# H→ℓℓ′ in the Simplest Little Higgs Model

Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs boson mass for generic new physics. However, their preservation of lepton universality forbids them to account for the Hτμ CMS hint and at the same time respect (as they do) the severe limits on Hμe inherited from the non-observation of μeγ. We compute the predictions of the Simplest Little Higgs Model for the H decays and conclude that the measurement of any of these decays at LHC (even with a much smaller rate than currently hinted) will rule out this model. This result is consistent with our earlier observation of very suppressed lepton flavor violating semileptonic tau decays within this model.

 Comments: 8 pages, 5 figures Subjects: High Energy Physics – Phenomenology (hep-ph); High Energy Physics – Experiment (hep-ex) Cite as: arXiv:1603.09663 [hep-ph] (or arXiv:1603.09663v1 [hep-ph] for this version)

### 5 Respuestas a “HEM 2016: H→ℓℓ′ in the Simplest Little Higgs Model”

1. Gabriel

There are some (very few) points in the plots that fall close to BR~1. A joke of the scan method?.

2. Pablo Roig

No, it is quite usual that this (or similar) things happen in models with a number of free parameters (in our case basically five) when you do not know well the limits on them and (specially) you ignore the correlations provided they are sizable. If you look at the paper on the LFV SLH by Del Águila et. al. that we were quoting in our previous paper on semileptonic LFV tau decays (they were doing processes without mesons, http://arxiv.org/abs/arXiv:1101.2936) you will see that for some ‘reasonable scans’ (they were already restricting quite a lot the parameter space according to 2011 information) they get portions of their parameter space with BRs which are four to five orders of magnitude larger than 2011 limits. We are already using previous limits on this model parameters but, still, it is not surprising that you may get a BR two orders of magnitude larger than the current upper bound. In fact, I would find surprising that with some thousands random points within the ‘reasonable intervals’ I do not get some ‘too large’ BRs.

3. Pablo Roig

I think it could be expected to have some points like that. We basically have 5 free parameters and, although there are some bounds on them, we ignore their correlations and they seem to be large in some cases. For instance, if you look at the paper by Del Aguila et. al on LFV within this model (http://arxiv.org/pdf/1101.2936.pdf) you will see that although they restrict the parameter space to a ‘reasonable’ interval (according to 2011 info, which is quite up-to-date) they get portions of it with BRs which are easily 2 orders of magnitude larger than 2011 limits (five orders of magnitude larger and even more are also seen). Then, with some thousands points in the parameter space I find reasonable to have very few points with BR of order 1 (two orders of magnitude above current bounds). If the Higgs width were measured with precision, you could kill those; but uncertainties on this are still quite large.
In our previous paper using the same model for semileptonic tau decays (http://arxiv.org/pdf/1601.07391.pdf, also in HEM2.0) we found BRs for tau to mu gamma that were, in some cases, larger than current bounds, killing a small portion of the ‘reasonable’ parameter space. This did not happen in the decays including mesons, which were more suppressed (a priori unexpected, as far as I know).

4. Pablo Roig

I think I missunderstood your comment before: our 1 is 1 % and the red line is the current CMS upper bound. If we did not use restrictions from L to l gamma we get BRs that can be larger than this bound, but if we use them, then we are well below in general (with only very few points among thousands close to 1%).

5. By the wat, your comment makes me note that we should have cited the paper by Del Águila et. al. also in our second pre-print on LFV in the SLH model. I will correct this.