From: tjroberts137@sbcglobal.net   
      
   On 6/25/17 6/25/17   2:26 AM, Lawrence Crowell wrote:   
   > On Saturday, June 24, 2017 at 3:15:06 PM UTC-5, Gregor Scholten wrote:   
   >> Lawrence Crowell  wrote:   
   >>   
   >>> The anti-screening effect of color charge does result in this   
   >>> inverted runn= ing coupling. What this does mean is that very high   
   >>> energy QCD is reasonabl= y tractable. This conforms to a usual   
   >>> situation that scattering states can = be computed well enough, but   
   >>> bound states are tough.   
   >>>   
   >>> As sqrt{s} --> 0 the number of diagrams blows up and they all   
   >>> contribute eq= ually.   
   >>   
   >> What does s mean? Obviously, you do not denote a spatial distance with s,   
   >> right?   
   >   
   > The Mandelstam variables are s, t, u. Often the transverse momentum in a   
   high energy process is referred to as sqrt{s}.   
      
   OOPS! s is NOT transverse, the transverse variables are t and u (they are   
   squares of momentum transfers). Sqrt(s) is the total energy, and is by far the   
   most commonly used of the three (e.g. the Particle Data Group plots total   
   cross-sections against sqrt(s)). Note all three Mandelstam variables are   
   invariant. They are defined for a 2-particle state scattering into a 2-particle   
   state.   
      
   Tom Roberts   
      
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