# Over which schemes can there exist non-trivial G_a bundles?

The group scheme G_a here is the one-dimensional additive group.

-
You can escape the underscores with a backslash so that they don't cause a problem (i.e. type \\_ to get _). Better yet, instead of typing H^1(X,O\\_X), you can type H<sup>1</sup>(X,O<sub>X</sub>) to get really pretty-looking output. –  Anton Geraschenko Oct 28 '09 at 5:16