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- TL;DR Summary
- I want to understand why some branching ratios (BRs) are greater than others and discuss some other features of the attached plot. Besides, I want to figure out the Feynman diagrams (FDs) I do not find in the literature.

I will bold the ideas I would like to discuss so that they are easier to identify.

Hi everyone!

I am studying Higgs phenomenology, in particular its BRs

My line of reasoning is this: I first had a look at the decays where the Higgs particle couples directly (i.e. without intermediate particles) to the products; those are ##H^0 \to b \bar b, \ H^0 \to \tau \bar \tau## and ##H^0 \to c \bar c \ ## (##H^0 \to t \bar t## is of course not allowed due to conservation of energy; the top quark is about ##t \approx 172 \ GeV## while ##H^0 \approx 125 \ GeV##). Given that the coupling constant is ##m/v##, where the vacuum expectation value is given by ##v \approx 246 \ GeV##, it makes sense to think that the more massive the particle is the stronger it couples to the Higgs particle.

Here comes the fun.

Once intermediate particles come into play I do not really understand why some channels have greater BRs than others. Next, let us look at the "massless" channels ##H^0 \to \gamma \gamma, \ H^0 \to gg##. I studied the golden channel ##H^0 \to \gamma \gamma## (Mandl & Shaw, page 446)

OK so W boson and quarks (only the top quark couples significantly to ##H^0## though) are the intermediators.

Regarding FDs,

Finally, let me comment on the last two channels: ##H^0 \to W W^*## and ##H^0 \to Z Z^*##. I have studied they have essentially the same FD (b and c below)

My argument to explain their difference in BRs is based on their coupling constants: we know that the Higgs particle couples to W and Z bosons as follows

We also know that ##M_W^2 = \frac{g^2v^2}{4}## and ##M_Z^2 = \frac{g^2v^2}{4 \cos \theta_W}## so we deduce that the ##HWW## coupling goes as ##M^2_W/v## whereas the ##HZZ## coupling goes as ##M^2_Z/v##. Hence this reasoning leads to think that we should expect a greater BR for Z.

I appreciate to discuss with you all

Thank you!

I am studying Higgs phenomenology, in particular its BRs

My line of reasoning is this: I first had a look at the decays where the Higgs particle couples directly (i.e. without intermediate particles) to the products; those are ##H^0 \to b \bar b, \ H^0 \to \tau \bar \tau## and ##H^0 \to c \bar c \ ## (##H^0 \to t \bar t## is of course not allowed due to conservation of energy; the top quark is about ##t \approx 172 \ GeV## while ##H^0 \approx 125 \ GeV##). Given that the coupling constant is ##m/v##, where the vacuum expectation value is given by ##v \approx 246 \ GeV##, it makes sense to think that the more massive the particle is the stronger it couples to the Higgs particle.

**Indeed, for those three ratios that argument seems to hold. Do you think it is OK?**Here comes the fun.

Once intermediate particles come into play I do not really understand why some channels have greater BRs than others. Next, let us look at the "massless" channels ##H^0 \to \gamma \gamma, \ H^0 \to gg##. I studied the golden channel ##H^0 \to \gamma \gamma## (Mandl & Shaw, page 446)

OK so W boson and quarks (only the top quark couples significantly to ##H^0## though) are the intermediators.

**I struggle to find information in the literature regarding the decay channel**##H^0 \to gg##. I looked up Higgs decay to gluon in Google Scholar and checked the first five but found no (modern i.e. not in terms of ) FD. One could guess and say "well, the gluon is massless as well so we could expect to have the exact same diagrams that for ##H^0 \to \gamma \gamma##" (this is actually the same guess a PF user made back in 2014). I do not think this is right, as the BRs differ quite significantly so I expect the associated FDs to differ as well. Hence**What are the FDs associated to**##H^0 \to gg##**and why does its BR differ that significantly with**##H^0 \to \gamma \gamma## (despite both products being massless)?Regarding FDs,

**I have the same issue with the channel**##H^0 \to Z \gamma##:**I do not find them in the literature.**Finally, let me comment on the last two channels: ##H^0 \to W W^*## and ##H^0 \to Z Z^*##. I have studied they have essentially the same FD (b and c below)

My argument to explain their difference in BRs is based on their coupling constants: we know that the Higgs particle couples to W and Z bosons as follows

We also know that ##M_W^2 = \frac{g^2v^2}{4}## and ##M_Z^2 = \frac{g^2v^2}{4 \cos \theta_W}## so we deduce that the ##HWW## coupling goes as ##M^2_W/v## whereas the ##HZZ## coupling goes as ##M^2_Z/v##. Hence this reasoning leads to think that we should expect a greater BR for Z.

**This is wrong and by far... How to explain their BR then?**

Last comment: in the plot we observe a sudden minimum in ZZ... why?Last comment: in the plot we observe a sudden minimum in ZZ... why?

I appreciate to discuss with you all

Thank you!