No radial excitations in low energy QCD. I. Diquarks and classification of mesons

Abstract

We propose a new schematic model for mesons in which the building blocks are quarks and flavor-antisymmetric diquarks. The outcome is a new classification of the entire meson spectrum into quark-antiquark and diquark-antidiquark states which does not give rise to a radial quantum number: all mesons which have so far been believed to be radially excited are orbitally excited diquark-antidiquark states; similarly, there are no radially excited baryons. Further, mesons that were previously viewed as "exotic" are no longer exotic as they are now naturally integrated into the classification as diquark-antidiquark states. The classification also leads to the introduction of isorons (iso-hadrons), which are analogs of atomic isotopes, and their magic quantum numbers, which are analogs of the magic numbers of the nuclear shell model. The magic quantum numbers of isorons match the quantum numbers expected for low-lying glueballs in lattice QCD. We observe that interquark forces in mesons behave substantially differently from those in baryons: qualitatively, they are color-magnetic in mesons but color-electrostatic in baryons. We comment on potential models and the hydrogen atom. The implications of our results for confinement, asymptotic freedom, and a new set of relations between two fundamental properties of hadrons -their size and their energy -are discussed in our companion paper [1]

Excluded-volume effects for a hadron gas in Yang-Mills theory

“…Although the idea that heavier hadrons have smaller radii has already been suggested in the theoretical literature [54] and is supported by experimental evidence [55], our finding of eigenvolume values inversely proportional to the particle mass may appear at odds with intuition, and in contrast to the expectations from simple semiclassical models [56]. In addition, it is perhaps worth mentioning that some lattice studies [57] found indication that heavier glueball states tend to have better overlap with more extended (rather than more localized) operators.…”

Model independent extraction of the proton magnetic radius from electron scattering

“…We would like to check if that holds true also in the magnetic case. We fit the same proton and neutron data for Q 2 max = 1 GeV 2 , t 0 = 0, k max = 8 and a bound of 15 on the coefficients using (23). For the first choice of G cut (t) we find the first two coefficients of the isoscalar form factor to be −2 +0.5 −0.3 , 3 +2 −6 and the first two coefficients of the vector form factor to be −13.5(3), 13 +6 −3 (The value of 13 +6 −3 was obtained by applying a bound of 15 on all the coefficients with the exception of the second one, which is left unbounded).…”

“…The discussion has focused on the one hand on recalculation of the theoretical input to the extraction of r p E from muonic hydrogen and on modifications of the theoretical calculation such as proton structure effects, e.g. [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,…”

Are there tetraquarks at largeNcin QCD(F)?

“…The phenomenon of cryptoexotic-conventional meson mixing is just as apparent for large-N c tetraquarks with nonexotic quantum numbers [5]. Note that, even though cleanly identifying the role of cryptoexotics in the spectrum has intrinsic difficulties, the literature has a long tradition of explaining various scalar resonances that do not fit into simple quark models as being cryptoexotics [8][9][10][11][12][13][14][15][16].…”