I'm pretty shaky with my understanding of much beyond simple tree-level calculations. When people talk about triangle diagrams, they sometimes say one will get a 'supression factor' of xxx. For example, in the consider the triangle diagram for H[itex]\rightarrow\gamma\gamma[/itex] with Ws running around the loop (attached). I want to know, without doing the full calculation, whether that would be more or less suppressed than second-order H[itex]\rightarrow b \bar{b}[/itex] (the same triangle diagram, except with bottom quark external legs instead of photons and a quark where the vertical W is.)(adsbygoogle = window.adsbygoogle || []).push({});

My thought was that you can use the cutting rules, so the relevant difference between the two is that H[itex]\rightarrow\gamma\gamma[/itex] has two WW[itex]\gamma[/itex] vertices and a W propagator, and H[itex]\rightarrow b \bar{b}[/itex] has two Wbb vertices and a fermion propagator. But plugging everything in, I get that H[itex]\rightarrow\gamma\gamma[/itex] should be more suppressed than second-order H[itex]\rightarrow b \bar{b}[/itex], which isn't correct. Does my approach make any sense?

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# Supression factor for triangle diagrams

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