“…Evidence that the conjecture may hold in four dimensions was presented in [4] while candidate counterexamples [5][6][7] were shown to actually be CFTs in [8,9]. As in the two-dimensional case, there is a connection between RG-flow and properties of the Wess-Zumino action [10,11] (see also [12,13]), the a-theorem, [14,15], and the scale vs conformal invariance problem. The conjecture is known to hold under some additional assumptions, for example for any scale invariant theory which is obtained by weakly coupled renormalisation group (RG) flows [8,13].…”