Pion structure from twisted mass lattice QCD down to the physical pion mass

TL;DR

This paper investigates pion structure using twisted mass lattice QCD at physical pion mass, computing key observables like the quark momentum fraction and electromagnetic form factor, and compares results with experimental data.

Contribution

The study provides the first direct lattice QCD calculation of the pion's electromagnetic form factor at the physical pion mass using twisted boundary conditions.

Findings

Results agree with vector meson dominance and experimental data at low Q^2.

The quark momentum fraction matches phenomenological values after extrapolation.

Calculations are performed directly at the physical pion mass, reducing systematic uncertainties.

Abstract

We present an investigation of pion structure based on ETMC $N_f=2$ and $N_f=2+1+1$ twisted mass configurations at maximal twist. We compute the first moment of the quark momentum fraction of the pion, $\langle x \rangle$ and the electromagnetic form factor, $F_\pi(Q^2)$. For the latter, momentum is injected using twisted boundary conditions and the calculation is carried out directly at the physical pion mass. We find that our data are consistent with vector meson dominance and experimental data in the region of small momentum transfer. For $\langle x \rangle$, we find that our chirally and continuum extrapolated result is compatible with its phenomenological value.