We discuss the importance of the background in order to understand the scattering in the J^{PC}=0^{++} low and intermediate energy region and in particular regarding the sigma meson. In order to appreciate better its importance we compare with the rho meson in the P-wave pipi scattering. We also point out that in present analyses of three-body heavy meson decays, like those of D^+ and B, the role of this background is still not properly settled although it happens to be considerably smaller.
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