Exchange currents and nucleon magnetic moments (original) (raw)

Six-quark bag, exchange currents and trinucleon magnetic moments

Physics Letters B, 1986

The magnetic moments of 3H and 3He are reexamined in the Karl-Miller-Rafelski model of six-quark bag formation. Realistic three-nucleon wavefunctions are taken, and long-range one-pion exchange current corrections are included. It is concluded that the model is compatible with the data.

Nucleon magnetic moments in light-front models with quark mass asymmetries

Brazilian Journal of Physics, 2004

We show that the systematic inconsistence found in the simultaneous fit of the neutron and proton magnetics moments in light-front models, disappears when one allows an asymmetry in the constituent quark masses. The difference between the constituent quarks masses is an effective way to include in the nucleon model the effect of the attractive short ranged interaction in the singlet spin channel.

Baryon magnetic moments in the effective quark Lagrangian approach

Physical Review D, 2002

An effective quark Lagrangian is derived from first principles through bilocal gluon field correlators. It is used to write down equations for baryons, containing both perturbative and nonperturbative fields. As a result one obtains magnetic moments of octet and decuplet baryons without introduction of constituent quark masses and using only string tension as an input. Magnetic moments come out on average in reasonable agreement with experiment, except for nucleons and Σ − . The predictions for the proton and neutron are shown to be in close agreement with the empirical values once we choose the string tension such to yield the proper nucleon mass. Pionic corrections to the nucleon magnetic moments have been estimated. In particular, the total result of the twobody current contributions are found to be small. Inclusion of the anomalous magnetic moment contributions from pion and kaon loops leads to an improvement of the predictions.

Anomalous magnetic moment of quarks

Physical Review C, 1999

In the case of massless current quarks we find that the breaking of chiral symmetry usually triggers the generation of an anomalous magnetic moment for the quarks. We show that the kernel of the Ward identity for the vector vertex yields an important contribution. We compute the anomalous magnetic moment in several quark models. The results show that it is hard to escape a measurable anomalous magnetic moment for the quarks in the case of spontaneous chiral symmetry breaking.

Magnetic moment of hyperons in nuclear matter by using quark–meson coupling models

2009

We calculate the magnetic moments of hyperons in dense nuclear matter by using relativistic quark models. Hyperons are treated as MIT bags, and the interactions are considered to be mediated by the exchange of scalar and vector mesons which are approximated as mean fields. Model dependence is investigated by using the quark-meson coupling model and the modified quark-meson coupling model; in the former the bag constant is independent of density and in the latter it depends on density. Both models give us the magnitudes of the magnetic moments increasing with density for most octet baryons. But there is a considerable model dependence in the values of the magnetic moments in dense medium. The magnetic moments at the nuclear saturation density calculated by the quark-meson coupling model are only a few percents larger than those in free space, but the magnetic moments from the modified quark-meson coupling model increase more than 10% for most hyperons. The correlations between the bag radius of hyperons and the magnetic moments of hyperons in dense matter are discussed.

Strange Quark Magnetic Moment of the Nucleon at the Physical Point

Physical Review Letters, 2017

We report a lattice QCD calculation of the strange quark contribution to the nucleon's magnetic moment and charge radius. This analysis presents the first direct determination of strange electromagnetic form factors including at the physical pion mass. We perform a model-independent extraction of the strange magnetic moment and the strange charge radius from the electromagnetic form factors in the momentum transfer range of 0.051 GeV 2 < ∼ Q 2 < ∼ 1.31 GeV 2. The finite lattice spacing and finite volume corrections are included in a global fit with 24 valence quark masses on four lattices with different lattice spacings, different volumes, and four sea quark masses including one at the physical pion mass. We obtain the strange magnetic moment G s M (0) = −0.064(14)(09) µN. The four-sigma precision in statistics is achieved partly due to low-mode averaging of the quark loop and low-mode substitution to improve the statistics of the nucleon propagator. We also obtain the strange charge radius r 2 s E = −0.0043(16)(14) fm 2 .

Heavy quark and magnetic moment

Lettere al Nuovo Cimento, 1979

The spectacular discovery of T particles (1) has introduced heavy quarks, namely bottom or top quarks, for the phenomenological description of these particles under SU 5 symmetry. This symmetry has recently become topical. The conventional symmetry scheme of SU a and SU 4 (~) proved very useful in predicting a reIation among magnetic moments of hadrons. The basic assumptions underlying these calculations are that the space part of the overlapping integral of hadron wave functions becomes equal to unity and the principle of additivity is exploited, according to which some properties of hadrons are described as the sum of the contributions from the constituent quarks. As the Y resonance is assumed to be in the tt state, this hypothesis leads to the possible existence of hadrons with nonzero beauty/truth quantum numbers. The quark structure of such hadrons has been given by us (a). The quark structures and calculations of hadronic properties become clearer when represented in terms of state vectors (4). hi this paper we calculate the magnetic moment and transition moment of truthful hadrons using their state vectors and make use of the quark additivity principle. We define the magnetic moment of the hadron A as the maximum z component of the spin as (I) ~(A) = <~(A, J~ = J)[]/I~(A, Jo = J)~.

Magnetic moments of the octet baryons in a chiral quark potential model

1995

In quark potential models, two{body current contributions to baryon magnetic moments arise necessarily to satisfy the continuity equation for the electromagnetic current. On the other hand, the na ve additive quark model predicts the experimental octet magnetic moments to within 5%. We demonstrate that consistently derived two{body current contributions to the octet baryon magnetic moments are individually large, but tend to cancel each other globally.

Isoscalar currents and nuclear magnetic moments

Nuclear Physics A, 1987

We investigate meson-exchange current effects on isoscalar nuclear magnetic moments taking a one-boson exchange model. For some cases we find appreciable cont~butions, though the rest&s are very model dependent,

Nucleon properties in the covariant quark-diquark model

The European Physical Journal A, 2000

In the covariant quark-diquark model the effective Bethe-Salpeter (BS) equations for the nucleon and the ∆ are solved including scalar and axialvector diquark correlations. Their quark substructure is effectively taken into account in both, the interaction kernel of the BS equations and the currents employed to calculate nucleon observables. Electromagnetic current conservation is maintained. The electric form factors of proton and neutron match the data. Their magnetic moments improve considerably by including axialvector diquarks and photon induced scalar-axialvector transitions. The isoscalar magnetic moment can be reproduced, the isovector contribution is about 15% too small. The ratio µ GE/GM and the axial and strong couplings gA, gπNN , provide an upper bound on the relative importance of axialvector diquarks confirming that scalar diquarks nevertheless describe the dominant 2-quark correlations inside nucleons. PACS. 11.10.St (Bound states; Bethe-Salpeter equations) -12.39.Ki (Relativistic quark model) -12.40.Yx (Hadron mass models and calculations) -13.40.Em (Electric and magnetic moments) -13.40.Gp (Electromagnetic form factors) -13.75.Gx (Pion-baryon interactions) -14.20.Dh (Protons and neutrons)