C-theorem
THEOREM THAT, UNDER RENORMALISATION FLOW OF 2-DIMENSIONAL QUANTUM FIELD THEORIES, A QUANTITY CALLED C NEVER INCREASES
A-theorem
In quantum field theory the C-theorem states that there exists a positive real function, C(g^{}_i,\mu), depending on the coupling constants of the quantum field theory considered, g^{}_i, and on the energy scale, \mu^{}_{}, which has the following properties: