Strange Sea Asymmetry in Nucleons

The strange content of the nucleon is under particular attention by the high energy physics society recently. Ji and Tang suggested that if a small locality of strange sea in nucleon is confirmed, some phenomenological consequences can be resulted in. The CCFR data indicate that s(x)/s̄(x) ∼ (1 − x)−0.46±0.87. Assuming an asymmetry between s and s̄, Ji and Tang analyzed the CCFR data and concluded that ms = 260 ± 70 MeV and ms̄ = 220 ± 70 MeV. So if only considering the central values, δm ≡ ms −ms̄ ∼ 40 MeV. In the framework of the Standard Model SU(3)c ⊗ SU(2)L ⊗ U(1)Y , we would like to look for some possible mechanisms which can induce the asymmetry. The self-energy of strange quark and antiquark Σs(s̄) = ∆ms(s̄) occurs via loops where various interactions contribute to Σs(s̄) through the effective vertices. Obviously, the QCD interaction cannot distinguish between s and s̄, neither the weak interaction alone in fact. Practical calculation of the self-energy also shows that ∆ms = ∆ms̄. In fact, because of the CPT theorem, s and s̄ must be of exactly the same mass. If we evaluate the self-energy ∆ms and ∆ms̄ in vacuum, the CPT theorem demands ∆ms ≡ ∆ms̄. However, when we evaluate them in an asymmetric environment of nucleons, an asymmetry ∆ms 6= ∆ms̄ where the superscript M denotes the medium effects, can be expected. In other words, we suggest that the asymmetry of the u and d quark composition in nucleons leads to an asymmetry of the strange sea. There exist both short-distance and long-distance medium effects. The shortdistance effects occur at quark-gauge boson level, namely a self-energy loop including a quark-fermion line and a W-boson line or a tadpole loop. The contributions of u and d-types of quark-antiquark to the asymmetry realize through the KabayashiMaskawa-Cabibbo mixing.