Low-Energy Pion-Pion Scattering in the Unitarized Strip Approximation

We present an improved set of parameters for a successful bootstrap of the ρ and Pomeranchon Regge trajectories in pion-pion scattering. The resulting π-π amplitudes are compared with the experimental data, with particular reference to the low-energy S-wave phase shifts, which agree fairly well with present indications. We obtain for the trajectory intercepts αP(0)=1.0 and α_ρ(0)=0.55; for the ρ-meson width Γ_ρ=143 MeV; and for the S-wave scattering lengths a₀=(0.15±0.05)m_π^-1, a₂=(-0.04±0.015)m_π^-1.