We all know and love the Higgs boson — which to physicists' chagrin has been mistakenly tagged in the media as the "God particle" — a subatomic particle first spotted in the Large Hadron Collider (LHC) back in 2012. That particle is a piece of a field that permeates all of space-time; it interacts with many particles, like electrons and quarks, providing those particles with mass, which is pretty cool.
But the Higgs that we spotted was surprisingly lightweight. According to our best estimates, it should have been a lot heavier. This opens up an interesting question: Sure, we spotted a Higgs boson, but was that the only Higgs boson? Are there more floating around out there doing their own things?
Though we don't have any evidence yet of a heavier Higgs, a team of researchers based at the LHC, the world's largest atom smasher, is digging into that question as we speak. And there's talk that as protons are smashed together inside the ring-shaped collider, hefty Higgs and even Higgs particles made up of various types of Higgs could come out of hiding. [Beyond Higgs: 5 Elusive Particles That May Lurk in the Universe]
If the heavy Higgs does indeed exist, then we need to reconfigure our understanding of the Standard Model of particle physics with the newfound realization that there's much more to the Higgs than meets the eye. And within those complex interactions, there might be a clue to everything from the mass of the ghostly neutrino particle to the ultimate fate of the universe.
All about the boson
Without the Higgs boson, pretty much the whole Standard Model comes crashing down. But to talk about the Higgs boson, we first need to understand how the Standard Model views the universe.
In our best conception of the subatomic world using the Standard Model, what we think of as particles aren't actually very important. Instead, there are fields. These fields permeate and soak up all of space and time. There is one field for each kind of particle. So, there's a field for electrons, a field for photons, and so on and so on. What you think of as particles are really local little vibrations in their particular fields. And when particles interact (by, say, bouncing off of each other), it's really the vibrations in the fields that are doing a very complicated dance. [The 12 Strangest Objects in the Universe]
The Higgs boson has a special kind of field. Like the other fields, it permeates all of space and time, and it also gets to talk and play with everybody else's fields.
But the Higgs' field has two very important jobs to do that can't be achieved by any other field.
Its first job is to talk to the W and Z bosons (via their respective fields), the carriers of the weak nuclear force. By talking to these other bosons, the Higgs is able to give them mass and make sure that they stay separated from the photons, the carriers of electromagnetic force. Without the Higgs boson running interference, all these carriers would be merged together and those two forces would merge together.
The other job of the Higgs boson is to talk to other particles, like electrons; through these conversations, it also gives them mass. This all works out nicely, because we have no other way of explaining the masses of these particles.
Light and heavy
This was all worked out in the 1960s through a series of complicated but assuredly elegant math, but there's just one tiny hitch to the theory: There's no real way to predict the exact mass of the Higgs boson. In other words, when you go looking for the particle (which is the little local vibration of the much larger field) in a particle collider, you don't know exactly what and where you're going to find it. [The 11 Most Beautiful Mathematical Equations]
In 2012, scientists at the LHC announced the discovery of the Higgs boson after finding a few of the particles that represent the Higgs' field had been produced when protons were smashed into one another at near light-speed. These particles had a mass of 125 gigaelectronvolts (GeV), or about the equivalent of 125 protons — so it's kind of heavy but not incredibly huge.
At first glance, all that sounds fine. Physicists didn't really have a firm prediction for the mass of the Higgs boson, so it could be whatever it wanted to be; we happened to find the mass within the energy range of the LHC. Break out the bubbly, and let's start celebrating.
Except that there are some hesitant, kind-of-sort-of half-predictions about the mass of the Higgs boson based on the way it interacts with yet another particle, the top quark. Those calculations predict a number way higher than 125 GeV. It could just be that those predictions are wrong, but then we have to circle back to the math and figure out where things are going haywire. Or the mismatch between broad predictions and the reality of what was found inside the LHC could mean that there's more to the Higgs boson story.
There very well could be a whole plethora of Higgs bosons out there that are too heavy for us to see with our current generation of particle colliders. (The mass-energy thing goes back to Einstein's famous E=mc^2 equation, which shows that energy is mass and mass is energy. The higher a particle's mass, the more energy it has and the more energy it takes to create that hefty thing.)
In fact, some speculative theories that push our knowledge of physics beyond the Standard Model do predict the existence of these heavy Higgs bosons. The exact nature of these additional Higgs characters depends on the theory, of course, ranging anywhere from simply one or two extra-heavy Higgs fields to even composite structures made of multiple different kinds of Higgs bosons stuck together.
Theorists are hard at work trying to find any possible way to test these theories, since most of them are simply inaccessible to current experiments. In a recent paper submitted to the Journal of High Energy Physics, and published online in the preprint journal arXiv, a team of physicists has advanced a proposal to search for the existence of more Higgs bosons, based on the peculiar way the particles might decay into lighter, more easily-recognizable particles, such as electrons, neutrinos and photons. However, these decays are extremely rare, so that while we can in principle find them with the LHC, it will take many more years of searching to collect enough data.
When it comes to the heavy Higgs, we're just going to have to be patient.