Identifying optimal large $N$ limits for marginal $\phi^4$ theory in 4d

Abstract

We apply our previously developed approach to marginal quartic interactions in multiscalar QFTs, which shows that one-loop RG flows can be described in terms of a commutative algebra, to various models in 4d. We show how the algebra can be used to identify optimal scalings of the couplings for taking large $N$ limits. The algebra identifies these limits without diagrammatic or combinatorial analysis. For several models this approach leads to new limits yet to be explored at higher loop orders. We consider the bifundamental and trifundamental models, as well as a matrix-vector model with an adjoint representation. Among the suggested new limit theories are some which appear to be less complex than general planar limits but more complex than ordinary vector models or melonic models.