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,wτ（x）,which is not fully determined from first principles.We show that,owing to the flexibility of wT（x）,the large-x profile uπ（x）～（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 uπ（x）～（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.