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AdrianTheRock
#4
Mar4-12, 07:28 AM
P: 136
How abundant are the different generations of matter in the universe?

ττ ~ 2.9 x 10-13s - see http://en.wikipedia.org/wiki/Tau_lepton.

Showing antiparticles would be redundant, as all particles have them (though some particles eg γ are their own antiparticle).

Dark matter particles and gravitons have not yet actually been discovered in experiments, and as such are outside the current scope of the standard model - they are only postulated by other, as yet unconfirmed, theories. Though cosmological observations provide strong evidence for the existence of CDM, we don't yet know whether it actually exists or, if so, what exactly the particle(s) is(are).

Nor, so far, has the Higgs been confirmed in experiments, even though it is a key part of the standard model theory. If the recent "hints" at LHC are confirmed, then it would belong in a separate column on the diagram. We don't yet know how many rows this column should have, as different theories predict different numbers of Higgs bosons.