Baryons As Hyperspherical O(4) Partial Waves -- Is This The Message From The Spectra?

Abstract

It is argued that the baryon excitations group to four-dimensional partial waves described by means of the three Rarita-Schwinger (RS) fields [(\sigma -1 )/2 ,(\sigma -1)/2]* [(1/2, 0)+(0,1/2)] with \sigma =2,4 and 6, where all components happen to be occupied. In the O(4) decomposition of the \pi N scattering amplitudes, the RS spin- and parity clusters appear as poles on the complex energy plane, socalled H"ohler poles. This phenomenon indicates that the symmetry of the \pi N scattering amplitude is O(4) and thereby the space-time version of chiral symmetry, rather than O(3). Accordingly, the baryon spectrum generating algebra is su(2)_I*su(3)_c*o(1,3)_{ls} rather than su(6)_{sf} * su(3)_c * o(3)_l. The nucleon and \Delta spectra below \sim 2500 MeV are complete up to only 5 `missing' resonances. The three O(4) poles are distributed over two distinct Fock spaces of opposite vacuum parities thus defining the energy scale of the chiral phase transition for baryons. Within this new symmetry scenario, the covariant description of the RS baryon clusters is straightforward and their averaged masses are fitted by a Balmer-series like formula emerging from a simple quark-diquark model in the O(4) basis with Coulomb potential and a four-dimensional rigid rotator.