Trans-categorical representations

Example (module -algebras of -rings)

We have

Hence these assemble into an -algebra with .

Verbally we’ll refer to this as the “universal -algebra of -modules”: it encodes -categorical modules of the -algebra , for each , and the de-categorification comparison maps.

Example (comodule -algebras of -corings) Dually, we have for an -coalgebra , an -algebra ,

Example (representations of affine commutative algebraic groups) Let be a cocoommutative Hopf algebra. We’ll view it geometrically as an affine -algebraic group in the world of non-connective spectral algebraic geometry, . We’ll then define

where is the image of under

Warning An -coalgebra does NOT give an algebra. So only -commutative algebraic groups get a infinite tower of categorified representations. For example, this construction applies to Quillen-oriented spectral formal groups, objects appearing in TMF and TAF. It does NOT apply to a general descent groupoid, which is in general, very non-.