  Angular correlations in dense solutions and melts of flexible polymer chains
are investigated with respect to the distance $r$ between the bonds by
comparing quantitative predictions of perturbation calculations with numerical
data obtained by Monte Carlo simulation of the bond-fluctuation model. We
consider both monodisperse systems and grand-canonical (Flory-distributed)
equilibrium polymers. Density effects are discussed as well as finite chain
length corrections. The intrachain bond-bond correlation function $P(r)$ is
shown to decay as $P(r) \sim 1/r^3$ for $\xi \ll r \ll \r^*$ with $\xi$ being
the screening length of the density fluctuations and $r^* \sim N^{1/3}$ a novel
length scale increasing slowly with (mean) chain length $N$.
