Parada T. P. Hutauruk, Terry Mart, Kazuo Tsushima

Physical Review D

18/12/2025

Abstract

The dynamics of partons inside the light 𝜌 meson is found to be essential for its properties and internal structure, both in free space and in the nuclear medium. In this paper, we systematically investigate the in-medium structure changes of 𝜌+ mesons within the covariant Nambu-Jona-Lasinio (NJL) model, utilizing the Schwinger proper-time regularization scheme. We solve the Bethe-Salpeter equations to guarantee the bound meson-state condition. At the quark level, the nuclear medium effects are also derived within the same NJL model to maintain a consistent approach with the in-medium 𝜌+ meson electromagnetic form factors. To this end, we analyze the spacelike electromagnetic form factors of the 𝜌+ meson in free space and in a nuclear medium. We find that the charge radius and quadrupole moment of the 𝜌+ meson increase with increasing nuclear matter density, while the magnetic moment decreases, in agreement with the existing previous theoretical predictions. The enhancement of the 𝜌+meson charge radius at normal density relative to that in free space is about 11% (0.08 fm), while the reduction of 𝜌+ meson magnetic moment is about 8% (0.20  𝜇𝑁). Our predictions for the charge radius, magnetic moment, and quadrupole moment of the 𝜌+ meson in both free space and nuclear medium, remain challenging to be verified experimentally.

10.1103/95yl-nwds