  A formalism for representing the fully relativistic propagator of the
Rarita-Schwinger field in the nuclear medium is developed. Using a convenient
basis for expanding the propagator, or the self energy, it is shown that they
can be represented by 40 energy and momentum dependent quantities which can be
combined into a 2x2 and a 6x6 matrix. In this way calculations reduce to matrix
multiplication. Using the presented formalism the full relativistically
covariant contribution of the pion-nucleon loop to the isobar self energy and
propagator in isospin-symmetric spin-saturated nuclear medium is computed.
Utilizing this propagator the photoabsorption cross-section on in-medium
nucleons in the isobar region is calculated and the result compared with
experimental data.
