5.2 Beyond the Higgs

summary

The whole picture is still incomplete. The Higgs must be measured further.

It is still somewhat unclear whether or not the Higgs that was discovered in 2012 is the Standard Model Higgs. Its properties are now being studied in more detail, and will continue to be studied as the LHC moves to higher energy scales.
We also will have to determine if there is more than one Higgs, and if so, how many more. Supersymmetry predicts at least five kinds of Higgs bosons, each with differing masses and other properties.
Finding heavy Higgs bosons with non-standard interactions is a major long-term challenge for the LHC.
In fact, physicists are still scratching their heads about why the mass of the Higgs was found to be 125 GeV. It is suspiciously light for a composite Higgs boson, and suspiciously heavy for minimal SUSY, so it is right at the edge of stability.
And many questions about connecting the Higgs to other physics still remain:
- Does the Higgs destabilize the vacuum?
- How does the electroweak scale emerge?
- Is there a Higgs “portal” to dark matter?
- Is the Higgs sector responsible for the genesis of matter in the early universe?
- How does the Higgs “talk” to neutrinos?
- Is the Higgs related to inflation or dark energy?
These questions motivate much work in modern particle physics.

Dark matter may also be connected to the Higgs.

We can’t see dark matter directly, but we can observe its effects due to gravitational lensing. If dark matter is in front of luminous matter, we will see the light bend due to the dark matter.
Fritz Zwicky examined the Coma galaxy cluster, and noticed that upon calculating the gravitational mass of the galaxies within the cluster, his value was more than 400 times greater than what was expected from their luminosity, implying there had to be unseen dark matter. Vera Rubin later found the same phenomenon inside individual galaxies, when she measured a flat rotation curve of the stars. We know today that galaxies themselves are immersed in a dark matter “halo.”
Many, many theories exist as to what kind of particle the dark matter is made of. We still are no closer to determining an answer, but we have many good candidates, including Weakly Interacting Massive Particles (WIMPs), axions, and a few other exotic particles.

Dark matter is very 'shy' and can prove difficult to study.

We know that dark matter interacts gravitationally with normal matter, but it very rarely will collide with atomic matter.
One theory postulated that dark matter could interact with atomic matter via weak interactions, like neutrinos, but there has since been evidence to dispute this.
Another theory suggests that dark matter can interact with normal matter through the Higgs. This is still a distinct possibility that is being actively researched. And, of course, dark matter might be interacting with normal matter in a totally different way.
Particle physics experiments today might soon be able to say with certainty how the dark matter interacts with baryonic matter—or even better, discover it.

We can look forward to many exciting upcoming discoveries.

So far, we still have no evidence of supersymmetry at the LHC. Without supersymmetry, we don’t understand exactly how the Higgs boson can exist without violating basic mechanisms of quantum physics.
The potential of instability in the Higgs vacuum adds even more to the mystery.
More data from many other experimental sources, including those from particle physics, astrophysics, and cosmology, will guide us in our understanding.
In the near future, either the new run of the LHC will discover superpartners, or radical new ideas will be needed.