Some problems of symmetry breaking

NSTAR 2004 - Proceedings of the Workshop on the Physics of Excited Nucleons, 2004

Physics Letters B, 2004

We study J P = ( 3 2 ) − baryon resonances as generated by chiral coupled-channel dynamics in the χ−BS(3) approach. Parameter-free results are obtained in terms of the Weinberg-Tomozawa term predicting the leading s-wave interaction strength of Goldstone bosons with baryon-decuplet states. In the 'heavy' SU(3) limit with m π = m K ∼ 500 MeV the resonances turn into bound states forming a decuplet and octet representation of the SU(3) group. Using physical masses the mass splitting are remarkably close to the empirical pattern.

Physical Review D, 1997

The isospin symmetry breakings of qq are investigated in the QCD sum rule method. The electromagnetic effects are evaluated following the procedure requiring that the electromagnetic effects for charged meson be gauge invariant. We find that the electromagnetic effects are also dominant in the isospin violations of the ρ mesons, which have been shown to be the case in the mass splittings of pions. The numerical results for the differences of pion decay constants and the masses of ρ mesons are presented, which are consistent with the data.

Physical review, 1995

Baryon masses are calculated in chiral perturbation theory at the one-loop-O(p 3) level in the chiral expansion and to leading order in the heavy baryon expansion. Ultraviolet divergences occur requiring the introduction of counter-terms. Despite this neccessity, no knowledge of the counter terms is required to determine the violations to the Gell-Mann Okubo mass relation for the baryon octet or to the decuplet equal mass-spacing rule, as all divergences cancel exactly at this order. For the same reason all reference to an arbitrary scale µ is absent. Neither of these features continue to higher-powers in the chiral expansion. We also discuss critically the absolute neccessity of simultaneously going beyond the leading order heavy baryon expansion, if one goes beyond the one-loop-O(p 3) level. We point out that these corrections in 1/MB generate new divergences ∝ m 4 /M10. These divergences together with the divergences occuring in one-loop-O(p 4) graphs of chiral perturbation theory are taken care of by the same set of counter-terms. Because of these unknown counter-terms one cannot predict the baryon mass splittings at the one-loop-O(p 4) level. We point out another serious problem of going to the one-loop-O(p 4) level. When the decuplet is off its mass-shell there are additional πN ∆ and π∆∆ interaction terms. These interactions contribute not only to the divergent terms ∝ (m 4 /M10), but also to nonanalytic terms such as ∝ (m 4 /M10)ln(m/M10). Thus without a knowledge of the coupling constants appearing in these interactions one cannot carry out a consistent one-loop-O(p 4) level calculation.

1997

We study electromagnetic mass splittings of charmed baryons. We point out discrepancies among theoretical predictions in non-relativistic potential models; none of these predictions seems supported by experimental data. A new calculation is presented.

Physical Review D, 1972

2006

We present results for the helicity amplitudes of the lowest-lying hyperon resonances Y * , computed within the framework of the Bonn constituent-quark model, which is based on the Bethe-Salpeter approach 1,2,3. The seven parameters entering the model are fitted against the best known baryon masses 4. Accordingly, the results for the helicity amplitudes are genuine predictions. Some hyperon resonances are seen to couple more strongly to a virtual photon with finite Q 2 than to a real photon. Other Y * 's, such as the S 01 (1670) Λ resonance or the S 11 (1620) Σ resonance, have large electromagnetic decay widths and couple very strongly to real photons. The negatively-charged and neutral members of a Σ * triplet may couple only moderately to the Σ(1193), while the positively-charged member of the same Σ * triplet displays a relatively large coupling to the Σ + (1193) state. This illustrates the necessity of investigating all isospin channels in order to obtain a complete picture of the hyperon spectrum.

Nuclear Physics B - Proceedings Supplements, 2009

The European Physical Journal A, 2005

We study the spin-and flavour-dependent SU (6) violations in the baryon spectrum by means of a Gürsey-Radicati mass formula. The average energy of each SU (6) multiplet is described using the SU (6)-invariant interaction given by a hypercentral potential containing a linear and a hyper-Coulomb term. We show that the nonstrange-and strange-baryon masses are, in general, fairly well reproduced and moreover that the Gürsey-Radicati formula holds in a satisfactory way also for the excited states up to 2 GeV.

Lettere Al Nuovo Cimento Series 2, 1977

In previous calculations of the masses of charmed baryons by 5akimow and Kalman (1,~) and by Kalman (s) the mass of each baryon was given by (1) where Co, C1, C2 and C3 are all constants. It was then assumed that since the masses of the u and d quarks are much smaller than those of the s and e quarks, the last two terms are expected to be small and could be ignored. In this paper these terms are explicitly calculated. The effect is to renormalize the masses of all the mesons without changing the results of the previous calculations and to split the isoplets. A calculation of isoplet mass splittings was made by Kalman (4) for charm-zero baryons. In that paper, in addition to the Coleman-Glashow relation, two mass sum rules were obtained for JP= 89 baryons consistent within 10% of the experimental values. Correspondingly, based on eq. ( ) one obtains the Coleman-Glashow relation and the mass relations for charmed baryons obtained by Franklin (s) and three other mass sum rules. However, one of these relations is not consistent with experimental values. This is not unexpected, since no interactions between the quarks is included in eq. ( ). Following LICHTEN-BERG (e,v) and ITOH, MINA~IKAWA, MIURA and WATANAB]~ (s) a Coulomb and magnetic (*)

Physics Letters B, 2005

Physical Review Letters, 1995

arXiv:nucl-th/9505001v1 4 May 1995 Submitted to Phys. Rev. Lett. FSU-SCRI-95-37 IU/NTC 95-05 nucl-th/9505001

Zeitschrift f�r Physik C Particles and Fields, 1984

We calculate explicitly the electromagnetic mass splittings induced within the ground state baryons by the mass difference between the u and d quarks. This is performed in the framework of the non-relativistic potential model with an accurate treatment of the three-body problem. We also discuss the charge radius of the neutron.

Physical Review D, 1997

In previous publications we have analyzed the strong and electromagnetic decays of heavy mesons and heavy baryons in a formalism which incorporates heavy-quark and chiral symmetries. There are two possible symmetry-breaking effects on the chiral dynamics of heavy hadrons: the finite-mass effects from light quarks and the 1/m Q corrections from heavy quarks. In the present paper, chiral-symmetry-breaking effects are studied and applications to various strong and radiative decays of heavy hadrons are illustrated. SU(3) violations induced by chiral loops in the radiative decays of charmed mesons and charmed baryons are compared with those predicted by the constituent quark model. In particular, available data for D * decays favor values of the parameters in chiral perturbation theory which give There are two strong motivations, among others, for promoting a systematic study of both the 1/m Q corrections and the effects of chiral symmetry breaking. First, we have calculated in paper II the decay rates of D * → Dγ. When combined with our prediction for the strong decays D * → Dπ given in paper I, we are able to predict the branching ratios for the D * decays. Agreement is excellent between theory and the most recent experiment of CLEO II . Nevertheless, our predicted total width for D * + is Γ tot (D * + ) = 150 keV, ⋆ which is to be compared with the upper limit Γ tot (D * + ) < 131 keV published by the ⋆ The difference between this number (see ) and the result 141 keV obtained in Ref.

Physics Letters B

The masses of the baryon octet and decuplet are reproduced with a (10-20)% accuracy by ratios of exponential moment QCD spectral sum rules, obeying the z (sum rule variable) stability criterion. The onset of the QCD continuum is determined by consistency with the lowest dimensional finite energy sum rule. The N-A mass splitting is mainly controlled by the size of the mixed (@aG~u) condensate. The observed masses of the strange baryons can only be reproduced if there is a large breaking of the chiral condensates (~V) and (~trG~,). This result is independent of the choice of the nucleon current.