We conclude that the lower-spin components of the Rarita-Schwinger fields are forced upon by the properties of the Lorentz boost and should not be projected out. These fields are realized in the spectra of the light-flavor baryons, where the landscape of the excitations is well structured along the RS classification scheme, rather than populated by randomly distributed resonances. The (approximate) degeneracy symmetry turned out to be SU(2)I⊗O(1,3)ls. Within this context, the 22I,%2b, 42I,-, and 62I,- RS clusters observed so far in the π N scattering channel by the LAMPF at LANL, constitute an almost accomplished excitation mode with only five states missing. We further showed how presence or absence of the independent cluster-excitation sequence 32I,-, 32I,%2b, and 52I,%2b, probes the scale of the chiral phase transition for baryons. In this way, the missing-state search program through the CLAS collaboration at JLAB [13] obtains an additional motivation, which is conceptually different from the SU(6)SF⊗ O(3)L classification scheme. The dynamical origin for the RS clustering is still lacking a unique explanation and it remains a challenge for future research. The factorization of isospin from the space-time symmetry in SU(2)I⊗O(1,3)ls is strongly supported by QCD, where the isodoublet light quarks and the isosinglet heavy-flavor quarks are the established isospin degrees of freedom. On the other hand, any QCD solution has necessarily to be a Lorentz-covariant object. In Ref. [11] the bosonic parts of the Lorentz clusters, such as (k/2, k/2) from the RS field in Eq. (19), were considered as independent fundamental bosonic degrees of freedom of baryon structure, and the term hyperquark was coined for them. There, the clustering was modeled after an O(4)-invariant quark-hyperquark correlation. From a slightly different QCD perspective, the clusters can also be viewed as string solutions associated with a linear action. Such strings are also complex multi-fermion systems having the Dirac state as a limit [14]. They can be described in terms of a multi-dimensional Lorentz-invariant field Ψ that satisfies the Dirac-like equation (Γμpμ - M)Ψ = 0, where Lorentz invariance imposes certain conditions onto the Γ matrices. The considerations presented above show that the RS fields naturally fit into this QCD string scheme. In Ref. [14], a solution with a RS-like degeneracy was reported. On the whole, our view is that a structured baryon spectrum that shares common flavor and relativistic symmetries with QCD is more likely to be linked, via an appropriate effective theory, to first principles of strong-interaction dynamics, than a spectrum with states distributed at random.
