MASS _ _ _ _ _ _ _ _ _ _ _ _ command

The mass command associates a scalar variable as a mass with the corresponding vector variable, in high-energy physics calculations.

syntax:

mass<vector-var>=<scalar-var> {,<vector-var>=<scalar-var>}*

<vector-var> can be a declared vector variable; mass will declare it to be of type vector if it is not. This may override an existing matrix variable by that name. <scalar-var> must be a scalar variable.

examples:

vector bb,cc; 

mass cc=m; 

mshell cc; 

cc.cc; 

   2
  M

Once a mass has been attached to a vector with a mass dec laration, the mshell declaration puts the associated particle ``on t he mass shell.'' Subsequent scalar (.) products of the vector with itself will be replaced by the square of the mass expression.