“…In the Δ-resonance region, also several theories, theoretical models and approximations as, but not restricted to, the multiple scattering theory (Eisenberg and Koltun, 1980) including both Watson's multiple scattering theory and Glauber's multiple scattering theory (Shalaby et al, 2007), the -hole formalism (Hirata et al, 1979;Kisslinger and Wang, 1976), eikonal approximation with the interacting boson model (Zhang, 1993), strong absorption model (Begum et al, 2003;Rahman and Sen Gupta, 1991), the single folding -cluster model (ElAzabFarid and Ebrahim 2015), equivalent local Kisslinger optical potential with analytical distorted wave approximation (Safari, 2005), a density dependent optical pion-nuclear potential (Gmitro et al, 1987), local and equivalent local optical potentials (Satchler, 1992;Johnson and Satchler, 1996;Khallaf and Ebrahim, 2000;Ebrahim and Khallaf, 2005;Khallaf and Ebrahim, 2005;Akhter et al, 2001;Hong and Kim, 1999) have been used with varying degrees of success. The deficiencies of these theories are alluded to 1) fail in reproducing backward elastic scattering data for both pion charges 2) difficulty in calculation due to non-localities 3) true quantitative description of the scattering process 4) disagreement between theory and experiment especially around maximum and minimum 5) unphysical meaning for some used parameters and 6) uncertainties in the data.…”