Search results for "electrodynamics"

Relativistic effects in quasifree deuteron electrodisintegration compared to a covariant model

1994

Deuteron disintegration by electrons is calculated in a covariant model for the quasifree region, where final-state interaction and two-body currents can be negiected, and is compared to a phenomenological approach in which one adds to the nonrelativistic one-body current relativistic contributions of lowest order and the kinematic wave-function boost. It is shown that ap/M-reduction of the relativistic theory contains the expressions of the phenomenological approach. The inclusion of relativistic contributions leads to a less frame-dependent description and the deviation from the covariant theory becomes small at low and medium energy and momentum transfers. Furthermore, the dependence of …

Chiral Instabilities and the Onset of Chiral Turbulence in QED Plasmas

2020

We present a first principles study of chiral plasma instabilities and the onset of chiral turbulence in QED plasmas far from equilibrium. By performing classical-statistical lattice simulations of the microscopic theory, we show that the generation of strong helical magnetic fields from a helicity imbalance in the fermion sector proceeds via three distinct phases. During the initial linear instability regime the helicity imbalance of the fermion sector causes an exponential growth(damping) of magnetic field modes with right(left) handed polarization, for which we extract the characteristic growth (damping) rates. Secondary growth of unstable modes accelerates the helicity transfer from fer…

Phenomenological applications of rational approximants

2016

We illustrate the powerfulness of Padé approximants (PAs) as a summation method and explore one of their extensions, the so-called quadratic approximant (QAs), to access both space- and (low-energy) time-like (TL) regions. As an introductory and pedagogical exercise, the function [Formula: see text] is approximated by both kind of approximants. Then, PAs are applied to predict pseudoscalar meson Dalitz decays and to extract [Formula: see text] from the semileptonic [Formula: see text] decays. Finally, the [Formula: see text] vector form factor in the TL region is explored using QAs.

Longitudinal dynamics of multiple conserved charges

2021

Abstract It is the goal of the RHIC BES program and the future FAIR and NICA facilities to produce compressed baryonic matter. In experiments such as these, strong gradients in baryon density are expected, and therefore the diffusion of baryon number could play a major role in the description of the fireball. The constituents of the produced matter carry a multitude of conserved charges, namely the baryon number, strangeness and electric charge, so that the diffusion currents of conserved charge couple with each other. Therefore, baryon density gradients in the above-mentioned high-density collision experiments will generate equalizing currents in all conserved charges. In common fluid dyna…

Gravitational waves from oscillating accretion tori: Comparison between different approaches

2005

Quasi-periodic oscillations of high density thick accretion disks orbiting a Schwarzschild black hole have been recently addressed as interesting sources of gravitational waves. The aim of this paper is to compare the gravitational waveforms emitted from these sources when computed using (variations of) the standard quadrupole formula and gauge-invariant metric perturbation theory. To this goal we evolve representative disk models using an existing general relativistic hydrodynamics code which has been previously employed in investigations of such astrophysical systems. Two are the main results of this work: First, for stable and marginally stable disks, no excitation of the black hole quas…

The asymmetry in π−3He scattering

1992

Abstract We show that the π + − 3 He asymmetry data obtained in a recent TRIUMF experiment at T π = 100 MeV can be understood in terms of the elementary π N amplitudes. Through a comparison to a full optical-potential calculation that employs realistic Faddeev wave functions for the trinucleon we show that all nuclear-structure dependence cancels for A y at lower energies. At higher pion energies around the Δ-resonance region the sign flip of A y offers the possibility of extracting information about the smaller partial waves.

Peripheral nucleon-nucleon phase shifts and chiral symmetry

1997

Within the one-loop approximation of baryon chiral perturbation theory we calculate all one-pion and two-pion exchange contributions to the nucleon-nucleon interaction. In fact we construct the elastic NN-scattering amplitude up to and including third order in small momenta. The phase shifts with orbital angular momentum $L\geq2 $ and the mixing angles with $J\geq2$ are given parameterfree and thus allow for a detailed test of chiral symmetry in the two-nucleon system. We find that for the D-waves the $2\pi$-exchange corrections are too large as compared with empirical phase shifts, signaling the increasing importance of shorter range effects in lower partial waves. For higher partial waves…

Unsubtracted dispersion-relation for longitudinal compton amplitude

1975

Abstract It is shown that there is a simple connection between the slope, at q2 = 0, of the longitudinal Compton amplitude and the electric polarizability of the nucleon. The longitudinal subtraction function is thus known to order q2. The assumption of an unsubtracted dispersion relation for the longitudinal amplitude leads to a sum rule for the electric polarizability. This is a model independent test of the high-energy behaviour of the forward virtual Compton amplitude.

Erratum to: “A quark model analysis of orbital angular momentum” [Phys. Lett. B 460 (1999) 8–16]

2000

Additivity of effective quadrupole moments and angular momentum alignments in the A~130 nuclei

2007

The additivity principle of the extreme shell model stipulates that an average value of a one-body operator be equal to the sum of the core contribution and effective contributions of valence (particle or hole) nucleons. For quadrupole moment and angular momentum operators, we test this principle for highly and superdeformed rotational bands in the A~130 nuclei. Calculations are done in the self-consistent cranked non-relativistic Hartree-Fock and relativistic Hartree mean-field approaches. Results indicate that the additivity principle is a valid concept that justifies the use of an extreme single-particle model in an unpaired regime typical of high angular momenta.