# Expresion for amplitude

1. Feb 22, 2006

### Sombrero

Gents I have one question:

If I have expresion for amplitude of some process and this amplitude has pole, I say I have particle caryring such features (suppose mass that makes this pole), if I change some parameters in expression for amplitude and if I get another pole, I say in this case there is particle having anothe features. So my question is why poles in expressions correspond to particles?

Thanks

2. Feb 22, 2006

### Perturbation

Because the field theory describes the dynamics of particles with a mass m. The pole comes from the equality of the norm of the four-momentum and square of the mass in the denominator. The quantised field will only create particles with mass m but the norm norm of the four-momentum of the field at some point doesn't have to be equal to the square of the physical mass of the particle it describes.

Last edited: Feb 23, 2006