Gluons in glueballs: Spin or helicity?

Understand

In the last decade, lattice QCD has been able to compute the low-lying glueball spectrum with accuracy.

• Like other effective approaches of QCD, potential models still have difficulties to cope with gluonic hadrons.
• Assuming that glueballs are bound states of valence gluons with zero current mass, it is readily understood that the use of a potential model, intrinsically non covariant, could be problematic in this case.
• The main challenge for this kind of model is actually to find a way to introduce properly the more relevant degree of freedom of the gluon: spin or helicity.