The Masses of the Light Quarks

Talk given at the Conference on Fundamental Interactions of Elementary Particles, ITEP, Moscow, Oct. 1995. The paper reviews the current status of knowledge concerning m_u, m_d and m_s. Qualitative aspects of the resulting picture for the breaking of isospin and eightfold way symmetries are discussed. At a more quantitative level, the review focuses on the chiral perturbation theory results for the masses of the Goldstone bosons. The corresponding bounds and estimates for the ratios m_u/m_d and m_s/m_d are described in some detail.Comment: 23 pages, 3 figure

Extraction of the pion-nucleon sigma-term from the spectrum of exotic baryons

The pion nucleon sigma-term is extracted on the basis of the soliton picture of the nucleon from the mass spectrum of usual and the recently observed exotic baryons, assuming that they have positive parity. The value found is consistent with that inferred by means of conventional methods from pion nucleon scattering data. The study can also be considered as a phenomenological consistency check of the soliton picture of baryons.Comment: 8 pages, 2 figures, references added, discussion extended, to appear in Eur.Phys.J.

Electromagnetic mass differences of SU(3) baryons within a chiral soliton model

We investigate the electromagnetic mass differences of SU(3) baryons, using an "model-independent approach" within a chiral soliton model. The electromagnetic self-energy corrections to the masses of the baryon are expressed as the baryonic two-point correlation function of the electromagnetic currents. Using the fact that the electromagnetic current can be treated as an octet operator, and considering possible irreducible representations of the correlation function, we are able to construct a general collective operator for the electromagnetic self-energies, which consists of three unknown parameters. These parameters are fixed, the empirical data for the electromagnetic mass differences of the baryon octet being employed. We predict those of the baryon decuplet and antidecuplet. In addition, we obtain various mass relations between baryon masses within the corresponding representation with isospin symmetry breaking considered. We also predict the physical mass differences of the baryon decuplet. The results are in good agreement with the exisiting data.Comment: 8 pages. To appear in Phys. Lett.

S-wave Meson-Nucleon Interactions and the Meson Mass in Nuclear Matter from Chiral Effective Lagrangians

Chiral effective lagrangians may differ in their prediction of meson-nucleon scattering amplitudes off-meson-mass-shell, but must yield identical S-matrix elements. We argue that the effective meson mass in nuclear matter obtained from chiral effective lagrangians is also unique. Off-mass-shell amplitudes obtained using the PCAC choice of pion field must therefore not be viewed as fundamental constraints on the dynamics, the determination of the effective meson mass in nuclear matter or the possible existence of meson condensates in the ground state of nuclear matter. This hypothesis is borne out by a calculation of the effective mass in two commonly employed formulations of chiral perturbation theory which yield different meson-nucleon scattering amplitudes off-meson-mass-shell.Comment: 23 pages, LaTeX, 2 Postscript figures (fig1.ps, fig2.ps

Properties of "35" Spin-(5/2) Baryon Resonances in a Model with Broken SU(3)

We investigate the properties of a set of J =(5/2)^+ resonances appearing in a 35-dimensional representation of SU(3), as proposed by Abers, Balázs, and Hara. A simple dynamical calculation gives an estimate for the mass differences within the supermultiplet. The matrix elements for the SU(3) allowed decays into meson plus resonance are given in terms of one parameter and the SU(3)-violating matrix elements for decay into meson plus baryon are given by two parameters

Self-Consistent Determination of Coupling Shifts in Broken SU(3)

The possibility that certain patterns of SU(3) symmetry breaking are dynamically enhanced in baryon-meson couplings is studied by bootstrap methods. For the strong couplings, a single dominant enhancement is found. It produces very large symmetry-breaking terms, transforming like an octet, as often conjectured. Experimental consequences are listed, such as a reduction of K-baryon couplings relative to π-baryon couplings which is in accord with the experimental weakness of K relative to π production in many circumstances, such as photoproduction and multi-BeV cosmic-ray collisions. For parity-violating nonleptonic couplings, a dominant octet enhancement is again found, as mentioned in a previous paper, which leads to an excellent fit with experiment. For parity-conserving nonleptonic couplings, on the other hand, several different enhancements compete, and the only conclusion we can draw is that terms with the "abnormal" transformation properties brought in by strong symmetry-breaking corrections are present. Our work provides a dynamical derivation of various phenomenological facts associated with SU(6), such as the dominance of the 35 representation in parity-violating nonleptonic decays

Mass splittings of SU(3) baryons within a chiral soliton model

Considering simultaneously isospin and SU(3) flavor symmetry breakings, we investigate the complete mass splittings of SU(3) baryons within a chiral soliton model, a {}"model-independent approach" being employed. In linear order several new mass relations are derived, which are mostly generalizations of existing mass formulae. The dynamical quantities appearing in the expressions for the masses are fixed by fitting them to the masses of the baryon octet and the masses of $\Omega^{-}$ and $\Theta^{+}$ as input rather than by extracting them from a calculated self-consistent soliton profile. In particular, the consideration of isospin symmetry breaking allows us to use the experimental data of the whole octet baryon masses as input. We predict the masses of the baryon decuplet and antidecuplet without any further adjustable free parameter. In addition, we also obtain the pion-nucleon sigma term which turns out to be $\Sigma_{\pi N} = 36.4\pm3.9\,\mathrm{MeV}$. We get the ratio of the current light quark masses $R = 58.1\pm1.3$. The present results indicate that the recent experimental data for the $\Theta^{+}(1524)$ are compatible with the experimental data of the octet and decuplet masses.Comment: 13 pages. No figure. Final version accepted for publication in Prog. Theor. Phys. arXiv admin note: substantial text overlap with arXiv:1102.178