ar X iv : n uc l - th / 0 51 21 08 v 1 3 0 D ec 2 00 5 Λ ( 1520 ) at finite density

We study the decay channels of the Λ(1520) in a nuclear medium and find a sizable change of the order of factor five of the width of this hyperon at normal nuclear matter density. The mass shift of the Λ(1520) is moderate. The change of resonance properties in the nuclear medium is a field that captures permanent attention, and basic symmetries can be tested through medium modification of particle properties. The later is particularly interesting for resonances which are not the genuine three quark states surviving in the large-Nc limit of QCD, but can be generated dynamically using the effective degrees of freedom and effective forces constrained by the symmetry pattern underlying the QCD. The Λ(1520) is an example of such dynamic state which can be generated from the s-wave interaction of the decuplet of baryons with the octet of pseudoscalar mesons using the leading order chiral Lagrangian in combination with resummation schemes which respect the unitarity in coupled channels [1, 2]. In particular, the Λ(1520) appears basically as a quasibound state of the πΣ(1385) system. The small free width of the Λ(1520) of ≃ 15.6 MeV comes from the decay into K̄N and πΣ channels, but the decay into πΣ(1385) is forbidden for the nominal mass of the Σ(1385). The coupling of the Λ(1520) to K̄N and πΣ makes the picture of the Λ(1520) more elaborate, with πΣ(1385) being a very important component but with also sizable admixtures of K̄N and πΣ [3]. At finite baryonic density, the decay of the Λ(1520) bears resemblance to the one of the ∆(1232) in the nuclear medium. The ∆ decays into πN and the π gets renormalized in the medium by exciting ph and ∆h components, as a consequence of which the ∆ is renormalized and its pion (photon) induced excitation in nuclei incorporates now the mechanisms of pion (photon) absorption in the medium. In the present case, the Λ(1520) decay into πΣ(1385), only allowed through the Σ(1385) width, gets drastically modified when the π is allowed to excite ph and ∆h components in the nucleus, since automatically the phase space for the decay into phΣ(1385) gets tremendously increased. This fact, together with the large coupling of the Λ(1520) to the πΣ(1385) channel predicted by the chiral unitary approach, leads to a very large width of the Λ(1520) in nuclei. Similar nuclear effects will modify the πΣ decay channel and the K̄N will be analogously modified when the K̄ is allowed to excite hyperon-hole excitations. All these channels lead to a considerable increase of the width of the Λ(1520) in the nucleus. In the description of the Λ(1520) properties in the nuclear medium we closely follow Λ∗ Λ∗ Ν− Λ∗ Λ∗ Σ(1189) Λ∗ Λ∗ Ν− Σ(1189) Σ(1189) Λ∗ Λ∗ Ν− Λ∗ Λ∗ Λ∗ Λ∗ Ν− Λ∗ Λ∗ Ν− Λ∗ Λ∗ Λ∗ Λ∗ Ν− Σ (1385) ∗ Σ (1385) ∗ Σ (1385) ∗