How to parameterize a light and broad resonance (the σ meson)
Abstract
We point out that a commonly used parameterization form to describe the σ resonance is problematic by introducing a spurious singularity below two particle threshold, on the second sheet. The spurious singularity violates chiral symmetry and leads to sizable contribution when the resonance is light and broad -- as what happens to the σ resonance, hence must be removed.
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