Pion parton distribution function in light-front holographic QCD

The valence-quark distribution function of the pion has been of interest for decades; particularly, the profile it should adopt when x -> 1 (the large-x behavior) has been the subject of a long-standing debate. In the lightfront holographic QCD (LFHQCD) approach, this behavior is controlled by the so-called reparametrization function,, which is not fully determined from first principles. We show that, owing to the flexibility of omega(tau)(x), the large-x profile u(pi)(x) similar to (1 - x)(2) can be contained within the LFHQCD formalism. This is in contrast to a previous LFHQCD study (Guy F. de Teramond et al., Phys. Rev. Lett., 120(18), 2018) in which u(pi)(x) similar to (1 - x )(1) was found instead. Given our observations, augmented by perturbative QCD and recent lattice QCD results, we state that the large-x exponent of 2 cannot be excluded.