QCD sum rules for $\Delta$ isobar in nuclear matter
  The self-energies of $\Delta$ isobar propagating in nuclear matter are calculated using the finite-density QCD sum-rule methods. The calculations show that the Lorentz vector self-energy for the $\Delta$ is significantly smaller than the nucleon vector self-energy. The magnitude of the $\Delta$ scalar self-energy is larger than the corresponding value for the nucleon, which suggests a strong attractive net self-energy for the $\Delta$; however, the prediction for the scalar self-energy is very sensitive to the density dependence of certain in-medium four-quark condensate. Phenomenological implications for the couplings of the $\Delta$ to the nuclear scalar and vector fields are briefly discussed. 
Xuemin Jin