Hochschild Cohomological Dimension is Not Upper Semi-Continuous
  It is shown that the Hochschild Cohomological dimension of an associative algebra is not an upper-semi continuous function, showing the semi-continuity theorem is no longer valid for non-commutative algebras. A family of $\mathbb{C}$ exhibits this-algebras parameterized by $\mathbb{C}$ all but one of which has Hochschild cohomological dimension $2$ and the other having Hochschild cohomological dimension $1$. 
Anastasis Kratsios
math.RA math.KT