Inquiring Minds

Physics Questions People Ask Fermilab

Glenn,

I guess what I want to ask you is a stupid question. But since I am a lay person with a lot of curiousity let me be bold enough to ask it.

I understand the the standard particle theory says that large masses indicated by boson masses can only be created by lots power in accelerators. That is why the supercollider would have been great. But how does this relate if the Big Bang theory is correct? What does the current trend in elementary particle physics have to do to confirm the Big Bang?

Also, it seems logical, since physicists are the smartest of logicians, that the Standard Theory, expecting masses of bosons to be zero, and finding that they are not, is really incorrect. Why do physicists regard logic to everything except their own theory, which cannot be right, since the masses of bosons are very very large?

Dear Dave,

No these are two excellent questions. Let me restate them as I believe you meant.

1. What do the results of high energy particle physics experiments do to constrain theories about the Big Bang?
2. Why are the masses of the so-called "intermediate vector" bosons responsible for the weak nuclear force non-zero and in fact quite large in mass ?

1. There are various answers here.

   For one, better understanding of nuclear and high energy cross sections helps us to understand nucleosynthesis. One tries to estimate the age of the universe for example, by measuring how much of each element(isotope) is out there and using production, etc. probabilities, reconstruct how long it took for stars to create the present amounts. That's mostly nuclear physics.

   Physicists try to reconstruct what they think the conditions were like at times very close to the initiation of the Big Bang. Obviously high energies/temperatures were involved. This is true both for very high energy single particle on particle collisions and also with heavy ion collisions where the quark-gluon plasma is being sought after. This is a hot, dense soup where the protons and neutrons are no longer clearly defined.

   Another interaction of high energy and astrophysics is the subject of dark matter. Finding a dark matter candidate to explain why galaxies spin the way they do and perhaps to prove whether the universe will collapse back in on itself or not is a hot topic and incompasses various proposed particles or objects.

   I should make it clear - the overwhelming evidence in favor of the Big Bang theory of creation is the red shift of astronomical objects. Just about everything from nearby stars to galaxies to far-away quasars support the expansion of the universe. Learning more about this will surely convince you of the Big Bang. Particle physics, on the other hand, goes along way to explaining HOW it happened.

2. Actually the Standard Model can incorporate the large vector boson masses by various techniques. The one that seems to make the most sense is called spontaneous symmetry breaking. Basically it is a phenomenon which is not unique to high energy physics. Superconductors exist because of a symmetry breaking mechanism so we know it exists in nature.

   In the Standard Model, the electroweak interactions (electromagnetic and weak nuclear) of the known particles are described by a set of bosons which follow a symmetry known as SU(2)xU(1) which has 4 bosons as force carriers. But all the particles of the theory are massless. In order to generate masses, you can introduce (two) (scalar) particles known as Goldstone bosons (actually they are complex fields so there are 4 components).

   The forces in the system including the Goldstone bosons can be arranged such that an ambiguity in the vacuum expectation value of the system exists. As soon as you have to choose a vacuum value as a starting parameter, you have "broken the symmetry". The layman's description is usually that, at this point, 3 of the 4 boson components are eaten by the 3 intermediate vector bosons and acquire a mass. The massless boson that is left is the photon.

   The fourth component of the Goldstone field is known as the Higgs boson, is probably a couple of hundred GeV in mass and is the last particle not yet found (except for the tau neutrino) in the Standard Model. This is why the physics community is building the Large Hadron Collider at CERN in Switzerland/France. It may be found at Fermilab though. The mass of the top quark and the mass of the W intermediate vector boson can be used to predict the mass of the Higgs boson but the range is still too large to be sure without trying various scenarios.

Sincerely,

Glenn Blanford, PhD
Fermilab Public Affairs

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