Let $X$ be a topological space and $A$ a sheaf of noncommutative associative algebras over a fixed field $k$. My questions are:


1) Does the category of modules over A have enough injective?


2) If we have the affirmative answer of question (1), then suppose $M$ is a quasi-coherent sheaf over $A$ then the first cohomology of M: $H^1(X,M)$ is $0$?


I learn the cohomology of module over a scheme $X$ in Hartshorne book. But when we deform the structure sheaf $O\_X$ of $X$, then does the cohomology theory still hold for quasi-coherent sheaves? Would you please tell me some books/papers about cohomology theory of module over a sheaf of (noncommutative) rings?


Many thanks!!!



Sheaf cohomology in non-commutative setup
For the first question, the answer is yes, since the category of sheaves of $A$-modules is a Grothendieck Abelian Category. The least obvious condition one has to check is that this category has a generator - to construct it, just use


$\bigoplus\_{U\subseteq X} (j\_U)\_!(A|\_U)$,


where $U$ ranges over all open sets of $X$, $A$ is considered as sheaf of (left or right) $A$-modules, $j\_U:U\rightarrow X$ is the natural inclusion, and $(j\_U)\_!$ is extension by zero.


For a nice introduction to Grothendieck Abelian Categories, check out section 14 of <http://stacks.math.columbia.edu/download/injectives.pdf>.


For the second question, if we take $X$ to be an elliptic curve, take $A = O\_X$, and $M=A$, then we already have $H^1(X,M) \ne 0$.


