Gluon and valence quark distributions for the pion and kaon in nuclear matter

TL;DR

This study investigates how gluon and valence quark distributions in pions and kaons are affected by nuclear matter using the NJL model, revealing minimal changes for pions but significant increases for kaons at various densities.

Contribution

It provides a detailed analysis of in-medium gluon and valence quark distributions in pions and kaons within the NJL model, including their evolution with nuclear density and comparison with experimental data.

Findings

Vacuum distributions agree with experimental and lattice data.

In-medium pion distributions remain nearly unchanged at higher scales.

Kaon distributions increase significantly with nuclear density.

Abstract

In this paper we study the gluon and valence quark distributions in the pion and kaon in nuclear medium for various nuclear densities as well as in vacuum within the Nambu--Jona-Lasinio (NJL) model with the help of the proper-time regularization scheme which simulates a confinement of QCD. The nuclear medium effect is also determined in the same model for the symmetric nuclear matter. We then analyze the gluon and valence quark distributions for the bound pion and kaon in symmetric nuclear matter as well as those in vacuum. We find that the valence quark and gluon distributions in vacuum have relatively good agreements with the experimental data, the lattice QCD simulations, and the JAM Monte-Carlo (MC) global fit QCD analysis. Evolving to the higher factorization scale $Q = $ 4 GeV, the in-medium gluon and valence-quark distributions of the pion for various nuclear densities are turned out to be almost unchanged in comparison to the vacuum cases. On the contrary, for the kaon, they increase significantly with respect to the densities. Finally, we find that the vacuum gluon distribution for the kaon is smaller than that for the pion, which is consistent with other theoretical predictions. This feature holds for the in-medium gluon distribution in the nuclear density up to the saturation density.