7 papers
A non-semisimple Kitaev lattice model
Sebastian Halbig, Ulrich Krähmer
The construction of the topologically protected code space of Kitaev's model for fault-tolerant quantum computation is extended from complex semisimple to arbitrary finite-dimensio…
Duplicial functors, descent categories and generalized Hopf modules
Ivan Bartulović, John Boiquaye, Ulrich Krähmer
Böhm and Ştefan have expressed cyclic homology as an invariant that assigns homology groups to right and left coalgebras respect…
The ring of differential operators on a monomial curve is a Hopf algebroid
Ulrich Krähmer, Myriam Mahaman
This article considers cuspidal curves whose coordinate rings are numerical semigroup algebras. Using a general result about descent of Hopf algebroid structures, their rings of di…
A remark on the Hochschild dimension of liberated quantum groups
Tomasz Brzeziński, Ulrich Krähmer, Réamonn Ó Buachalla +1
Let be a Hopf algebra equipped with a projection onto the coordinate Hopf algebra of a semisimple algebraic group . It is shown that if admits a suitabl…
Pointed Hopf algebra (co)actions on rational functions
Ulrich Krähmer, Blessing Bisola Oni
This article studies the construction of Hopf algebras acting on a given algebra in terms of algebra morphisms . The approach is par…
Cyclic duality for slice and orbit 2-categories
John Boiquaye, Philipp Joram, Ulrich Krähmer
The self-duality of the paracyclic category is extended to a certain class of homotopy categories of (2,1)-categories. These generalise the orbit category of a group and are associ…
Clones from comonoids
Ulrich Krähmer, Myriam Mahaman
The fact that the cocommutative comonoids in a symmetric monoidal category form the best possible approximation by a cartesian category is revisited when the original category is o…