  We evaluate the antikaon spectral density in isospin symmetric nuclear
matter. The in-medium antikaon-nucleon scattering process and the antikaon
propagation is treated in a self consistent and relativistic manner where a
maximally scheme-independent formulation is derived by performing a partial
density resummation in terms of the free-space antikaon-nucleon scattering
amplitudes. The latter amplitudes are taken from a covariant and chiral
coupled-channel SU(3) approach which includes s-, p- and d-waves
systematically. Particular care is taken on the proper evaluation of the
in-medium mixing of the partial waves. Our analysis establishes a rich
structure of the antikaon spectral function with considerable strength at small
energies. At nuclear saturation density we predict attractive mass shifts for
the $\Lambda(1405)$, $\Sigma (1385)$ and $\Lambda(1520)$ of about 60 MeV, 60
MeV and 100 MeV respectively. The hyperon states are found to exhibit at the
same time an increased decay width of about 120 MeV for the s-wave
$\Lambda(1405)$, 70 MeV for the p-wave $\Sigma (1385)$ and 90 MeV for the
d-wave $\Lambda(1520)$ resonance.
