  Although neutron stars have been studied for decades, their internal
structure remains enigmatic, mainly due to large uncertainties in the equation
of state. In neutron stars, nucleons are strongly interacting by exchanging
mesons, which leads to significant quantum many-body correlation effects.
Previous mean-field calculations failed to capture these effects. Here, we
develop a non-perturbative quantum field-theoretic approach to handle strongly
correlated nuclear matters. Based on a linear $\sigma$-$\omega$-$\rho$ model
with a density-dependent isovector coupling $\Gamma_{\rho}$, we reproduce all
the six frequently-used nuclear matter observables by tuning six parameters.
After including quantum many-body effects into the equation of state of
realistic neutron-star matters, we obtain a mass-radius relation that is in
good agreement with recent astrophysical observations. Our results show that
the maximal neutron-star mass supported by neutron-dominated matters is $\sim
2.67M_{\odot}$, where $M_{\odot}$ is solar mass.
