Observation of a dynamical QCD string

TL;DR

This paper observes a dynamical QCD string in mesons where the energy levels are independent of quark spin and parity, indicating a higher symmetry and the absence of magnetic interactions, revealing fundamental aspects of QCD.

Contribution

It demonstrates the existence of a higher symmetry in mesons with suppressed low-lying Dirac eigenmodes, identifying a dynamical QCD string characterized by spin-independent energy levels.

Findings

Degeneracy of all chiral and U(1)_A multiplets for same-spin states

Absence of magnetic interactions in the ultrarelativistic quark-antiquark system

Energy levels independent of quark spin orientation and parity

Abstract

Mesons constructed from the quark propagators without the lowest-lying eigenmodes of the Dirac operator reveal not only restored SU(2)_L * SU(2)_R chiral and U(1)_A symmetries, but actually a higher symmetry. All possible chiral and U(1)_A multiplets for the states of the same spin are degenerate, i.e., the energy of the observed quantum levels does not depend on the spin orientation of quarks in the system and their parities. The quark-spin independence of the energy levels implies absence of the magnetic interactions in the system. The ultrarelativistic quark-antiquark system with only the color-electric interactions can be interpreted (or defined) as a dynamical QCD string.