  Replicated theoretical attempts of relativistic approaches to the pion
self-energy in nuclear matter yield unphysical pion spectra. We demonstrate the
crucial dependence of the calculated pion spectra on the correct relativistic
accounting for the short-range correlation effects on the pion self-energy in
the medium. To do this, we simulate the short-range interactions by
phenomenological contact terms in the relativistic Lagrangian density, and
derive the pion self-energy by carefully taking into account the relativistic
kinematics. The obtained spectrum for the pion-like excitations in cold nuclear
matter shows physically meaningful branches, in contrast to those obtained
before by different authors by the use of simplified relativistic approaches to
the short-range correlations.
