“…We consider this somewhat surprising: for example, we do not expect this conclusion to hold for co-dimension one (boundaries). Indeed, for d > 2 several non-trivial boundary conditions appear possible [3,[25][26][27][28][29] and for d = 2 there exists a family of conformal boundary conditions for a free (compact) scalar [30]. Also, non-trivial defects do exist in other cases where the bulk is free, like the non-trivial co-dimension two monodromy defects for a free hypermultiplet in 4d with N = 2 [31,32] (see also [33,34] for not necessarily conformal defects in this theory) and the co-dimension four surface operators in the abelian (2, 0) theory [35][36][37][38][39][40][41].…”