# Feynman rules

1. Sep 22, 2014

### asal90

Hi
I want to drive the amplitude by feynman rules?
a spin 0

particle with mass m0 that couples to spin 0 particles with masses m1, . . ., mN by a point-coupling ig and a target that interacts with only one of the constituents.
the transverse momentum transfer dependence proportional to \exp{-\beta \vec{q}^2_\perp}

the answer is below but I don't know how to reach this answer.

$${\cal M}=\frac{2 i g p_N.q}{(p_0-\sum_{j=1}^{N}p_j)^2 - m_N^2} \exp (-\beta \vec{q}^2_\perp /2 )$$

I just know in the form below to write
$${\cal M}=\bar{u}(p_1)...\bar{u}(p_N) i g u(p_0)\frac{\gamma ^\mu (p_0-\sum_{j=1}^{N}p_j)_\mu + m_N}{(p_0-\sum_{j=1}^{N}p_j)^2 - m_N^2} X u(q)$$

Last edited by a moderator: Sep 22, 2014