QCD sum rules for Λ hyperons in nuclear matter

The self-energies of a Λ hyperon propagating in nuclear matter are studied using finite-density QCD sum-rule methods. A correlator of Λ interpolating fields is evaluated in the nuclear matter ground state using both an operator product expansion and a dispersion relation with a spectral ansatz. The Lorentz vector self-energy of the Λ is found to be substantially smaller than the corresponding nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the Λ is also smaller than the corresponding value for nucelon; however, this prediction is sensitive to the assumed density dependence of certain four-quark condensates. The scalar and vector self-energies tend to cancel, but not completely. The implications for the Λ spin-oribt force in a finite nucleus are discussed.