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Xuqiang QIN
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Connectedness of moduli space

Let $X$ be a smooth projective variety. Given fixed Chern classes with positive rank $r$, let $M$ be the moduli space of semistable sheaves with such Chern classes. In general we only know $M$ is a projective scheme. (if $\mathrm{dim}(X)$ is $1,2$ a lot more can be said)

1st Question: Is there an example where $M$ is smooth but not connected?

2nd Question: I am trying to show the following scenario cannot happen: $M$ is smooth of dimension $d$ but disconnected and one of the connected components consists merely of stable vector bundles. I feel we might be able to use the fact that the component only contains vector bundles to contradicts the projectivity but not sure how.

Thanks in advance!

Xuqiang QIN
  • 815
  • 5
  • 14