symmetric monoidal (∞,1)-category of spectra
Let be a homomorphism of algebraic objects such as rings. Let be an action of on a module , then
defines an action of on . This construction extends to a functor
between categories of modules, sending to . This is called restriction of scalars (along ).
This functor has a left adjoint functor
called extension of scalars, since for an -module and an -module we have that is a well defined tensor product of modules which becomes an module by the operation of on itself in the second factor of the tensor. We have an adjunction .
Not only is restriction of scalars a right adjoint, it is also a monadic functor. This can be shown using the monadicity theorem or by direct computation.
Furthermore, not only is restriction of scalars a right adjoint, it is also a left adjoint. That is, it has a right adjoint of its own, called coextension of scalars:
extension of scalars restriction of scalars coextension of scalars
Last revised on August 14, 2024 at 12:05:41. See the history of this page for a list of all contributions to it.