The Emc Spin Crisis: Comparing Proton and Photon

TL;DR

This paper proposes a kinematical solution to the $U_A(1)$ problem, explaining the proton and photon spin structure functions' behavior through anomaly cancellation and deriving a new sum rule, linking sum rule $Q^2$-dependence to structure functions.

Contribution

It introduces a novel kinematical resolution to the $U_A(1)$ problem and derives a new sum rule for the photon spin structure function.

Findings

Cancellation of photonic and gluonic anomalies explains zero singlet contributions.

Derived a new sum rule for the photon spin structure function.

Linked the $Q^2$-dependence of the Gerasimov-Drell-Hearn sum rule to the $G_2$ structure function.

Abstract

The "kinematical" resolution of the $U_A(1)$ problem is proposed. The cancellation of photonic and gluonic anomalies suggested by the t'Hooft consistency principle naturally explains the zero singlet contributions to the first moments of proton and photon spin structure functions. The new sum rule for the photon spin structure function is derived. The strong strong $Q^2$-dependence of the Gerasimov-Drell-Hearn sum rule is related to the $G_2$ structure function and to the gluonic anomaly.