# New Higgs triple coupling

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1. Sep 27, 2014

### Safinaz

Hi,

I wonder if a theory like 2HDM has a new triple Higgs coupling, like $g_{hH^+H^-}$, what governs how much is this coupling ?

For example a paper as : arXiv:1405.3584v1 [hep-ph], they normalize $g_{hH^+H^-}$ by the SM $g_{hWW}$,
they plotted at fig. 3 (f) $C_{hH^+H^-}=g_{hH^+H^-}/g_{hWW}$ ratio ranges from 15 to -15, but couldn't this range extends to even -30 for example ? they mentioned at Sec. B that ranges determined by
perturbativity requirements, but this is not clear for me ..

Bests,

2. Sep 28, 2014

### Orodruin

Staff Emeritus
Yes, in general you will get triplet couplings of the Higgs fields after symmetry breaking. These terms appear in the Lagrangian from the quartic terms in the scalar potential once the vev has broken the symmetry, much like Yukawa couplings give mass terms for fermions.

The normalization of the coupling is mainly conventional and the actual range of values the ratio can take of course depends on what you chose to normalize with. The perturbativity requirement is just saying that you want your theory to be perturbative and not dominated by higher order contributions. Thus, the maximum value is dependent on how far from being non-perturbative the coupling $g_{hWW}$ is. It may also be slightly author dependent what is considered to be a perturbative theory ...

3. Sep 28, 2014

### Safinaz

So if I have a new model and have a new $g_{hH^+H^-}$ coupling , how I determine how large is this coupling ?

In case the SM $g_{hww}$ ~ 51 ( gw mw) , can the new coupling reaches 2341, some say if there is a coupling
large like that why this interaction did not seen until now by experiment ..

4. Sep 28, 2014

### Orodruin

Staff Emeritus
One thing is having a theory that predicts a certain coupling due to some relation that relates it to other observables. Another approach is starting with some general argument (such as perturbativity) and try to put model independent bounds on the coupling based on existing experimental data.