New paper on composite Higgs

Today, a new paper entitled “Direct and indirect signals of natural composite Higgs models” by Christoph Niehoff, Peter Stangl and myself appeared on the preprint archive. Weighing 72 pages, it might be a good read on the beach in your well-deserved summer vacation!? Anyway, here is some information about why we made this analysis and what we found.

The idea of the Higgs boson being a composite particle is a compelling and fascinating solution to the electroweak hierarchy problem (also called the Higgs naturalness problem) and, according to many, is among the two most attractive solutions to this problem (the other one being supersymmetry). Many brilliant people have contributed to the construction of elaborate models that address a variety of challenges that arise when formulating a realistic theory implementing the composite Higgs idea. Given the plethora of experimental tests of the Standard Model, from precision electroweak measurements to flavour physics, direct searches for the production of heavy particles and precision measurements of the properties of the Higgs boson, it is not easy to determine whether a given model is viable, or what an experimental exclusion (or discovery!) in one observable implies for other observables.

In the past, many studies have either focused on a limited set of experimental tests – e.g. on Higgs physics, flavour physics or direct searches – or have studied the interplay between different tests in a qualitative way, while being as model-independent as possible. While this approach certainly has its advantages, to really study the correlations between different experimental tests of a new physics model (which is the overarching goal of our research group), one needs to select a specific model and perform a numerical analysis of all experimental constraints on its parameters. This is exactly what we have set out to do.

For several reasons (detailed in the paper), this turned out to be quite challenging on a technical level, and it was only thanks to a local computing cluster that we were able to obtain the results we were interested in. In the end, we think the results we got are interesting enough to justify the efforts. Just to mention two of the most exciting results of our analysis:

  • Some hints of a resonance at 2 TeV seen by ATLAS and CMS in diboson final states can be perfectly accomodated, while being in agreement with all other experimental constraints.
  • Deviations from Standard Model expectations in $B$ physics, in particular in angular observables in $B\to K^*\mu^+\mu^-$ and the branching ratio of $B_s\to\phi\mu^+\mu^-$, can be explained as well. To be honest, this came as a surprise to us! But most exciting about this is that it implies the existence of a neutral spin-1 resonance below 1 TeV which should show up soon in the dijet or $t\bar{t}$ mass distribution at LHC! And if it doesn’t show up, it’s clear that the models studied by us cannot explain these anomalies.

Many more big and small results can be found in the 61 plots and the accompanying text. Of course, having set up the analysis for one particular model (with four different flavour structures), we are now eager to apply this strategy also to other models or scenarios, and we are looking forward to discussing this with the community.

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