# negative cross-section for chiral interaction

Asked by
samwell187

Hi,

I have a FCNC-type Lagrangian of the form

X Gmu ( a + b G5 ) y v + Y Gmu ( c + d G5 ) x V

where capital letters denote antiparticles, Gmu is the Dirac gamma matrix, G5 is gamma5, x and y are fermions, and v is a (complex) vector (so it carries an index like v_mu or V_mu).

I am interested in the process v V -> y Y -- so the vector is annihilating

If I set a = c, b = d (which is required to make this Lagrangian hermitian) and make neither of these vanish, then I get a negative cross-section. On the other hand, if I set any of the following :: b = d = 0, a = c = 0, a = - c, b = -d :: then I get a positive cross-section.

Any idea why this might be?

Thanks,

Sam

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