Dynamical spin effects in the holographic light-front wavefunctions of light pseudoscalar mesons

TL;DR

This paper investigates the role of dynamical spin effects in holographic light-front wavefunctions of light pseudoscalar mesons, showing significant effects in pions and eta' but not in kaons, and providing a comprehensive data description.

Contribution

It introduces a detailed analysis of dynamical spin effects in holographic meson wavefunctions, highlighting their varying importance across different mesons and matching multiple experimental data sets.

Findings

Maximal spin effects in pion improve data fit

No spin effects preferred in kaon for data consistency

Spacelike transition form factors favor maximal effects in eta and eta'

Abstract

We quantify the importance of dynamical spin effects in the holographic light-front wavefunctions of the pion, kaon, $\eta$ and $\eta^\prime$. Using a universal AdS/QCD scale and constituent quark masses, we find that such effects are maximal in the pion where they lead to an excellent simultaneous description of a wide range of data: the decay constant, charge radius, spacelike EM and transition form factors, as well as, after QCD evolution, both the parton distribution function and the parton distribution amplitude data from Fermilab. These dynamical spin effects lead up to a $30\%$ chance of finding the valence quark and antiquark with aligned spins in the pion. The situation is very different for the kaon, where a simultaneous description of the available data (decay constant, radius and spacelike EM form factor) prefer no dynamical spin effects at all. The situation is less clear for the $\eta$ and $\eta^\prime$: while their radiative decay widths data are consistent with dynamical spin effects only in $\eta^\prime$, the data on their spacelike transition form factors clearly favor maximal dynamical spin effects in both mesons.