Pion and kaon valence-quark quasiparton distributions

TL;DR

This paper uses algebraic models of pion and kaon wave functions to compute various parton distributions, revealing insights into flavor symmetry breaking and the effectiveness of quasi-distributions at accessible momenta.

Contribution

It introduces algebraic Bethe-Salpeter wave functions to calculate light-front and quasi-parton distributions for pions and kaons, providing new insights into their internal structure.

Findings

qPDAs at Pz=1.75 GeV approximate true PDAs semiquantitatively.

qPDF ratios for kaon and pion u-quarks match true ratios between x=0.3 and 0.8.

Flavor-symmetry violation in kaons is about 15%.

Abstract

Algebraic Ansaetze for the Poincar\'e-covariant Bethe-Salpeter wave functions of the pion and kaon are used to calculate their light-front wave functions (LFWFs), parton distribution amplitudes (PDAs), quasi-PDAs (qPDAs), valence parton distribution functions (PDFs), and quasi-PDFs (qPDFs). The LFWFs are broad, concave functions; and the scale of flavour-symmetry violation in the kaon is roughly 15%, being set by the ratio of emergent masses in the $s$-and $u$-quark sectors. qPDAs computed with longitudinal momentum $P_z =1.75\,$GeV provide a semiquantitatively accurate representation of the objective PDA; but even with $P_z=3\,$GeV, they cannot provide information about this amplitude's endpoint behaviour. On the valence-quark domain, similar outcomes characterise qPDFs. In this connection, however, the ratio of kaon-to-pion $u$-quark qPDFs is found to provide a good approximation to the true PDF ratio on $0.3\lesssim x \lesssim 0.8$, suggesting that with existing resources computations of ratios of quasi-parton-distributions can yield results that support empirical comparison.