# Singularities of Multiple Scattering Processes

## Abstract

- 1.
The

*one-particle exchange graph*(Fig. 1) is currently interpreted as representing the “exchange” of a “virtual” particle; it contributes a pole for an*unphysical*value*t = m*^{2}of the momentum transfer squared:*t*≡ (*p*_{x}−*p*_{3})^{2}(*m*is the mass of the exchanged particle).† - 2.
The

*N-particle threshold*(or*normal threshold*)*graph*(Fig. 2) contributes a square root (*N*even) or logarithmic (*N*odd) branch point, at the value*s =*(*m*_{1}+*m*_{2}+*m*_{3}+ … +*m*_{N})^{2}of the total energy squared:*s*= (*p*_{1}+*p*_{2})^{2}. Thus this singularity occurs for a*physical*value of the total energy, corresponding to the “opening of an*N*-particle channel” (*m*_{1},*m*_{2}, …,*m*_{N}, are the masses of these*N*-particles).

## Keywords

Multiple Scattering Mass Shell Landau Equation Internal Line Effective Contact## Preview

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## References and Comments

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