Real scalars for complex scalar results

earth2

Hi guys,

I'm a bit puzzled. I'm just reading some offline lecture notes where the Feynman rules of real (!) scalars coupled to gluons are given. However, with these rules the amplitude for phi g -> \bar{phi} g is considered. There are no further instructions. I'm just wondering how one can use Feynman rules for a real scalar-gluon theory to construct the result for its complex sibling. I mean, i know that a complex scalar can be written as two real ones but still there should be a mess in terms of numerical prefactors, shouldn't there? Moreover, how does one apply this to Feynman rules?

Well, I just don't see how to use the real rules to construct the complex result...

Any help is appreciated,
earth2