Scope and limitations of a string theory dual description of the proton structure

Abstract

Symmetric and antisymmetric structure functions from electromagnetic deep inelastic scattering of charged leptons off spin-1/2 hadrons are investigated in the framework of a top-down holographic dual description. We consider the BPST Pomeron, type IIB superstring theory scattering amplitudes, and type IIB supergravity on AdS$_5 \times S^5$. In all cases it is used the hard-wall prescription. Different kinematic regions of the Bjorken variable $x$, as well as the squared momentum of the virtual photon $Q^2$, are studied in detail for $F_2^P$ and $g_1^P$ structure functions of the proton. Also, the virtual Compton scattering asymmetry of the proton $A_1^P$ is investigated. Comparison with data from several experimental collaborations is presented. In addition, the holographic Pomeron leads to predictions for the mentioned observables for very small $x$ values. In particular, we present predictions for $g_1^P$ at $Q^2$ around 10 GeV$^2$, for data expected to be measured in a future electron-ion collider. Limitations of this holographic dual approach are discussed.