Thursday, November 10, 2005

Standard Model and the Higgs Field

The Standard Model unifies the nuclear, electromagnetic, and weak forces and enumerates the fundamental building blocks of the universe:

6 leptons: electron, electron neutrino, muon, muon neutrino, tau, tau neutrino

6 quarks: d (down), u (up), s (strange), c (charm), b (bottom), t (top)

Each of these has half-integral spin (called fermions) and each has an anti-particle equivalent.

4 Bosons(integral spin): gluon (nuclear force), photon (electromagnetic force), W and Z bosons (weak force).

The model also has serious flaws--it does not account for gravity, does not explain or predict the masses of the various particles, and requires a number of parameters to be measured and inserted into the theory.

According to the Standard Model, the vacuum in which all particle interactions take place is not actually empty, but is instead filled with a condensate of Higgs particles. The quarks, leptons, and W and Z bosons continuously collide with these Higgs particles as they travel through the "vacuum". The Higgs condensate acts like molasses and slows down anything that interacts with it. The stronger the interactions between the particles and the Higgs condensate are, the heavier the particles become.

Quantum electrodynamics requires the photon to have zero mass, but early attempts to develop an electroweak theory required the bosons to be massless, which is bad because then they would be as abundant as the photons in the universe, which indeed they are not. Peter Higgs and other researchers (who worked independently of Higgs) came across the same idea for settling the puzzle. If there is an otherwise undetectable field filling the universe (now called the Higgs field), it could have associated with it a previously unknown kind of boson, the Higgs particle, which has mass. This would allow any photon-like particle to become massive by swallowing up a Higgs boson. It is thought that all-massive particles get their mass this way.
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