File:PhysRevC.100.025201.pdf

English: We calculate the scattering T-matrix of I=0 ¯¯¯¯KN−πΣ coupled channels taking a ladder sum of the Weinberg-Tomozawa interaction without on-shell factorization, regularizing three types of divergent meson-baryon loop functions by dimensional regularization and renormalizing them by introducing counter terms. We show that not only infinite but also finite renormalization is important for the renormalized physical scattering T-matrix to have the form of the Weinberg-Tomozawa interaction. The results with and without on-shell factorization are compared. The difference of the scattering T-matrix is small near the renormalization point, close to the observed Λ(1405). The difference, however, increases with the distance from the renormalization point. The scattering T-matrix without on-shell factorization has two poles in the complex center-of-mass energy plane as with on-shell factorization, the real part of which is close to the observed Λ(1405). While the difference is small with and without on-shell factorization in the position of the first pole, closer to the observed Λ(1405), the difference is considerably large in the position of the second pole: the imaginary part of the center-of-mass energy of the second pole without on-shell factorization is as large as or even larger than twice that with on-shell factorization. Also, we discuss the origin of the contradiction about the second pole between two approaches, the chiral unitary approach with on-shell factorization and the phenomenological approach without on-shell factorization.