Octet baryon electroweak form factors in dense nuclear matter

TL;DR

Understanding how the electroweak structure of baryons changes in a dense nuclear medium, this work combines a covariant spectator quark model with meson cloud dressing and the quark-meson coupling (QMC) model to compute in-medium electromagnetic and axial form factors of the octet baryons across densities from $\rho=0$ to $2\rho_0$. The study reveals general suppression of in-medium form factors with density and an increase in charge and magnetic radii, with a neutron-sector enhancement in the ratio $G_E^*/G_M^*$; it also implements an in-medium $f_\pi^*/f_\pi$ via a smooth chiral perturbation theory extension to access higher densities. For finite nuclei, the results show that density-profile effects are small at low $Q^2$ (validating average-density approximations) but can differ at higher $Q^2$, and the framework enables exploration of neutrino-nucleus scattering cross sections and polarization-transfer observables relevant to existing and future experiments. Overall, the work provides a cohesive, density-dependent description of baryon electroweak structure in nuclear matter with potential applications to heavy-ion collisions and astrophysical environments.

Abstract

Motivated by the necessity of developing theoretical models for studying the electroweak structure of baryons in a nuclear medium, we apply a covariant quark model to study interactions of baryons with nuclear matter. The electromagnetic and axial form factors of the octet baryons are determined by combining a covariant quark model that takes into account the meson cloud dressing of the baryon cores, developed for free space, with the quark-meson coupling model in the extension to the nuclear medium. We discuss the medium modifications on the electroweak form factors of octet baryons for the range of densities from $ρ=0$ up to $ρ=2 ρ_0$, where $ρ_0= 0.15$ fm$^{-3}$ is the normal nuclear matter density. We also study how the shape of the form factors is modified in finite nuclei due to the profile of the nuclear density distributions compared with calculations using the average density of the nucleus

Figures (2)

• Figure 1: Proton and neutron form factors ($\ell =E,M,A$) for the densities $\rho=0$, $\rho= \rho_0$ and $\rho=2 \rho_0$. The magnetic form factors are in natural units (magnetic moment: $\mu_N^\ast = G_M^\ast(0) \frac{e}{2 M_N^\ast}$, $M_N^\ast$ is the in-medium nucleon mass) Medium1.
• Figure 2: Left: Nuclear density profile $\rho(r)$ of $^{12}$C. The dashed line represent the average density $\rho_A$. Center: Ratio $G_E^\ast/G_E$ for bound protons. Right: Ratio $G_M^\ast/G_M$ for bound protons.