2024-06-11
Hi! Let me introduce myself. I'm a Physics student from Brazil. This website is my brain dump. I will to use it to write about whatever I feel like. There is nothing serious planned, though you can expect me to talk about two things: Physics and programming.
I'm not yet a real physicist, in the sense that I haven't published any papers or made any discoveries. But we'll see what happens in the future.
Right now I'm doing some particle physics. Specifically, I'm translating a model called the MCHM5 to a computer version that can be used for simulating experiments. In this model, the Higgs boson is not an elementary particle, but a composite one. That just means it can be divided (with sufficiently high energy) into smaller parts, the hypothetical particles called techniquarks. This is reminescent of how atoms are divisible into protons, neutrons and electrons; and protons are themselves made of quarks and gluons.
The MCHM5 solves a theoretical problem with the Standard Model, called the hierarchy problem. The issue is that we naively expect, from theoretical arguments, that the Higgs boson mass should be large, very very large if it is indeed an elementary particle, because it is a scalar. But we have measured its mass and it is "only" 125 GeV (pretty massive compared to most particles, but many orders of magnitude lighter than expected). Something must explain why the Higgs is so light.
(You might wonder, by the way, how in the world we talk about the Higgs mass if people say all the time that it is only by interacting with the Higgs that elementary particles get mass in the first place. Does the Higgs interact with itself? Yes. Is that the reason it is massive? No, but I won't explain this now.)
("Wait a minute", you say, "why do we need to explain why particles have mass in the first place?" Excellent question. The reason nobody tells you this in popular science accounts is that it's a bit technical. To be short, the elementary fermions that we know of can't have mass without the Higgs because they are chiral (they don't behave the same when you look at them in a mirror), and the vector bosons that we know of can't have mass without the Higgs because of gauge symmetry (and we don't know how to do the math for them without gauge symmetry.) So there you have it. Do with this information what you will.)
So, back to the MCHM5. The Higgs being composite instead of elementary completely kills the reason we expect its mass to be large, which is what we call a quadratic divergence. This is because at high enough energies, the Higgs breaks down into more elementary components, and there is no more Higgs to speak of. Then its mass can be small with no theoretical problem.
Why care about this? Personally, I care because it's cool. And because theoretical issues like this in the history of Physics have often been quite pregnant with new developments.
In the future I might tell you more about the MCHM5, the SM, particles, etc. Stay tuned.