English

How many adjunctions give rise to the same monad?

Category Theory 2016-06-30 v2 Representation Theory

Abstract

Given an adjoint pair of functors F,GF,G, the composite GFGF naturally gets the structure of a monad. The same monad may arise from many such adjoint pairs of functors, however. Can one describe all of the adjunctions giving rise to a given monad? In this paper we single out a class of adjunctions with especially good properties, and we develop methods for computing all such adjunctions, up to natural equivalence, which give rise to a given monad. To demonstrate these methods, we explicitly compute the finitary homological presentations of the free AA-module monad on the category of sets, for AA a Dedekind domain. We also prove a criterion, reminiscent of Beck's monadicity theorem, for when there is essentially (in a precise sense) only a single adjunction that gives rise to a given monad.

Keywords

Cite

@article{arxiv.1501.01739,
  title  = {How many adjunctions give rise to the same monad?},
  author = {Andrew Salch},
  journal= {arXiv preprint arXiv:1501.01739},
  year   = {2016}
}
R2 v1 2026-06-22T07:54:39.775Z