In the Mathur-Mukhi-Sen (MMS) classification scheme for rational conformal field theories (RCFTs), a RCFT is identified by a pair of non-negative integers $\mathbf{ [n, \ell]}$, with $\mathbf{ n}$ being the number of characters and $\mathbf{ \ell}$ the Wronskian index. The modular linear differential equation (MLDE) that the characters of a RCFT solve are labelled similarly. All RCFTs with a given $\mathbf{ [n, \ell]}$ solve the modular linear differential equation (MLDE) labelled by the same $\mathbf{ [n, \ell]}$. With the goal of classifying $\mathbf{ [3,3]}$ and $\mathbf{ [3,4]}$ CFTs, we set-up and solve those MLDEs, each of which is a three-parameter non-rigid MLDE, for character-like solutions. In the former case, we obtain four infinite families and a discrete set of $15$ solutions, all in the range $0 < c \leq 32$. Amongst these $\mathbf{ [3,3]}$ character-like solutions, we find pairs of them that form coset-bilinear relations with meromorphic CFTs/characters of central charges $16, 24, 32, 40, 48, 56, 64$. There are six families of coset-bilinear relations where both the RCFTs of the pair are drawn from the infinite families of solutions. There are an additional $23$ coset-bilinear relations between character-like solutions of the discrete set. The coset-bilinear relations should help in identifying the $\mathbf{ [3,3]}$ CFTs. In the $\mathbf{ [3,4]}$ case, we obtain nine character-like solutions each of which is a $\mathbf{ [2,2]}$ character-like solution adjoined with a constant character.
Categories: hep-th math-ph math.MP