Positive and negative parity hyperons in nuclear medium

Abstract

The effects of the nuclear medium on the residue, mass, and self-energy of the positive- and negative-parity Σ, Λ, and Ξ hyperons are investigated using the QCD sum-rule method. In the calculations, the general interpolating currents of hyperons with an arbitrary mixing parameter are used. We compare the results obtained in medium with those of the vacuum and calculate the shifts in the corresponding parameters. It is found that the shifts on the residues in nuclear matter are overall positive for both the positive- and negative-parity hyperons, except for the positive-parity Σ hyperon which has a negative shift. The shifts on the masses of these baryons are found to be negative. The shifts on the residues and masses of negative-parity states are large compared to those of positive-parity states. The maximum shift belongs to the residue of the negative-parity Λ hyperon. The vector self-energies gained by the positive-parity baryons are large compared to the vector self-energies of the negative-parity particles. The maximum value of the vector self-energy belongs to the positive-parity Σ hyperon. The numerical values are compared with the existing predictions in the literature.