Chiral perturbation theory analysis of the baryon magnetic moments reexamined

Abstract

We reexamine critically the chiral expansion for the baryon magnetic moments including the contributions from loops which involve intermediate octet and decuplet baryons. We find that, contrary to some claims, the nonanalytic loop contributions of orders m 1/2 s and m s ln m s are of the same general size because of large coupling factors for the latter, and that the decuplet contributions are as large as the octet contributions and must be included in a consistent calculation. There is no clear evidence of the convergence of the chiral series. The adequacy of the theory will not be established until dynamical models are able to calculate the contributions from the counterterms that largely hide the loop effects in fits to the data.

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

“…Moreover, the agreement with the data is even worse than in HBχPT. The size of NLO terms raises the question about the convergence of the chiral series [7,9,16].In this letter we present a covariant calculation of the baryon-octet magnetic moments at O(p 3 ) (NLO) using the EOMS renormalization technique. In contrast to the previous works, we find small loop-corrections leading to a considerable improvement over the SU(3)-symmetric description.…”

“…The leading non-analytical correction to the SU(3)-symmetric prediction amounts up to 80% of the leading contribution for some of the baryons. In this approach, it is necessary to come up to O(p 4 ) to achieve reasonable convergence, although the role of the loop contributions is not clear in a scenario where one has the same number of parameters as of experimental values to fit [7]. One expects that the covariant theory, with the proper higher-order chiral terms, should overcome the problem of convergence.…”

“…Moreover, the agreement with the data is even worse than in HBχPT. The size of NLO terms raises the question about the convergence of the chiral series [7,9,16].…”

“…However, it was soon noticed that the leading-order chiral corrections are large and tend to worsen the results [5,6]. This problem has often been used to question the validity of SU(3)-χPT in the baryon sector.In the last decade several calculations in HBχPT up to nextto-next-to-leading order (NNLO) have been performed both with [6,7,8] and without [9] the inclusion of the baryon decuplet. The large number of LECs appearing at this order reduces the predictive power of the theory.…”

“…In the last decade several calculations in HBχPT up to nextto-next-to-leading order (NNLO) have been performed both with [6,7,8] and without [9] the inclusion of the baryon decuplet. The large number of LECs appearing at this order reduces the predictive power of the theory.…”