Transition from real to virtual polarized photon structures

Abstract

We investigate the transition of the polarized photon structure function $g_1^\gamma(x,Q^2,P^2)$ when the target photon shifts from on-shell ($P^2=0$) to far off-shell ($P^2\gg \Lambda^2$) region. The analysis is performed to the next-to-leading order in QCD. The first moment of $g_1^\gamma$ which vanishes for the real photon, turns to be a negative value when target photon becomes off-shell. The explicit $P^2$-dependence of the first moment sum rule as well as of the structure function $g_1^\gamma(x,Q^2,P^2)$ as a function of $x$ is studied in the framework of the vector meson dominance model.Comment: 16 pages, 4 eps figure

The U(1)A Anomaly and QCD Phenomenology

“…For the light quarks, however, we expect the crossover scale to be a typical hadronic scale ∼ m ρ rather than m u,d,s . This can be justified by a rough OPE argument and is consistent with old ideas of vector meson dominance [6,85]. This behaviour would be an interesting manifestation of the spontaneous breaking of chiral symmetry.…”

Polarised structure functions and two-photon physics at Super-B

“…6 6 The VMD analysis has been carried through in detail in ref. [12] to obtain a numerical estimate of g γ 1 (x, Q 2 ; K 2 ) in the non-perturbative region. Essentially, VMD involves evaluating the AVV correlation function by replacing the electromagnetic currents with the corresponding vector mesons ρ, ω and φ.…”

“…The photon structure functions are defined from the Green function T µνλρ (q, k) = 0|J µ (q)J ν (−q)A λ (k)A ρ (−k)|0 . 2 There are two independent Lorentz structures, which we denote [11,12] as I µνλρ and J µνλρ where…”

“…This result was verified in refs. [11,12] and subsequently extended to NNLO, O(αα 2 s ), in ref. [13].…”

“…See also refs. [12,13,16,[27][28][29][30][31][32][33][34] for a selection of further papers on the g γ 1 and g γ 2 photon structure functions, mainly from a parton perspective. Here, our focus is on deriving cross-section formulae and investigating the experimental requirements to measure g γ 1 (x, Q 2 ; K 2 ), g 2 (x, Q 2 ; K 2 ) and g P γ * γ * at a high-luminosity, polarized e + e − collider.…”