More than one Higgs means more structure

We have published once more a new paper, and I would like again to outline what we did (and why).

The motivation for this investigation started out with another paper of mine. As described earlier, back then I have taken a rather formal stand on proposals for new physics. It was based on the idea that there is some kind of self-similar substructure of what we usually call the Higgs and the W and Z bosons. In this paper, I speculated that this self-similarity may be rather exclusive to the standard model. As a consequence, this may alter the predictions for new physics models.

Of course, speculating is easy. To make something out of it requires to do real calculations. Thus, I have started two projects to test them. One is on the unification of forces, and still ongoing. Some first results are there, but not yet anything conclusive. It is the second project which yielded new results.

In this second project we had a look at a theory where more Higgs particles are added to the standard model, a so-called 2-Higgs-doublet model, or 2HDM for short. I had speculated that, besides the additional Higgs particles, further additional particles may arise as bound states. I. e., as states which are made from two or more other particles. These are not accounted for by ordinary methods.

In the end, it now appears that this idea is not correct, at least not in its simplest form. There are still some very special cases left, where this may still be true, but by and large not. However, we have understood why the original idea is wrong, and why it may still be correct in other cases. The answer is symmetry.

When adding additional Higgs particles, one is not entirely free. It is necessary that we do not alter the standard model where we have already tested it. Especially, we cannot easily modify the symmetries of the standard model. However, the symmetries of the standard model then induce a remarkable effect. The additional Higgs particles in 2HDMs are not entirely different from the ones we know. Rather, they mix with it as a quantum effect. In quantum theories, particles can change into each other under certain conditions. And the symmetries of the standard model entail that this is possible for the new and the old Higgses.

If the particles mix, the possibilities to distinguish them diminish. As a consequence, the simplest additional states can no longer be distinguished from the states already accounted for by ordinary methods. Thus, they are not additional states. Hence, the simplest possible deviation I speculated about is not realized. There may still be more complicated ones, but to figure this out is much more complicated, and has yet to be done. Thus, this work showed that the simple idea was not right.

So what about the other project still in progress? Should I now also expect this to just reproduce what is known? Actually no. The thing we learned in this project was why everything fell into its ordinary places. The reason is the mixing between the normal and the additional Higgs particles. This possibility is precluded in the other project, as there the additional particles are very different from the original ones. It may still be that my original idea is wrong. But it has to be wrong in a different way than in the case we investigated now. And thus we have also learned something more about a wider class of theories.

This shows that even disproving your ideas is important. From the reasons why they fail you learn more than just from a confirmation of them - you learn something new.