Abstract

We predict the twist-2 Transverse Momentum Dependent parton distribution functions (TMDs) of the pion, namely the unpolarized quark TMD, $f_{1}(x, k_\perp)$, and the transversely polarized quark TMD, also known as the Boer-Mulders function, $h^\perp_{1}(x, k_\perp)$, using a holographic light-front pion wavefunction with dynamical spin effects. These spin effects, in conjunction with gluon rescattering, are crucial to predict a non-zero holographic Boer-Mulders function. We investigate the use of a non-perturbative SU(3) gluon rescattering kernel, thus going beyond the usual approximation of perturbative U(1) gluons. We find that the non-perturbative color dynamics offer a more promising way to describe the available lattice data on the generalized Boer-Mulders shifts.

Highlights

  • Transverse momentum dependent parton distributions functions (TMDs) contain important information on the three-dimensional internal structure of hadrons, especially the spin-orbit correlations of quarks within them [1]

  • The Boer-Mulders function is naively a T-odd distribution and such distributions were initially thought to vanish due to the time reversal invariance of QCD [4] but later it became apparent that they can be dynamically generated by initial or final state interactions [5,6]

  • A string theory in the higher dimensional anti-de Sitter (AdS) space. In this gauge/gravity duality, the radial lightfront variable ζ maps onto the fifth dimension in AdS space and the mass scale κ emerging from the dAFF mechanism governs simultaneously the strength of the confining harmonic potential in physical spacetime and that of the dilaton field which breaks conformal invariance in AdS space

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Summary

INTRODUCTION

Transverse momentum dependent parton distributions functions (TMDs) contain important information on the three-dimensional internal structure of hadrons, especially the spin-orbit correlations of quarks within them [1]. F1ðx; k⊥Þ describes the momentum distribution of unpolarized quarks within the pion while h⊥1 ðx; k⊥Þ describes the spin-orbit correlations of transversely polarized quarks within the pion. The gauge link makes these distributions process-dependent, flipping their sign from semi-inclusive deep inelastic scattering (SIDIS) to DrellYan (DY) scattering. In conjunction with their nucleon counterparts, the pion unpolarized TMD and the Boer-Mulders function are inputs in the theoretical predictions of the cross sections and azimuthal asymmetries for unpolarized pion-induced DY scattering [10,11] which have both been measured [12,13,14]. We shall predict the so-called generalized Boer-Mulders shifts in order to compare with the lattice data of Ref. [26]

HOLOGRAPHIC LIGHT-FRONT WAVE FUNCTIONS
THE GLUON RESCATTERING KERNEL
THE LENSING FUNCTION
HOLOGRAPHIC TMDS
COMPARISON TO LATTICE
VIII. CONCLUSIONS
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