Moments In Chiral Perturbation Theory Research Articles

Lowest-lying spin-1/2 and spin-3/2 baryon magnetic moments in chiral perturbation theory

We review some recent progress in our understanding of the lowest-lying spin-1/2 and spin-3/2 baryon magnetic moments (MMs) in terms of Chiral Perturbation Theory (ChPT). In particular, we show that at next-to-leading-order ChPT can describe the MMs of the octet baryons quite well. We also make predictions for the decuplet MMs at the same chiral order. Among them, the MMs of the Δ++ and Δ+ are found to agree well with data within the experimental uncertainties.

Leading-order decuplet contributions to the baryon magnetic moments in chiral perturbation theory

We extend an earlier study of the baryon magnetic moments in chiral perturbation theory by the explicit inclusion of the spin-3/2 decuplet resonances. We find that the corrections induced by these heavier degrees of freedom are relatively small in a covariant framework where unphysical spin-1/2 modes are removed. Consequently, implementing the leading SU(3)-breaking corrections given by both the baryon and decuplet contributions, we obtain a description of the baryon-octet magnetic moments that is better than the Coleman–Glashow relations. Finally, we discuss the uncertainties and compare between heavy baryon and covariant approaches.

Leading SU(3)-Breaking Corrections to the Baryon Magnetic Moments in Chiral Perturbation Theory

We calculate the baryon magnetic moments using covariant chiral perturbation theory (chiPT) within the extended-on-mass-shell renormalization scheme. By fitting the two available low-energy constants, we improve the Coleman-Glashow description of the data when we include the leading SU(3)-breaking effects coming from the lowest-order loops. This success is in dramatic contrast with previous attempts at the same order using heavy-baryon chiPT and covariant infrared chiPT. We also analyze the source of this improvement with particular attention to the comparison between the covariant results.

Baryon magnetic moments in chiral perturbation theory

We consider the chiral expansion of the octet baryon magnetic moments in heavy baryon chiral perturbation theory including all terms which are of order q 4. These terms are formally of quadratic order in the quark masses. We show that despite the large non-analytic quark mass corrections to the Coleman-Glashow relations at order q 3, including all analytic and non-analytic corrections at order q 4, which in total are of moderate size, allows for a fit to the measured magnetic moments due to the appearance of counter terms with free coupling constants of natural size. In this scheme, the ΛΣ 0 transition moment is predicted to be μ ΛΣ 0 = (1.40 ± 0.01) μ N .

QCD equalities for baryon current matrix elements

An examination of the symmetries manifest in the QCD path integral for current matrix elements reveals various equalities among the quark sector contributions. QCD equalities among octet baryon magnetic moments lead to a determination of the disconnected sea-quark contribution to nucleon magnetic moments, which is the most reliable determination in the literature. Matching QCD equalities to recent calculations of decuplet baryon magnetic moments in chiral perturbation theory (\ensuremath{\chi}PT) reveals an equivalence between \ensuremath{\chi}PT to O(${\mathit{p}}^{2}$) and the simple quark model with an explicit disconnected sea-quark contribution. New insights into SU(3)-flavor symmetry breaking, sea contributions, and constituent quark composition are obtained. The strangeness contribution to nucleon magnetic moments is found to be large at ${\mathit{G}}_{\mathit{M}}^{\mathit{s}}$(0)=-0.75\ifmmode\pm\else\textpm\fi{}0.30${\mathrm{\ensuremath{\mu}}}_{\mathit{N}}$. The QCD equalities must be followed by any model which hopes to capture the essence of nonperturbative QCD. Not all models are in accord with these symmetries. \textcopyright{} 1996 The American Physical Society.