The Lorentz structure of the imaginary optical potential

The relativistic imaginary optical potential is calculated to lowest order in nuclear matter for the exchange of sigma-, ω- and π-mesons. Analytic results are obtained which show that: (I) the imaginary scalar potential is positive (a probability source); (II) both it and the imaginary vector potential are large (about five times the nonrelativistic net absorption); (III) there is an important imaginary spatial three-vector potential. These results can explain the sign, magnitude and energy dependence of the imaginary spin-orbit optical potential. For pions, orders of magnitude larger potentials are obtained for pseudoscalar rather than pseudovertor πN coupling. The pseudovector results represent moderate corrections to sigma- and ω-exchange. (orig.)