Triangulated endofunctors of the derived category of coherent sheaves which do not admit DG liftings
Abstract
Recently, Rizzardo and Van den Bergh constructed an example of a triangulated functor between the derived categories of coherent sheaves on smooth projective varieties over a field $k$ of characteristic $0$ which is not of the Fourier-Mukai type. The purpose of this note is to show that if $char \, k =p$ then there are very simple examples of such functors. Namely, for a smooth projective $Y$ over $\mathbb Z_p$ with the special fiber $i: X\hookrightarrow Y$, we consider the functor $L i^* \circ i_*: D^b(X) \to D^b(X)$ from the derived categories of coherent sheaves on $X$ to itself. We show that if $Y$ is a flag variety which is not isomorphic to $\mathbb P^1$ then $L i^* \circ i_*$ is not of the Fourier-Mukai type. Note that by a theorem of Toen (\cite{t}, Theorem 8.15) the latter assertion is equivalent to saying that $L i^* \circ i_*$ does not admit a lifting to a $\mathbb F_p$-linear DG quasi-functor $D^b_{dg}(X) \to D^b_{dg}(X)$, where $D^b_{dg}(X)$ is a (unique) DG enhancement of $D^b(X)$. However, essentially by definition, $L i^* \circ i_*$ lifts to a $\mathbb Z_p$-linear DG quasi-functor.
- Publication:
-
arXiv e-prints
- Pub Date:
- April 2016
- DOI:
- 10.48550/arXiv.1604.08662
- arXiv:
- arXiv:1604.08662
- Bibcode:
- 2016arXiv160408662V
- Keywords:
-
- Mathematics - Algebraic Geometry;
- Mathematics - K-Theory and Homology