Ga-ACTIONS OF FIBER TYPE ON AFFINE T-VARIETIES
نویسنده
چکیده
Let X be a normal affine T-variety, where T stands for the algebraic torus. We classify Ga-actions on X arising from homogeneous locally nilpotent derivations of fiber type. We deduce that any variety with trivial Makar-Limanov (ML) invariant is birationally decomposable as Y × P, for some Y . Conversely, given a variety Y , there exists an affine variety X with trivial ML invariant birational to Y × P. Finally, we introduce a new version of the ML invariant, called the FML invariant. According to our conjecture, the triviality of the FML invariant implies rationality. This conjecture holds in dimension at most 3.
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