== Top quark width ==

The top quark mainly decays into a botton quark and an on-shell W boson. Compute the decay width (You may neglect the mass of the bottom quark).

You may also have a look at the following Mathematica [http://cp3wks05.fynu.ucl.ac.be/twiki/bin/viewfile/Physics/Tt?rev=1;filename=TDecay.nb notebook].