Weak bimonads and weak Hopf monads

Abstract

We define a weak bimonad as a monad T on a monoidal category M with the property that the Eilenberg–Moore category M T is monoidal and the forgetful functor M T → M is separable Frobenius. Whenever M is also Cauchy complete, a simple set of axioms is provided, that characterizes the monoidal structure of M T as a weak lifting of the monoidal structure of M . The relation to bimonads, and the relation to weak bimonoids in a braided monoidal category are revealed. We also discuss antipodes, obtaining the notion of weak Hopf monad.