The scaling function for deep inelastic hadronic scattering

Constituent quarks and g 1

“…of the eigenstates |m of dσ µ K µ = 0 [14,91]. Here σ µ is a large surface which is defined [91] such that its boundary is spacelike with respect to the positions z k of any operators or fields in the physical problem under discussion.…”

“…of the eigenstates |m of dσ µ K µ = 0 [14,91]. Here σ µ is a large surface which is defined [91] such that its boundary is spacelike with respect to the positions z k of any operators or fields in the physical problem under discussion. For integer values of the topological winding number m, the states |m contain mf quark-antiquark pairs with non-zero Q 5 chirality l χ l = −2ξ R f m where f is the number of lightquark flavours.…”

The spin structure of a polarized photon

“…It is interesting to extend our results to QCD with massless quarks. If we could turn the up, down and strange quark masses to zero in QCD, then the pion and the η would evidently become massless but, because of U A (1) dynamics [36], the η ′ would remain massive. Consider the gedanken world of massless QCD where we define real photons by first taking the light-quark masses to zero and then taking the photon virtuality to zero -that is, working in the limit m 2 ≪ P 2 → 0.…”

Improved lattice operators: Case of the topological charge density

“…Considering a lattice version of q(x), q L (x), the classical continuum limit must be in general corrected by including a renormalization function. In pure QCD, where q(x) is renormalization group invariant, [3] q L (x) → a 4 Z(g 2 0 )q(x) + O(a 6 ) ,…”

“…with the topological susceptibility χ is further complicated by an unphysical background term, which eventually becomes dominant in the continuum limit. (We recall that the definition of χ requires also a prescription to define the product of operators [6].) Indeed…”