Eigensystem

For nonsymmetric matrices, the eigenvalues can have imaginary parts. (Mathematica’s Manual)

Unphysical Degrees of Freedom and Gauge Fixing

In the previous section we introduced the gauge field Aaμ, a massless spin-1 field with two degrees of freedom. Note that the vector Aaμ in general has four degrees of freedom, and […]

Definition of hard, soft, and co-linear particles

“We have assumed that we can isolate individual particles. The reasoning behind this was explained in section 5, and it depends on the existence of an energy gap between the […]