coupled 40K gas when the coupling between |9/2,9/2) and |9/2,7/2) states, acting as an effective Zeeman magnetic field, is much stronger than the spin-orbit coupled field. Both the transverse and longitudinal spin relaxations are investigated with small and large spin polarizations. It is found that with small spin polarization, the transverse (longitudinal) spin relaxation is divided into four (two) regimes: the normal weak scattering regime, the anomalous D'yakonov-Perel'-like regime, the anomalous Elliott-Yafet-like regime, and the normal strong scattering regime (the anomalous Elliott-Yafet-like regime and the normal strong scattering regime). With large spin polarization, we find that the Hartree-Fock self-energy, which acts as an effective magnetic field, can markedly suppress the transverse spin relaxation in both weak and strong scattering limits. Moreover, by noting that as both the momentum relaxation time and the Hartree-Fock effective magnetic field vary with the scattering length in cold atoms, the anomalous D'yakonov-Perel'-like regime is suppressed and the transverse spin relaxation is hence divided into three regimes in the scattering length dependence: the normal weak scattering regime, the anomalous Elliott-Yafet-like regime, and the strong scattering regime. On the other hand, the longitudinal spin relaxation is again divided into the anomalous Elliott-Yafet-like and normal strong scattering regimes. Furthermore, it is found that the longitudinal spin relaxation can be either enhanced or suppressed by the Hartree-Fock effective magnetic field if the spin polarization is parallel or antiparallel to the effective Zeeman magnetic field. [ABSTRACT FROM AUTHOR]

A new test of Lorentz invariance in the weak interactions has been made by searching for variations in the decay rate of spin-polarized 20Na nuclei. This test is unique to Gamow-Teller transitions, as was shown in the framework of a recently developed theory that assumes a Lorentz symmetry breaking background field of tensor nature. The nuclear spins were polarized in the up and down direction, putting a limit on the amplitude of sidereal variations of the form (Tup -- Tdown)|/(Tup + Tdown) < 3 X 10-3. This measurement shows a possible route toward a more detailed testing of Lorentz symmetry in weak interactions. [ABSTRACT FROM AUTHOR]

The impact of both exchange interaction and electron correlation, as well as their combined impact, on electron elastic scattering off a semifilled-shell Mn(...3d54s², 6S) atom are theoretically studied in the electron energy range of e=0-25 eV. Corresponding elastic-scattering phase shifts dl(e) as well as partial sl(e) and total s(e) cross sections are found to be subject to a strong correlation impact. The latter is shown to drastically differ for oppositely spin-polarized scattered electrons in some cases, thereby bringing significant differences in corresponding dl(e)s, sl(e)s, and s(e)s between these electrons. This is proven to be an inherent feature of electron scattering off a semifilled-shell atom in general. Electron correlation is accounted for in the framework of the self-energy part S of the Green function of a scattered electron concept. The latter is calculated both in the second-order perturbation theory in the Coulomb interelectron interaction as well as beyond it by solving the Dyson equation for S. The significance of the "Dyson" correlation corrections in e- + Mn scattering is unraveled. They are shown to noticeably increase the inherent differences between elastic-scattering phase shifts and cross sections of spin-up (↑) and spin-down (↓) polarized electrons scattered off a spin-polarized Mn atom, in some cases. In particular, the existence of a narrow resonant maximum in s↑(e) near e8 eV but the absence of such in s↓(e) in e- + Mn scattering is predicted. [ABSTRACT FROM AUTHOR]

In this paper we present and discuss the relativistic correlation function in a bipartite system of two electrons, originating from the e-e- → e-e- scattering of a polarized electron beam on an unpolarized target. We also calculate and investigate the probabilities of the definite outcomes of spin-projection measurements performed by two observers. The presented results might help in experimentally verifying whether relativistic quantum theory is able to reproduce the behavior of real quantum systems. [ABSTRACT FROM AUTHOR]

We show that ionization of noble gas atoms by a strong infrared circularly polarized laser field under standard experimental conditions can yield electrons with up to 100% spin polarization in energy-resolved measurements. Spin polarization arises due to the interplay of the electron-core entanglement and the sensitivity of ionization in circularly polarized fields to the sense of electron rotation in the initial state. [ABSTRACT FROM AUTHOR]

We have studied analytically the longitudinally boost-invariant motion of a relativistic dissipative fluid with spin. We have derived the analytic solutions of spin density and spin chemical potential as a function of proper time τ in the presence of the viscous tensor and the second order relaxation time corrections for spin. Interestingly, analogous to the ordinary particle number density and chemical potential, we find that the spin density and spin chemical potential decay as ∼τ-1 and ∼τ-1/3, respectively. These solutions can serve both to gain insight on the dynamics of spin polarization in relativistic heavy-ion collisions and as test beds for further numerical codes. [ABSTRACT FROM AUTHOR]

We systematically develop a density functional description for the equilibrium properties of a two-dimensional, harmonically trapped, spin-polarized dipolar Fermi gas based on the Thomas-Fermi-von Weizsäcker approximation. We pay particular attention to the construction of the two-dimensional kinetic energy functional, where corrections beyond the local density approximation must be motivated with care. We also present an intuitive derivation of the interaction energy functional associated with the dipolar interactions and provide physical insight into why it can be represented as a local functional. Finally, a simple and highly efficient self-consistent numerical procedure is developed to determine the equilibrium density of the system for a range of dipole interaction strengths. [ABSTRACT FROM AUTHOR]

This article reviews our present understanding of QCD spin physics: the proton spin puzzle and new developments aimed at understanding the transverse structure of the nucleon. Present experimental investigations of the nucleon's internal spin structure, the theoretical interpretation of the different measurements, and the open questions and challenges for future investigation are discussed. [ABSTRACT FROM AUTHOR]

Evolution of the z component of a single spin in a finite cyclic XY spin-1/2 chain is studied. Initially one selected spin is polarized while other spins are completely unpolarized and uncorrelated. Polarization of the selected spin as a function of time is proportional to the autocorrelation function gzz0(t) at infinite temperature. Initialization of the selected spin gives rise to two wave packets moving in opposite directions and winding over the circle. We express gzz0(t) as a series in winding number and derive tractable approximations for each term. This allows us to give qualitative explanations and quantitative descriptions of various finite-size effects such as partial revivals and transition from regular to erratic behavior. [ABSTRACT FROM AUTHOR]

We propose a method to generate a source of spin-polarized cold atoms which are continuously extracted and guided from a magneto-optical trap using an atom-diode effect. We show that it is possible to create a pipe-like potential by overlapping two optical beams coupled with the two transitions of a three-level system in a ladder configuration. With alkali-metal atoms, and in particular with 87Rb, a proper choice of transitions enables both the potential generation and optical pumping, thus polarizing the sample in a given Zeeman state. We extend the Dalibard and Cohen-Tannoudji dressed-atom model of radiative forces to the case of a three-level system. We derive expressions for the average force and the different sources of momentum diffusion in the resonant, nonperturbative regime. We show using numerical simulations that a significant fraction of the atoms initially loaded can be guided over several centimeters with output velocities of a few meters per second. This would produce a collimated continuous source of slow spin-polarized atoms suitable for atom interferometry. [ABSTRACT FROM AUTHOR]

We analyze the impact of effective axial-vector coupling of the gluon on spin polarization observables in tt pair production at the LHC. Working at leading order in QCD, we compute the tt spin correlation and left-right spin asymmetry coefficients in the helicity basis in the laboratory frame as functions of the new physics scale A associated with this coupling. We found that the tt invariant mass dependent asymmetries are more sensitive to the scale A than the corresponding inclusive ones, in particular when suitable cuts selecting high tt invariant mass regions are imposed. In the context of this scenario, we show that the LHC has potential either to confirm or to rule out the Tevatron forward-backward top asymmetry anomaly by analyzing the tt spin correlation and left-right polarization asymmetries. On the other hand, stringent lower bound on the new physics scale A can be set in this scenario if no significant deviations from the standard model predictions for those observables will be measured. [ABSTRACT FROM AUTHOR]

Spin Hall effect (SHE) is the generation of spin current due to an electric field, and has been observed in a variety of materials. In this work, we use linear response theory to verify that the analogous spin Hall current can be induced by chemical potential and temperature gradient, both of which are present in hot and dense nuclear matter created in heavy-ion collisions. We propose to measure "directed spin flow", the first Fourier coefficients of local spin polarization of Λ (Λ) hyperon, at central collisions to probe spin Hall current in heavy-ion collision experiments. We benchmark the magnitude of the induced "directed spin flow" at two representatively collisions energies, namely √sNN=200 GeV and √sNN=19.6 GeV, by employing a phenomenologically motivated freeze-out prescription. At both beam energies, the resulting "directed spin flow" ranges from 10-4 to 10-3, and is very sensitive to the rapidity. [ABSTRACT FROM AUTHOR]

The work presents the study of the polarization observables in the single pion production (SPP) induced by the interaction of the muon neutrino (antineutrino) with nucleons. The SPP cross sections and spin asymmetries are computed within two phenomenological models. One is based on the nonlinear sigma model [E. Hernandez, J. Nieves, and M. Valverde, Phys. Rev. D 76, 033005 (2007)] and the other has origin in the linear sigma model [G. L. Fogli and G. Nardulli, Nucl. Phys. B160, 116 (1979)]. First, we show that the final nucleon polarization and target spin asymmetries are good observables to obtain information about the CA5 axial form factor. Second, we demonstrate that the nucleon polarization and the target spin asymmetries are sensitive to the relative phase between resonance and nonresonance amplitudes. We conclude that the polarization of the final nucleon and the target spin asymmetry are promising observables for testing SPP models, including studies of the axial content of Δ(1232) resonance and unitarization procedures. [ABSTRACT FROM AUTHOR]

We describe a code which utilizes partial-wave amplitudes to calculate a variety of physical quantities studied in electron–atom scattering. For elastic scattering and excitation of atoms with arbitrary angular momenta in collisions with spin-polarized and unpolarized electrons, the program can calculate angle-integrated and angle-differential cross sections, the spin polarization of scattered electrons, the spin left–right (up–down) asymmetry, generalized STU parameters, and the statistical tensors of the final atomic state, which determine polarization and correlation parameters in radiative and nonradiative decays of these states. In addition, the program transforms partial-wave scattering amplitudes into a representation of projections of the angular momenta in the natural and collision coordinate frames, thereby providing the possibility for a user to conveniently calculate any observable not explicitly included in the code. The program can be used directly as a final module after running the Belfast R-matrix codes in the Breit–Pauli mode. [Copyright &y& Elsevier]

Evolution of spin polarization in the presence of external electric field is studied for collision energies √sNN=27 GeV and √sNN=200 GeV. The numerical analysis is done in the perfect-fluid Bjorken-expanding resistive magnetohydrodynamic background and novel results are reported. In particular, we show that the electric field plays a significant role in the competition between expansion and dissipation. [ABSTRACT FROM AUTHOR]

Evolution of spin polarization in the Gubser-expanding conformal perfect-fluid hydrodynamic background is studied. The analysis of the conformal transformation properties of the conservation laws is extended to the case of the angular momentum conservation. The explicit forms of equations of motion for spin components are derived and analyzed, and some special solutions are found. [ABSTRACT FROM AUTHOR]

M. Pirbhai et al. [Phys. Rev. A 88, 060701(R) (2013)] reported a new optically pumped spin-exchange polarized-electron source developed to avoid the limitations of the traditional GaAs-type source and to enable a broader range of experiments. The spin-exchange gaseous source has introduced its own limitations with 650-mW laser power producing only 4 µA of spin-polarized current with a 24% polarization and a 2-eV energy spread depending markedly on tenuous roles of various buffer gases which we consider are not explained cogently. Spin-related beam experiments over many decades have significant achievements using GaAs spin sources. [ABSTRACT FROM AUTHOR]

We present UNDI, an open-source program to analyze the time dependent spin polarization of an isolated muon interacting with the surrounding nuclear magnetic dipoles in the context of standard muon spin rotation and relaxation spectroscopy experiments. The code can perform both exact and approximated estimates of the muon polarization function in presence of external fields and electric field gradients on the nuclei surrounding the muon. We show that this tool, combined to ab initio estimations of the electric field gradient at the nuclei interacting with the muon, can become a valuable complement to supercell based identifications of muon sites in crystals when large nuclear magnetic moments are present in the sample. In addition, it allows to properly investigate physical properties influenced by the presence of a non-negligible electric field gradient such as avoided level crossing resonance, nature of the ground state, disentanglement of electronic and nuclear magnetic moments or charge ordered states. The efficiency and effectiveness of this method is shown along the lines of three realistic examples. Program Title: UNDI CPC Library link to program files: http://dx.doi.org/10.17632/grp8njy6gz.1 Developer's repository link: https://github.com/bonfus/undi Code Ocean capsule: https://codeocean.com/capsule/8365303 Licensing provisions: GPLv3 Programming language: Python Nature of problem: To simplify and potentially automate the analysis of the nuclear contribution to muon polarization functions in crystalline materials. Solution method: A python library that provides a set of tools to efficiently solve the spin Hamiltonian describing the interaction between the muon and its neighboring nuclei. The code provides the time development of the spin polarization of the muon subject to external fields and accounts for quadrupolar interactions at the nuclear sites. The solution is sought at quantum level accuracy and Hilbert spaces with dimension up to one million can be handled, thus providing accurate results for all standard experimental conditions. [ABSTRACT FROM AUTHOR]

We study the inclusive production of bottom-flavored hadrons from semileptonic decays of polarized top quarks at next-to-leading order in QCD using fragmentation functions recently determined from a global fit to e+e- data. We provide the relevant differential decay widths at parton level in analytic form. These results fill an important gap in the theoretical interpretation of recent measurements of the top-quark polarization and the tt spin correlations using dilepton final states in proton-proton collisions at the CERN Large Hadron Collider. As an illustration, we study the distributions in the scaled bottom-hadron energy of the polarized-top-quark decay widths for different W-boson helicities. [ABSTRACT FROM AUTHOR]

Before cosmic reionization, hydrogen atoms acquire a spin polarization quadrupole through interaction with the anisotropic 21-cm radiation field. The interaction of this quadrupole with anisotropies in the cosmic microwave background (CMB) radiation field gives a net spin orientation to the hydrogen atoms. The 21-cm radiation emitted by these spin-oriented hydrogen atoms is circularly polarized. Here, we reformulate succinctly the derivation of the expression for this circular polarization in terms of Cartesian (rather than spherical) tensors. We then compute the angular power spectrum of the observed Stokes-V parameter in the standard CDM cosmological model and show how it depends on redshift, or equivalently, the observed frequency. [ABSTRACT FROM AUTHOR]

The axial-vector form factors of the spin-3/2+ decuplet baryons are investigated in the chiral constituent quark model using their explicit quark spin polarizations. The quark sea arises from the chiral symmetry breaking, which results in the Goldstone bosons mediating the interaction between constituent quarks. The axial-vector form factors, which have some physical significance corresponding to the flavor singlet current, flavor isovector (triplet) current, and the flavor hypercharge axial (octet) current at zero momentum transfer, are, respectively G0AV,B*3/2(0), G³AV,B*3/2(0), and G8AV,B*3/2(0). In order to further understand the Q2 dependence of these form factors, we have used the dipole form of parametrization. The qualitative and quantitative contribution of the quark sea has also been investigated by varying the transition probability of the chiral fluctuation. [ABSTRACT FROM AUTHOR]

Finite energy QCD sum rules involving nucleon current correlators are used to determine several QCD and hadronic parameters in the presence of an external, uniform, large magnetic field. The continuum hadronic threshold s0, nucleon mass mN, current-nucleon coupling λN, transverse velocity v⊥, the spin polarization condensate ⟨̄qσ12q⟩, and the magnetic susceptibility of the quark condensate χq, are obtained for the case of protons and neutrons. Due to the magnetic field, and charge asymmetry of light quarks up and down, all the obtained quantities evolve differently with the magnetic field, for each nucleon or quark flavor. With this approach it is possible to obtain the evolution of the above parameters up to a magnetic field strength eB<1.4 GeV². [ABSTRACT FROM AUTHOR]

We propose an improved quark coalescence model for spin alignment of vector mesons and polarization of baryons by spin density matrix with phase space dependence. The spin density matrix is defined through Wigner functions. Within the model we propose an understanding of spin alignments of vector mesons ϕ and K*0 (including K*0) in the static limit: a large positive deviation of ρ00 for ϕ mesons from 1/3 may come from the electric part of the vector ϕ field, while a negative deviation of ρ00 for K*0 may come from the electric part of vorticity tensor fields. Such a negative contribution to ρ00 for K*0 mesons, in comparison with the same contribution to ρ00 for ϕ mesons which is less important, is amplified by a factor of the mass ratio of strange to light quark times the ratio of ⟨pb²⟩ on the wave function of K*0 to ϕ (pb is the relative momentum of two constituent quarks of K*0 and ϕ). These results should be tested by a detailed and comprehensive simulation of vorticity tensor fields and vector meson fields in heavy ion collisions. [ABSTRACT FROM AUTHOR]

The gluon transversity distribution in the deuteron is defined by the matrix element between linearly polarized deuteron states, and it could be investigated in proton-deuteron collisions in addition to lepton-deuteron scattering. The linear polarization of photon is often used, whereas it is rarely used for the spin-1 deuteron. Therefore, it is desirable to express deuteron-reaction cross sections in term of conventional deuteron spin polarizations for actual experimental measurements. In this work, we investigate how proton-deuteron Drell-Yan cross sections are expressed by the conventional polarizations for finding the gluon transversity distribution. In particular, we show that the gluon transversity can be measured in the proton-deuteron Drell-Yan process by taking the cross section difference between the deuteron spin polarizations along the two-transverse axes. Since the gluon transversity does not exist for the spin-1/2 nucleons, a finite gluon transversity of the deuteron could indicate an "exotic" mechanism beyond the simple bound system of the nucleons in the deuteron. Therefore, the gluon transversity is an interesting and appropriate observable to shed light on a new hadronic mechanism in nuclei. [ABSTRACT FROM AUTHOR]

In this paper we show how to recast the results of the semiclassical method of Baier, Katkov and Strakhovenko for pair production, including the possibility of specifying all the spin states and photon polarization, in a form that is suitable for numerical implementation. In this case, a new type of integral appears in addition to the ones required for the radiation emission process. We compare the resulting formulas with those obtained for a short pulse plane wave external field by using the Volkov state. We investigate the applicability of the local constant field approximation for the proposed upcoming experiments at FACET II at SLAC and LUXE at DESY. Finally, we provide results on the dependence of the pair production rate on the relative polarization between a linearly polarized laser pulse and a linearly polarized incoming high energy photon. We observe that even in the somewhat intermediate multiphoton regime of these experiments, there is roughly a factor of 2 difference between the pair production rates corresponding to the two relative photon polarizations, as predicted by Ritus in the monochromatic highly multiphoton weak field limit. This finding is of interest in light of the vacuum birefringence of QED. [ABSTRACT FROM AUTHOR]

We show how the semiclassical formulas for radiation emission of Baier, Katkov and Strakhovenko for arbitrary initial and final spins of the electron and arbitrary polarization of the emitted photon can be rewritten in a form which numerically converges quickly. We directly compare the method in the case of a background plane wave with the result obtained by using the Volkov state solution of the Dirac equation, and confirm that we obtain the same result. We then investigate the interaction of a circularly polarized short laser pulse scattering with GeV electrons and see that the finite duration of the pulse leads to a lower transfer of circular polarization than that predicted by the known formulas in the monochromatic case. We also see how the transfer of circular polarization from the laser beam to the gamma ray beam is gradually deteriorated as the laser intensity increases, entering the nonlinear regime. However, this is shown to be recovered if the scattered photon beam is collimated to only allow for passage of photons emitted with angles smaller than 1/γ with respect to the initial electron direction, where γ is the approximately constant Lorentz factor of the electron. The obtained formulas also allow us to answer questions regarding radiative polarization of the emitting particles. In this respect we briefly discuss an application of the present approach to the case of a bent crystal and high-energy positrons. [ABSTRACT FROM AUTHOR]

We investigate the ferromagnetic (spin polarization) condensation in (2+1)-flavor Nambu-Jona-Lasinio (NJL) model with nonzero current quark masses at finite temperature and density, which may be relevant in the context of neutron stars. The spin polarization condensation arises due to a tensor-type interaction that may be generated due to nonperturbative effects in QCD. In this investigation, we study the interplay between the chiral condensate and spin polarization condensation for different values of tensor coupling. Spin polarization in the case of (2+1) flavor is different from two-flavor case because of an additional F8~⟨ψ̅Σzλ8ψ⟩ along with a F3~⟨ψ̅Σzλ³ψ⟩ condensate associated with the λ8 flavor generator. We find nonzero values of the two spin condensates in the chirally restored phase. Beyond a certain temperature, the spin polarization condensates vanish for any value of quark chemical potential. The spin condensates affect the chiral phase transition, quark masses, and quark dispersion relation. Thermodynamic behaviors of F3 and F8 are found to be different, and they affect the quark masses differently. We discuss the phase diagram in the temperature and chemical potential plane in the presence of such condensates. [ABSTRACT FROM AUTHOR]

We derive a quantum kinetic theory for fermions with arbitrary mass in a background electromagnetic field using a Wigner-function approach. Since spin of massive fermions is a dynamical degree of freedom (d.o.f.), kinetic equations with leading-order quantum corrections describe entangled dynamics of not only vector- and axial-charge distributions but also of the spin polarization. Therefore, we obtain one scalar and one axial-vector kinetic equations with magnetization currents pertinent to the spin-orbit interaction. We show that our results smoothly reduce to the massless limit where the spin of massless fermions is no longer an independent dynamical d.o.f. but is enslaved by the chirality and momentum, and the accordingly kinetic equations turn into chiral kinetic theory for Weyl fermions. We provide a kinetic theory covering both massive and massless cases and hence resolving the problem of constructing a bridge between them. Such a generalization may be crucial for applications to various physical systems. Based on our kinetic equations, we discuss the anomalous currents transported by massive fermions in thermal equilibrium. [ABSTRACT FROM AUTHOR]

Measurements of the top quark polarization and top quark pair (t¯t) spin correlations are presented using events containing two oppositely charged leptons (e+e-, e±μ∓, or μ+μ-) produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb-1. A set of parton-level normalized differential cross sections, sensitive to each of the independent coefficients of the spin-dependent parts of the t¯t production density matrix, is measured for the first time at 13 TeV. The measured distributions and extracted coefficients are compared with standard model predictions from simulations at next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD), and from NLO QCD calculations including electroweak corrections. All measurements are found to be consistent with the expectations of the standard model. The normalized differential cross sections are used in fits to constrain the anomalous chromomagnetic and chromoelectric dipole moments of the top quark to -0.24

Measurements of the top quark polarization and top quark pair (t¯t) spin correlations are presented using events containing two oppositely charged leptons (e+e-, e±μ∓, or μ+μ-) produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb-1. A set of parton-level normalized differential cross sections, sensitive to each of the independent coefficients of the spin-dependent parts of the t¯t production density matrix, is measured for the first time at 13 TeV. The measured distributions and extracted coefficients are compared with standard model predictions from simulations at next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD), and from NLO QCD calculations including electroweak corrections. All measurements are found to be consistent with the expectations of the standard model. The normalized differential cross sections are used in fits to constrain the anomalous chromomagnetic and chromoelectric dipole moments of the top quark to -0.24

We present the quantum kinetic equation for the spin polarization of massive quarks in leading-log order of perturbative QCD, which describes time evolution of the spin density matrix in momentum space of a massive quark interacting with a background QCD plasma. We find that the time evolution operator of the spin density matrix or the quantum kinetic collision terms are universally of order α²slog(1/αs) in terms of the QCD coupling constant αs=g²/(4π). Our quantum kinetic equation is valid for an arbitrary quark mass m≫mD∼gT, where mD is the Debye mass, and can be used to study relaxation dynamics of spin polarization of massive quarks in the perturbative QCD regime. [ABSTRACT FROM AUTHOR]